COMPANY PROFILE
ABHAY OCEAN INDIA PVT LTD Established in 1998 at Mumbai, by Capt. Jagdish Khokhar an ex
Indian naval officer, having over 35 years experience in managing & executing wide variety of
projects in Marine/Offshore Construction Services.
ABHAY OCEAN INDIA PVT LTD is a Company which has acquired multi skill industry knowledge &
experience to have an extremely competitive & cost effective market presence.
We are a young and dynamic company with core skills established in the field of Marine / Offshore
construction services. We aim to provide innovative engineering construction solutions with
technical excellence and total commitment to our clients' needs with special emphasis on quality and
safety.
AbhayOcean India Pvt. Ltd. is a Mumbai
(India) based company engaged in Marine
engineering Projects such as Submarine
Pipelines, Marine Intakes/ Outfalls and
Dredging /Trenching etc. Some of the
Marine Outfall projects implemented by
AOIL are as fallows..
Project: Marine Outfall Dahej, Gujarat.
Client: PunjLloyds, New Delhi.
Description: The system consisted of a
20 tons Diffuser and submarine
C.S. Pipeline of 24” Diameter for Indian
Petrochemicals Ltd.
In Gujarat
b) Project: Effluent disposal Outfall,
Pondicherry.
Client: Pondicherry Distilleries.
Description : The system consisted of a
Diffuser and submarine HDPE
Pipeline of 8” Diameter and 1.2 Km.
Long at Pondicherry
c) Project: Effluent Disposal Outfall, Goa.
Client : ZuariAgrochemicals Ltd.
Description : The system consisted of a Diffuser and submarine HDPE
Pipeline Of 12” Diameter and 2 Km. Long.
d) Project : Effluent Disposal Outfall, Karwar.
Client : Ballarpur Industries Ltd.
Description: The system consisted of a Diffuser and submarine HDPE
Pipeline of 12” Diameter and 3.5 Km. Long.
Project Client: Gulf petro Chemialservice
Pipe Line of 1200 mm Diaas intake for Muscat Refibery.
Some of the recently completed prestigious jobs
a)AOIL has recently executed near shore Trenching for M/s Leighton India Ltd for Kochi
Refinery SPM & Pipeline 58 inches for crude transportation.approx550 Mtrs
b)AOIL was also involved and part completed trenching work for Indian Oil Offshore Project at
PARADIP -HALDIA CRUDE RECEIPT FACILITIES. For Iranian offsore
c)AOIL completed the Pipe Transportation work. For Lay Barge “ABOUZAR”
d) Cairn Energy-Provision & management of Dipper Dredger, marine equipment, etc., and
carrying-out 14 Kms. trenching & burial work for 24” submarine gas pipelines at Suvalipoint,
Suratin currents of upto5-6 Knots and tidal variations of upto8 meters, as a subcontractor to
Hyundai Heavy Industries (HHI). We also helped HHI for pipe pull.
e)ONGC-Dredging and trenching at Mindholariver in a current levels of 7 Knots, for SHBT
Pipeline on behalf of M/s HundaiHeavy Industries (HHI).
M/s De DongeHolding shall be keeping one of their Dipper Dredgers and two in number hopper
barges (value approx. USD 14.0 Million) in India, which we would be managing/operating and
carrying out dredging / trenching works.
DREDGING WORKS:
The equipment we have access:
· Dipper Dredger with LeibherrP 994
· Two nosself propelled Hopper barges 850 Cu M each.
· Trailer Suction Dredgers
· Cutter Suction Dredgers
PIPELAY WORK:
AOIL has Two Number Flat Top Work Barges (230ftX 60ftX14ft) along with Two 1800 BHP Tugs
for any Offshore work
These Barges are suitably modified for Pipe Line Pull or Pipe Lay mode to undertake work
AOIL has access to qualified & Experienced project Managers / Supervisors and
specialisedEquipment like heavy lift Barges to complete a project ON Time /ON Cost
2 BASIS OF THE PROPOSAL.
This Proposal has been prepared based on the documents made available by TEC by E-Mail.
The proposed 100 MLD sea water reverse osmosis desalination plant located in Nemmalivillage
on the east coast road, approximately 35 Km south of the town of Chennai requires 265 mldof
sea water from reliable source of water of consistent quality. The rejects having TDS of 67000
ppmfrom the SWRO plant is designed for 165 mld. The following were taken into consideration
for selection and design of sea water and intake facilities.
Scope of works includes the supply by
contractor of all material, machinery, plant
site, supervision, labour, safety personnel and
all expenses necessary for the installation,
testing & commissioning of the sea water
intake and the reject outfall system.
Moreover, the scope includes but it is not
limited to:
•The review of the contract documents
related to design and construction of sea
water intake and outfall system comprising of
offshore & onshore feildstudy reports, data
and related analysis, computer modelling
reports, design drawings etc.
•Review of the oceanographic survey data
enclosed in chapter-3, volume IIA, and it felt
necessary, carryout the survey of the area
offshore to verify the nature of the sea
bottom in order to confirm the results of the
boreholes and stratigraphicdata enclosed
with the tender and to find the correct means
for the marine works.
•Excavation of the appropriate trench in the
sea bottom as per design drawings with
appropriate and supply and receive the HDPE
pipes along with associated accessories
constituting the intake and the outfall.
•Backfilling of the trench, supply and
installation of the various sizes stones &
materials in the areas indicated in the
drawings enclosed with this tender
specification.
Supply, Welding, laying and connection of the high density polyethylene (HDPE) pipes in the
submarine trench in accordance with the specifications. Prefabrication and installation of
concrete blocks for the anchorage of the pipes.
Prefabrication & installation of the concrete blocks for the system towards protection against
trawling fishing & other possible causes of damage.
Fabrication & installation of the intake screen (head) at the extremity of the sea water intake
pipeline and connection of the pipeline with special expansion spool piece joint as indicated in
the drawing. Fabrication & installation of the reject outfall diffusers section & connection with
special expansion spool piece joint as indicated in the drawings.
Fabrication & installation of the expansion special spool pieces connecting the 1600 mm dia. and
the 1200 mm dia. Pipelines for intake & outfall system respectively with the structures at their
extremities onshore and offshore. The selection of spool pieces shall be done based on previous
experience of similar installation and the same shall be procured from a reputed manufacturer
after prior approval from client/consultant.
Supply & installation of all necessary flanges, pipes & structures for the completion of the system
in accordance with the drawings. Supply & installation of the necessary Navigational Aids like
buoy with red laternmarks to mark the position of the structures as per drawings.
The battery limit considered for commencement of the Marine Intake / Outfall Pipeline is the
termination point of pipeline on the Shore. TEC will provide a concrete inspection chamber for
this purpose. Only 2 nos. of Valves, one at the Battery limit and one at the diffuser assembly has
been included and no manhole is included in this Proposal. 3. Scope of Work: Scope of work,
Supply and services envisaged under this proposal is as fallows.
a)Scope of Services Alignment Survey for Marine Intake Outfall Pipeline. b) Proposed Pipeline
route and & Diffuser Intake Sructurelocation will be marked with the help Of DGPS. c) Bottom
topography –Bathometric Survey Depth contours covering an area 1 km on either side of the
proposed pipeline route d)Geotechsurveys with bore hole at every Two hundred meters on both
pipe lines roué. e)Design and Engineering Pipe lines designed & Engineering based upon surveys
i) HDPE Pipes 1600M. long ii) Diffuser Intake Structure Assembly and other attachment.
c) Scope of Work.
i)Supply & Preassembly of the Pipelines
ii) Dredging of Trench & Back fill BurrialInstallation of the Pipelines
iii) Insulation & Installation of the Diffuser System. / intake structure
iv) Testing.
v) Commissioning.
vi) Operation and Maintenance
4. PLANNING of SUBMARINE OUTFALL.
At the outset fallowing information will be obtained from available sources, Nautical charts,
bathymetric maps, oceanographic maps, SONAR charts and sounding, as bottom samples,
Meteorological records, oceanographic studies, reports of marine biology and any other
information available.
In planning a submarine outfall the first step should be to determine a suitable location for the
diffuser/ Intake Structure. The determination of the location and design of the diffuser for a
submarine Intake outfall would be based on obtaining adequate distance from sensitive areas
and sufficient depth, dispersion and/or die off of pollutants commensurate with the level of
treatment prior to discharge, to assure negligible environmental or health impact. Suitable
computer programs will be used to carry out the analysis to determine the location and the
basic.
design of the diffuser/ Intake structure. After the diffuser location is determined then the route
that the Marine intake outfall would follow will be established, the necessary internal diameter
to accommodate the flows anticipated throughout the useful life of the outfall will be
determined, and the method for protecting the outfall against the hydrodynamic forces of the
ocean would also be designed. The oceanographic information and data that is required to carry
this out includes following:
a) Topography, hydrography, and geomorphology of the sea bed which is used to determine the
route of the , Marine Intake Outfall
b) Wave and current data which are used to determine the method of physically stabilizing the
outfall.
c) Current data and salinity temperature profiles of the water column. This is used to
Determine the location and design of the diffuser, the static hydraulic head, and to the
Physical stability of the Marine Intake outfall.
5. SUBMARINE ROUTE SURVEY
Preliminary route survey of the Pipeline route will be conducted by using a DGPS System. By
establishing two control points on shore, it is possible to use triangulation to the buoys to record
the route with sufficient accuracy. The Marine Intake Outfall on-shore distance between the
triangulation points would not be less than
1/4 of the length of the Marine Intake Outfall.
Submarine route location survey will also be conducted by divers to locate problem areas such
as reefs, environmentally sensitive areas, large rocks, cliffs, drop-offs, high points, areas used for
ship anchorage, weak or unstable soils, and areas subject to erosion or deposition etc.
6. MARINE INVESTIGATIONS
Having established tentative Diffuser location and Pipeline route, fallowing activities may be
conducted.
a) Sonar determined bathymetry with horizontal control linked to a global positioning
System. Both the horizontal and vertical precision would be within one meter.
b) Side-scan sonar imaging to determine the geomorphology of the seabed.
c) Sea Currents.
c) Visual imaging of the possible Marine intake & outfall routes by use of video.
While carrying out activities related to Marine Survey fallowing precautions shall be taken
Safety
The generally hazardous nature of working at sea makes it imperative to have in place an
adequate safety program that will ensure the safe return of all personnel at the end of each
working day. Topics that should be addressed in any safety program include (but are not limited
to): Periodic first aid/CPR training,
Hazardous materials training,
The physical condition of the crew/field members and adequate training in the safe operation of
equipment used in the field to complete the survey.
Navigation
Accurate location of sites is important for any survey. In order to effectively meet this objective,
navigational equipment that will be aboard monitoring vessels is a Global Positioning System
(GPS) and a Fathometer. The GPS instrument would be capable of displaying Differential GPS
(DGPS) positions.
Throughout a survey work, the Team Leader will navigate to sites using a set of Nominal station
coordinates. The coordinates of each station location must be based on a determined Datum and
will be expressed in degrees, minutes,
and thousandths of a minute. Fathometer readings would be recorded in meters and
Direction (e.g. course and heading) would be reported as degrees from magnetic North. An
accurate log of general activities and specific site data sheets will be maintained.
Vessel and Site Data
A specific set of Vessel and site data will be recorded .
Following data would be recorded for each activity.
1) Date
2) Vessel
3) Crew
4) Check box indicating that the GPS system is functioning properly
Following standard data will be recorded
1) Date
2) Station coordinates of the actual work location
3) Time
4) Depth for each sampling position
5) Weather observations; sky, wind speed, and wind direction
6) Sea conditions; swell height, period and direction
7) Tide height, and time of low and high tides bracketing the sampling event.
8) Comments section
Additional specific types of data also will be recorded depending on the type of sampling being
conducted.
For water quality sampling these data might include:
1) Instrument identification if more than one CTD is used for sampling.
2) Specific depth information if any water samples are collected during a cast
For benthic sampling, additional data categories will include:
1) Time at which a replicate was sampled
2) Depth of sediment in grab
3) Sediment descriptions; to include color and type of sediment
4) Replicate identification; whether a sample was collected for community or
Chemical analysis
5) Checkboxes for each chemical constituents sampled
Hydrographic Survey shall be conductedtocollect information regarding Marine conditions. The
Proposed location of diffuser intake structure along with alignment of Pipeline shall be marked
with the help of DGPS and the Depth of the water column shall be measured by Echo Sounder.
Area covered under this Survey will be 1 Km. On either side of the Proposed location of the
Diffuser intake structure and 1 Km. Out towards sea. Equipment required for Survey shall be
mounted on a Survey Boat. Brief description of the system is as fallows.
BATHYMETRY AND
MICROTOPOGRRAHY.
In NMEA-0183 format for navigation
with high degree of accuracy. The
positioning data received will have
high reliability and integrity. The
system will be calibrated at a known
location within the survey area.
Navigation & Data Logging
HydroProis a world's leading
software solution provider for
navigation, hydrographic survey, data
acquisition and processing needs.
This will be interfaced to all the data
acquisition systems on board and the
data logged will be processed by
using Hydro Process data processing
software.
Vertical Control
Observed tides close to the survey area will be used for converting raw water depths to chart
datum.
Echo sounder
ODOM DF3200 MKII Dual frequency or equivalent Echo sounder, integrated with a DGPS
positioning system will be used during the entire survey to record geographically referenced
bathymetric data for measuring water depths. Sea
swell will be eliminated by SETEX MRU 5 motion sensor (heave compensator). Digitized data
will be confirmed by the inspection of analogue records.
Depth contours (Sea Bottom Topography) over the same area shall be studied by using Side Scan
Sonar as fallows.
Side Scan Sonar
EG & G 272TD dual channel `towfish' and an EG & G 260 recorder (or equivalent) will be
provided to investigate the sea floor for morphology and other features. The survey lines will be
run with a range setting of 50 meters either side at a scanning frequency of 100 KHz along the
survey lines. The tow system will be operated following recommended manufacturers
procedures. The tow fish will be towed astern of the survey vessel at a depth providing optimum
seabed return. Layback and cable-out will be logged from each survey line..
TIDES, CURRENTS AND CIRCULATION
Anderra(or equivalent) Current meters shall be used for measuring currents at various locations
and tide poles measurements shall be undertaken to measure the tides. Float drogues shall be
released and monitors to study the circulation patterns.
Processing of Data
The survey data logged in Hydro Profile format will be processed in Hydro Process software and
finally presented in drawing form using AutoCAD Rel.14 for windows.
WATER-COLUMN PROFILING
Purpose
Water-column profiles will be collected at sampling sites to characterize depth related gradients
in temperature, salinity, hydrogen ion content (pH), transmissivity, Dissolved oxygen (DO), and
chlorophyll fluorescence. For example, water-column
Profiles can describe whether stratification (layering) is present and, if so, the depth of the
thermoclineor pycnocline. Variation in these parameters at the same depth among Stations may
indicate anthropogenic or natural perturbations of the environment: low Salinity values at some
stations may indicate the presence of an effluent plume whereas high pH and dissolved oxygen,
and low transmissivitymay indicate a phytoplankton bloom.
Equipment
A conductivity-temperature-depth profiler (CTD) with an expanded compliment of Sensors will
be used to provide a continuous water-column profile of the attributes
Described above.
Pre Survey Equipment Checkout
A pre-survey equipment checkout will be conducted before calibrating the sensors and
Also within 24 hrs prior to starting the work. The inspection will include following:
1) Visually inspect the CTD for any obvious defects.
2) Check all metal components for corrosion and clean or replace as necessary.
3) Inspect and clean all of the sub sea connections with contact cleaner as
Necessary.
4) Lubricate newly cleaned connectors with silicone grease and ensure they are Securely
reconnected.
5) Check all cables for nicks, cuts, abrasions, or other signs of physical damage.
6) Test the CTD to see if connections and software work properly.
7) Clean or replace all accessory tubing as necessary.
8) Check the battery status for all units using RAM data storage.
CTD Pre-Survey Calibration and Equipment Checkout
Pre-survey Calibration
Equipment checkout and calibration will be carried out as per the specific recommendations of
manufacturers. General procedure is given below; however it is subject to change at the time of
actual work.
Hydrogen Ion Content (pH)
The pH sensor is calibrated by employing commercially available buffer solutions as Standards.
When sampling in the ocean it is best to bracket the
pH range by using the Three buffers, pH 7, 8, and 9. It is important that the buffer is thermally
Equilibrated with the water bath; this is best accomplished by keeping the CTD in the Water
bath and by using a holding bracket for the buffer container. Depending on the CTD model, the
appropriate readings for each of the three buffers (e.g. water
Temperature, pH, and voltage output) should be recorded on the calibration log. The pH probe
should be adjusted according to the manufacturer‟s specifications using this Information.
Agreement between the measured sensor output and the known buffer values should be within
+/-0.1 pH units. If this range is exceeded, the buffer readings should be used to calculate the
values necessary to properly adjust the pH sensor. When the calibration has been successfully
completed, the pH electrode should be stored in a KCL-saturated, pH 4 buffer solutions.
Dissolved Oxygen (DO) Ensure that the pump being used to supply water to the sensor during
the calibration is operating correctly and that it flows within the factory specifications. Compare
the sensor-measured DO values with the saturation values taken from the most recent edition of
Standard Methods; it should match to within 0.1 ml/L (0.143 mg/L). Sensor performance should
be Information. Agreement between the measured sensor output and the known buffer values
should be within +/-0.1 pH units. If this range is exceeded, the buffer readings should be used to
calculate the values necessary to properly adjust the pH sensor. When the calibration has been
successfully completed, the pH electrode should be stored in a KCL-saturated, pH 4 buffer
solutions.
Dissolved Oxygen (DO) Ensure that the pump being used to supply water to the sensor during
the calibration is operating correctly and that it flows within the factory specifications. Compare
the sensor-measured DO values with the saturation values taken from the most recent edition of
Standard Methods; it should match to within 0.1 ml/L (0.143 mg/L). Sensor performance should
be monitored over time and it must either be repaired or replaced if the results do not meet the
manufacturer‟s minimum specifications. TransmissometerThe transmissometershould be
calibrated prior to each sampling survey according to the manufacturer‟s recommended
procedures. FluorometerThis calibration is performed using a 50 μg/L solution of
Coproporphyrinas a substitute for chlorophyll (a) and distilled water for a blank. Pressure The
pressure sensor should be checked before each sampling survey. Again, follow the factory
recommended adjustment procedures. The pressure reading in air at sea level should be a
negative number between 0.00 and -0.60 decibars(db). If the correct pressure cannot be
displayed by adjusting the offset, the manufacturer should service the sensor as soon as possible.
CTD Deployment
The objective of water-column profiling is to collect data for every meter of depth while
Lowering the CTD. Ideally a scan-rate of eight scans per second or greater may be used. The
absolute minimum scan-rate is two scans per second and should be reserved for use in small
bodies of water, where deploying smaller units is more practical. In larger bodies of water,
where larger units are easier to deploy, it is strongly recommended that the scan-rate be eight
scans per second. Some manufacturers‟ software allow the descent rate to be monitored
digitally when the CTD is deployed using a real-time means of data collection by displaying and
viewing lowering rate variable. Descent rates should always be greater than the upward
acceleration of the instrument caused by the swell to minimize shed wake spiking of the data.
Onboard water bath will be used for the CTD to prevent excessive heating of the sensors while
traveling between stations. Rinse the lenses of the transmissometerwith deionizedwater to
remove any crystallized salt prior to each cast.
Before beginning a cast where dissolved oxygen is being measured, the sensor will be brought to
thermal equilibration with the ambient sea-water by soaking the CTD for a minimum of three
minutes at the first station of the day and for 90 seconds at every station thereafter. Surface
equilibration time is performed for two reasons; DO sensor re-polarization and thermal
equilibration. Additionally, air bubbles may become trapped in the CTD‟s tubing that can
adversely affect the performance of the DO sensor unless they are removed. The air bubbles can
be purged from the tubing simply by lowering the unit five meters below the surface for a short
time, then raising it back to the surface so that the top of the CTD is just below the surface prior
to starting the cast. The recommended optimal descent rate while lowering the CTD is 1 m/s.
BENTHIC SAMPLING
Purpose
The purpose of benthic sampling is to obtain at each site one or more samples of the
Seafloor sediment. The Sediment samples are used to describe the biological physical and
chemical Characteristics of the site. This information is particularly useful in characterizing the
Extent and impact of The discharge from an outfall relative to the prevailing natural conditions.
Equipment A 0.1 m2 modified Van Veengrab will be used to collect sediment samples for
physical, chemical, and infaunalanalysis. The grab may be galvanized, stainless steel, or Teflon-
coated. All surfaces of the grab must be clean and free of rust. Either single or tandem-rigged Van
Veengrabs may be used. Tandem-rigged Van Veengrabs are two grabs mounted on a shared
hinge pin.
Grab Sampling Procedures
Prior to deployment, the grab will be cocked and then the safety key will be put in place. The
grab is next hoisted over the side; the safety key is removed and then lowered at a rate of
approximately 2 m/sec until it is about 5 m above the bottom. From this point, it is lowered at 1
m/sec to minimize the effects of bow wave disturbance. After bottom contact has been made
(indicated by slack in the hydro wire), the tension on the wire is slowly increased which causes
the lever arms to close the grab. The grab is then brought back to the surface and retrieved back
on deck as quickly and as safely as possible to avoid any “washing” at the surface caused by the
boat rolling in the sea. Once the grab is back onboard, the top doors are opened so that the
sample can be inspected.
Criteria for Acceptable Grab Samples Before the grab can be processed, the acceptability of the
sample must be determined.
This determination is based upon sample condition and depth of penetration. Sample
condition is judged using criteria for surface disturbance, leakage, canting, and washing. An
acceptable sample condition is characterized by an even surface, with minimal surface
disturbance, and little or no leakage of the overlying water. Heavily canted samples are
unacceptable. A sample with a large amount of humping along the midline of the grab, an
indication the sample was “washed” during retrieval, is also Unacceptable. While some humping
might be evident in samples taken from firmer substrates, this is primarily due to the closing
action of the grab and is not evidence of nunacceptable washing.
If the sample condition is deemed acceptable, the overlying water is drained into an Underlying
container by slightly opening the jaws of the grab. This water must be Retained for later
screening with the sediments (see Sample Processing below). Extra Caution should be taken to
drain the overlying water from the grabs for chemistry and Toxicity samples so as to avoid
disturbance and loss of the surface sediments. The next step in processing the grab is measuring
the depth of penetration. For infaunalsamples, sediment penetration depth must be at least 5
cm; however, penetration depths of at least 7-10 cm should be obtainable in silt (fine sand to
clay). Inserting a plastic ruler vertically along the grab midline and measuring the depth of the
sediment to the nearest 0.5 cm determines the depth of penetration.
Sediment Description
Sediment characteristics will be described following the measurement of penetration depth. The
general sediment type will be characterized (e.g., clay, silt, sand, gravel, or any combination of
these) and if the sample contains large quantities of shell hash, this should also be noted on the
data sheet. The presence of petroleum tar should be recorded, as well as any obvious odors such
as sulfides (the odor of H2S or rotten eggs), oil (the odor of petroleum tar), or humicsmells (a
musty, organic odor). Sediments will usually have no particular odor. General sediment color
(e.g., black, green, brown, red, yellow) will also be recorded .
Sample Processing
Benthic InfaunalSamples
After the sample description has been completed, the sediment sample intended for
Infaunalanalysis is washed completely from the sampler, saving sediment, overlying
Seawater, and wash water for subsequent screening. All raw wash waters used on the
Sample are to be filtered in some fashion to preclude the accidental introduction of
Surface-water organisms. Two methods that may be used are an in-line filter in the boat's
seawater pumping system, or the fitting of all wash hoses with fan nozzles having small
apertures (<0.5 mm diameter).
A sediment-washing table is recommended for benthic sample processing. The table
Provides a flat, smooth surface over which to spread and wash the sample. This provides a
means of gently breaking up the sediment before it runs off the end of the table into the screen
box. The screen box must be equipped with a stainless steel mesh with 1.0-mm openings. Wire
diameter should be similar to that found in the Standard 1.00 mm Sieve . The surface area of
screen should be adequate to easily accept the sample without build up. Water pressure should
be controlled while washing the sample to avoid damaging the organisms. Minimize direct
application of water from the hose to the material and organisms collecting on the screen.
Once the sample has been washed through the screen, the material (debris, coarse Sediment, and
organisms) retained on the screen should be transferred to a sample Container. The sample
container should be labeled with an external, water resistant Adhesive label naming the station,
depth, date, replicate and "split number" (i.e. 1 of 2, 2 of 2, etc.), if applicable. This label should
be waterproof and marked using a pencil or indelible ink.
The sample container will have an adequate watertight closure and be sufficiently large to
accommodate the sample material, relaxant and fixative. If necessary, a sample may be split
between two or more containers, however, each container must have the appropriate labels
(described above) with the corresponding split number clearly marked. Splitting samples should
be avoided if possible. Splitting samples is usually unnecessary if the field crews have a broad
range of sample container sizes available.
The material retained on the screen should be gently removed in order to avoid damaging the
organisms. The sample container should be filled to approximately 40% (no more than 50%) of
capacity with screened material. After the sample material has been transferred to the container,
the screen should be closely examined for any remaining organisms caught in the mesh. Those
organisms should be removed with forceps and added to the sample container. The screen box
should be thoroughly washed and the mesh scrubbed with a stiff brush before the next sample is
screened.
It is recommended that all infaunalsamples be treated with a relaxant solution for
Approximately 30 minutes prior to fixation. Either an Epsom salts (MgSO4) solution or a
propylene phenoxytolsolution may be used for this purpose. The relaxant solution may be used
as the diluentwater for the fixative, or may be decanted after exposure and replaced with diluted
fixative.
If the relaxant is used as diluentwater, fill the sample container to 80% of its volume,
Close the container and invert it several times to distribute the solution. Leave the sample in the
relaxant for 30 minutes. After 30 minutes top off the container with enough sodium borate
buffered formalin to achieve a 10% formalin solution. Close the container once again and invert
it several times to assure mixing. Store the sample for return to the laboratory.
If the relaxant solution is not used as the diluentwater, the relaxant must be removed
From the sample container and replaced with 10% formalin. After the 30-minute
Treatment, decant the relaxant from the sample through a screen with a mesh size of less than
1.0 mm. Make sure that all of the material and animals have been removed from the screen and
placed in the sample container. Fill the sample container with a 10% solution of sodium borate
buffered formalin rather than with undiluted formalin. Close the container, invert it several
times to assure mixing and then store it for return to the laboratory.
Relaxant and fixative stock solutions are as follows:
1) Epsom salts relaxant solution: 1.5 kg Epsom salts (MgSO4· 7H2O)
per 20 L of freshwater.
2) Propylene phenoxytolsolution: 30 ml propylene phenoxytolto 20 L
of seawater.
3) Buffered formalin solution: 50 g sodium borate (NA2B4O7) per
liter of formalin.
4) Buffered 10% formalin solution: 1 part buffered formalin solution to 9
parts fresh or salt water.
Sediment grain-size and chemistry (e.g., TOC, trace metals, trace organics) samples will be
collected from the top 2 cm by randomly subsamplingundisturbed surface material with a
stainless steel, Teflon-coated, or plastic scoop. A metallic scoop should be replaced if any signs of
rust are visible. Sediment in contact with, or within 1 cm of the metal sides of the grab should be
avoided to reduce the chance of sample contamination (e.g. metals, organics, etc.). Care should
be taken not to touch any surfaces of the grab Sampler with the scoop. At a minimum, the scoop
will be thoroughly rinsed to remove any traces of sediment form the previous station then
stored to avoid being contaminated between stations. Chemistry samples should always be
placed in precleanedcontainers. Sediment grain size and some sediment chemistry (e.g., TOC and
trace metals) samples can be collected in glass or plastic containers, but trace organics samples
should always be made of glass. Sediment chemistry sample containers should have Teflon-lined
lids, although this is not a requirement for sediment grain-size samples. An air space should be
left at the top of each sample.
Quality Assurance
The quality of benthic sediment samples is dependent on following the field procedures
1) Prior to each deployment the interior of the grab must be thoroughly washed
With seawater to remove any sediment from the previous sample.
2) Once the grab is returned to the surface, it should be recovered as quickly as Safe handling
permits as a means of avoiding sample washing as the boat rolls in the sea.
3) The grab sample should be visually inspected to ensure the overall condition is Acceptable
and it should be measured to guarantee the minimum depth of Penetration.
4) Gentle water pressure should be employed when washing and screening the
Infaunalsamples to avoid damaging any of the organisms.
5) The screen must be thoroughly washed and scrubbed between samples.
6) A relaxant is recommended for use on all infaunalsamples to minimize Fragmentation of the
organisms during fixation.
7) The infaunalsample container should be filled no more than 40% full of Screening material.
After adding relaxant and fixative solutions, the container needs to be inverted several times to
assure a thorough mixing and exposure to Relaxant and fixative.
8) Timers should be used to ensure that fixation of the samples takes place 30
Minutes after being exposed to the relaxant solution A distinctive sticker may be Affixed to the
lid of the sample container to visually distinguish between the Samples being treated with
relaxant and those having been fixed.
9) Extra care should be taken when draining the overlying water from grabs
Intended for chemistry samples. This minimizes disturbance and loss of surficialSediments. Use
of a tygontubing siphon is highly recommended.
10) Field personnel must be thoroughly trained to recognize and avoid potential Sources of
contamination of chemistry samples (e.g., engine exhaust, winch wires, Deck surfaces, ice used
for cooling).
11) Grabs for sediment chemistry samples must be of similar sediment type and Have similar
penetration as the grab used for the infaunalsample. This is to ensure an adequate volume of
surface sediments for subsampling, and that the chemistry Samples come from sediments of
similar character as the infaunalsample. Tandem-rigged Van Veengrabs can facilitate this by
simultaneously collecting sediment samples from the same site for chemistry and benthic
analyses.
12) Sample devices that come in direct contact with the chemistry sample
sediment should be made of non-contaminating materials (e.g. plastic, glass, high
quality stainless steel, and/or Teflon) and should be thoroughly cleaned between
Sampling stations.
13) Chemistry sample containers must be of the recommended type of material
and must be carefully precleaned.
14) Sample holding conditions and holding times specified for chemistry samples
Must be followed explicitly.
SOIL INVESTIGATION
Soil Investigation will be carried out at the Proposed location of Diffuser and along the proposed
Pipeline route by drilling Boreholes. Location of the Boreholes will be decided in consultation
with Design Engineers. It is assumed at this stage that on Marine side 5 bore holes will be drilled.
Depth of the Boreholes considered is 20M.s
Wherever required by the Seabed conditions Rotary Drilling Method along with Mud Circulation
technique will be used in order to ensure borehole stability in unconsolidated soils.
Equipment to be used for this purpose will be Hydraulic Voldrill90 mounted on a Spud Barge.
Procedure to be fallowed will be in accordance with B.S. 5930-1999.The InsituTests and visual
analysis made during Site Investigation will be augmented by a series of Laboratory Tests. Tests
on Soil samples will be carried out in accordance with B.S.-1377(1990) “Methods of Test for Soil
for Civil engineering Purposes.” Test to be carried out will be as fallows.
1) Grain Size Analysis (BS 1377:1990: Part2)
2) Chemical Analysis (BS 1377:1990: Part3)
3) Natural Moisture Content Test. (BS 1377:1990: Part2)
4) AtterbergLimit Determinations (BS 1377:1990: Part2)
5) Bulk Density Test. (BS 1377:1990: Part2)
6) Organic Matter Content (BS 1377:1990: Part3)
7) Compaction Test. (BS 1377:1990: Part4)
8) Specific Gravity Test. (BS 1377:1990: Part2)
9) California Bearing Ratio Test (ASTM D1883)
10) Unconfined Compression Test (ASTM D 2938)
Based on the Observations and all the results obtained from insituTest and Laboratory Tests
Final Report shall be submitted. This Report will be used to derive recommendations on
Designing suitable Anchor foundations for the Diffuser and Pipeline.
DISPERSION MODEL
Dispersion Model test to show the practical suitability of the Sea Outfall and size the diffusers
required at the end of the in co-Marine Intake & Outfall ordination with MRMEWR. Services of a
well-experienced, very well known and well-equipped Organization in the field of marine
modeling will be utilized for undertaking this work. National Environmental Engineering
Research Institute (NEERI) will be associated with us for dispersion Model studies and EIA.
Their profile and facilities are attached as Annexure.
Hydrodynamics of an effluent continuously discharging in to a receiving body can be
conceptualized as a mixing process occurring in two separate regions. In the first region the
momentum flux, buoyancy flux and outfall geometry influence the jet trajectory and mixing. This
region is called as near field. At the end of the initial mixing region the waste field is established.
Conditions prevailing in the ambient environment will control trajectory and dilution of the
turbulent plume through buoyant spreading motion. This
region is referred to as far field or dispersion zone.
The Cornell Mixing Zone Expert Marine Intake & Outfall System (CORMIX) is a series of software
elements for analysis and design of submerged buoyant or non-buoyant discharge containing
conventional or toxic pollutants in to stratified waters with emphasis on the geometry and
dilution characteristics of the initial mixing zone. CORMIX2 addresses multyportDiffusers
/intake structure. This expert system developed by EPA of USA IS ACCEPTED internationally as
an excellent tool to provide information in initial Dilution.CORMIXsoftware is proposed to be
used to predict initial dilution under various tidal conditions. The inputs required for predicting
initial Dilutions in the pre design stage will be obtained from the Marine Surveys and
Investigations.
There are several mathematical models used for hydraulic studies for dispersion patterns at far
field of the. MIKE21 software developed by DHL Denmark can model wave transformation,
Currents due to waves and tides, advection and dispersion, water quality, mud and sand
transport etc. This software will be used to carry out the Dispersion Model of the far field.
MIKE21 is a well-proven professional engineering and extensively used software package for
simulation of flows, waves, sediments and ecology. T he two dimensional modeling system is
designed in an integrated modular framework with a variety of add on modules. It is possible to
match and study almost any real world free surface water phenomena using this software.
Further more these simulations tools facilitate easy application at all project stages. This
Software will be used at all the stages of the Project from feasibility through design, Construction
to Operation and Maintenance.
MIKE21 Provides
• A complete and effective design environment with flexible and easy water quality modeling.
• Advanced Graphical user interphasecombined with a series of efficient computational engines.
• GIS Integration
• Free tools e.g. for processing of model data in MATLAB.
• Modules for virtually any kind of 2D water modeling.
• Sophisticated tools for data handling, analysis and visualization.
• Multiple Computational grid option ensuring optimal model application.
The seawater quality and coral population, if any will be Periodically monitored, to assess any
change/impact due to discharge of wastewater.
DESIGN & ENGINEERING
After receiving the necessary approvals to the survey and modeling works, a Design Philosophy
Report for the Marine Intake & Outfall shall be prepared, that presents a conforming Outfall
option using the materials, pipe sizes, diffuser dimensions, burial, cover, rock fill and all other
arrangements for the Outfall, together with construction methods to install, secure, verify and
commission the Outfall.
Preliminary data based on Design at the Proposal stage is as fallows.
Intake Pipeline
• Pipeline material-OD 1600 HDPE pipe -1042m,2NosOD 90 HDPE pipe -1042m.
• Pipeline diameter -OD 1200 HDPE pipe 620m
• Diffuser diameter 1200mm, Tapered, length 50m
• Trench excavation depth to provide 1.5 mtrson top of the pipes.
• Depth of cover for offshore pipeline------------------------(will be installed by float and
( sink Method.
• Backfill and rock protection --------------------------------Only wherever required.
• Arrangement of diffuser ports -------------------------------Inclined at 45 degrees to the
axis Of Pipeline alternatively in Opposite direction.
Information stated above is subject to change at final Design stage.
The Design Philosophy Report shall contain a thorough design analysis and report
And the analysis will include following aspects
• Foundation conditions and settlement
• Marine Intake & Outfall hydraulics and air removal
• Loads on pipeline, including buoyancy
• Pipeline materials, including corrosion protection and service life
• Transition between different seabed materials and sediments.
• Concrete weights, tie-downs or anchors
• Protection of pipeline and diffuser risers and ports from Damage
Fallowing aspects will be taken in to account in designing.
• Materials selected for the pipeline and diffusers, and joints should prevent ingress of seawater
and sediment, and preclude corrosion as far as practicable
• The ports shall be designed (and opened over time) to prevent seawater intrusion into the
conduit. The FoudeNumber at every port shall exceed 2.0 at the minimum flow (but not when
the flow to the Marine Intake & Outfall is shut off)
• The diffuser ports should be designed to facilitate replacement in case of damage by a dragged
anchor, net or any other reason by providing a coupling or flange connection
in the riser above the sea floor and a designed weak point at the coupling or flange
• Diffusers and/or rock armourshall be designed to facilitate shedding of dragged nets and
trawls
• All portions of the Marine Intake & Outfall in navigable waters shall be sufficiently
protected by either depth of cover and/or armouringto survive anchors dragging across the
pipeline
• The ports shall be designed to facilitate entry by remotely operated inspection devices such as
TV cameras
• The pipe radius shall not exceed 20 % of the pipes critical radius of curvature during all pipe
handling operations, installation and service
• The minimum design pressure rating shall achieve a minimum factor of safety of 1.5 for the
maximum operating internal pressure
• Pigging of outlet to diffuser, prior to diffuser installation
• Pressure testing of Marine Intake & Outfall sections and entire Marine Intake & Outfall with
Diffuser / intake structure
• Post construction survey
• Head loss flow once flow is initiated
7. SUPPLY AND INSTALLATION
DIFFUSER / Intake Structure.
Design of the Diffuser envisaged in this Proposal will be with objective to achieve balanced flow
distribution under most of the operational conditions with minimized energy loss. The
hydraulics occurring both outside and inside of diffuser/ intake structure will be carefully
considered. Final design will be based on the external environmental hydraulics, which deals
with effluent mixing with the ambient fluid downstream of the ports and Internal hydraulics
including flow partitioning and related pressure losses along the manifold, which will result in
discharge profile along the diffuser.
.
Based on the data made available at this stage, the Diffuser / intake structure intake structure
shall be made out of a Pipe of 1.2 m. internal Diameter and 50 m. long, which disposes 5,796 Cu.
M. per hour under 10 water column head by gravity discharge. It may be tapered towards
upstream for increasing the diffuser / velocities for scouring purpose, and fitted with number of
risers at an angle of 45 degrees to the axis of the pipeline and alternately in opposite direction
(One to the right side and other to the left side of the Axis of Pipeline.)
DREDGING & TRENCHING
The work relating to dredging a trench for laying . Pipeline material-OD 1600 HDPE pipe -
1042m,2NosOD 90 HDPE pipe -1042m. Pipeline diameter -OD 1200 HDPE pipe 620m.
2. SCOPE OF WORK
2 2.1 SCOPE OF WORK
Excavation of trench upto35m water depth for laying 30inch submarine pipelines and back
filling with local material & engineered material as required
2.1.1 Excavation trench from LFP to KP , inter tidal zone KP 0. to KP and shallow water from KP
to KP along with pipe line route which is being laid for M/s PETROIRAN OFFSHORE FACILITIES
as per requirement and specifications of the client
2.1.2 Once the pipe is laid in the pipe line trench in the dredged channel, work involves back
filling the trench with local material earlier dredged or new material dredged from nearby or
transported from ashore & graded stones and an armourlayer of rocks ..
2.1.3 The trench to be excavated will have width of 2 Mt. At bottom and depth of 3 Mt
2.1.4 Provision of Survey equipment and personnel to carry out the survey of the trench for
correct dimensions.
The dredged material shall be disposed of at approved dumping ground about 1000 Mts. away
from the pipe line route as approved by the port authorities.
The side slopes shall be such that the trench shall be stable under the site conditions that prevail
at the site for the time required.
3
4 2.2 SEQUENCE OF ACTIVITIES
-Mobilisationof marine spread, vessels, crafts for dredging and trenching.
-Provide manpower for the dredging and trenching works.
-Project Management for dredging and trenching works.
-Planning, organisingand progress monitoring.
-Provide positioning services.
-Pre-dredging survey
-Intermediate dredging surveys
-Post dredging surveys
-Dredging and trenching by dipper Dredger and Cutter dredger
-Dumping of dredged material at designated dumping location.
-Conduct/Perform maintenance dredging until pipeline laying.
-Measure progress of dredging and trenching works
-Clear site of all debris and construction equipment
-Demobilisationof marine spread, vessels and crafts, personnel, site office etc.
5 2.3 TRENCH DIMENSIONS
The trench dimensions etc. envisaged in the tender are proposed to be modified partially as
under, after detailed study of site conditions etc and all relevant drawings including trench
profiles, alignment and cross sections etc.
Note: Side slopes shall be 1 : 3
3.0 PROCEDURE FOR PRE-TRENCHING BY DREDGING
6 3.1 INTRODUCTION
Work involves Pre-trenching by dredging from ChainageKP to ChainageKP dredging of coral
rufsoil like corals, sand stone / clay and other materials not exceeding compressive strength of
3.2 .
7 3.2 TRENCHING IN SOFT SOIL
MARINE SPREAD
The following Marine Spread for dredging and disposal of soft soil and clay will be utilized
-Shallow portion with Excavators -Shallow zone upto5 mtrsdepth with cutter section dredgers
-Up to ---mtrswater depth with Dipper Dredger in combination with hopper barges and tugs
The dipper Dredger (1 No.) and Cutter section Dredger (2 No.) and Excavator ( 1 No. ) will be
utilized for excavation of the trench by dredging. Hopper barges and tugs shall be used for
transportation of the dredged material from the dredging area to the designated dumping
grounds and disposal.
Dipper dredger –working method
Non propelled dipper dredger will be towed to dredging place and positioned with the help
DGPS system using navigation software. Necessary data will be fed into the onboard computer to
maintain trench section profile and depth. Dredging operation involves lowering of the
excavator‟s bucket to the sea bed level, excavation of the material and discharging dredged
material in the along side placed hopper barge. The barge is utilized for transportation and
disposal of the dredged material at designated dumping with the help of a towing tug.
CUTTER SECTION DREDGER
Cutter section dredger will be positioned on pipe line route with the help of DGPS system. The
dredged material will be discharged about 500 Mts. away with help of pipes. .
8 3.3 PRE-TRENCHING –SEQUENCING IN SECTIONS
Land portion trenching will be done with help of excavators.
Shallow water upto5 mtrsdepth -Will be carried out with the help of Cutter section dredgers.
Shallow water /deep water dredging we propose to mobilisea Dipper dredger “Obscured By
Clouds”. The dredger is fitted with 16 Mts. boom, 9.5 Mts. stick suitable 4.5 M3bucket.
The Boom and stic6s can be changed for required depths.
The Dipper dredger will be supported by two number of hopper barges of approx. 450 M3 and
towing Tugs to collect the excavated material and for dumping.
The excavated material shall be disposed off at a distance of approx. 1000 Mtrsaway, along the
pipe line route near the beach for reusing the same material for backfill. Floating buoy will be
placed to mark the position.
Survey Boat duly fitted with echo sounder will keep on checking the trench till the pipe lay barge
is mobilized and pipe is pulled in the trench.
We expect considering the soil a trench with 4 Mtrsat the bottom and 1:3 slope should stabilize
and trench should stay till pipe pull is completed.
9 3.5 DUMPING GROUND
The dredged material is transported through hopper barges and dumped at dumping ground or
1000 m away from the pipe line route as explained above.
10 3.6 DREDGING -CONTINGENCY PLAN
UNEVEN BED LEVELS / OVER DREDGING
The dredger “Obscured By Clouds” is fitted with Seatecon board, every bucket operation is
monitored and there is very little scope of over dredging. However, over dredging, if any, over
the permitted tolerances will be known immediately upon survey of that area and excavation
will continue at this level to bring the trench bottom close to natural flexibility tolerance.
UNDER DREDGING
After completion of dredging, post-dredging survey shall be conducted. In case, the designed
depths have not been achieved, the area shall be re-dredged to attain the designed level.
TOLERANCES
Vertical –0 to + 30 cm and horizontal –Nil tolerance as required shall be maintained. There is no
tolerance above the bed level or within the minimum trench width stipulated in the contract.
SIDE SLOPES
Dredging plan shall take care of 1:3 side slopes as required in designed width of the trench
before the pipeline is laid
MAINTENANCE DREDGING
Before the pipeline is laid, the area shall be surveyed to see whether profile of the trench is
maintained or not. If the profile is not maintained, the area shall be re-dredged and the trench
profile is obtained as per the design.
BACK FILLING -The excavated material dumped near the beach, KP and KP will be loaded into
the split hopper barges with help of Excavator/dredger and transported to the pipe line. With
the help of survey boat, split hopper barges will be guided across the trench , to discharge, in
order to lock the pipe in the trench at every 50 ML. After locking the pipe in the trench, hopper
barge will discharge the material over the pipe line route travelling over the trench and
discharge, still with help of survey boat, second hopper barge material overlapping the discharge
from the previous hopper barge and so on to complete the back filling operation alternatively.---
---------------
Cutter section shall be placed about 100 Mts. away parallel to the pipe line route and discharge
shall be guided in to the trench
REPORTING
Daily Progress Report indicating the KP chainagevalues, environmental parameters, survey
analysis of trench profiles, quantity dredged, number of loads shall be furnished. Individual daily
progress reports for each hopper barge will be prepared and enclosed with the main report.
4. SCHEDULE OF OPERATIONS
11 4.1 WORK SCHEDULE
The work schedule for execution of the work is furnished in Bar Chart attached
4.2 IHS surveys shall be conducted in following phases of work to determine trench
profiles:
1) Pre-dredging survey to ascertain the existing bed levels
2) Intermediate surveys as required to access the progress
3) Post-dredging survey to ensure that the levels after dredging complies with the specifications.
5. EXECUTION PLAN
One dipper dredger, one cutter section dredger and excavator 300 supported by hopper barges,
tugs and other supporting vessels shall be deployed for execution of the work
PIPELINE.
This Proposal is based on Pipe Diameter as 1600 HDPE –1042 MTRS 2 NosOD 90 HDPE pipe -
1042mtr –OD 1200 HDPE pipe –620m. mm and length of the pipeline
3 Km. The pipe material proposed to be used is HDPE Pipe, Manufactured by Amiantitof Oman or
equivalent.
Pipe of these materials have fallowing advantages:
a) It is light in weight and, thus, requires no specialized handling equipment.
b) An outfall pipeline can be quickly fabricated on shore by butt fusion.
c) Correctly butt fused joints are stronger than the pipe itself essentially precluding future leaks
at the joint due to settlement or movement.
d) HDPE pipe is sufficiently flexible for it to be installed on a tortuous route
e) The butt fusion method of joining is sufficiently rapid to enable the fabrication of long
Ocean Marine Intake & Outfall.
f) Polyethylene is essentially immune to the corrosive effects of seawater and attack by marine
organisms.
g) The HDPE pipe is light enough, yet strong enough to be pulled and floated into place using a
tugboat for towing and small boats for alignment of the outfall.
h) If necessary, the pipe can be re-floated by injectinof compressed air.
HDPE pipe is suitable for bottoms of sand, mud gravel and small rocks but requires external
weights (usually concrete) or mechanical anchors to hold it in place and prevent it from floating
of from moving due to hydrodynamic forces. It can also be placed on a seabed of rock as long as
the pipe itself is not resting on a point or sharp ridge.
PIPE DIAMETER SELECTION
Selection of pipe diameter for HDPE Marine Intake & Outfall is made through the same series of
determinations as for other pipe material. This is usually done through a balancing of friction
loss reduction against the flow velocities necessary to maintain sufficient scour to prevent
deposition of suspended solids, or grease build up on the pipe wall. New HDPE pipe has excellent
flow characteristics. Because of its exceptionally smooth its Hazen and Williams Formula
coefficient of C = 155 but for outfalls that have been in use the C is usually estimated to be 140
due to build up of grease on the pipe wall.
For sewage outfalls utilizing HDPE, the flow velocity ranges that have proven satisfactory
from both a friction and a cleansing standpoint usually fall within the ranges of 2 to 3 m/s. The
amount of and characteristics of the suspended solids and grease in the effluent influences the
necessary velocity for self-cleansing.
It is important that cleansing velocities be achieved at least one time every day for a sufficient
period of time to obtain complete flushing of the line. If this does not occur, depositions of solids
and bacterial growth on the walls will occur and it will be necessary to send a cleaning plug (a
pig) through the outfall at regular intervals to prevent pipe constriction or closure. When
designing an outfall for a 100-year projected flow it is important
check the velocities at the present maximum flows to see if sufficient scour velocities are
obtained during the first few years of operation. If not, then a maintenance schedule utilizing a
cleaning plug would have to be implemented until such time that flows reach a level to obtain
cleansing velocities. Facilities for the removal of grit and grease from the effluent prior to its
discharge into the outfall will help minimize problems due to deposition and is recommended.
This removal of grease along with floatable serves a second purpose of maintaining
Acceptable aesthetic conditions. Computer programs will be used to develop a head loss-
discharge curves for of Pipe to facilitate the selection of an optimal diameter. HDPE plastic pipe
is described by a specified exterior diameter and by a minimum wall thickness needed to obtain
the pressure rating of the pipe. it may well be assumed that the highest tide and peak sewage
flow can probably occur simultaneously. The submarine outfall and appurtenances such as flow
equalizers of pumps should be designed accordingly, so as to avoid undesirable surcharge of
gravity sewers that have service connections. The fact that seawater has a density that is
approximately 2.5 percent greater that the density of sewage also to be taken into account. This
static head must be overcome by the gravity head available.
In the ocean normalytidally driven strong currents occur twice a day. Tidally generated
movement of water can also reach high velocities on a daily basis. Frequently such areas have
geomorphologicallysheltered from the open ocean and are thereby protected from large waves.
In such cases the currents are the critical factor in determining the method of stabilizing the
outfall. An equation that can be used to evaluate the necessary ballast weight necessary to
stabilize a HDPE Pipeline against a current perpendicular to the centerline of the outfall is…
WB= the buoyant weight (submerged weight of the Marine Intake & Outfall) of length L
CD = the drag coefficient
CL = the lift coefficient
r = the mass density of seawater (the unit weight of seawater divide by acceleration of gravity)
ms = the static friction coefficient between the ballast anchor (or pipe wall) and the seabed
D = pipe diameter
L = length of pipe section considered (usually a length of 1 meter)
V = the velocity of the current moving perpendicular to the pipe
It is important to note that WB is the submerged weight of the outfall not the weight in air. This
can be calculated by multiplying the weight in air by (the sink factor –1). The sink factor is
explained in the following sections. The friction factor ms varies between about 0.6 and 1.4 for
sand and between 0.2 and 0.7 for silt and clay.
It is critically important to take into consideration the forces that are exerted by ocean waves on
a submarine Marine Intake & Outfall Pipeline particularly where the outfalls extend from a
coastline facing the open ocean especially in regions that are frequented by hurricanes or other
violent storms. The first step is to decide on a recurrence interval of a rare but possible deep-
water wave that would travel to the Marine Intake & Outfall site during the useful life of the
submarine outfall being planned. For ocean outfalls a common
Recurrence interval (return period) is 50 years and sometimes a rather conservative interval of
100 years is used.
Historical database of storms and hurricanes that pass within a selected radial distance of the
outfall site will be analysed. A distance of 300 nautical miles is a common figure used for this
purpose. One of a number of hurricane/tropical storm hindcastwind models is applied to each of
the storms/hurricanes. These models incorporate into them such factors as the storms
maximum wind speed, the speed that the eye of the hurricane travels, radius to maximum wind
speed, and distance from the eye of the storm to the maximum wind speed. The model is used to
determine the maximum deep-water wave height and period at the outfall location for each of
the storms. After this a statistical analysis is used to determine wave heights and periods for
different return periods. The results are usually presented in tabular form that correlates
various return periods with the respective maximum wave height, wave period, standard
deviation, and probability of excedence Return periods commonly presented are for
2,5,10,20,25,50, and 100 years.
Now the person designing the submarine outfall must use the derived design wave to determine
the Hydrodynamic forces that this wave will cause to be exerted on the outfall. The first step is to
determine the maximum velocity and maximum acceleration that the deep-water design wave
would generate at the water depths in which the outfall is to be located. The maximum velocity
is used to determine the drag force and the acceleration is used to determine the inertia force
that the design wave exerts on the outfall Pipeline as it passes over the outfall.
Entering the maximum velocity and maximum acceleration into any of several available
computer programs the maximum horizontal and maximum vertical forces exerted by the
design wave can be calculated. It is also necessary to adjust the coefficients of these equations to
account for the angle of incidence of the design wave‟s approach to the axis of the outfall pipe.
Knowing the maximum horizontal and vertical forces to which the outfall Pipeline would be
subjected during its design life it is possible to make a decision on how to assure the stability of
the outfall. It may be necessary to bury the Marine Intake & Outfall Pipeline in the seabed to
adequately protect it. It might be feasible to fasten the outfall to the seabed with mechanical
anchors that are screwed or driven into an unconsolidated seabed. It also might be possible to
stabilize the HDPE outfall by attaching sufficiently heavy ballast anchor weights onto the HDPE
pipe to affix it to the seabed.
The outfall may be stabilized with a combination of these methods.
STABILIZING HDPE OUTFALLS WITH CONCRETE BALLAST ANCHORS (WEIGHTS)
HDPEoutfalls Pipeline stabilized by concrete ballast anchors rarely fail because the HDPE pipe
and anchors tend to settle into the scour excavation without causing breakage of the pipe thanks
to the flexible characteristics of HDPE. HDPE can also tolerate movement better than almost any
other submarine pipeline material.
10.1 Determination of the spacing of anchor weights
The worst beam-stress condition usually occurs during installation and this is due to the weight
of the anchors during the floating and towing of the pipeline. It may also occur from
hydrodynamic forces due to currents and possibly from the sinking of the anchors into a soft
seabed. It is important that distances between anchor collars not be too great. The stress exerted
can be estimated as a uniformly loaded simple beam with a unit-loading equal to the unit
buoyancy of the pipe. The greatest
Stress and deflection occurs during the sinking of the Marine Intake & Outfall during the
installation on the seabed.
Determination of anchor collar weight
There are two distinct considerations in determining the amount of weight to adequately anchor
ocean outfalls of HDPE. One consideration is the ballast necessary to preclude flotation in areas
outside of the surge-surf zone, the other is to prevent movement inside the surge-surf zone
during worst expected storm conditions. Two altogether different approaches are used.
The term sink factor is used in HDPE submarine pipelines to describe the ratio of the total
downward force to the total upward force of the pipeline system including pipe, pipe contents
and anchor weights (collars). The sink factor is nothing more than the systems "specific gravity".
It is used as an indicator of the pipeline's stability and resistance to the various hydrodynamic
forces exerted by the ocean, and rules of thumb for appropriate use of sink factor values range
between.
Polyethylene pipe in soft sediment shall be secured by concrete weights or piles against flotation
with a factor of safety against uplift of 1.5.
Key design details are as follows:
• Minimum cover for all reinforcement shall be 75 mm.
• Rubber sheet 5 mm thick between block and PE pipe.
• PVC sleeves cast into blocks for connecting bolts.
• Each nut shall have a zinc nut of the same size.
• Weight blocks and collars on pipe shall be designed with a low center of
gravity to Prevent rolling and twisting of the pipe.
• Connecting bolts can be 316 SS or galvanized steel, with zinc Anodized
• Concrete used for blocks shall have minimum 28-day strength of 36 MPa.
• Typical spacing of blocks shall be 2.5 m to avoid gas pockets.
• Concrete blocks shall not extend more than 250 mm above the top of the pipe.
Ballast anchor design
Ballast anchors for HDPE submarine outfalls are usually made of reinforced concrete because of
concrete's suitable density and durability in seawater. There are many possible designs, but
generally a trapezoidal or square design is used in the open ocean so that the ballast anchor will
resist rolling when subject to lateral forces due to currents or wave action. In any case the
specific design chosen would be based on:
a) Ease of fastening the anchors to the pipeline;
b) Fasteners resistant to salt water corrosion;
c) Ease of bending and placing the reinforcing steel and:
d) Ease of casting the concrete.
particular variation uses two bolts of saltwater corrosion resistant material. It is possible to also
use fiberglass bolts, or polyethylene plastic pipe with heat formed ends as a means of fastening
the halves together.
Concrete ballast anchors may be factory cast and hauled to the outfall assembly site or cast at
the assembly site by the same labor crew to be used for installing and assembling the HDPE
outfall. Ballast anchors cast at worksite In casting the two halves of the Type A design, the form
shown in Figure 6 is usually constructed so that both halves of the collar can be cast at the same
time, using a short piece of the HDPE outfall pipe to achieve an exact fit. The two halves are
separated by 1/2 cm (1/4 inch) plywood. This provides sufficient play to insure a tight fit when
the two halves are bolted together when the anchor collar is attached to the pipe. The holes for
the bolts are formed using thin wall PVC pipe with an internal diameter 50 percent larger than
the diameter of the bolts to be used. They are held in place by a rod extending through the form
so as to help assure bolt alignment.
It is important to schedule casting of concrete anchor collars to be completed at least one month
in advance of outfall installation to allow adequate time for curing. Consideration should be
given to casting the anchor collars at the outfall shore line site to avoid unnecessary handling
and transportation.
It is also a good idea to number the matching halves when they are removed from the form
to assure compatibility of bolt holes. In any case, a little extra care in form precision will pay for
itself many times over during the attachment process.
The concrete used in the ballast weights should have a minimum cement content of 375 kg/m 3
and a 28 day strength of 300 kg/cm2 so as to be resistant to the salt water environment and
reduce the potential for corrosion of the reinforcing steel. High early strength cement may be
used to allow early removal from the forms, thus, reducing the number of forms needed over the
casting period. The type of cement used should be for marine use.
.
JOB SITE FOR BUTT FUSION AND ANCHOR COLLAR ATTACHMENT
Careful planning of the butt fusion and concrete ballast anchor attachment operations is always
necessary. The primary objective is to get the outfall constructed properly and into the water as
quickly and as easily as possible. The strategy to accomplish this should include the following
components:
a) Material storage in a convenient, easily accessibly location.
b) Adequate size and number of pieces of heavy equipment to handle material.
c) Selection of butt fusion equipment that is adequate for the diameter and DR of the outfall pipe
and which automatically records the essential details of the fusion of each joint. Experienced
fusion equipment operator will be employed for the job.
d) Protection of the butt fusion process from wind, dust, rain, snow. If necessary an enclosed or
semi-enclosed shelter for this operation will be provided. The pipe manufacturer‟s
recommendations for the fusion process will be strictly fallowed. Assure adequate time (at
least 35 seconds for each cm of diameter) for the newly fused joint to cool sufficiently before
the pipe is removed from the clamps of the fusion machine and an additional 20 minutes
before the joint is subjected to traction or flexure.
e) Adequate temporary facilities will be provided on which to fabricate the outfall Pipeline and
from which to launch the outfall Pipeline in to the ocean. The temporary facilities should be
designed to require as little motion and as little handling of materials as possible, especially the
ballast anchors.
e) The system for attaching the ballast anchors should enable the ballast anchors to be
accurately spaced at the designated intervals on the outfall Pipeline.
g) The temporary facilities should enable the completed outfall assembly to be moved into the
ocean as efficiently and quickly as possible with as little handling as possible.
h) Doing all this in a safe manner.
It will be planned to construct a temporary facility ( a small rail system) on which butt fuse and
fabricate the entire outfall with the ballasts, end plates, and pulling heads securely attached .
After pressure testing the outfall it will then pulled and towed down the rail system to launch it
into the ocean. The entire outfall will then towed into place and carefully submerged by
releasing air and allowing water to enter the outfall. It will be guided into the desired seabed
route by divers that instruct the boats for direction of pull and advise a person at the terminal
end when and how much air to release.
A variation of this method is to fabricate the outfall, with ballasts attached, in 2 or 3 long sections
and then launch the sections consecutively and butt fuse them together during the launching
process. It is important that the methodology chosen for ballast anchor installation make the job
as easy as possible.
When this method is used it is common practice to install a temporary working platform at the
waters edge so the concrete anchor collars can be attached immediately before the pipe is
dropped into the water. A gantry with block and tackle will be installed at this platform for
handling and attaching the concrete anchors. Typically a system or rollers is used to guide the
pipe from the butt fusion area to the platform and facilitate the forward movement of the butt
fusion area to the platform and facilitate the forward movement of the pipe.
TRENCHING FLOATING, SUBMERGING AND PLACING THE OUTFALL
The HDPE submarine outfall is designed to be buoyant with the anchor collars attached and the
pipe filled with air and to be strongly negatively buoyant when it is subsequently filled with
water. Air is contained in the pipe by means of a sealed and plug or plate securely attached to the
end of the pipe. The plate or plug is fitted with an air release/inlet valve and then it is attached to
the terminal end of the pipe. By gradually releasing air from this valve and allowing water to
enter the outfall at the shore end. The rate of descent is controlled through the release of air at
the terminal end and the controlled entrance of water at the shoreline. It is important that the
pipe be sunk from the shore progressing to the terminal end so as to preclude entrapment of air
in a high spot.
A number of small boats are needed to tow the pipeline out from shore as it is fused together
and the anchor collars are attached and to tow it into place for submergence. Several boats are
stationed at intervals along side the pipe on the up current side of the route pulling the pipe into
place. During the sinking, the boat at the terminal of the pipe operates the air release valve. The
boat at the terminal end of the pipe does not have to be in place until the final length is sent into
place. Three placement boats are usually required in the vicinity of the section being sunk.
It is usually easier to allow the pipe to flex with the current gradually pulling it into place along
the route as it is sunk.
Divers on the pipeline communicate with both the three or four placement boats, which are
towing the pipe into place, and the boat on the terminal end releasing the air. The divers advise
the placement boats to move the pipe to right or left, or hold, so as to keep the pipe on alignment
as it reaches the bottom and also advise the air release operator when to release the air to obtain
descent of the pipe.
Air is released in a series of short bursts with sufficient time between bursts to receive
communication from the divers. Release of the air should be controlled slowly. It should be
equivalent to the pressure of water at the depth of submergence. The end plate (or plug) must be
securely fastened to the terminal end. The pulling head should be fitted with a check valve and a
quick connect coupling to permit attachment to an air compressor if needed. It should also be
fitted with a strong, corrosion resistant air release valve of a diameter appropriate for the
diameter of Pipe. The terminal/air release boat will have a small air compressor with a hose at
least 50 percent longer that the depth of the end of the outfall to allow refloating and adjustment
if necessary.
The shoreward end of the HDPE outfall will be fitted with a butt fused flange adapter and with a
bolted plate with an air-tight gasket. It would also be fitted with a water valve of sufficient
diameter to allow water to enter the pipe at a reasonable rate for submergence of the outfall.
In addition, all boats would be fitted with two-way radios or supplied walkie-talkies.
A communication system to enable the divers to give instructions directly to the boats. All
divers would be instructed to stay above the pipe at all times. The divers would have available
several large air lift bags with lifting straps each capable of lifting 400 lbs. so, if necessary, to
make minor adjustments in the pipe without having to refloat it. There should be a sufficient
number of divers on hand to enable shifts so as to avoid the necessity for decompression,
otherwise a decompression chamber should be on hand.
Markers shall installed on the seabed along the alignment of the Outfall. And will then make a
detailed topographical survey of the seabed sufficient to define the precise profile of the Marine
Intake & Outfall. The Contractor shall make an underwater video Along the full length of the
Outfall pipeline to document seabed conditions prior to the Installation Work. The video shall
show chainagemarkers at 100 m intervals. And then second underwater video along the full
length of the installed Intake & Outfall pipeline shall be made to document seabed conditions on
completion of construction. The second video shall show the pipeline, all supports and sufficient
area of the adjacent seabed to record biological Conditions.
The as-constructed video shall be recorded soon after the Outfall is commissioned. A
photographic record and video record of the land and vegetation at the shoreline and across the
beach prior to the works commencing will be provided. A post-construction survey of the pipe
alignment using bathymetric and side-scan sonar surveys to document that the seabed has been
restored to near pre-construction Conditions will be made. Survey control will be by GPS. A
detailed survey of all works including the Outfall, diffuser, supports, piles, deaerationchamber
and other facilities will also be made. On completion of all construction, the Outfall shall be
commissioned using effluent from the treatment plant. Until commissioning, the facility shall be
maintained stop logs in the access chamber to prevent sediment, flow or material entering the
Outfall.
A commissioning plan addressing fallowing shall be Prepared.:
• Outfall conditioning to preclude internal biofouling(eg. Capped ports, fill with fresh water, or
Filtered, disinfected seawater)
• Inspections prior to commissioning
• Removal of port caps
• Assurance tests
As part of commissioning, fallowing shall be demonstrated:
• De-aeration structures operate and that air is released at
each vent • Effluent discharges from each of the ports
OPERATION & MAINTENANCE.
A long term operations and maintenance (O&M) plan shall prepare and submitted to. The O&M
plan will depend on the actual design and construction arrangements, however following
elements will be included:
• Time schedule of recommended inspection and maintenance activities for theMarineIntake &
Outfall, diffuser ports, air release points,
• The hydraulic head shall be measured continuously in the theMarine Intake & Outfall l at the
shore to allow hydraulic (conveyance capacity) evaluation and identification of any blockage or
riser damage
• Contingency plan to control biofouling
• Contingency plan to repair any damage to ports
• Procedures for diver access to the pipeline and diffuser
• Procedures for monitoring long term settlement of the pipeline
• An Outfall shutdown and re-commissioning protocol.
Organization envisaged for O&M is as fallows.
Operation Manager
Facility Supervisor
Marine Environmentologist.
Divers
Pipe Fitter
Pipe Welder
Fallowing Equipment may be required to hire as and when required.
Boat with Diving Station
Barge mounted with Crane. By: Abhay Ocean Team
Top Related