Drilling and Sampling of Soil and Rock
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Transcript of Drilling and Sampling of Soil and Rock
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Unit 2: Drilling and sampling of soil and rock
Exploration in soil Soil drilling
Soil samples Soil samplers
Sampling interval
Sample identification and tests
Exploration in rock Rock drilling and sampling
Non-core drilling
Core drilling
Observation during core drilling
Geologic mapping
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References
GEO. 1987. Geoguide 2-Guide to site investigation.Geotechnical Engineering Office, Hong Kong SAR.
Mayne, P.W., Christopher, B.R., and DeJong, J. 2001.Manual on Subsurface Investigations. National HighwayInstitute Publication No. FHWA NHI-01-031, Federal
Highway Administration, Washington, DC. (Chapter 3)
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Existing guidance
Key guidance on site investigations is contained in GEOs Guide toSite Investigation (Geoguide 2). Other relevant documents
include: AGS-HKs Ground Investigation Guidelines. GEO (2001). Geospec 3, Model Specification for Soil Testing.
BS5930 (BSI, 1999) gives international guidance. International Society for Rock Mechanics and American Society
for Testing and Materials standards for rock testing.
IMMM-HK (2003). Ground Investigation Working Party Final
Report. GEO (2005). Site Investigation for Tunnel Works, Technical
Guidance Note No. 24 (TGN 24).
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Soil drilling
A wide variety of equipment is available for performingborings and obtaining soil samples. The method used to
advance the boring should be compatible with the soiland groundwater conditions to assure that soil samplesof suitable quality are obtained.
Solid stem continuous flight augers
Hollow stem continuous flight augers
Rotary wash borings
Bucket auger borings
Exploration pit excavation
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Solid stem continuous flight augers
Solid Stem Continuous Flight Auger Drilling System: (a) In use on drill rig, (b) Finger and
fishtail bits, (c) Sizes of solid stem auger flights, (d) Different assemblies of bits and augerflights. (All pictures in the above format are courtesy of DeJong and Boulanger, 2000)
(b)
(c) (d)
Limited to stiff
cohesive soils
where the boring
walls are stable forthe entire depth of
boring.
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Hollow stemcontinuous flightaugers
Hollow Stem Continuous Flight
Auger Drilling Systems: (a)Comparison with solid stemauger; (b) Typical drillingconfiguration; (c) Sizes of hollowstem auger flights; (d) Stepwisecenter bit; (e) Outer bits; (f)Outer and inner assembly.
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Hollow stem continuous flight augers
Dimensions of common hollow-stem augers
(1 8.500)470(17.500)446(12.250)311
(14.750)375(14.000)356(10.250)260
(13.000)330(12.250)311(8.250)210
(12.000)318(11.250)295(7.250)184
(10.250)260(9.625)244(6.250)159
(8.250)210(7.625)194(4.250)108(7.750)197(7.125)181(3.750)95
(7.250)184(6.625)168(3.250)83
(6.750)171(6.125)156(2.750)70
(6.250)159(5.625)143(2.250)57
Cutting Diameter ofAuger Head
mm (in)
Outside Diameter ofFlighting
mm (in)
Inside Diameter ofHollow Stem
mm (in)
Note: Adapted after Central Mine Equipment Company. For updates, see: http://www.cmeco.com/
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Hollow stem continuous flight augers
Hollow-stem augering methods are commonly used in claysoils or in granular soils above the groundwater level,
where the boring walls may be unstable. The augers form a temporary casing to allow sampling of
the "undisturbed soil" below the bit. The cuttings
produced from this drilling method are mixed as theymove up the auger flights and therefore are of limited usefor visual observation purposes.
At greater depths there may be considerable differencesbetween the soil being augered at the bottom of theboring and the cuttings appearing at the ground surface.The field supervisor must be aware of these limitations inidentification of soil conditions between sample locations.
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Rotary wash borings
The most appropriate method for
use in soil formations below the
groundwater level. In rotary wash
borings, the sides of the boreholeare supported either with casing or
with the use of a drilling fluid.
Where drill casing is used, the
boring is advanced sequentially by:
driving the casing to thedesired sample depth,
cleaning out the hole to the
bottom of the casing, and
inserting the sampling deviceand obtaining the sample from
below the bottom of the casing.
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(a) Typical drilling configuration;
(b) Casing and driving shoe;
(c) Diamond, drag, and roller bits;
(d) Drill f luid discharge;
(e) Fluid cuttings catch screen;
(f) Settling basin (mud tank).
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Dimensions of common drill rods, Http://www.boartlongyear.com/
34.9 (1.375)57.2 (2.250)66.7 (2.625)NW
19.0 (0.750)44.5 (1.750)54.0 (2.125)BW
15.9 (0.625)31.0 (1.250)44.4 (1.750)AW
12.7 (0.500)22.2 (0.875)34.9 (1.375)EW10.3 (0.405)18.3 (0.720)27.8 (1.095)RW
Inside Diameter ofCoupling mm (in)
Inside Diameter ofRod
mm (in)
Outside Diameter ofRod
mm (in)
Size
Dimensions of common f lush-joint casings, http://www.boartlongyear.com/
(3.000)76.2(3.500)88.9NW
(2.375)60.3(2.875)73.0BW
(1.906)48.4(2.250)57.1AW
(1.500)38.1(1.811)46.0EW
(1.185)30.1(1.437)36.5RW
mm (in)
Inside Diameter of CasingOutside Diameter of Casingmm (in)
Size
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Bucket auger boring
Used where it is desirable toremove and/or obtain large
volumes of disturbed soilsamples;
Bucket diameter: 0.6-1.2 m
Cylinder height: 0.6-0.9 m Good for most soils,particularly gravel andcobble soils.
Setup of Bucket Auger & Rig (from ASTM D 4700)
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Exploration pit
Exploration pits and trenches permit detailed examination of the soiland rock conditions at shallow depths and relatively low cost.
Depth: 2-3 m depending on requirements Sequence:
Logging vertical profile The contacts between geologic units should be identified and drawn
Characteristics and types of soil or lithologic contacts should be
noted Variations within the geologic units must be described and indicated
on the pit log wherever the variations occur.
Sample locations should be shown in the exploration pit log and theirlocations written on a sample tag showing the station location andelevation.
Groundwater should also be noted on the exploration pit log.
Photography and video logging
Backfilling
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Soil samples
Disturbed samplesDisturbed samples are those obtained using equipment that destroy themacro structure of the soil but do not alter its mineralogical composition.
Specimens from these samples can be used for determining the generallithology of soil deposits, for identification of soil components and generalclassification purposes, for determining grain size, Atterberg limits, andcompaction characteristics of soils.
Undisturbed samplesUndisturbed samples are obtained in clay soil strata for use in laboratorytesting to determine the engineering properties of those soils. It should benoted that the term undisturbed soil sample refers to the relative degree of
disturbance to the soils in-situ properties. Undisturbed samples are obtainedwith specialized equipment designed to minimize the disturbance to the in-situ structure and moisture content of the soils. Specimens obtained byundisturbed sampling methods are used to determine the strength,stratification, permeability, density, consolidation, dynamic properties, and
other engineering characteristics of soils.
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Common sampling methods
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Soil samplers
Split barrel sampler Both granular and cohesive soils
Thin wall sampler Cohesive soils
Piston sampler
Soft soils Pitcher tube sampler:
Both hard and soft soils
Other samplers
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Split barrel sampler
The split-barrel (or split spoon)sampler is used to obtaindisturbed samples in all types of
soils. The split spoon sampler istypically used in conjunction withthe Standard Penetration Test(SPT).
Standard lengths of 457 mm (18
in) and 610 mm (24 in) withinside diameters ranging from38.1 mm (1.5 in) to 114.3 mm(4.5 in) in 12.7 mm (0.5 in)increments. The 38.1 mm (1.5 in)inside diameter sampler is
popular because correlations havebeen developed between thenumber of blows required forpenetration and a few selectedsoil properties.
Split-Barrel Samplers:
(a) Lengths of 457 mm (18 in) and 610 mm (24 in);
(b) Inside diameters from 38.1 mm (1.5 in) to 89 mm
(3.5 in).
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(a) Open sampler with soil sample and cutting shoe; (b) Sample jar, split-spoon, Shelby tube, and storage box
for transport of jar samples.
(a) Stainless steel and brass retainer rings (b) Sample catchers.
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Thin wall sampler
The thin-wall tube (Shelby)
sampler is commonly used to
obtain relatively undisturbed
samples of cohesive soils forstrength and consolidation testing.
The sampler commonly used has
a 76 mm outside diameter and a
73 mm inside diameter, resulting
in an area ratio of 9 percent.
Thin wall samplers vary in outside
diameter between 51 mm and 76
mm and typically come in lengthsfrom 700 mm to 900 mm. The test
method for thin-walled tube
sampling is described in ASTM D
1587.
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(a) (b)
The sample in Shelby Tube should be sealed with (a) 25 mm thickMicrocrystalline wax, or (b) O-ring packer.
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Piston sampler
Piston Sampler. (a) Picture with thin-walled tube cut-out toshow piston, (b) Schematic (After ASTM D 4700)
(a)
The piston sampler is
basically a thin-wall tube
sampler with a piston, rod,
and a modified samplerhead. This sampler, also
known as an Osterberg or
Hvorslev sampler, is
particularly useful for
sampling soft soils where
sample recovery is often
difficult.
The quality of sampleobtained is excellent.
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Pitcher tube sampler
The pitcher tube sampler isused in stiff to hard clays andsoft rocks, and is well adaptedto sampling deposits consistingof alternately hard and softlayers. This
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Pitcher Sampler. (a) Sampler Being Lowered into Drill Hole; (b) Sampler During Sampling of Soft Soils, (c)
Sampler During Sampling of Stiff or Dense Soils. (Courtesy of Mobile Drilling, Inc.)
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Bulk and block samples
Bulk samples are suitable for soil classification, index testing, compaction,California Bearing Ratio (CBR), and tests used to quantify the properties ofcompacted geomaterials. The bulk samples may be obtained using hand tools
without any precautions to minimize sample disturbance. The sample may betaken from the base or walls of a test pit or a trench, from drill cuttings, froma hole dug with a shovel and other hand tools, by backhoe, or from astockpile.
For projects where the determination of the undisturbed properties is verycritical, and where the soil layers of interest are accessible, undisturbed blocksamples can be of great value. Undisturbed block sampling is limited tocohesive soils and rocks. The procedures used for obtaining undisturbedsamples vary from cutting large blocks of soil using a combination of shovels,hand tools and wire saws, to using small knives and spatulas to obtain smallblocks. For cohesive soils, the Sherbrooke sampler has been developed and isable to obtain samples 250 mm diameter and 350 mm height (Lefebvre andPoulin 1979). In-situ freezing methods for saturated granular soils and resinimpregnation methods have been implemented to lock the soil in the in-situcondition prior to sampling.
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Taking block rectangular sample(ASTMD7015-04)
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Taking cylindrical sample(ASTMD7015-04)
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Sampling interval
The sampling interval will vary between individual projects andbetween regions.
A common practice is to obtain split barrel samples at 0.75 mintervals in the upper 3 m and at 1.5 m intervals below 3 m.
In some instances, a greater sample interval, often 3 m, is allowedbelow depths of 30 m. In other cases, continuous samples may berequired for some portion of the boring.
In cohesive soils, at least one undisturbed soil sample should beobtained from each different stratum encountered. If a uniform cohesive soil deposit extends for a considerable depth,
additional undisturbed samples are commonly obtained at 3 m to 6 mintervals.
Where borings are widely spaced, it may be appropriate to obtainundisturbed samples in each boring; however, for closely spacedborings, or in deposits which are generally uniform in lateral extent,undisturbed samples are commonly obtained only in selected borings.
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Unit 2: Drilling and sampling of soil and rock
Exploration in soil Soil drilling
Soil samples Soil samplers
Sampling interval
Sample identification and tests
Exploration in rock Rock drilling and sampling
Non-core drilling
Core drilling Observation during core drilling
Geologic mapping
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Exploration in rock
Drilling Non-core drilling
Core drilling
Exploration pits (test pits) Observation during core drilling
Geologic mapping Geophysical methods: seismic refraction and ground
penetrating radar (Unit 8)
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Soil or rock?
Defining the top of rockfrom drilling operations can be difficult,especially where large boulders exist, below irregular residual soilprofiles, and in karst terrain.
As per ASTM D 2113, core drilling procedures are used whenformations are encountered that are too hard to be sampled by soilsampling methods.
A penetration of 25 mm or less by a 51 mm diameter split-barrelsampler following 50 blows using standard penetration energy orother criteria established by the geologist or engineer should indicatethat soil sampling methods are not applicable and rock drilling orcoring is required.
In many instances, geophysical methods, such as seismic refraction,can be used to assist in evaluating the top of rock elevations in anexpedient and economical manner.
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Core drilling
(b) Single Tube Core Barrel; (a) Rigid Type Double Tube Core Barrel; (c) Swivel Type Double
Tube Core Barrel, Series M with Ball Bearings. (Courtesy of Sprague & Henwood, Inc.)
(c)
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Double tube core barrel
(a) Outer barrel assembly (b) Inner barrel assembly. The double-tube core
barrel offers better recovery by isolating the rock core from the drilling fluidstream and consists of an inner and outer core barrel.
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Dimensions of core sizes
(after Christensen Dia-Min Tools, Inc.)
(4.827)122.6(3.346)85.0CP, PQ Wireline
(3.791)96.3(2.500)63.5HQ Wireline
(3.650)92.7(2.406)61.1HWD4,HXB Wireline, HWD3
(2.980)75.7(1.874)47.6NQ Wireline, NV
(2.980)75.7(1.874)47.6NXB Wireline, NWC3
(2.980)75.7(2.059)52.3NWD4,NWD3
(2.980)75.7(2.154)54.7NX
(2.358)59.9(1.433)36.4BQ Wireline, BV
(2.358)59.9(1.433)36.4BXB Wireline, BWC3
(2.358)59.9(1.614)41.0BWD4, BWD3
(2.358)59.9(1.654)42.0BX
(1.890)48.0(1.067)27.1AQ Wireline, AV
(1.890)48.0(1.185)30.1AWM
(1.890)48.0(1.138)28.9AWD4, AWD3
(1.890)48.0(1.185)30.1AX
(1.484)37.7(0.835)21.2EWD3
(1.484)37.7(0.846)21.5EX,EXM
Diameter of Boreholemm (in)
Diameter of Coremm (in)
Size
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Coring bits
Coring bits. From left to right:
Diamond from soft to extremely hard rock
Carbide soft to medium hard rock
Sawtooth overburden and very soft rock
The coring bit is the bottommost
component of the core barrel
assembly. It is the grinding action
of this component that cuts thecore from the rock mass. Three
basic categories of bits are in use:
diamond, carbide insert, and
sawtooth. Coring bits are generally
selected by the driller and are
often approved by the
geotechnical engineer. Bit
selection should be based on
general knowledge of drill bitperformance for the expected
formations and the proposed
drilling fluid.
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Drilling fluids
In many instances, clear water is used as the drilling fluidin rock coring. If drilling mud is required to stabilize
collapsing holes or to seal zones when there is loss of drillwater, the design engineer, the geologist and thegeotechnical engineer should be notified to confirm thatthe type of drilling mud is acceptable.
Drilling fluid should be contained in a settling basin toremove drill cuttings and to allow recirculation of the fluid.Generally, drilling fluids can be discharged onto the
ground surface. Water flow over the ground surface should be avoided, as
much as possible.
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Observation during core drilling
Drilling rate/time Drilling process monitoring devices
Core photographs Rock classification Core recovery
Rock quality designation Drilling fluid recovery
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Core recovery
The core recovery is the length of rock core recovered from a corerun (whether solid intact with no full diameter or non-intact), and therecovery ratio is the ratio of the length of core recovered to the total
length of the core drilled on a given run, expressed as either afraction or a percentage.
Core length should be measured along the core centerline. When therecovery is less than the length of the core run, the non-recovered
section should be assumed to be at the end of the run unless there isreason to suspect otherwise (e.g., weathered zone, drop of rods,plugging during drilling, loss of fluid, and rolled or recut pieces ofcore).
Non-recovery should be marked as NCR (no core recovery) on theboring log, and entries should not be made for bedding, fracturing, orweathering in that interval.
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Rock QualityDesignation(RQD)
L h f RQD d i i
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Length measurement for core RQD determination
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Core handling
and labeling
Core Box for Storage of Recovered Rock and Labeling
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Boring closure
All borings should be properly closed at the completion of the fieldexploration. This is typically required for safety considerations and toprevent cross contamination of soil strata and groundwater. Boringclosure is particularly important for tunnel projects since an openborehole exposed during tunneling may lead to uncontrolled inflow ofwater or escape of compressed air.
Any time groundwater or contamination is encountered the boreholeshould be grouted using a mixture of powdered bentonite, Portland
cement and potable water. It is good practice to grout all boreholes. Holes in pavements and
slabs should be filled with quick setting concrete, or with asphalticconcrete, as appropriate. Backfilling of boreholes is generallyaccomplished using a grout mixture . The grout mix is normally
pumped though drill rods or other pipes inserted into the borehole. Inboreholes filled with water or other drilling fluids the tremied groutwill displace the drill fluid. Provisions should be made to collect anddispose of all displaced drill fluid and waste grout.
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Geologic mapping Geologic mapping is the systematic collection of local, detailed geologic data, and, for engineering
purposes, is used to characterize and document the condition of a rock mass or outcrop. The dataderived from geologic mapping is a portion of the data required for design of a cut slope or forstabilization of an existing slope. Geologic mapping can often provide more extensive and lesscostly information than drilling. The guidelines presented are intended for rock and rock-likematerials.
The first step in geologic mapping is to review and become familiar with the local and regionalgeology from published and non-published reports, maps and investigations. The mapping teamshould be knowledgeable of the rock units and structural and historical geologic aspects of thearea. A team approach (minimum of two people, the buddy system) is recommended formapping as a safety precaution when mapping in isolated areas.
Procedures for mapping are outlined in an FHWA Manual (1989) on rock slope design, excavation
and stabilization and in ASTM D 4879. The first reference describes the parameters to beconsidered when mapping for cut slope design, which include (details in Unit 3): Discontinuity type Discontinuity orientation Discontinuity in filling Surface properties
Discontinuity spacing Persistence Other rock mass parameters
These parameters can be easily recorded on a structural mapping coding form shown in Figure 3-24. ASTM D 4879 also describes similar parameters and presents commonly used geologicsymbols for mapping purposes. It also presents a suggested report outline. Presentation of
discontinuity orientation data can be graphically plotted using stereographic projections.
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