Geotechnical Bridging - Assignment 1 - correct.pdf

BTEC Higher National Diploma in Civil Engineering MT/Bsc Civil/04/33

A.A.M.ASAM Page 1

Task 1 Engineering Geology (P1)

a) List the main types of rock according to their mode of formation.

In geology, a rock is a naturally occurring solid aggregate of one or more minerals or

mineralogist. For example, the common rock, granite, is a combination of the quartz, feldspar

and biotitic minerals. The Earth's outer solid layer, the lithosphere, is made of rock.

Rocks have been used by mankind through out history. From the Stone Age rocks have been

used for tools. The minerals and metals we find in rocks have been essential to human

civilization.[1]

Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific

study of rocks is called petrology, which is an essential component of geology.

There are three basic types of rocks according to the mode of formation.

Igneous Rock

Sedimentary Rock

Metamorphic Rock

Igneous: these are rocks that solidified directly from molten silicates, which geologists

call magma. Igneous rock is formed by magma (molten rock) being cooled and becoming

solid. They may form with or without crystallization, either below the surface as intrusive

(plutonic) rocks or on the surface as extrusive (volcanic) rocks

Examples are: granite, basalt, pumice and flint (which is a form of quartz).

Sedimentary: these are formed when igneous rocks are eroded as a sediment under the

sea. Sedimentary rock is formed by deposition and consolidation of mineral and organic

material and from precipitation of minerals from solution. The processes that form

sedimentary rock occur at the surface of the Earth and within bodies of water.Fossils are

often found in this layer.

Examples are limestone, chalk, sandstone.

Metamorphic: Any of a class of rocks that result from the alteration of preexisting rocks

in response to changing geological conditions, including variations in temperature,

pressure, and mechanical stress. The preexisting rocks may be igneous, sedimentary, or

other metamorphic rocks.

Examples are: slate, marble, quartzite.


A.A.M.ASAM Page 2

Task - 1

b) List the main types of soil based on their mode of transportation and deposition.

Types of soil

The types of soils can be presented in different forms which are shown below:-

Transported soils

Any soil that has been transported from its place of origin by wind, water or ice or any other agency and has been redeposit is called transported soil. These soils are more common as

compared to residual soils. The particles features such as size, shape, and texture of transported

soils depends on source by which they were transported. These soils can further be categorized

as alluvial, Lacustrine, Marine, Aeolian and Glacial deposits.

Residual soils

There is no specific or particular definition for residual soils, however all the definitions that are

in literature do indicate that these soils are formed on site as a result of weathering of rocks and

they remain at that same place.

Soils which are formed by weathering of rocks may remain in position at the place of region. Theses soils are found at large scale in area where the climate is hot and humid and cause the

weathering of rocks easily. The sizes of grains of these soils are not specific and may break into

smaller pieces by small amount of load.

So it can be conclude that soils which remain at the place where they were created from

weathering of rocks are known as residual soils and the soils which are moved or blown from

their original place of formation by different activities are transported soils.

Types of soils based on texture

Soil texture refers to the particle size of each mineral present in soil. It also includes the

proportion of each particle size in soil. Based on soil texture, the soils can be divided into three

types sand silt and clay.

Sand

The particle size for sand is considered to be largest as compared to other types. Most

classification systems considers the particle size of sand from 2mm to 0.05mm in diameter. The

soils which consists of high proportion of sandy particles is known as sandy soils


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Clay

Clay consists of particle size lesser then 0.002mm.The soil which contains higher proportion of

clay particles is known as clayey.

Silt

The particle size for silt is considered to be from 0.05mm to 0.002mm or in some countries it

also taken as 0.02mm.However in case of silt the soil containing higher proportion of silt are

considered as loamy soils.

The loamy soils are further divided into different types based on proportion of clay, sand and slit

particles. Soils with sand and silt particles in higher proportion is called sandy loams or loamy

sands. Clayey particles in majority result in sandy clay loam or sandy clay. The soil containing

approximately the same quantity of clay, sand and silt particles is considered as clay loam.

Soil Components

The ideal soil consists of 50% solid particles, the solid part may consist of up to 5% of organic

matters. The rest of 50% is shared equally among air and water contents which cover 25% each

in soil composition.

Water

Water makes up 25% of soil composition in ideal situation. The amount of water can vary based

on conditions. In fully dry condition the water content is less as compared to saturated

conditions.

Air

Air is 25% of soil composition. Like water the air content also changes depending upon soil

condition. For example as it rains the voids in soil filled with air are replaced by water thus

reducing the quantity of air or when the soil becomes dry the void filled with water are occupied

by air.

Organic matter

The decaying process of living organisms such as plants and animals in soil results in formation

of organic matter.

The organs of dead animals, roots, leaves and wood of plants go through decaying process due to

physical and chemical activities due to this decomposition the organic matter is formed.


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Mineral particles

The solid components of soils consist of crystalline material called minerals. Mineral particles

are categorized based on their structure and chemical composition. Oxygen and silicon minerals

are most significant to geotechnical engineers. Fine grained soils consist of mineral particles

which are platy in nature.

Task 02


A.A.M.ASAM Page 5

a)

=

+

=

+

=

1 +

=

1 +1

=

1 +

b)

= +

+

= = (1 )

= = (1 )

= 1 =

1 =

1 +

,

=

=

(1 )1 + = (1 )

=

=

+ =

1 + (1 )1

= 1 + 1 = 1 + 1

1 + =(1 + )

1 +


A.A.M.ASAM Page 6

Task-03

Sample size 75 75 30

Normal stress : 200 /2

Shear Stress at failure : 175 /2

a)

= 1 + 1 1

1 = 0,

= 1

175=200 1

1 =175

200

1 =ta1(175

200)

1 = 410


A.A.M.ASAM Page 7

b)

Soil friction angle is a shear strength parameter of soils. Its definition is derived from the Mohr-

Coulomb failure criterion and it is used to describe the friction shear resistance of soils together

with the normal effective stress.

In the stress plane of Shear stress-effective normal stress, the soil friction angle is the angle of

inclination with respect to the horizontal axis of the Mohr-Coulomb shear resistance line.

Description USCS

Soil friction angle []

Reference min max

Specific

value

Well graded gravel, sandy gravel, with little or

no fines GW 33 40 [1],[2],

Poorly graded gravel, sandy gravel, with little

or no fines GP 32 44 [1],

Sandy gravels Loose (GW,

GP) 35 [3 cited in 6]

Sandy gravels Dense (GW,

GP) 50 [3 cited in 6]

Silty gravels, silty sandy gravels GM 30 40 [1],

Clayey gravels, clayey sandy gravels GC 28 35 [1],

Well graded sands, gravelly sands, with little

or no fines SW 33 43 [1],

Well-graded clean sand, gravelly sands Compacted

SW - - 38 [3 cited in 6]

Well-graded sand, angular grains Loose (SW) 33 [3 cited in 6]

Well-graded sand, angular grains Dense (SW) 45 [3 cited in 6]

Poorly graded sands, gravelly sands, with little

or no fines SP 30 39 [1], [2],

Poorly-garded clean sand Compacted SP - - 37 [3 cited in 6]

Uniform sand, round grains Loose (SP) 27 [3 cited in 6]

Uniform sand, round grains Dense (SP) 34 [3 cited in 6]

Sand SW, SP 37 38 [7],

Loose sand (SW, SP) 29 30 [5 cited in 6]

Medium sand (SW, SP) 30 36 [5 cited in 6]


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Dense sand (SW, SP) 36 41 [5 cited in 6]

Silty sands SM 32 35 [1],

Silty clays, sand-silt mix Compacted SM - - 34 [3 cited in 6]

Silty sand Loose SM 27 33 [3 cited in 6]

Silty sand Dense SM 30 34 [3 cited in 6]

Clayey sands SC 30 40 [1],

Calyey sands, sandy-clay mix compacted SC 31 [3 cited in 6]

Loamy sand, sandy clay Loam SM, SC 31 34 [7],

Inorganic silts, silty or clayey fine sands, with

slight plasticity ML 27 41 [1],

Inorganic silt Loose ML 27 30 [3 cited in 6]

Inorganic silt Dense ML 30 35 [3 cited in 6]

Inorganic clays, silty clays, sandy clays of low

plasticity CL 27 35 [1],

Clays of low plasticity compacted CL 28 [3 cited in 6]

Organic silts and organic silty clays of low

plasticity OL 22 32 [1],

Inorganic silts of high plasticity MH 23 33 [1],

Clayey silts compacted MH 25 [3 cited in 6]

Silts and clayey silts compacted ML 32 [3 cited in 6]

Inorganic clays of high plasticity CH 17 31 [1],

Clays of high plasticity compacted CH 19 [3 cited in 6]

Organic clays of high plasticity OH 17 35 [1],

Loam ML, OL,

MH, OH 28 32 [7],

Silt Loam ML, OL,

MH, OH 25 32 [7],

Clay Loam, Silty Clay Loam

ML, OL,

CL, MH,

OH, CH

18 32 [7],

Silty clay OL, CL,

OH, CH 18 32 [7],

Clay CL, CH, 18 28 [7],


A.A.M.ASAM Page 9

OH, OL

Peat and other highly organic soils Pt 0 10 [2],

Correlation between SPT-N value, friction angle, and relative density

SPT N3

[Blows/0.3 m - 1 ft] Soi packing

Relative Density

[%]

Friction angle

[]

< 4 Very loose < 20 < 30

4 -10 Loose 20 - 40 30 35

10 - 30 Compact 40 - 60 35 40

30 - 50 Dense 60 - 80 40 45

> 50 Very Dense > 80 > 45

REFERENCES

1. Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers

2. JON W. KOLOSKI, SIGMUND D. SCHWARZ, and DONALD W. TUBBS, Geotechnical Properties of Geologic Materials, Engineering Geology in Washington,

Volume 1, Washington Division of Geology and Earth Resources Bulletin 78, 1989, Link

3. Carter, M. and Bentley, S. (1991). Correlations of soil properties. Penetech Press Publishers, London.

4. Meyerhof, G. (1956). Penetration tests and bearing capacity of cohesionless soils. J Soils Mechanics and Foundation Division ASCE, 82(SM1).

5. Peck, R., Hanson,W., and Thornburn, T. (1974). Foundation Engineering Handbook. Wiley, London.

6. Obrzud R. &Truty, A.THE HARDENING SOIL MODEL - A PRACTICAL GUIDEBOOK Z Soil.PC 100701 report, revised 31.01.2012

7. Minnesota Department of Transportation, Pavement Design, 2007


A.A.M.ASAM Page 10

Citation :

Geotechdata.info, Angle of Friction, http://geotechdata.info/parameter/angle-of-friction.html (as

of September 14.12.2013).

c)

= 1

= 150 410

= 130 /2

Task 04

a)

=

= 0.48

0.17 = 2.82

=()

= (0.27)2

0.480.17 = 0.89


A.A.M.ASAM Page 11

b)

The Unified Soil Classification System (USCS) is a soil classification system used in

engineering and geology to describe the texture and grain size of a soil. The classification system

can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each

letter is described below (with the exception of Pt):

First and/or second letters Second letter

Letter Definition

G gravel

S sand

M silt

C clay

O organic

Letter Definition

P poorly graded (uniform particle sizes)

W well-graded (diversified particle sizes)

H high plasticity

L low plasticity

According to particle size distribution curve

Coarse grained soils more than 50% of retained on No 200 sieve

% of gravel


A.A.M.ASAM Page 12

Task 05

a) Find the total expected settlement after the fill is placed.

Settlement in a structure refers to the distortion or disruption of parts of a building due to either;

unequal compression of its foundations, shrinkage such as that which occurs in timber framed

buildings as the frame adjusts its moisture content, or by undue loads being applied to the

building after its initial construction Settlement should not be confused with subsidence which

results from the load-bearing ground upon which a building sits reducing in level, for instance in

areas of mine workings where shafts collapse underground.

Some settlement is quite normal after construction has been completed, but unequal settlement

may cause significant problems for buildings. Traditional green oak framed buildings are

designed to settle with time as the oak seasons and warps, lime mortar rather than Portland

cement is used for its elastic properties and glazing will often employ small leaded lights which

can accept movement more readily than larger panes.

= ( + )

= ( 0.5 0.4

1 + 0.5) 4

= 0.27

b) Construction is expected to start after the consolidation is 90% complete. If the

coefficient of consolidation (cv) is 2.8 106 /, calculate the duration between placement of fill and commencement of construction work

=

0.848 = 2.8106

4

t = 1211428.57 min / 841days


A.A.M.ASAM Page 13

c) What techniques would you recommend to speed up the consolidation process so

that construction work could start sooner?

Primary consolidation

This method assumes consolidation occurs in only one-dimension. Laboratory data is used to

construct a plot of strain or void ratio versus effective stress where the effective stress axis is on

a logarithmic scale. The plot's slope is the compression index or recompression index. The

equation for consolidation settlement of a normally consolidated soil can then be determined to

be:

where

c is the settlement due to consolidation.

Cc is the compression index.

e0 is the initial void ratio.

H is the height of the soil.

zf is the final vertical stress.

z0 is the initial vertical stress.

Cc can be replaced by Cr (the recompression index) for use in overconsolidated soils where the

final effective stress is less than the preconsolidation stress. When the final effective stress is

greater than the preconsolidation stress, the two equations must be used in combination to model

both the recompression portion and the virgin compression portion of the consolidation process,

as follows:

wherezc is the reconsolidation stress of the soil.

Secondary compression

Secondary compression is the compression of soil that takes place after primary consolidation.

Even after the reduction of hydrostatic pressure some compression of soil takes place at slow

rate. This is known as secondary compression. Secondary compression is caused by creep,

viscous behavior of the clay-water system, compression of organic matter, and other processes.


A.A.M.ASAM Page 14

In sand, settlement caused by secondary compression is negligible, but in peat, it is very

significant. Due to secondary compression some of the highly viscous water between the points

of contact is forced out.

Secondary compression is given by the formula

Where H0 is the height of the consolidating medium

e0 is the initial void ratio

Ca is the secondary compression index

t is the length of time after consolidation considered

t90 is the length of time for achieving 90% consolidation


A.A.M.ASAM Page 15

Task 07

a)

= 25 = 20 = 18/3

= 18 1.5 = 27/3

= + + 0.5

= 20 20.72 + 27 10.66 +1

2 18 6.765 1.5

= 793.567

Let FOS

=5

=793.597

3= 264.516

=

500

3

1.5 1.53

= 222.22/3

>

b)

= 750/3

1.5 1.5

= 333.33 /3


A.A.M.ASAM Page 16

=1 + +

1

2

= 3

=1

3 20 20.72 + 27 10.66 +

1

2 18 6.765

=750/

1.5

750

1.5 =

1

3 20 20.72 + 27 10.66 +

1

2 18 6.765

1500 = (702.22 + 60.885)

0 = 60.8852 + 702.22 1500

= 1.841

c)

In developing the bearing capacity equations given in the preceding section we assumed that the

groundwater table is located at a depth much greater than the width, B of the footing. Three

different conditions can arise regarding the location of the groundwater table with respect to the

bottom of the foundation.


A.A.M.ASAM Page 17

If the groundwater table is located at a distance D above the bottom of the foundation, the

magnitude of q in the second term of bearing capacity equation should be calculated as

= +

For shallow foundations, the negative effects of high water table on the added pressure to the soil

can be compensated by ensuring that the foundation is wide enough to distribute the resultant

force evenly on the ground. The influence of water table on the bearing capacity of a structure is

reduced. The worst scenario arises when the soil supporting a structure becomes completely

saturated.

When the level of water table is considered to be directly at the base of a foundation in

comparison to the slip lines, the water table influences the stability lines by extending them

deeper in lateral direction.


A.A.M.ASAM Page 18

Task - 08

= 24 /3

= 17.5 /3

= 5 /2

= 28

= tan2 45

2

= tan2 45 28

2

= 0.361

= 1/ = 2.77

= 1 , = 5

a)

Active pressure

0.361 17.5 5

= 31.59 /2

Active force

= 0.5

0.5 31.59 5

= 78.97

Passive pressure

2.77 17.5 1

= 48.47 /2


A.A.M.ASAM Page 19

Passive force

= 0.5( )

= 0.5 48.47 1

= 24.23

Pressure due to surcharge

0.361 5

= 1.81 /2

Surcharge force

=

= 1.81 5

= 9.05

b)

1 = 1 = 24 2 1 1 = 48

2 = 1 = 24 7 1 1 = 168

3 = 1 = 24 0.5 6 1 1 = 72

Overturning

| = / :

= (1 1) + (2 1.5) + (3 0.5) + ( 0.333)

( 2.5) + ( 1.666)

= 344.07/154.2

= 2.23 > = 1.5


A.A.M.ASAM Page 20

c) Modern retaining wall types such as gabion walls and mechanically stabilized earth (MSE) walls are gaining popularity of conventional retaining walls types. Try to

explain the reasons for this trend by identifying the advantages they have over

conventional systems.

Traditionally, retaining walls were known as mass retainers or gravity walls and were made of stone

or rubble heavy enough to hold back the weight of the earth heaped against them. Often these

structures would be built at an angle, or batter, leaning back into the retained soil. This kind of

structure, however, is expensive because of the amount of material and labour involved in its

construction, and is now rarely used.

Due to advantages in economics, constructability, and

aesthetics, the construction of mechanically stabilized

earth (MSE) walls is now commonplace. An MSE wall

consists of soil, reinforcement, and facing to retain earth

and support overlying structures. Thirty- to forty-foot

high walls are not uncommon. Reinforcement often

consists of geogrids or steel reinforcement strips, while

the facing commonly consists of segmental precast

concrete units, gabion baskets, metallic panels, or

geosynthetic facing. There are many different MSE wall

construction materials, making it more important for

Contractors and design Engineers to understand how the

products work with the remainder of the system.

Advantages of gabion walls

1. Strong base that provides strength from being drag away by river or stream. 2. Reduce velocity of water as the energy dissipated by the rocks, thus reduce erosion. 3. Its flexibility gives allowance to small ground movement. 4. In most cases, as time goes, voids will be filled by vegetation and silt which will

reinforce the structure and give extra strength.

5. Depends on the availability of material and equipment, handling and transporting material is easy and this reduce the time of construction.

6. Voids can be easily seen between the rocks which makes high permeability to the gabion wall. It allows water to flow through the structure which can maintain the water level in

the ground (Groundwater level) to be low.


A.A.M.ASAM Page 21

Task 9 Moment Distribution (P9, M3)

Determine the reactions at the supports (RA, RB, RC, MA) using the moment distribution method. Assume A is fixed and B & C are roller supports. EI is constant.

All calculations should be provided.

Fix end moment

FEMAB=W L2

12 =

1252

12= -25kN/M

FEMBA=+wL2

12=

1252

12= 25kN/m

FEMBC=PL

8=102.5

8=3.125kN/m

FEMCB=+PL

8=

102.5

8= 3.125kN/m

Stiffness factor

KAB=KBA =4EI

L=

4EI

5= 0.8EI

KBC = KCB=4EI

L=

4EI

2.5= 1.6EI


A.A.M.ASAM Page 22

Distribution factor

DFAB=KBA

KAB +K wall=

0.8EI

0.8EI+(wall stiffness ) =0.0

DFBA=KBA

KBA +KBC=

0.8EI

0.8EI+1.6EI =0.33

DFBC=KBC

KBA +KBC =

1.6EI

0.8EI+1.6EI =0.67

DFCB=KCB

KCB= 1.00

Joints A B C

members AB BA BC CB

Distribution factor 0 0.33 0.67 1

Carry over factor 0.5 0.5 0.5 0.5

Computed end

moment

-25 25 -3.125 3.125

Distribution 7.218 14.656

Carry over moment 3.609 7.328

Geotechnical Bridging - Assignment 1 - correct.pdf

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