soil mechanics report 2 copy

LECTURER Dr. Frederick Owusu-Nimo

DATE 01/11/2014

DZAKLO COURAGE KWASI

SOIL MECHANICS 2 REPORT 1

Table of Contents

1 CONSOLIDATION TEST (OEDOMETER) .................................................................... 3

1.1 INTRODUCTION:...................................................................................................... 3

1.2 OBJECTIVE OF THE EXPERIMENT: ..................................................................... 3

1.3 PRINCIPLE OF EXPERIMENT: ............................................................................... 3

1.4 EXPERINMENT SETUP: .......................................................................................... 4

1.5 EQUIPMENT USED: ................................................................................................. 5

1.6 BRIEF DESCRIPTION OF THE TEST PROCEDURE: ........................................... 5

1.7 SUMMARY OF RESULTS: ....................................................................................... 5

1.7.1 TABLE OF RESULTS: ....................................................................................... 5

1.7.2 SAMPLE CALCULATION: ............................................................................... 5

1.8 PRECAUTIONS: ........................................................................................................ 8

1.9 CONCLUSION: .......................................................................................................... 8

2 PERMEABILITY TESTS: ................................................................................................ 8

2.1 INTRODUCTION:...................................................................................................... 8

2.2 PURPOSE OF THE EXPERINMENT: ...................................................................... 9

2.3 FALLING HEAD PERMEABILITY TEST: .............................................................. 9

2.3.1 APPARATUS: ..................................................................................................... 9

2.3.2 BRIEF DESCRIPTION OF THE TEST: ............................................................. 9

2.3.3 SUMMARY OF RESULTS: ............................................................................... 9

2.3.4 CONCLUSION: ................................................................................................. 11

2.4 CONSTANT HEAD PERMEABILITY TEST: ....................................................... 11

2.4.1 APPARATUS: ................................................................................................... 11

2.4.2 BRIEF DESCRIPTION OF THE TEST: ........................................................... 11

2.4.3 SUMMARY OF RESULTS: ............................................................................. 12

2.4.4 CONCLUSION: ................................................................................................. 13

REFERENCES:………………………………………………………………………… 13



1 CONSOLIDATION TEST (OEDOMETER)

1.1 INTRODUCTION: When a saturated soil is loaded a state of stress is set up and nearly all the load is initially

carried by the water in the soil pores since the water is almost incompressible. The pressure in

the water causes it to drain away to the surrounding materials and produces a change in the

water content of the soil consolidation however depends upon the number of voids in the soil.

Structures are constructed with and/or in soils and as such, making the study of soil properties

very important in construction projects. Soil properties such as consolidation become very

important in the construction of these structures where settlements are of great concern. The

coefficient of consolidation provides much information on the amount of settlement and also

helps in the determination of the stability of structures.

1.2 OBJECTIVE OF THE EXPERIMENT: This test is performed to determine the magnitude and rate of volume decrease that a laterally

confined soil specimen undergoes when subjected to different vertical pressures. From the

measured data, the consolidation curve (pressure-void ratio relationship) can be plotted. This

data is useful in determining the compression index (𝐶𝑐), the recompression index (𝐶𝑟) and the

preconsolidation pressure (or maximum past pressure) of the soil. In addition, the data obtained

can also be used to determine the coefficient of consolidation (𝐶𝑣 ) and the coefficient of

secondary compression of the soil. Also data collected can be to compute the coefficient of

volume change (mv) and the pre-consolidated pressure (σ𝑝).

1.3 PRINCIPLE OF EXPERIMENT: Consolidation is defined as the reduction of the volume of a soil due to the expulsion of water.

Considering the situation above, the two conditions that prevail are;

I. Excess pore pressure only exist in the silty-clay stratum

II. Settlement arises predominantly because of volume change within the clay

For conditions stated above the horizontal dimension over which this change occurs is large

compared to the thickness of the consolidation stratum and hence all vertical sections have the

same pore pressure and stress distribution and flow of water occurs only in the vertical

direction. Equations governing the consolidation are those of:

Equilibrium

Stress-strain distribution

One-dimensional continuity

By combining the above equations the co-efficient of consolidation Cv is calculated

Cv = k / ɣw × mv

Where k = coefficient of permeability

ɣw= unit weight of water

mv=coefficient of volume compressibility



1.4 EXPERINMENT SETUP:

SOIL SPECIMEN

Loading piston

Dial gauging

cutting ringporous stone

SET UP FOR SAMPLE IN OEDOMETER TEST

A PICTURE OF OEDOMETER APPARATUS



1.5 EQUIPMENT USED: 1. Oedometer

2. A mould and collar

3. Pans for mixing and weighing

4. A metal straightedge

5. A drop hammer

6. An electronic balance

7. Oven

8. Stop watch

9. Trimming knife

10. Meter scale

1.6 BRIEF DESCRIPTION OF THE TEST PROCEDURE: The process of performing the test is outlined below:

1. 1000 grams of soil was weighed and used for the permeability test, of which 50 % was

laterite and the remaining 50 % sand. The weight of water added to the soil sample was

taken as 12 % of the soil weight which measured 120 ml.

2. The different soils were mixed together with water in a pan while the mould and drop

hammer were being prepared for compaction.

3. After a thorough mixture has been achieved, the obtained sample was transferred into

the mould in three layers.

4. Each layer attracted 15 blows from the drop hammer during compaction of the soil.

5. After the compaction, the collar of the mould was carefully removed so as not to disturb

the surface of the sample required for the permeability test and the trimming knife was

used to evenly level the soil surface. The base plate of the mould was also removed.

6. The ring was then pushed into the compacted soil until fully submerged

7. The ring with soil is then taken out and the soil trimmed to dimensions of the ring.

8. The specimen is now put into the oedometer and saturated with water for 24hrs and

then the various loads are applied.

9. The readings of the dial gauge values were taking for the various loads applied within

24 hours.

1.7 SUMMARY OF RESULTS:

1.7.1 TABLE OF RESULTS:

Table of results is provided at the back of the report.

1.7.2 SAMPLE CALCULATION:



1.7.2.1 DEFINITION OF PARAMETERS:

PARAMETERS MEANINGS

𝑨𝑻 Cross sectional area of sample

𝒉𝟏 Height of sample at the end of test

𝑽𝒕 Volume of sample at the end of test

𝑽𝑻 Volume of sample at the beginning of

test

𝑽𝑺 Volume of solids

𝑽𝒗𝒊 Volume of voids initial

𝑽𝒗𝒇 Volume of voids final

𝑮. 𝑺 Specific Gravity

𝑯𝑺 Height of solids

𝒆𝒐 Initial void ratio

𝒆𝒇 Final void ratio

𝛔𝒏 The applied loadings

𝑺𝒓𝒊 Degree of saturation initial

𝑺𝒓𝒇 Degree of saturation final

𝑽𝒘𝒇 Volume of water final

𝑽𝒘𝒊 Volume of water initial

𝒉𝒊 Height of ring

1.7.2.2 Calculation of volume of solids.

𝒉𝟏 = 𝟏. 𝟑𝟗𝟗𝒄𝒎 and 𝑨𝑻 = 𝝅(𝟕.𝟓)𝟐

𝟒= 𝟒𝟒. 𝟏𝟖𝒄𝒎𝟐

𝑽𝒕 = 𝑨𝑻𝒉𝟏 = 𝟔𝟏. 𝟖𝟏𝒄𝒎𝟑

Since the soil is considered fully saturated,

𝑽𝒘𝒇 = 𝑽𝒗𝒇 = 𝑴𝒘 = 𝟐𝟔. 𝟗𝟖𝒄𝒎𝟑

𝑽𝒕 = 𝑽𝒗𝒇 + 𝑽𝑺

𝑽𝑺 = 𝟑𝟒. 𝟖𝟑𝒄𝒎𝟑

1.7.2.3 Calculation of final void ratio.

𝒆𝒇 =𝑽𝒗𝒇

𝑽𝒔=

𝟐𝟔.𝟗𝟖

𝟑𝟒.𝟖𝟑= 𝟎. 𝟕𝟕𝟓

1.7.2.4 Calculation of height of solids.

𝑯𝒔 =𝑽𝑺

𝑨𝑻= 𝟎. 𝟕𝟖𝟖𝒄𝒎

1.7.2.5 Final degree of saturation. 𝑺𝒓𝒇 = 𝟏𝟎𝟎%

1.7.2.6 Computations of initial void ratio and other values.

𝑽𝑻 = 𝑨𝑻𝒉𝒊 = 𝟕𝟗. 𝟓𝟐𝒄𝒎𝟑

𝑽𝒗𝒊 = 𝟕𝟗. 𝟓𝟐 − 𝟑𝟒. 𝟖𝟑 = 𝟒𝟒. 𝟔𝟗𝒄𝒎𝟑



𝒆𝒐 =𝑽𝒗𝒊

𝑽𝑺= 𝟏. 𝟐𝟖𝟑

𝑺𝒓𝒊 =𝑽𝒘𝒊

𝑽𝒗× 𝟏𝟎𝟎% = 𝟒𝟖. 𝟏𝟏%

1.7.2.7 Other values computed on the table.

𝒅𝒉 = (𝒍𝒂𝒔𝒕 𝒓𝒆𝒂𝒅𝒊𝒏𝒈 − 𝒇𝒊𝒓𝒔𝒕 𝒓𝒆𝒂𝒅𝒊𝒏𝒈 𝒐𝒇 𝒅𝒊𝒂𝒍 𝒈𝒂𝒖𝒈𝒆 𝒓𝒆𝒂𝒅𝒊𝒏𝒈𝒔) × 𝒄𝒐𝒓. 𝒇𝒂𝒄𝒕𝒐𝒓

e.g. 𝒅𝒉 = (𝟐𝟒𝟎𝟒 − 𝟐𝟒𝟎𝟗) × 𝟎. 𝟎𝟎𝟏𝒄𝒎 = 𝟎. 𝟎𝟎𝟓𝒄𝒎

𝒉 = 𝒊𝒏𝒊𝒕𝒊𝒂𝒍 𝒉𝒆𝒊𝒈𝒉𝒕 + 𝒅𝒉

𝒉 = 𝟏. 𝟖 + 𝟎. 𝟎𝟎𝟓 = 𝟏. 𝟖𝟎𝟓𝒄𝒎

𝒅𝒆 =𝒅𝒉

𝑯𝒔=

𝟎.𝟎𝟎𝟓

𝟎.𝟕𝟖𝟖= 𝟎. 𝟎𝟎𝟔

𝒆 = 𝒆𝒐 + 𝒅𝒆 = 𝟏. 𝟐𝟖𝟑 + 𝟎. 𝟎𝟎𝟔 = 𝟏. 𝟐𝟖𝟗

𝑴𝒗 =𝟏

𝟏+𝒆𝒐[

𝒆𝒐−𝒆𝟏

σ𝟏−σ𝟎]

For 20 ibf,

𝑴𝒗 =𝟏

𝟏+𝟏.𝟐𝟖𝟗[

𝟏.𝟐𝟖𝟗−𝟎.𝟗𝟏𝟏

𝟏𝟗𝟔.𝟐−𝟎] = 𝟎. 𝟖𝟒𝟏𝒎𝟐/𝑴𝑵

𝒉𝒅𝒓𝒂𝒊𝒏 =𝒉

𝟐=

𝟏.𝟓𝟏𝟐

𝟐= 𝟎. 𝟕𝟓𝟔𝒄𝒎

1.7.2.8 THE COEFFICIENT OF CONSOLIDATION CALCULATION:

For the 196.2 KPa

𝐶𝑣 =0.848(𝐻𝑑𝑟)2

𝑡90=

0.848×0.756^2

1.2^2= 0.3366𝑐𝑚2/𝑚𝑖𝑛

𝐶𝑣 = 5.61 × 10−3𝑐𝑚/𝑠

1.7.2.9 Evaluation of coefficient of permeability (K)

𝑲 = 𝑪𝒗 × 𝒎𝒗 × ɣ𝒘

= 𝟎. 𝟓𝟔𝟏 × 𝟎. 𝟖𝟒𝟏𝟕 × 𝟗. 𝟖𝟏𝟎

= 𝟎. 𝟎𝟎𝟒𝟔 × 𝟏𝟎^ − 𝟐𝒄𝒎/𝒔

𝑲𝒂𝒗 = (𝟎.𝟎𝟎𝟒𝟔+𝟎.𝟎𝟎𝟏𝟒+𝟎.𝟎𝟎𝟎𝟐)×𝟏𝟎−𝟐

𝟑

= 𝟔. 𝟐 × 𝟏𝟎−𝟓 𝒄𝒎/𝒔

1.7.2.10 TOTAL SETTLEMENT OF THE SAMPLE:

𝑆𝐶 =∆𝑒

1+𝑒0𝐻0

𝑆𝑐 =0.508

1+1.283× 1.8 = 0.4000𝑐𝑚



1.8 PRECAUTIONS: o Voids or over sized particles in the specimen must be avoided.

o The loads should be concentrically applied to the specimen.

o Inaccuracy in dial-guage reading must be avoided.

1.9 CONCLUSION: After the test, from the table of results, the coefficient of permeability determined was very

small in value showing that the rate of movement of water through the soil sample is very

minimal. This indicates low permeability of the soil sample. The total settlement calculated

was also very small and it can be as a result of proper compaction to remove air from the soil

or the soil has little pore spaces to be reduced by the loadings.

2 PERMEABILITY TESTS:

2.1 INTRODUCTION: The permeability tests are laboratory methods used to determine the coefficient of permeability

of sample of soils taken or collected from the field. The property of soil which permits

percolation (seepage) of water through it is called permeability. A high permeability indicates

flow occur rapidly and vice versa. Flow can be laminar or turbulent. Laminar flow indicates

that adjacent part of water particles is parallel even when changing direction and part never

cross. Turbulent flow indicate disorderly random part of moving water particles with a high

degree of mixing

Darcy established experimentally that for laminar flow through saturated soil , the rate of flow,

q defined as volume of water flowing per unit time across a total sectional was proportion to

the hydraulic gradient i, as;

q=K i A, where the constant of proportionality is the permeability. Permeability is therefore

the flow velocity under unit hydraulic gradient. It has unit of velocity. Permeability of a soil is

affected by;

i. Size and gradation of the particles.

ii. Structure and stratification.

iii. Density or void ratio of the soil.

iv. Adsorption complex

v. Degree of saturation and foreign matter.

Determination of the permeability can be obtained directly or indirectly. The direct method

in include;

i. Falling head method

ii. Constant head method

And indirectly by;



i. Grading characteristics

ii. Consolidation

The falling method which we used in our experiment is suitable for fine grained soils

such as silts and some clay.

2.2 PURPOSE OF THE EXPERINMENT:

The test results of the permeability experiments are used:

1. To estimate ground water flow.

2. To calculate seepage through dams.

3. To find out the rate of consolidation and settlement of structures.

4. To plan the method of lowering the ground water table

5. For the calculation of the uplift pressures and piping.

6. To design the grouting

7. And also for soil freezing tests.

8. To design pits for recharging.

2.3 FALLING HEAD PERMEABILITY TEST: This test is used with fine grained soils were the rate of flow of water is too small to be

accurately measured using the constant head apparatus/test.

2.3.1 APPARATUS:

Constant head apparatus.

2.3.2 BRIEF DESCRIPTION OF THE TEST:

1. The test was carried out on a prepared sample.

2. With the top and bottom filters in place the sample is stood in the water reservoir.

3. The top of the sample/filter is connected to a glass standpipe of known diameter

4. The de-aired water contained in the standpipe allowed to seep through the sample.

5. The height of the water (h1 , h2 , etc.) is recorded at several time intervals (t1 , t2 , etc.)

during the test.

2.3.3 SUMMARY OF RESULTS:

2.3.3.1 TABLE OF RESULTS:

Table of results is provided at the back of the report.



2.3.3.2 SAMPLE CALCULATIONS:

Table of results with calculations:

Diameter of sample (D) cm 10.00

Diameter of standpipe (d) cm 1.00

Area of sample (A) cm2 𝐴 =

𝜋(10)2

4= 78.54

Area of standpipe (a) cm2 𝐴 =

𝜋(10)2

4= 0.79

Length of soil(L) cm 11.70

Adjustment height cm 92.00

Test 1 2 3

Initial water level in the pipe cm 90.00 85.00 80.00

Final water level in the pipe cm 83.10 78.20 73.60

Time elapsed sec 15 15 15

Initial head of water in the pipe h0 182 177 172

Final head of water in the pipe h1 175.1 170.2 165.6

h0/h1 1.04 1.04 1.04

2.3log(h0/h1) 0.04

0.04 0.04

Permeability(K) cm/sec 3.138×10-4 3.138×10-4 3.138×10-4

Average permeability cm/sec 3.138×10-4

Average permeability m/sec 3.138×10-6

2.3.3.3 SAMPLE CALCULATION FOR TEST ONE.

Initial head of water in the pipe (ho) = 182.0cm

Final head of water in the pipe (h1) =175.1cm

Time elapsed =15 seconds



Hence from the relation;

K =𝑎𝑙

𝐴𝑡2.3log(ℎ0

ℎ1)

Where,

a =Area of standpipe a = 0.79 cm2

A =Area of sample A =78.54 cm2

t=time elapsed t= 15sec

l = length of soil l = 11.70cm

K= permeability of soil K =0.79×11.7

78.54×152.3log ( 182

175.1)

K =3.138×10-4 cm/s

2.3.4 CONCLUSION:

The average coefficient of permeability that was determined on the table which is very also

small. This value indicates low permeability which ranges between silty soil and clayey soil.

2.4 CONSTANT HEAD PERMEABILITY TEST: This test is most suitable for coarse grained soils.

2.4.1 APPARATUS:

Constant head apparatus

2.4.2 BRIEF DESCRIPTION OF THE TEST:

Below is setup of experiment;



1. Apply a vacuum to the sample by opening valve C with valves A and B closed.

2. Close valve C and open valves A and B and allow water to flow through the sample

from the reservoir until steady state flow is achieved (the levels in the two manometers

remain constant).

3. Flow of water through the sample is controlled by adjusting valve A. Once the steady

state flow has been achieved the quantity of water flowing ( Q ) in a given time ( t ) is

recorded together with the readings on the two manometers.

4. The difference in the two manometer readings giving the head difference ( H ) over the

sample length ( L).

2.4.3 SUMMARY OF RESULTS:

2.4.3.1 TABLE OF RESULTS:

The table of results is provided at the back of the report.

2.4.3.2 SAMPLE CALCULATIONS USING THE TABLE RESULTS:

UNIT TEST NO. 1

Head of water in right manometer cm 71.40

Head of water in left manometer cm 97.5

Length of sample between nipple points(l) cm 10

Diameter of sample cm 7

Cross sectional area of sample cm^2

𝐴 =𝜋(7)2

4= 38.48

Elapsed time sec 10

Volume of water discharge cc/ml 56

Discharge cc/sec 𝑞 =

56

10= 5.60

Head of difference cm ℎ = 97.5 − 71.40 = 26.10

Permeability cm/sec 𝐾 =

𝑞𝑙

ℎ𝐴=

5.60 × 10

26.10 × 38.48= 0.06

Average permeability



2.4.4 CONCLUSION:

The average permeability calculated was very large compared to that of the falling head test

indicating that the granular soil has more pores and well connected.

soil mechanics report 2 copy

Engineering

test procedure

consolidation test oedometer

summary of results

saturated soil

brief description

table of results

soil pores s

permeability tests