SOIL MECHANICS PRACTICAL REPORT

MODULE 8

Cone Penetration Test

GROUP PI 1

Asti Diar Syafitri 1206292414

Christopher Kevinly 1206223846

Wednesson Lawijaya 1206230593

Date of Practicum : 3rd of May 2014

Laboratory Assistant : Ahmad Syihan

Date Approved :

Grade :

Assistant’s Signature :

Laboratory of Soil Mechanics

Department of Civil Engineering

Faculty of Engineering

University of Indonesia

Depok

2014

8.1. Introduction:

8.1.1. Objective of the Field Test:

To know the cone resistance (end bearing) and shear resistance of

the soil in a certain depth, so the determination of the soil’s bearing

capacity can be determined.

8.1.2. Apparatus:

Hydraulic Dutch Penetrometer

2 Manometers, one’s capacity is 0-60 kg/cm2 and 0-250 kg/cm2

Penetrometer’s tube along with the bar inside

Standard biconus which area is 10 cm2 and mantel’s area of 150 cm2

2 anchors with locks

4 channel steels

Screwdriver

Oil, brush, and castrolie

8.1.3. Brief Theorem:

Cone penetration test is one of some methods available to

determine the bearing capacity of the soil tested. This test is taken by

penetrating the soil with a cylindrical penetrometer, the lower end of

which is fitted with a cone having an apex angle of 60o. The penetrometer

is attached to the lower end of a string of hollow boring rods which is

connected to a rig.

Figure 8.1. (a) Electric Penetrometer, (b) mantle cone and (c) friction jacket cone.

(Source: Craig Soil Mechanics)

There will be two resistance values which can be determined; the

cone resistance and the mantle resistance. In order to determine the

correlation between them, this formula is used:

Ft ×qt=Fc × qc+Fm× f

f =( Ft× qt )−(Fc ×qc )

Fm

By substituting the values of Fm, Ft, and Fc;

fs=10 qt−10 qc150

fs=qt−qc15

Where:

Ft = Fc = the cross-sectional area of the biconus (10 cm2)

qt = total earth pressure which is read at the manometer due to

cone and friction pressure (Kg/cm2)

qc = cone pressure read at the manometer (Kg/cm2)

Fm = Area of the mantle (150 cm2)

Sticking resistance (HP)

HP=l × f

Where:

l = the length of sticking = 20cm (the cone is pressed in every 20cm

Interval)

The sum of sticking resistance (JHP):

JHP=∑ li × fi

The Friction Ratio of this experiment can be determined by using:

FR=( fsqc )× 100 %

8.2. Procedure:

8.2.1. Preparations

a. Prepare a 30cm-sided square hole with a depth of 20cm or to a depth

where no soil layer containing grass or roots exists.

b. Install the anchor at the two sides of where the CPT rig wanted to be

erected.

c. The CPT rig is then placed on channel-shaped steel so the rig is stable,

then anchor the rig with the anchor prepared before. Make sure that the

rig is perpendicular with the land profile. It is important to lock the

anchor properly to prevent any rotation or translation occur during the

CPT.

d. Both of the manometers should be calibrated.

e. The cone should be checked, CPT pipes and the bars inside should be

oiled in order to minimize the friction effect

8.2.2. Practical Activity:

a. Connect the cone with a CPT pipe, then install it to the CPT rig, lock

the gap between the manometer and the centre bar of the CPT pipe.

b. The handle of the CPT rig is rotated, so the cone goes down until it

penetrates the first 20cm of the soil.

c. Release the lock between the manometer and the CPT tube, do the

readings afterwards by reading the manometer to get the qc. qt is gained

by penetrating the soil consistently until the manometer reading

“jumps”.

d. When the manometer reading has exceeds 50kg/cm2, do the reading on

the larger manometer.

e. Penetration is ceased if the qc has exceeds 150kg/cm2.

8.3. Experimental Data

After doing the cone penetration test, the result of the test:

Table 8.1. Data Tabulation

qc (Kg/cm2) qt (Kg/cm2)Depth (m) qc (Kg/cm2) qt (Kg/cm2)0.20 0 00.40 14 250.60 20 300.80 19 241.00 10 221.20 17 301.40 19 271.60 12 241.80 13 282.00 12 272.20 15 282.40 12 232.60 18 252.80 10 293.00 15 223.20 18 283.40 16 283.60 30 403.80 12 234.00 12 204.20 10 204.40 10 204.60 10 184.80 10 185.00 10 155.20 11 155.40 9 125.60 14 185.80 10 186.00 12 186.20 20 286.40 18 246.60 9 186.80 11 187.00 18 227.20 15 267.40 18 227.60 10 207.80 15 20

Depth (m)8.00 20 268.20 12 208.40 12 208.60 12 208.80 10 209.00 15 209.20 9 209.40 20 229.60 22 309.80 15 20

10.00 13 1810.20 20 3010.40 28 3010.60 20 3010.80 22 3411.00 20 2511.20 22 3211.40 20 4011.60 20 3011.80 20 2912.00 40 6312.20 12 2412.40 10 2212.60 18 2812.80 20 2513.00 16 2013.20 16 2513.40 18 3013.60 25 2813.80 25 2714.00 18 3214.20 23 4514.40 40 4314.60 30 5514.80 25 3015.00 20 4015.20 150 200

8.4. Data Processing

Each of the parameters of every depth tested should be considered.

Since the depth considered is too many, only one depth (depth = 0.40 m) is

calculated manually as an example. The rest of the depths are computed by

computer.

At depth = 0.40 m:

qc = 14 kg/cm2

qt = 25 kg/cm2

fs=qt−qc15

=25−1415

=0.733

HP=l × f =20 ×0.733 = 14.667

JHP=0+14.667=14.667

FR=( fsqc )× 100 %=( 0.733

14 )× 100 %=5.24 %

Table 8.2. Calculation result.

Depth (m)

qc (Kg/cm2)

qt (Kg/cm2)

fs (Kg/cm2)

HP (Kg/cm2)

JHP (Kg/cm2)

FR (%)

0.00 0 0 0.000 0.000 0.00 0.00%0.20 0 0 0.000 0.000 0.00 0.00%0.40 14 25 0.733 14.667 14.67 5.24%0.60 20 30 0.667 13.333 28.00 3.33%0.80 19 24 0.333 6.667 34.67 1.75%1.00 10 22 0.800 16.000 50.67 8.00%1.20 17 30 0.867 17.333 68.00 5.10%1.40 19 27 0.533 10.667 78.67 2.81%1.60 12 24 0.800 16.000 94.67 6.67%1.80 13 28 1.000 20.000 114.67 7.69%2.00 12 27 1.000 20.000 134.67 8.33%2.20 15 28 0.867 17.333 152.00 5.78%2.40 12 23 0.733 14.667 166.67 6.11%2.60 18 25 0.467 9.333 176.00 2.59%2.80 10 29 1.267 25.333 201.33 12.67%

Depth (m)

qc (Kg/cm2)

qt (Kg/cm2)

fs (Kg/cm2)

HP (Kg/cm2)

JHP (Kg/cm2)

FR (%)

3.00 15 22 0.467 9.333 210.667 3.11%3.20 18 28 0.667 13.333 224.000 3.70%

3.40 16 28 0.800 16.000 240.000 5.00%3.60 30 40 0.667 13.333 253.333 2.22%3.80 12 23 0.733 14.667 268.000 6.11%4.00 12 20 0.533 10.667 278.667 4.44%4.20 10 20 0.667 13.333 292.000 6.67%4.40 10 20 0.667 13.333 305.333 6.67%4.60 10 18 0.533 10.667 316.000 5.33%4.80 10 18 0.533 10.667 326.667 5.33%5.00 10 15 0.333 6.667 333.333 3.33%5.20 11 15 0.267 5.333 338.667 2.42%5.40 9 12 0.200 4.000 342.667 2.22%5.60 14 18 0.267 5.333 348.000 1.90%5.80 10 18 0.533 10.667 358.667 5.33%6.00 12 18 0.400 8.000 366.667 3.33%6.20 20 28 0.533 10.667 377.333 2.67%6.40 18 24 0.400 8.000 385.333 2.22%6.60 9 18 0.600 12.000 397.333 6.67%6.80 11 18 0.467 9.333 406.667 4.24%7.00 18 22 0.267 5.333 412.000 1.48%7.20 15 26 0.733 14.667 426.667 4.89%7.40 18 22 0.267 5.333 432.000 1.48%

7.6 10 20 0.667 13.333 445.333 6.67%7.8 15 20 0.333 6.667 452.000 2.22%

8 20 26 0.400 8.000 460.000 2.00%8.2 12 20 0.533 10.667 470.667 4.44%8.4 12 20 0.533 10.667 481.333 4.44%8.6 12 20 0.533 10.667 492.000 4.44%8.8 10 20 0.667 13.333 505.333 6.67%

9 15 20 0.333 6.667 512.000 2.22%9.2 9 20 0.733 14.667 526.667 8.15%9.4 20 22 0.133 2.667 529.333 0.67%9.6 22 30 0.533 10.667 540.000 2.42%9.8 15 20 0.333 6.667 546.667 2.22%10 13 18 0.333 6.667 553.333 2.56%

10.2 20 30 0.667 13.333 566.667 3.33%10.4 28 30 0.133 2.667 569.333 0.48%10.6 20 30 0.667 13.333 582.667 3.33%10.8 22 34 0.800 16.000 598.667 3.64%

11 20 25 0.333 6.667 605.333 1.67%11.2 22 32 0.667 13.333 618.667 3.03%

Depth (m)

qc (Kg/cm2)

qt (Kg/cm2)

fs (Kg/cm2)

HP (Kg/cm2)

JHP (Kg/cm2)

FR (%)

11.4 20 40 1.333 26.667 645.333 6.67%11.6 20 30 0.667 13.333 658.667 3.33%

11.8 20 29 0.600 12.000 670.667 3.00%12 40 63 1.533 30.667 701.333 3.83%

12.2 12 24 0.800 16.000 717.333 6.67%12.4 10 22 0.800 16.000 733.333 8.00%12.6 18 28 0.667 13.333 746.667 3.70%12.8 20 25 0.333 6.667 753.333 1.67%

13 16 20 0.267 5.333 758.667 1.67%13.2 16 25 0.600 12.000 770.667 3.75%13.4 18 30 0.800 16.000 786.667 4.44%13.6 25 28 0.200 4.000 790.667 0.80%13.8 25 27 0.133 2.667 793.333 0.53%

14 18 32 0.933 18.667 812.000 5.19%14.2 23 45 1.467 29.333 841.333 6.38%14.4 40 43 0.200 4.000 845.333 0.50%14.6 30 55 1.667 33.333 878.667 5.56%14.8 25 30 0.333 6.667 885.333 1.33%

15 20 40 1.333 26.667 912.000 6.67%15.2 150 200 3.333 66.667 978.667 2.22%

Graph 8.1. qc vs depth graph:

0 20 40 60 80 100 120 140 1600.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

qc vs Depth

qc (Kg/m2)

Dept

h (m

)

Graph 8.2. FS vs depth graph:

0 0.5 1 1.5 2 2.5 3 3.50.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

fs vs Depth

fs (Kg/m2)

Dept

h (m

)

Graph 8.3. JHP vs depth graph:

0 200 400 600 800 1000 12000.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

JHP vs Depth

JHP (Kg/m)

Dept

h (m

)

Graph 8.4. FR vs depth graph:

0 0.02 0.04 0.06 0.08 0.1 0.12 0.140.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

FR vs Depth

FR (%)

Dept

h (m

)

8.5. Analysis

8.5.1. Experimental Analysis

In this experiment, there are several steps which are necessary to

be done in order to get an accurate result. In the preparatory step of this

experiment, it is necessary for us to prepare a small square hole on the

field. This step is done in order to ensure that the CPT cone directly

penetrate the soil without being covered with any roots or plants. The next

step is putting the two anchor between the spot which wanted to be tested.

The anchors are necessary to be established because they act as the

stabilizer and support for the rig, so the rig do not rotate or translate during

the CPT test. The channel steel acts as stabilizer, since putting the rig over

the steel will provide more support to the rig, compared to the soil support.

The steel itself will connect the rig with the anchor. Manometers are

required to be mended because the manometer itself should be easy to

read, so setting their initial values to zero will ease the readings. The last

step of the preparation is oiling the connections and bars inside the CPT

tubes. This step is done to reduce the friction at both the connections and

the bar inside the tube. Slippery connection between tubes will ease the

installation, while slippery internal bar will ensure the accuracy of the

manometer readings, since the manometer readings are taken through the

internal bars.

The main part of the experiment is the data collecting process. The

very first step of the main part is installing the cone in the rig. In this

installation, there must be a gap between the bar inside the first tube and

the manometer, so that the manometer reading is not disturbed. In order to

maintain this gap, a lock is required. This lock may only be released when

the readings are being done, which allows the tip of the manometer to

contact rod inside the tube. The readings are taken once in 20 centimetres

because it provides an adequately accurate interval while the samples are

not too many so the experiment can still be done quickly. When doing the

readings, note that there will be two values; the qc and the qt. The qc is a

value of pressure beard by the cone, while the qt is the pressure beard by

both the cone and the mantle. The ‘jump’ of the readings is caused by the

gap between the cone and the mantle. After each metre, the tube should be

extended, because the length of each tube is only 1 metre. In the

procedure, it is said that the readings can be done by two manometers, but

in the experiment, the small manometer was out of service, so the

manometer being used was only the large manometer, which gives

relatively inaccurate readings in small scale. The penetration should be

stopped when the qc has exceeded 150 kg/cm2 because the rock bed has

been reached, so continuing the CPT may damage the apparatus. In fact,

the pipe was inadequate so the penetration did not reach the rock bed, so it

is assumed that the rock bed was located at depth = 15.20m.

After the test, all the tubes should be extracted carefully. If the

extraction is not done neatly, it is possible for the cone to fall into the soil.

In this case, the extraction will be much more difficult. After extracting the

cone, returning the rig should be done carefully, since it is very heavy. The

anchors should also extracted, so it can be used next time.

8.5.2. Result Analysis

After gaining the data, the soil classification can be done. Soil

classification according to the result of cone penetration test can be

correlated with the following graph:

Graph 8.5. Soil Type based on CPT result

(extracted from Principles of Foundation Engineering by Braja M. Das)

According to this result, the area which was tested possess qc

which ranges between 9 to 150 kg/cm2, where most of the result lies in the

value of 10 to 30 kg/cm2, while the f varies well throughout the depth,

with a range of 0.133 to 3.333. from the table, it is known that the most

dominant component of the soil is clay or silty clay. After analysing all the

layers, it is possible for us to know the layers of the soil:

Table 8.3. The classification of the layers of tested soil

Depth (m) Type of Soil0.40-0.80 Clays0.80-1.00 Silty clays1.00-1.40 Clays1.40-3.80 Silty clays3.80-6.20 Clays6.20-6.60 Silty clays6.60-7.00 Clays7.00-7.20 Silty clays7.20-7.40 Clays7.40-7.60 Silty clays7.60-8.00 Clays8.00-8.20 Silty clays8.20-9.40 Clays9.40-9.80 Silty clays

9.80-10.20 Clays10.20-10.60 Silty clays10.60-11.00 Clays11.00-11.20 Silty clays11.20-12.00 Clays12.00-12.20 Silty clays12.20-12.80 Clays12.80-13.20 Silty clays13.20-13.60 Clays13.60-14.00 Silty clays14.00-14.40 Clays14.40-14.60 Silts14.60-15.20 Clays

15.20 and below Sands

8.5.3. Error Analysis

During the execution of this cone penetration test, there are some

errors that may affect the result of the CPT. In the preparation of the test,

not all the pipes were oiled. Only the older pipes were oiled, and these

pipes were not very smooth even after oiling. This made the distribution of

stress along the internal bar into the pipe. This may result in inaccuracy of

the manometer readings.

When installing the CPT rig, the rig itself may not very

perpendicular with the soil. This may cause inaccuracy of the depth

measured, since the depth may actually shallower than the readings (due to

an angle exists).

When penetrating the soil, sometimes mistake was done. One or

two points were over-penetrated by two or three centimetres, while the

readings may also not accurate in some of the depth due to inconsistency

of the penetration rate during the reading. The large manometer being used

was not suitable for this experiment, since the scale was too large, so the

value obtained was based on interpolation of its scales.

The most influential error was the inadequacy of the CPT pipes.

Due to this inadequacy, the next reading depth after the last pipe was

assumed as the bedrock, which made this experiment inaccurate.

8.6. Conclusion

This experiment is aimed to determining the type of soils per layer and

knowing the depth of the bedrock.

The qc of the soil layers lies between 9 to 150 kg/cm2, while the fs lies

between 0.133 to 3.333 kg/cm2

The soils being tested consists of clay, silty clay, silt and sand.

Most of the layers of the soil tested were clay or silty clay.

According to this experiment, the bedrock is located at depth = 15.20m

with a qc of 150kg/cm2

8.7. Reference

Budhu, Muni. “Soil Mechanics”. John Willey and Sons. New York.

2011

Craig, R.F. “Craig’s Soil Mechanics”. Spon Press. New York. 2004

Das, Braja. “Principles of Foundation Engineering”. Thomson.

Toronto. 2007

Lambe T.W. “Soil Testing for Engineers”. John Willey and Sons.

New York. 1951.

8.8. Attachment

Installing the cone into the rig