# 10 types of soil tests for construction- Importance, Procedure, Calculation

When civil engineers began to design any structure like a building, bridge, or dam then they need to test the soil. There are different types of soil tests for construction which gives us different characteristics of the soil.

The test of soil clarifies which types of structure, how much load of structure can be constructed on the given types of soil. Here you will see the details of different types of soil tests for construction one by one.

## Types of soil tests for construction

1. Moisture Content Test
2. Specific Gravity Test
3. Dry Density Test
4. Atterberg Limits Test
5. Plastic Limit Test (PL)
6. Proctor’s Compaction Test
7. California Bearing Test (CBR test)
8. Consolidation test
9. Penetration test
10. Permeability test etc

## Moisture content test

#### Definition

Moisture content is defined as the ratio of the weight of water to the dry weight of solid particle in a given soil mass. It is expressed in terms of percentage.

#### Importance

The engineering behaviour of soil is largely influenced by the presence of water and its quantity present in the voids of the soil.

This test is one of very important soil tests for construction.

Therefore, it is necessary to determine the quantity of water present in the soil deposit at a given location.

#### Apparatus required

• Can
• Weighing Balance (with 0.01 accuracy)
• Thermostatically controlled oven

#### Procedure to calculate moisture content in soil by Oven Drying Method

Step 1: First of all, the soil sample is collected from the site.

Step 2: Then, the mass of empty can is recorded (say M1).

Step 3: Then, the mass of moist soil and can is recorded (say M2).

Step 4: Now, the can containing moist soil is kept in the oven for 24 hours. Then the mass of dry soil with can is recorded (say M3).

Step 5: Moisture content is calculated using the formula given below:

Where Mw is the mass of water= M2-M3

Ms is the mass of dry soil solid= M3-M1

Step 6: The process is repeated for three specimens and the average of these three specimens is considered as the actual moisture content of the soil.

#### Precaution

• The temperature of the oven should be maintained at 110ºC ± 5ºC. But if the soil sample contains a significant amount of gypsum or organic material, the temperature of the oven should be between 60ºC to 90ºC.
• While putting the can in and taking the can out of the oven special care should be given otherwise, you may burn your hands.

## Specific gravity test

#### Definition

The ratio of the weight of soil in the air to the weight of an equal volume of water at 4ºC is known as the specific gravity of the soil.

#### Importance

Engineering properties of soil play an important role in the design and construction of any structure. Therefore, it is very important to determine the engineering properties of the soil.

The specific gravity of the soil is one of the engineering properties of the soil. It is useful for finding the degree of saturation of soil and unit weight of moist soil. The unit weights are needed in the pressure, settlement, and stability problems in soil engineering.

#### The determination of the specific gravity of soil in the lab can be done using three methods:

1. Pycnometer method: This method is done for coarse-grained soil.
2. Flask method: Similar to the pycnometer method, this method is done for coarse-grained soil.
3. Density bottle method: This method is suitable for all types of soil. This method is considered as a standard method for the determination of specific gravity of soil.

#### Apparatus required

• Density bottle (50 ml capacity with stopper)
• Constant Temperature Water bath (at temperature 27ºC)
• Desiccator (containing anhydrous silica gel)
• Thermostatically controlled oven (that can maintain a temperature of 105 to 110ºC)
• Weighing balance (with accuracy 0.01 gm)
• Plastic Wash Bottle (containing distilled water)

Procedure to calculate the specific gravity of soil by using Density Bottle Method as per IS code 2720 Part 3.

Step 1: First of all, take a clean density bottle with a stopper and it is dried at 105 to 110ºC. Then cool it in the desiccator.

Step 2: Now, the density bottle is weighed and the weight is recorded (say W1).

Step 3: Then prepared soil sample of about 10 to 20 gm is taken. Now it is dried at 105 to 110ºC and then cooled in the desiccator.

Step 4: Then the soil sample is transferred carefully into the density bottle and weighed. The weight of the density bottle containing soil sample is recorded as W2.

Step 5: Some distilled water is added to the density bottle until the sand is fully soaked. Then it is left for 2-10 hours depending upon the type of soil.

Step 6: More water is added after the waiting time until the bottle is half-filled and the solution is mixed properly. The entrapped air in the bottle should be removed completely.

Step 7: Then the bottle is filled fully and the stopper is put and mixed thoroughly.

Step 8: The bottle is then placed in the constant water bath for about 1 hour so that the temperature of the soil and water in the bottle reaches 27ºC.

Step 9: The bottle is taken out and cleaned and dried with the help of wipes. Then the capillary of the stopper is filled with drops of distilled water in case it is not full.

Step 10: The density bottle full of soil and distilled water is then weighed and the weight is recorded as W3.

Step 11: The density bottle is emptied and cleaned thoroughly and then filled with distilled water and stopper is put. The bottle is wiped from outside until completely dry.

Step 12: The weight of the density bottle with distilled water only is weighed and recorded as W4.

Step 13: Necessary calculation is done to find the specific gravity of soil.

Step 14: The procedure is repeated for two more times and the average of three specimens is taken as the specific gravity of soil at 27ºC.

Precaution

• The test soil sample should be free from lumps.
• Every weight taken during the experiment must be taken precisely.
• The entrapped air in the density bottle must be removed completely.
• The soil sample taken must be oven-dried fully.

Read Also, Black cotton soil – Properties, Chemical composition, and Stabilization

## Dry density test

#### Definition

The weight of a solid per unit volume of soil mass is known as the dry density of the soil.

Mathematically, Dry density= Weight of the oven-dried soil/Volume of the soil

#### Importance

This types of soil tests for construction is done for:

• Stability analysis
• Determination of bearing capacity
• Determination of degree of compaction

The dry density of soil can be determined mainly by two methods:

1. Sand replacement method
2. Core cutter method

## Core Cutter Method

#### Apparatus required

• Cylindrical Core Cutter (100 mm internal diameter and 130 mm height)
• Steel Dolley (100 mm diameter and 25 mm height)
• Steel rammer (weight 9 kg)
• Weighing balance
• Palette knife
• Straight edge steel rule
• Sample extruder
• Water content determination apparatus

#### Procedure

1. First of all, the volume of the core cutter is determined using the formula:

Where d is the internal diameter of the core cutter And H is the height of the core cutter

1. The weight of the empty core cutter is measured and recorded(say Wc).
2. A small area of about 350 mm² is exposed and levelled up.
3. Now, the bevelled edge of the core cutter is placed on the ground and Dolley is put on it. Then pressure is applied manually on the core cutter so that the cutter gets embedded in the ground.
4. Then the cutter is pushed vertically in the ground with the help of rammer ensuring minimum disturbance to the soil sample. The cutter is pushed in the ground until 15 mm of the Dolley protrudes above the soil surface.
5. Then the soil surrounding the core cutter is removed with the excavating tool. Now. The cutter is taken out from the embedded soil carefully.
6. Now, the Dolley is removed from the cutter and the top surface of the cutter is levelled up with the help of straight edge steel rule. The bottom of the core cutter is also trimmed.
7. Now the core cutter filled with soil is weighed (say Ws).
8. Then the weight of wet soil(unit gm) is calculated.

Then bulk density(unit gm/cm³)is calculated.

Now, the soil sample is taken from the core cutter and a representative sample is taken. Then the moisture content of the soil sample is calculated.

Then dry density (unit gm/cm³) of the soil is calculated.

The process is repeated for three specimens and average of dry density from each case is the required dry density of the soil.

#### Precaution

• The soil around the cutter should be removed before lifting it to avoid disturbances.
• The core cutter should be driven only till the dolly is halfway in the ground to avoid compaction of soil in the cutter.

## Atterberg limit test – soil tests for construction

#### Definition

In 1911, an Agronomist called Atterberg found about consistency limits. The consistency limit is the minimum water required by soil to pass from one state of consistency to another state. Therefore, these limits are called Atterberg’s limit. There are three types of Atterberg limits:

#### Liquid Limit (LL)

The liquid limit of a soil is the minimum water content at which the soil is still in liquid state but has a small setting strength against flowing which can be measure by standard procedure.

#### Apparatus required

• Mechanical liquid limit device
• Grooving tools like Casagrande’s type tool and ASTM type tool
• Porcelain Evaporating Dish
• Spatula
• Weighing machine (accuracy 0.01 gm)
• Thermostatically controlled oven
• Wash bottle containing distilled water
• Sample containers
• 425 micron IS sieve

#### Procedure

1. First, the mechanical liquid limit device is inspected to make sure the device is clean dry and in working condition.
2. Then 120 gm of soil sample passing through 425-micron sieve is weighed in the porcelain evaporating dish.
3. The distilled water is added to the soil sample and mixed thoroughly with the help of a spatula.
4. Then the mixture is taken and placed in the cup of liquid limit device. The mixture is squeezed down and spread in the cup with the help of a spatula.
5. The soil placed in the cup is trimmed so that the maximum depth of the soil in the cup will be 1 cm.
6. The excess soil is then transferred into the dish.
7. Now, for clayey soil, Casagrande’s type tool is used to cut the soil into two halves in the direction perpendicular to the axis of rotation of the liquid limit device. And for sandy soil ASTM type tool is used.
8. Then the cup is lifted and dropped by rotating the handle at the rate of two revolutions per second till two halves of the soil touch each other by flowing and not by sliding with the bottom of the groove along with the distance of about 12 mm.
9. The number of blows(range between 15 to 35) required is counted and the reading is recorded.
10. Now, a representative sample of soil is taken from the cup in a container for the determination of moisture content of the soil.
11. Then the process is repeated for different water content and the observed value is recorded.

#### Observation table

Now to analyse and interpret the results for the liquid limit test, a graph is plotted between the number of blows in X-axis and water content in Y-axis on a semi-log graph making use of reading recorded on various tests.

The water content corresponding to 25 number of blows is the liquid limit of the soil. In this way we can calculate liquid limit in soil tests for construction.

## Plastic Limit Test (PL)

The water content at which a soil just begins to crumble when rolled into a thread-like structure approximately 3 mm in diameter is called the plastic limit of the soil.

#### Apparatus required

• Porcelain evaporating disk
• Ground glass plate
• Metallic rod of 3 mm diameter
• Spatula
• Sample containers
• Thermostatically controlled ovens
• 425 micron IS sieve

#### Procedure

1. 50 gm of soil sample passing through 425-micron sieve is taken into a porcelain dish and is weighed.
2. Now, distilled water is added in the soil and mixed thoroughly until the soil becomes plastic enough to be moulded.
3. Then a round ball of soil sample weighing about 8 gm is taken and rolled in the glass plate with the help of fingers so that a thread of uniform diameter is formed. The thread should be rolled at the rate of 80 to 90 strokes per minute.
4. The rolling is continued until the thread becomes approximately 3 mm in diameter by taking reference of the metallic rod.
5. Again the taken soil is kneaded and rolled. This process should be continued until the soil starts to crumble when it is of 3 mm size thread.
6. Now, the pieces of the crumbled soil sample are taken into a container for the determination of water content.
7. The process is repeated for three specimens with different water content in it.

#### Observation table

The average water content of the three tests is the plastic limit of the soil sample taken.

After determining the liquid limit and plastic limit, we should calculate the plasticity index using

Plasticity Index (Ip)= Liquid limit- Plastic limit

Finally, for the classification of the soil, we should refer to the plasticity chart as per code 1498.

## Shrinkage limit Test

The water content of the soil which won’t decrease the volume of the specimen after the further loss of moisture content by the soil is the shrinkage limit. The test for this limit is performed less often. The test is described in ASTM D4943.

Importance

The consistency limits depend upon the amount and type of clay in the soil and form the basis for the soil classification system. The result obtained from the test has direct application in:

• The design of foundation of the structures
• Predicting the behaviour of soils in the fills
• Embankments and pavements

#### Precaution

• The soil sample should not be oven-dried before the test.
• The Soil sample taken for the determination of the moisture content should not be left in the air.
• The soil sample after being oven-dried should be weighed immediately.

## Proctor’s compaction test

#### Definition

Proctor compaction test is a simple test. It is carried out in the laboratory for the determination of the optimal moisture content at which a given soil type will be most dense and achieve its maximum dry density.

#### Importance

The proctor compaction test is done to understand the compaction characteristic of different soils containing different amounts of moisture content in it. Proctor compaction test is very important soil tests for construction.

#### Procedure

1. First of all, 5 kg of soil sample passing through 4.75 mm sieve is taken.
2. The soil sample is then placed in a modified mould of dimensions (150 mm diameter, 127.3 mm height having a capacity of 2299 cc).
3. The soil sample is then placed by 5 layers and each layer is compacted by 25 numbers of blows through standard rammer of weight 4.5 kg and the freefall of 415 mm.
4. The compaction energy required for compaction is 2700 KJ/m³. The compaction energy is calculated using the formula:

Where N is the number of blows per layer

n is the number of layers

h is the height of the freefall

V is the volume of the mould

w is the weight of the rammer

#### Observation table

Now, a graph is plotted between dry density in Y-axis and % water content in X-axis, then a parabolic curve with peak is obtained. This curve is known as the compaction curve.

With the increase in water content dry density also increases and becomes maximum at peak and a further increase in water content decreases dry density.

The corresponding value of dry density at the peak is the maximum dry density and the corresponding value of the water content is the optimum moisture content (OMC).

#### Precaution

• Hand gloves and safety shoes should be used while compacting.
• For clayey soils about 15 minutes and for coarse-grained soils 56 minutes should be given after mixing the water and before turning into the mould.
• There should be uniform blow over the surface of the mould.

## California Bearing Test (CBR test)

#### Definition

California bearing ratio value test was developed by California state highway department of USA for evaluation of subgrade strength of highway and airfield pavements.

California bearing ratio value is the ratio of load per unit area required to penetrate a soil mass by a standard plunger at a specific rate to that corresponding required for penetration of a standard material.

Mathematically,

The standard material is the one defined as having a CBR value of 100%. CBR value is generally determined at 2.5 mm or 5 mm penetration.

#### Importance

This type of soil tests for construction is done to determine the thickness of the flexible pavements using Indian Road Congress specifications.

Apparatus required as per IS: 2720 part 16

• Mould (internal diameter 150 mm and height 175 mm) with a detachable collar and base plate having perforations at the bottom.
• A spacer disc of 148 mm diameter and height of 47.7 mm.
• Surcharge weights (2.5 kg mass and having a central hole of 53 mm diameter)
• Slotted weight
• Penetration plunger of diameter 50 mm and height 100 mm
• A loading machine of capacity 5000 kg and capable of travelling vertically at a rate of 1.25 mm/min
• Others such as Compaction rammers, Dial gauges, weighing machine, Filter paper, Mixing tools, Trays and Measuring cylinder

#### Theory

The test procedure consists of two parts:

1. Preparing test specimen

The test specimen can be prepared by either static compaction or dynamic compaction.

The specimen prepared from the dynamic compaction method can be prepared either by light compaction or heavy compaction.

In light compaction, the specimen is prepared by filling it in three layers using a 2.6 kg rammer with a freefall pf 31 cm and 56 number of blows are given to each layer.

Whereas, the specimen is prepared in five layers using a 4.89 kg rammer with a freefall of 45 cm giving 75 numbers of blows to each layer, in heavy compaction.

## Penetration test – Soil tests for construction

#### Procedure

Step 1: First of all, the spacer disc with the threaded pole is placed in the bottom of the base to assemble the mould.

Step 2: Then filter paper is placed at the top of it.

Step 3: Now, lubricating oil is applied in the inner side of the mould to prevent the stickiness of the soil to the mould. Then collar is fixed on the top of the mould and spacer disc assembly.

Step 4: Now, about 5kg of the soil passing through 20 mm sieve is taken. Then water content as predetermination is mixed in the soil such that the water is equal to the OMC or equal to the field moisture content as the case may be.

Step 5: The water and soil are mixed thoroughly to prepare a mixture of uniform consistency.

Step 6: the mixture is then transferred to the mould such that it would fill one-third or one-fifth of the total thickness of the mould.

Step 7: Now, the mixture is compacted with a suitable number of uniform blows (56 nos. of blow) throughout the area.

Step 8: After the compaction, the top layer of the soil is scratched and more soil is added to the mould ass before and compacted. This process is repeated twice.

Step 9: After compacting the top layer, the collar is removed and the top surface is trimmed off. Then the baseplate is also removed. Then after the filter paper is also removed.

Step 10: The weight of the soil with the mould is taken and recorded.

Step 11: The filter paper on the spacer disc is removed. The spacer disc is removed from the base plate and cleaned properly.

Step 12: Now, a filter paper is placed on the base plate and the mould is placed on the base plate such that the compacted surface is at the bottom. Then an annular weight of mass 2.5 kg is placed in the mould.

Step13: Then the assembly is placed on the pedestal of the loading machine. Now, the proving ring and dial gauge is placed in the position. Then, the plunger is fixed and brought in contact with the soil surface.

Step 14: Now, a seating load of 4 kg is applied so that good contact is established between the soil and the plunger. Then a slotted weight is added at the top.

Step 15: The dial gauge is then set at zero and the plunger is allowed to penetrate the soil at the rate of 1.25mm/min.

Step 16: The reading on the proving ring is recorded as shown below:

Step 17: Now the graph is plotted between penetration in X-axis and load in Y-axis. From the curve, the load corresponding to 2.5 mm and 5 mm penetration is determined and CBR value is calculated is done using the formula:

The standard load values for particular penetration are chosen from this table:

#### Precaution

• The holes of the base plate and that of the perforated disc should be cleaned thoroughly.
• The surcharge weight should be aligned with the plunger as a result the plunger should penetrate freely into the soil.

## Consolidation test – Soil tests for construction

#### Definition

Consolidation is a process of a gradual reduction in the volume of the soil mass by the expulsion of pore water under sustained loading.

Consolidation test is carried out in the laboratory as One-Dimensional Consolidation test. This test is performed in a consolidometer also known as oedometer.

#### Importance

Consolidation test plays an important role in determining the rate and magnitude of settlement in soils.

The result obtained from consolidation test is used while designing the foundation of a structure and analysis stability of soil for embankment, footing and columns.

#### Procedure

1. The specimen from the representative sample of soil either undisturbed or compacted is prepared. Generally, the specimen shall be 60 mm in diameter and 20 mm thick.
2. The soil specimen is then put inside the ring with two porous stones. The porous stone should be one at the top of the specimen and other at the bottom. Then the load is applied on the specimen by using a lever arm. And the compression is measured by a micrometre dial gauge.
3. An initial setting load of 5 KN/m² is applied until there is no change in dial gauge reading for two consecutive hours or a maximum of 24 hours.
4. Then a load of 10 KN/m² is added and dial gauge readings are recorded after various time intervals: 10 sec, 20 sec, 30 sec, 1 min, 2 min, 4 min, 8 min, 16 min, 1 hour, 2 hours, 4 hours, 8 hours, 16 hours and 24 hours.
5. Then after 24 hours load is doubled and applied and reading is taken as in step 4.
6. Above procedure is repeated for loads of 40, 80, 160, 320 and 640 KN/m².
7. After the last load is applied for the required period, the load is decreased to one-fourth of the last load and allowed to stand for 24 hours, till the load intensity of 10 KN/m² is reached.
8. At the end of the test, the dry weight of the test specimen is taken.
9. Then a graph is plotted between deformation in Y-axis and Time(log scale in X-axis). From the graph, three distinct stages can be obtained as shown below:

Then the result of consolidation test is used to find different parameters like void ratio, the height of solid method, coefficient of compressibility, coefficient of volume change, coefficient of compression and coefficient of recompression.

#### Calculation

The volume of soil, Vs= A * Hs

Where A= area of soil solid

Hs = thickness of soil solid

Precaution

• The specimen used should be free from voids and over-sized particles.
• The load should be applied concentrically to the specimen.
• The inaccuracy that may occur in dial gauge reading should be avoided.

Among all types of soil tests for construction, we are going to discuss the last one which is the permeability test of soil.

## Permeability test

#### Definition

The permeability of the soil is defined as the property of the soil which permits the flow of water through it.

#### Importance

Permeability test is also unavoidable soil tests for construction. It is conducted to determine the coefficient of permeability of the sample of the soil taken.

Permeability of soil can be tested from two methods:

1. Falling head method (used for fine-grained soil)
2. Constant head method (used for coarse-grained soil)

Apparatus required

• Stopwatch

#### Procedure

• First of all, a cylindrical mould is taken and its diameter (D) is measured and area (A) is calculated.
• Then the mould is attached with two filter discs, one at top and another at the bottom. These discs are highly permeable and are provided with inlet at top and outlet at the bottom of the disc.
• Then the inlet is fitted with the vertical standpipe. Let the diameter of the inlet be ‘d’ and its area ‘a’ is calculated.
• Then the mould is filled with the sample soil and compacted uniformly. Now, the water is passed through the standpipe until the soil becomes fully saturated, and steady flow is obtained.
• The reading is then taken at an interval of 10 seconds to measure the falling head of the water.
• Then the coefficient of permeability is calculated using the formula:

Where t= time interval

L= length of the specimen

#### Precaution

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Sushmita Niraula