Deep foundations are necessary when the depth of a foundation exceeds twice the width of its footing. This is often due to factors such as soil instability or a need for additional support. To ensure that the soil can support the weight of the foundation, soil tests are necessary.
There are various types of soil tests that can be conducted for deep foundations. These tests aim to determine the soil’s properties, such as its bearing capacity and the extent to which it can be compressed. One commonly used test is the Standard Penetration Test (SPT), which involves driving a standardized sampler into the ground and measuring the number of blows required to penetrate a set distance. Another test is the Cone Penetration Test (CPT), which uses a cone-shaped probe to measure soil properties as it is pushed into the ground.
Other tests may be used depending on the specific needs of the foundation project. For instance, a plate load test may be conducted to measure the bearing capacity of the soil under the weight of a simulated foundation. A shear strength test may also be used to determine the maximum stress that the soil can withstand before it fails.
Overall, soil testing is an essential aspect of deep foundation construction, as it helps to ensure that the soil can support the weight of the foundation and prevent structural failure. By conducting appropriate tests, engineers and builders can make informed decisions about the type and design of foundation to use, as well as any necessary reinforcements or modifications to the soil.
Soil tests required for deep foundations
Pile foundations commonly encounter similar deposits in a local area, although the bearing layer for shallow foundations may vary from site to site. While soil parameters can be used to estimate pile capacity, load tests provide a more reliable measure. Therefore, it is crucial to obtain comprehensive information on the type, size, length, and capacity of piles used in the locality, including load-settlement graphs. This information can help correlate soil characteristics from investigation reports with load tests from completed projects. By doing so, one can determine the appropriate soil tests to be performed and make reasonable recommendations for the type, size, length, and capacity of piles. It is important to note that many formulae used in this process are empirical.
Fig.1:soil tests for deep foundation
The given context is discussing the process of obtaining reliable information about piles in a particular locality. When such information is not available or trustworthy, it may be necessary to conduct a test pile and correlate the results with soil data. In order to obtain the necessary data, several tests may be required.
To elaborate, the process of driving a test pile involves inserting a pile into the ground and recording data on the behavior of the soil during installation. This data can then be analyzed to determine the properties of the soil and the likely behavior of other piles in the area. Correlating this data with other soil data can help to confirm the reliability of the information obtained.
To obtain reliable information about the soil and the behavior of piles in the locality, it may be necessary to conduct several tests. These tests could include soil sampling and laboratory testing, in-situ testing, and geophysical testing. The results of these tests can provide valuable information about the soil’s properties and the likely behavior of piles in the area.
Overall, the process of obtaining reliable information about piles in a locality can be complex and time-consuming. However, by conducting appropriate tests and correlating the results with other data, it is possible to obtain accurate information about the soil and the behavior of piles in the area.
1. Direct shear test
The purpose of a certain test is to estimate the effective friction angle of cohesionless soil. However, there are also correlations that have been developed to assess the effective friction angle of this type of soil. If you are interested in learning more about the shear strength test of soil, you can click on the provided link.
Fig.2:Direct shear test
2. Standard penetration test (SPT)
The given context is describing a specific testing process that is used to determine the cohesion and adhesion of soil, as well as the angle of friction and point of resistance for each soil stratum. This testing process is carried out on cohesionless soil.
The purpose of the testing process is to gain a better understanding of how the soil behaves and interacts with other materials in its environment. By measuring the cohesion and adhesion of the soil, as well as the angle of friction between the soil and a pile, researchers and engineers can determine the point of resistance of the soil.
The testing process involves analyzing each soil stratum individually to determine its specific properties. This allows researchers and engineers to better understand how the soil will behave under various conditions and loads. Overall, the testing process is a critical step in the development of structures and infrastructure that are built on or with soil, as it provides important insights into the properties and behavior of the soil.
3. Static cone penetration test (CPT)
A test is being carried out to measure the cohesion of soft cohesive soils, and subsequently the adhesion. The results will also be compared to the SPT test results for fine to medium sands. This is necessary when dealing with soil layers that contain both cohesive and cohesionless soils. In such cases, both SPT and CPT tests are required to obtain accurate data on the soil’s properties.
4. Vane shear test
The given context describes a specific application of a certain method or technique. According to the context, this method is used to estimate the undrained in-situ shear strength of impervious clayey soils. The term “undrained” refers to the state where the soil is not allowed to drain water during the shear test.
The method is presumably a standardized or established one that has been validated and widely used in the field of geotechnical engineering or related areas. The context does not provide any details about the specific procedure or calculation involved in the method, but it suggests that the estimated shear strength is an important parameter for characterizing the mechanical behavior of the soil.
The context also implies that impervious clayey soils are a common type of soil encountered in geotechnical projects, and that their properties and behavior are of particular interest and concern due to their potential impact on the stability and performance of various structures or systems built on or within them.
Overall, the given context provides a concise and specific description of a practical application of a technical method, and it highlights the relevance and significance of the estimated parameter for the field of geotechnical engineering.
5. Undrained triaxial shear strength
Undisturbed soil samples, which are obtained using thin-walled tube samplers, undergo a specific type of test to determine their cohesion. This test is important because it helps to understand the strength of the soil and how it may behave under certain conditions.
The use of thin-walled tube samplers is crucial in obtaining undisturbed soil samples, as these samples must not be altered in any way before testing. The cohesive properties of the soil can be affected by even the slightest disturbance, which is why great care must be taken during the sampling process.
Once the undisturbed soil sample is obtained, it undergoes a test to determine its cohesion. This test is specifically designed to measure the shear strength of the soil, which is an important factor in determining how it will behave under various loads and pressures.
By understanding the cohesion of the soil, engineers and construction professionals can make more informed decisions about how to build structures on top of it. This knowledge can also be used to predict how the soil will behave over time, which is important for long-term planning and maintenance.
In summary, the determination of cohesion in undisturbed soil samples obtained with thin-walled tube samplers is a crucial step in understanding the strength and behavior of the soil. This information is vital for engineering and construction professionals as they make decisions about building structures on top of the soil and planning for long-term maintenance.
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The test that needs to be conducted for clayey soils is called the Standard Penetration Test (SPT). This test is commonly used to determine the consistency, density, and strength characteristics of soil. The SPT is conducted by driving a split-barrel sampler into the soil at a specified depth using a drop hammer. The number of blows required to drive the sampler a specific distance is recorded as the SPT N-value.
To conduct the SPT, the procedures outlined in ASTM D 2850-03, 2004 should be followed. These procedures provide detailed instructions on how to prepare the test site, perform the test, and record the data obtained. It is important to follow these procedures precisely to ensure that accurate and reliable data is collected.
In the case of driven piles proposed for stiff clays, it is necessary to check the soil’s strength characteristics using the SPT. This is because stiff clays can have a significant impact on the performance and stability of driven piles. By conducting an SPT, engineers can obtain valuable information about the soil’s shear strength, density, and stiffness, which can be used to design appropriate foundations for the piles.
In summary, the Standard Penetration Test (SPT) is a crucial test that needs to be conducted for clayey soils. By following the procedures outlined in ASTM D 2850-03, 2004, engineers can obtain accurate and reliable data about the soil’s strength characteristics. This information is particularly important for designing driven piles proposed for stiff clays, as it can help ensure the stability and performance of the foundation.
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The objective of the field vane shear test is to evaluate the undrained shear strength of soil at a particular depth. This test is performed by inserting a vane into the soil and then rotating it at a constant rate until the soil fails. The torque required to rotate the vane is measured, and this value is used to determine the undrained shear strength of the soil. The test is useful for determining the strength of soft to stiff clayey soils, and can be performed in both saturated and unsaturated conditions.
In addition to determining the undrained shear strength, the field vane shear test can also be used to evaluate the soil’s sensitivity, defined as the ratio of the undrained shear strength to the preconsolidation stress. This parameter is useful for predicting the potential for soil deformation under load.
The field vane shear test can also be used to estimate the in-situ shear strength of soil at the end of the construction phase. To do this, remoulded samples are taken and drained shear strength parameters are determined. These parameters are then used to represent the in-situ condition of the soil. The test procedure for this is outlined in ASTM D4767-02, 2004.
Fig.3:Triaxial shear test
6. Pressure meter test
The purpose of this test is to establish the stress-strain curve for horizontal loading. The test can be carried out using either an equipment that is inserted into a pre-drilled borehole or a self-boring pressure meter. It should be noted that if the soil being tested is not isotropic, the same value cannot be used for the vertical direction. This test is specifically conducted for piles that are subjected to lateral loading.
7. Ground water condition and permeability of soil
The type of pile that is recommended for a construction project is influenced by the condition of the groundwater and soil permeability. In order to determine the appropriate pile type, the level at which water remains in the bore hole is recorded in the bore logs. It should be noted that because the permeability of clay is very low, it can take several days for water in the drill hole to reach the ground water table.
To ensure the suitability of the chosen pile type, ground water samples should be tested to assess any potential chemical effects on the concrete and reinforcement. Additionally, the results of the cone penetration test for the same soil can be subject to substantial scatter, which makes it necessary to corroborate them with supplementary information obtained from other exploration methods.