Paper Example on Design Parameters and Soil Tests

Introduction

In today's world where expansions are always happening, the construction of buildings, roads, and other technological infrastructure have become quite common. All these types of developments, require to be built on soil structures that are favorable and will be able to hold the loads placed on them. Various tests thus have to be done on soil samples by geo-technicians to determine the geotechnical design parameters of the building sites. The most common properties that are usually investigated are soil compressibility, soil strength, and soil permeability. Various tests are performed to determine these properties in the soil samples. This paper will identify and describe some of these tests as well as outline the importance of conducting such tests on building sites.

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Common Tests Used to Determine Geotechnical Design Parameters

Tests conducted on soil samples help to reveal soil properties that tell whether it is acceptable for the required project to be carried out. Laboratory tests and field tests are interpreted to determine such outcomes. To make sure that the proper requirements are met, geotechnical data is usually included in the designs for various projects.

In-Situ Testing

These are tests that are usually conducted in the field. The most common methods are; Cone Penetration Test (CPT) and Standard Penetration Test (SPT) (Lancellotta, R. 2014, 58).

Standard Penetration Test (SPT)

This method was introduced in the 1920's and is most commonly used by geo-technicians all over the world (WSDOT. 2010, 30). SPT is used to measure soil strength and soil compressibility among other properties. The method is used on silts, clay, and sands from which technicians are unable to extract undisturbed samples. SPT is a cheap and straightforward method that involves the use of a sampling device, drill rods, and a hammer. The sampler is placed at the end of a drill rod of the required length and driven into the ground through the blows of the hammer which should weigh 140lbs. The number of strikes that allow the tube to drop 6 inches is recorded three times and the second and third number of blows is added to form the 'N-value.' The number of strikes per drop should not exceed 50. The standard penetration resistance (N) is used to estimate the resilience and strength of the soil. This method is used all over the world. As an example, SPT has been used to investigate residual soils in Hilla city in Iraq, Sao Paulo and the sands and clays of Santos.

Cone Penetration Test (CPT)

The CPT method was introduced in 2001 and has been widely used in the investigation of soil properties. The test is used to measure the relative density and permeability of soil among other features. The CPT method is cheap, time-saving and more accurate compared to the SPT method. For this method, a cone-shaped device is plunged into the ground at a speed 2-2.5cm/s, and it uses sensors to measure soil resistance and changes in water pressure in a drop that is approximately six inches. CPT has been widely used to measure pore water pressure in various places in Italy.

Laboratory Testing

Laboratory testing involves some tests that can determine various common soil properties such as permeability, strength, strain, and compressibility (Becker et al. 2014, 71). Soil samples are taken from the field and transported to the lab where various tests are conducted on them. Samples have to be handled with care since mishandling can lead to errors in the results. Conventional methods of lab testing include; shear box test and triaxial compression test.

Shear Box

The shear box is a laboratory testing method that is used to test the strength properties of a soil sample. The soil sample is placed on two square rings, and the lower part is moved horizontally while pressure is applied to the upper part. Coulomb's criterion is then used to estimate the strength through the displacement and force used records.

Triaxial Compression Tests

This method is used on a soil sample in the lab to determine soil strength and soil cohesion. Various trixial tests can be conducted on undisturbed soil samples. Soil samples are placed in cylindrical shapes surrounded by a rubber skin in a load cell that is filled with water. Axial stress is introduced at the top of the cylinder, and it deforms after a while due to differences between axial and lateral stresses. These stresses lead to changes in shape and volume of the sample from which a Mohr's Circles diagram is drawn and the soil properties determined.

Today, it is a requirement for ground investigations to be conducted during construction and civil engineering works. While some individuals know the importance of ground investigations in the measuring the geotechnical parameters of the building site, others take such crucial matters for granted. Markedly, geotechnical engineering goes hand in hand with civil engineering and construction projects. Detailed investigations of the ground are usually recommended during construction and civil engineering projects to help foresee any risks that might come about as a result of the geotechnical parameters of the soil. If not correctly quantified, the foundation of constructions could cause catastrophic problems in the future. Such a situation would result in loss of lives, property, time and money. An example can be seen in the simple mistake of a gravimetric survey conducted by a geophysicist which led to a collapse of 11 homes in the U.S.

Common Methods of In-Situ Testing

Other than those discussed above, various other testing methods are conducted in the field. They include; seepage tests, slug tests, flood tests, pumping tests and permeability tests.

Seepage Tests

The seepage tests commonly used by geo-technicians are rising head, falling head, and constant water level methods. If the hydraulic conductivity can allow precise estimation of the water level, the rising level, and falling level methods can be used. If the soil is too permeable the constant water level method can be used since it becomes difficult to measure the rising or falling level of water. Seepage tests can be done to how much water is leaking from a water resource to nearby places.

Slug Tests

There are two commonly used types of slug tests; the falling head method and the rising head method. Slug tests are done by inserting an object into a borehole and measuring the rate at which the water rises and falls. The test helps in determining the hydraulic conductivity by monitoring the rates. Slug tests are however not very accurate compared to other methods of In-situ testing. Slug tests are used to test the properties of wells and aquifers.

Flood Tests

Flood tests are usually used when there is a lot of water available to conduct the analysis. Most of the time it is not practical to carry out flood tests.

Pumping Tests

Pump tests are quite expensive to carry out, and the interpretation of pump test results requires someone with good geologic experience. Through pump tests, the overall hydraulic conductivity of a geologic site can be determined. The hydraulic characteristics of the site can be estimated regarding directionality and layering since pump tests are full-scale tests. Pumping tests provide useful data for dewatering projects and construction projects that are near a water resource.

Permeability Tests

Information acquired from permeability tests is used in seepage studies. The hydraulic conductivity of a particular type of soil can be measured using this method. This test is conducted with the use of packers which are inserted into a borehole to which water is added under controlled pressure. Flow rate measurements are then taken at various time intervals. Tests for multiple depths are, and they help estimate hydraulic conductivity. Before the testing, test depths should be determined. Permeability tests can provide useful information about water quality in wells and aquifers.

References

Becker, D.E., Eng, P., Principal, F.E.I.C. and Engineer, S.G., 2010. Testing in geotechnical design. Geotechnical Engineering, 41(1), p.17.

Lancellotta, R., 2014. Geotechnical engineering. CRC Press.

Washington State Department of Transportation. 2010, January. Geotechnical Design Manual M 46-03.01