![]() ![]() However, these load increments are not always satisfactory for defining the preconsolidation pressure from the shape of the void ratio-pressure curve for this purpose, a much smaller factor than 2.0 should be used during incremental loading. This procedure will produce time-consolidation curves that usually permit the most precise evaluation of the coefficients of permeability and consolidation. ![]() ![]() What is often called the “standard consolidation test” is performed by always doubling the previous load on the specimen. It is generally necessary to adapt the testing procedures to the specific requirements of an investigation.įor example, the consolidation test can be performed in various ways. Since soils exist in an enormous variety, and since the problems of applied soil mechanics exist in a very great variety, testing procedures for determining the engineering properties of soils (such as strength- deformation relationships) cannot be standardized.īefore any soils testing is requested of a laboratory, the design engineer responsible for formulating the testing program must clearly define the purpose of each test to himself and to the person who will supervise the testing. The process is called consolidation and results in a higher unit weight and a decreased void ratio. Then more and more load is gradually transferred to the soil grains until the excess pore pressure has dissipated and the soil grains readjust to a denser configuration. However, when the load on a saturated soil sample is quickly increased, the increase is carried entirely by the pore water until drainage begins. The more permeable a soil is, the faster the deformation under load will occur. In fact, tiny clay particles may be forced completely apart by water in the pore space.ĭeformation of a saturated soil is more complicated than dry soil as water molecules, which fill the voids, must be squeezed out of the sample before readjustment of soil grains can occur. As the amount of pore water in the void increases the pressure it exerts on soil grains will increase and reduce the intergranular contact forces. Adequate deformation is required to increase the grain contact areas to take the applied load. Experience has shown that rearrangement of soil grains due to sliding accounts for the most deformation. If no pore water exists, the sample deformation will be due to sliding between soil grains and deformation of individual soil grains. When a load is applied to a soil sample, the deformation that occurs will depend on the grain-to-grain contacts (intergranular forces) and the amount of water in the voids (pore water). Of particular note is the void ratio (e) that is a general indicator of the relative strength and compressibility of the soil sample, i.e., low void ratios generally indicate strong, incompressible soils, and high void ratios may indicate weak, compressible soils. Common terms associated with weight-volume relationships are shown in Table 3-1. The weight and volume of a soil sample depends on the specific gravity of the soil grains (solids), the size of the area between soil grains (voids or pores) and the amount of void space filled with water. The soil grains are irregularly shaped solids, which are in contact with other adjacent soil grains. The foundation engineer should recognize the project problems to be solved to optimize testing, particular strength and consolidation testing.Ī sample of soil may be composed of soil grains, water and air. However, testing can be expensive and time consuming. The complexity of testing required for a particular project may range from a simple moisture content determination to specialized strength testing. Laboratory testing is an important element in foundation engineering. For a complete version of this document click here. ![]()
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