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Soil mechanics - Chapter 15

Trong những chương trước, nó đã được giả định rằng sự biến dạng của đất là duy nhất được xác định bởi sự căng thẳng. Điều này có nghĩa rằng một phản ứng phụ thuộc thời gian đã được loại trừ. Trong thực tế hành vi này là phụ thuộc rất nhiều thời gian, tuy nhiên, đặc biệt là đối với đất sét. Điều này có thể được leo, nhưng trong một đất bão hòa, biến dạng cũng có thể bị chậm phát triển theo thời gian. | Chapter 15 CONSOLIDATION In the previous chapters it has been assumed that the deformation of a soil is uniquely determined by the stress. This means that a time dependent response has been excluded. In reality the behavior is strongly dependent on Figure 15.1 Uniform load. time however especially for clay soils. This can be creep but in a saturated soil the deformations can also be retarded by the time that it takes for the water to flow out of the soil. In compression of a soil the porosity decreases and as a result there is less space available for the pore water. This pore water may be be expelled from the soil but in clays this may take a certain time due to the small permeability. The process is called consolidation. Its basic equations are considered in this chapter. The analysis will be restricted to one dimensional deformation assuming that the soil does not deform in lateral direction. It is also assumed that the water can only flow in vertical direction. This will be the case during an oedometer test or in the field in case of a surcharge load over a large area see Figure 15.1. 15.1 Differential equation To simplify the analysis it will be assumed that the change in stress is small compared to the initial stress. In that case the stress-strain relation may be linearized using an elastic coefficient D K 3G see 14.19 . The precise value of that coefficient depends upon the initial stress. The relation between the increment of effective stress Aa and the increment of strain Ae can now be written as Aa - K 4G Ae. 15.1 In the remainder of this chapter the notation A will be omitted. Thus the increment of the effective stress will be denoted simply by a and the increment of the strain by e a - K 4G e. 15.2 Using stresses and strains with respect to some initial state is very common in soil mechanics. For the strains there is actually no other possibility. Strains can only be measured with respect to some initial state and in this initial state the soil is not