UNDRAINED HÀNH VI của đất Nếu không có hệ thống thoát nước là có thể từ đất, vì đất đã được niêm phong, hoặc vì tải được áp dụng một cách nhanh chóng và độ thẩm thấu là quá nhỏ mà không có thời gian cho dòng chảy của nước, sẽ không có hợp nhất của đất. Đây là hành vi undrained đất. Chương này chứa một giới thiệu về các mô tả về hành vi này undrained. | Chapter 25 UNDRAINED BEHAVIOR OF SOILS If no drainage is possible from a soil because the soil has been sealed off or because the load is applied so quickly and the permeability is so small that there is no time for outflow of water there will be no consolidation of the soil. This is the undrained behavior of a soil. This chapter contains an introduction to the description of this undrained behavior. Undrained tests In an undrained triaxial test on a saturated clay each increase of the cell pressure will lead to an increase of the pore water pressure. As discussed in the previous chapter this can be described by Skempton s formula Ap B Aơ3 A A 71 Aơs . The coefficient B can be expected to be about B 1 Azv 1 npK where p is the compressibility of the pore fluid including possible air bubbles and K is the compression modulus of the grain skeleton. The value of the coefficient B will be close to 1 as the water is practically incompressible. Increasing the cell pressure can be expected to result in an increment of the pore pressure by the same amount as the increment of the cell pressure or slightly less and thus there will be very little change in the effective stresses. If there is a possibility for drainage and there is sufficient time for the soil to drain the pore pressures will be gradually reduced with a simultaneous increase of the effective stresses. This is the consolidation process. If there is no possibility for drainage because the sample has been completely sealed off or because the test is done so quickly that there is no time for consolidation the test is called unconsolidated. In the second stage of a triaxial test in which only the vertical stress is increased distinction can also be made in drained or undrained tests. If in this stage no drainage can take place the test is called unconsolidated undrained a UU-test . If a second UU-test is done at a higher cell pressure the only difference with the first test will be that the pore .
