Consolidated-drained test (CD test) or slow test:
CD test or slow test is one of the conditions of the laboratory shear test. The other two conditions are UU test and CU test. UU test has low shear strength. Whereas in CU moisture is drawn out due to high pressure.
CD test is comparatively slower than others. It is used only for the search purposes. It requires more time and money than other methods. In this test soil consolidation occurs under normal load and drainage is allowed during the consolidation. At the completion of the consolidation process, the drainage conditions are to be allowed while normal stress is increased at such a rate that no pore pressure is developed. Thus the resulting parameters of the shear strength are in terms of effective stresses.
On engineering scale CD parameters are used in the problems where long term stability of clayey soil slopes and the long term lateral pressure on the cohesive soil retaining walls.
Consolidated drained or slow test is similar to the CU test except that the sample is allowed to drain. The axial load is applied in such a way that high excess pore pressure not to be developed.
The consolidated drained test is often referred to as the S, or slow test.