Stress strain behaviour of a cohesive soil deposited under water
A dilute suspension of soil particles in water will normally flocculate and settle under gravity to form a bed of consolidating soil. The essential difference between the suspension and the soil is that effective stresses exist in the soil. This thesis is concerned with the effective stress behaviour during the sedimentation and consolidation processes. Chapters two and three are a description of the equipment and experimental procedures used to determine void ratio changes, pore pressures and effective stresses during this soil formation process. The density measuring technique developed, using an X-ray source and a scintillation counter, is described in some detail. An experiment consists of monitoring the sedimentation, form an initially uniform suspension, of an inorganic clayey silt in a 102 mm I.D. column. Experimental results are presented and discussed in the next two chapters. Some novel aspects of stress/strain behaviour (in one dimensional consolidation) are revealed. In particular an intermediate zone is identified, which has properties between those of a suspension and a soil in the traditional sense. This zone does have effective stresses, but the effective stress/void ratio relationship is not unique. Theoretical consideration of settling suspensions and soil consolidation is covered in chapter six, forming an introduction to the next chapter, where a large strain soil consolidation theory is modified and applied to the intermediate zone. Differences between the theory and experimental results largely reflect the inaccuracies resulting from the simplifying assumptions necessary to keep the mathematics simple. The expulsion of pore water, rather than soil compressibility, is the major factor in determining consolidation behaviour of the intermediate phase. Finally, some recommendations are made as to how to continue the study and on applications to real problems such as dredging, pollution and land reclamation.