Analysis Of The Strain-Stress And Settlement Of Soft Ground Covered With A Dry Crust

Soft soil is widely distributed in coastal and inland plains and lake sediment areas, but above that distributing a layer of soil of greater hardness generally, because of natural evaporation. It is called dry crust. Compared with the soft cover, it's density is more greater, the compressibility and alkaline resistance are more higher and it has a certain stiffness to bear some of the load. Since the special mechanical effect of the dry crust, domestic and foreigners has did lots of study---which is based on the combination of laboratory tests and field trials-to double-layer foundation with similar effect of dry crust. All of this played a great role in promoting the further study of the Strain and Stress and settlement of soft soil which has the Stress proliferation effect of dry crust. But contrast to the double effect of foundation soil, above which is dry and below is soft, there hasn't been a quantified formula to solve the issue of Stress proliferation of dry crust. To these stratums, its stress calculation of Critical Edge Pressure and relevant Settlement Calculation are not mature yet. Especially for engineering properties of the deformation mechanism of dry crust lay on the soft soil, load deformation and so on, there have no systematic and further study. All of them are still in the testing stage.This paper carry out significant exploration work to the mechanical model of settlement characteristics of dry crust and theoretical formula derivation of settlement and stress proliferation, which selects Dongting lake area K1～K12 section with dry crust, above which is dry and below is soft, as the research object, in situ load test as a base of stress and strain and settlement analysis, combines experiment parameters of indoor and undisturbed soil mechanics. From the soil strength theory and the theory of limit equilibrium of soil and through the mmechanics study of dry crust, we obtained main theories as follows:(1) Derived the Critical Edge Pressure Pcr'formula which considering the diffusion effect of stress of cry crust. It is found that the new Critical Edge Pressure Pcr'formula full consider the diffusion effect of stress of these cry crust, and it provide the basis for the improved of followed settlement calculation.(2) Derived the soft tangent modulus correction factor Rf'based on Critical Edge Pressure of foundation. Through amendments to the original tangent modulus, it not only improved the accuracy of the results of the settlement calculation, but also to avoid theory of defects and calculation errors brought by randomly selecting practical experience factors.(3) It is found that thickness of cry crust on soft soil foundation, the width of the overlying load have a direct impact to Critical Edge Pressure Per'and tangent modulus correction factor Rf'of double-layer foundation, in which the thickness of cry crust has the greatest impact.(4) By analysis of stiffness ratio of double-layer foundation, with the increase of stiffness ratio, the results of Settlement Calculation is more closer than its measured results.