Research On One-dimensional Consolidation Characteristics Of Soft Soil Based On The Theory Of Equitime Curve

Soft soil, which has a high water content, large void ratio, great compressibility, poor permeability and poor shear strength, has a large deformation during the long-term consolidation. The structure, which is built on the soft soil foundation, would face the main problem of settlement. The deformation of soft soil is time-dependent, including both the consolidation and the creep caused by viscosity, which influence each other and determine the long-term settlement of soft soil. Therefore, the research on how to describe the time-dependent characteristic of consolidation and establish the consolidation model considering the time-dependent, is meaningful for forecasting the process and deformation of the long-term consolidation.The research of this paper is based on the land reclamation project in the east of Shantou. Based on capturing the physical and mechanical properties of the samples, a series of oedometer tests have been carried out to study on the characteristics of the consolidation and the regulars of the compression indexes under the different consolidation conditions. The main contents and conclusions are as follows.(1) A series of K0 oedometer tests have been carried out to analyze the characteristics of e-lgp equitime curve, the basic characteristics of the consolidation and the regulars of the compression indexes under the different consolidation conditions. The results show that, the e-lgp equitime curve, the basic characteristics of the consolidation and the regulars of the compression indexes have the same rules under the different consolidation conditions, and only the value of the compression indexes would be changed. Therefore, the e-lgp equitime curve has a general applicability, which can directly describe the consolidation deformation with the time-dependent under the different consolidation conditions.(2) As a comparison, the flexible confined oedometer test has been carried out to analyze the characteristics of the consolidation. In this test, the vertical stress and lateral stress ratio is kept as a constant. The results of the flexible confined oedometer test show that, it has an obvious instantaneous settlement during the 0~0.1min time of the normal consolidation, and then the same characteristics of compression would be presented as the K0 oedometer tests show. A certain lateral deformation would be allowed in the flexible confined oedometer tests, and it is the reason for the changing of the compression index. The compression index and secondary consolidation coefficient of the flexible confined oedometer tests is about 1.8~2.6 times and 2.3~2.4 times respectively as the K0 oedometer tests.(3) In order to know the rebound and recompression characteristics of soft soils, the rebound-recompression tests have been carried out to analyze the characteristics of deformation and the stress-strain relationship of each stage. The results show that, the rebound and recompression characteristics would be influenced by the initial state, the overlying soil pressure, structural strength and other factors. The Compression curve has an obvious characteristic of segmentation, and the elastic deformation can be counted as the main part of the total deformation in the over consolidation stage. The normal consolidation line after rebound can be regarded as the continuation of the normal consolidation line before rebound, and the viscoplastic deformation is the most part of the total deformation in the normal consolidation stage.(4) Based on the results of the consolidation tests, a segmented elastic visco-plastic consolidation model is established by introducing the theory of Bjerrum’s equitime curve and Yin & Graham’s concept of equivalent time, and its parameters are definite. This model shows a method to figure out the stress of the structure yield, and considers the time-dependent on the deformation and the structure yield stress during the process of consolidation. In addition, the results of the flexible confined oedometer tests can more comprehensively reflect the engineering properties of soft soil. Therefore, these indexes and conclusions are tried to use in this model to consider the influence of the lateral deformation on the model parameters, which has a certain reference value.