Study On Creep Property Of The Gassy Silty Clay

As the society and economy are developing in recent years,people are exploiting resources of the ocean,such as land reclamation,construction of maritime bridges and sub-sea tunnels.The construction is often affected by the gassy clay,in which the presence of gas may change the deformation property and long-term strength of the soil.Due to the complexity of submarine environment,offshore engineering may meet various geological difficulties.From the perspective of geotechnical engineering,the current research results show that the controlled release of gas in advance is the most common measure in engineering when there is gassy soil layer.Meanwhile,keep close contact with engineering practice to avoid the occurrence of accidents.Therefore,in order to prevent engineering accidents,it is necessary to study the creep property of the gassy soft clay.In this paper,silty clay in hole 8.1-29.9m of cross-river passage project DZT02 on north riverside high-speed railway is used as raw material soil.The zeolite method is used to simulate the preparation of gassy silty clay in the laboratory.Based on the stratigraphic distribution obtained from geophysical exploration and drilling,in-situ test and indoor experiment,apply theory,test results and prediction model to study the creep property of the gassy clay.The research achievements are as follows:（1）According to the engineering practice,carry out indoor experiment on the raw material soil,and measure its basic physical and mechanical indicators.When preparing the gassy silty clay by zeolite method in the laboratory,N2 is selected as the test gas considering absorbability and safety.In addition,the experiment gives out the components ratio table in the process of sample soil preparing and the pre-processing method before doing triaxial test.（2）By comparing the stress-strain curves when confining pressure is a single variable and when gas content is a single variable,it is found that the curve trend is consistent,and both increase of confining pressure and decrease of gas content raise the maximum yield stress of the tested soil sample.When the strain is small,the stress increases with the increase of strain.When the strain reaches a certain degree,the stress almost remains unchanged at this time,and the curve relationship presents a typical strain hardening type.Obtain the conventional triaxial yield stress of the gassy silty clay with gas content of 0%,8.36%,14.07% and 25.24% under four different confining pressures.A linear prediction model is established based on the test results analysis.By comparing yield stress of soil samples with gas content of 20.68% under four different confining pressures by conventional triaxial test with the predicted results,it is found that the prediction formula is reliable.（3）By comparing the creep curves when confining pressure is a single variable and when gas content is a single variable,it is found that the creep process mainly includes attenuation creep stage and constant creep stage.However,variation trend of the stress-strain curve of the gassy silty clay depends on the stress level.It changes from linear to nonlinear and the turning point usually occurs when the third load is added.However,the presence of gas has a significant effect on soil,and the deformation is positively correlated with the gas content.When the stress level is constant,the increase of confining pressure has a restraining effect on the deformation of the gassy clay.Meanwhile,long-term strength of the sample soil under certain conditions is obtained by isochronous curves,and the related mathematical expressions are established to predict the long-term strength values under different gas content and confining pressure.（4）Based on the creep experiment results,it is found that the exponential function has a high degree of coincidence when describing the whole process curve and isochronous curve.Based on this,introduce stress level and gas content parameters.It is suggested that creep deformation prediction formula of the gassy silty clay should be established under the exponent affected by gas content.The experiment verifies that this model has high reliability,so the model has strong adaptability to the gassy silty clay with different gas content.It provides theoretical reference for complicated engineering practice,so it has certain significance for the practice.