Analysis Of T-bar Penetration Characteristics In Clay Based On Modified Strain Softening Model

In recent years,with the proposal of the strategy of"carbon peaking and carbon neutrality goals",the effective development and rational utilization of Marine resources has become the important content of the construction of China’s Marine power,and is of great significance to our economic development.A large number of survey data are needed before the design and construction of ocean engineering.The investigation of Marine geotechnical engineering is a crucial link in the practice of ocean engineering.The parameter determination and reasonable design of geotechnical engineering are very important to improve the quality and economic benefits of engineering.The offshore conditions are complex and changeable.The soft soil deposited in the deep sea has the characteristics of low shear strength,high sensitivity and large porosity,which puts forward higher requirements for foundation evaluation and parameter determination in the early stage of engineering.In-situ static sounding technology（CPT）has the characteristics of fast,economical and reliable,and can obtain the most real soil properties.The probe used in traditional in-situ static sounding technology is conical.Due to the small cross-sectional area,there is less resistance when penetrating in soft clay,which will lead to a large error in the measured data.According to this phenomenon,Randolph proposed the full-flow penetration instrument based on the full-flow theory.The probes of this full-flow penetration instrument mainly include T-bar and Ball-bar.At present,there are four strain softening models in the cyclic testing of soft clay,namely Einav model,Randolph model,Pinkert model,and Han model.Based on previous research on soil strain softening model and cyclic resistance attenuation model,this paper proposes a soil modified resistance attenuation model based on T-shaped probe cyclic penetration in clay,verifying the superiority of this model and providing a basis for engineering practice.（1）The influence of different parameters on the penetration resistance and soil flow of the T-probe was analyzed in a single homogeneous clay,and the finite element model of the T-probe cyclic penetration was established to study the influence of different softening indices on the cyclic penetration curve.（2）Through a large number of numerical simulation calculations,the results of the critical reflux depth were analyzed and summarized,and the formula for calculating the critical reflux depth was derived,which is suitable for any soil strain softening indexλ（generally 0.5～1）.The new formula extends the empirical formula for the calculation of the critical depth to a large extent,and provides theoretical support for practical engineering investigation.（3）Based on 18 groups of cyclic test results,the existing resistance attenuation model was modified to establish the resistance attenuation model of T-probe cyclic penetration in clay,and the calculation method of N₉₅ was clarified,so that the modified model could reflect the relationship between initial brittleness and strain softening of soil more flexibly,so as to calculate the relevant parameters of soil more accurately.Such as S_t,and S_u0.（4）Establish the finite element model of the sinking of submarine pipelines and cable in clay due to the action of dead weight in practical engineering,analyze the influence of submarine pipelines and cable on the surrounding soil during the sinking process and the change law of cumulative shear strain under different strain softening indices.