| Engineering accidents such as pile deviation or even fracture caused by excavation in muddy soil region is not rare.The excessive lateral pressure of the muddy soil layer and the small lateral stiffness of piles are the root cause of the accidents.The lateral pressure of high-flowing muddy soil is much larger than that of unsaturated soil,but the reasons and calculations of that have not yet attracted enough attention from the engineering community.In this paper,a series of studies have been carried out on the pile response under excavation conditions and the lateral pressure distribution and characteristics of muddy soil.Combined with field test data analysis,designing device for laboratory model experiment and analyzing measured data,and theoretical derivation,the pile loads & deformation mechanism under the excavation of muddy soil and the lateral pressure character of muddy soil under closed boundary conditions are revealed.Based on the former results,the calculation method of lateral pressure of muddy soil on piles is proposed.The main research contents and results are as follows:(1)The causes of an accident that piles deviation and fracture during excavation in a muddy soil area were analyzed.It is found that under the action of excavation and unloading of muddy soil,the pile foundation bears two special effects: the “passive pile” effect caused by the lateral movement of the soil and the “pascal-like effect” produced by the muddy soil under the closure effect.The former causes the piles designed as the vertical loaded pile to passively bear the lateral load,while the latter exacerbates the strength and influence range of the lateral load,which lead to the pile suffer the large lateral force that not being considered at the design and cause accident.(2)Through the analysis of the field test data,it is found that the excavation and unloading of the muddy soil cause the pile foundation to bear large lateral pressure and deformation.The lateral pressure increases nonlinearly along the depth,the time effect is not obvious,and the lateral pressure during the muddy soil layer is trapezoidal;and the front pile and the rear pile have different stress and deformation characteristics.The lateral pressure of the front pile is smaller than that of the rear pile.However,the displacement of the pile is more severe,and there is a suspected pile broken phenomenon.The rear pile has obvious obstruction effect on the front pile,and the development of the deformation has a hysteresis effect.(3)In the muddy soil layer,the depth growth mode of lateral pressure has the characteristics of Rankine theory.The average lateral pressure of front pile is located near the at-rest earth pressure,and the lateral pressure of rear pile is between the at-rest earth pressure and the Rankine passive value.The test pile is far from the limit earth pressure state.In the plastic deformation theory method,the lateral mobilization factor αm of the front row pile is about 0.2,and the rear pile αm is about 0.25.(4)Through the closed lateral pressure test of muddy soil,it was found that the lateral pressure s of muddy soil has viscous fluid properties in the closed state.The lateral pressure is semi-parabolic distribution with depth,and there are stable regions and unstable regions.In the upper unstable zone,the lateral pressure coefficient increases along the depth.In the lower stable zone,the lateral pressure coefficient is close to 1,which is not obvious with the depth.At the same time,the integrity of the curst layer has a significant impact on the lateral transfer of muddy soil pressure,and the laboratory test proves the existence of the “Pascal-like effect”.(5)Based on the results of field and laboratory tests and the reference of previous theoretical results,considering the closure effect of crust layer and the dynamic effect of excavation,the calculation method of lateral pressure on pile in muddy soil under excavation is proposed and compared with the measured data.The results of proposed method agree well with the experimental data. |
