Study On Basic Mechanical Properties Of Transparent Clay And Application To Pile Penetration Effect

In geotechnical engineering tests,the traditional method to study the deformation of soil around structures is to bury sensing instruments to collect data,and analyze the deformation of soil after sorting out the data.When studying the internal deformation of soil,the traditional method is to use the embedded sensor method to observe the internal soil.But it is very difficult to embed the sensing instrument,and it is impossible to measure the information of continuous deformation of the soil.Later,many scholars used optical technology with transparent media to study the three-dimensional deformation and flow of soil.At present,the most widely used one is the transparent sand prepared from the mixed solution of n-dodecane and 15# white oil with fused quartz sand as the soil skeleton,and the second is the transparent clay prepared from amorphous silica micropowder.Transparent sand has been studied more mature.However,the research on transparent clay is not mature enough and in-depth enough.When optical technology and transparent medium are applied to study the three-dimensional deformation and flow law of soil,two requirements cannot be ignored.First,the laser beam emitted by the laser transmitter is used to cut the transparent soil,then the industrial camera is used to collect images,and finally PIV software is used to analyze and process the collected images.Therefore,the prepared transparent soil must ensure good transparency.Secondly,the mechanical properties of the prepared transparent soil should be close to those of natural soil.At present,the transparent clay studied has many problems such as low transparency and low strength.Therefore,in order to overcome these shortcomings,this paper selects spherical silica micropowder as transparent soil particle material,15#white oil and n-dodecane solution mixed solvent as pore fluid to prepare new transparent clay,and conducts permeability test,direct shear test,one-dimensional compression test and triaxial test on the new transparent clay to explore its basic mechanical properties and compare it with the mechanical properties of natural clay.It is found that the permeability coefficient,cohesion and friction angle of the transparent clay prepared in this paper are all within the clay range.The shear strength of triaxial test is slightly higher than that of natural clay.This difference can be eliminated by scaling.The e-lnp curve conforms to the compression rule of ideal remolded clay,and its inherent characteristics are similar to those of natural clay.The transparent clay prepared in this paper is used to carry out the model test research on the squeezing effect of special-shaped pile,and the modified reaming theory of rectangular pile is deduced according to the distribution law of soil displacement field around rectangular pile.The results indicate that the displacement field of soil around the special-shaped pile after penetration is divided into two regions: the transition zone near the pile and the circular hole expansion area far away from the pile.In the transition region,the displacement mode near the pile body presents non-cylindrical symmetrical characteristics,which is approximately elliptical.As it moves away from the pile body,the contour shape of the squeezing displacement slowly begins to transition to a circular expansion mode.Compared with the test results of the modified reaming theory model and the transparent soil model,it is found that the test results of the transparent soil model are larger than the predicted values of the modified reaming theory,but the basic trend is the same.This theory well reflects the distribution rule of the radial displacement of the rectangular pile driving pile squeezing soil in the transition zone along the radial direction.Based on the transparent clay prepared in this paper,the numerical simulation of pile penetration under the undrained condition of special-shaped pile is carried out to explore the law of stress distribution and displacement distribution around the pile.the numerical simulation results of the displacement field distribution of the soil around the pile are compared with the model test.The results of numerical simulation indicate that the displacement area of the soil around the pile is highly consistent to the model test results,the soil compaction effects of pile is more and more weak along the radial direction,and the vertical stress around the pile increases with the increase of soil depth and reaches the peak value at the end of the pile,then it decreases rapidly with the increase of penetration depth,and the absolute value of vertical stress near the pile-soil interface is the highest.