Comparative Experimental Study And Cause Analysis Of Mechanical Properties Of Strong Structural Clay In Zhanjiang Formation

The strong structural clay in Zhanjiang Formation is featured by high porosity ratio,medium compressibility and strong structural structure and other unique engineering characteristics,which exert great impact on the economic activities as well as engineering construction in the west coast of Guangdong and the northern part of Hainan Island.Therefore,it is urgent to analyze the regional distribution,mechanical effect and the cause of strong structural characteristics of the clay in Zhanjiang Formation.Based on the previous studies,the relationship between the physical and mechanical indexes of typical clay in Zhanjiang is statistically analyzed.The internal comparative analysis between the clays in the Zhanjiang Formation and the external comparative analysis between the clay in the Zhanjiang Formation and the general clay in other areas are carried out.Taking the clay samples taken from a steel project in Zhanjiang,Guangdong Province as the research object,the conventional triaxial compression test,unconfined compression test and consolidation test are carried out on the structural clay of Zhanjiang Formation respectively,and the strength and deformation regularity of the clay under different stress stages are analyzed.Finally,the strong structural causes of the Zhanjiang Formation clay are analyzed from the perspective of geology.To summarize the full text,this paper has the following conclusions:（1）The structural clay of Zhanjiang Formation has a higher natural moisture content w and a larger natural porosity ratio e.The average w of the clay in the study area is 49.27%,and the maximum value is 52.75%;the average value of e is 1.41,and the maximum value is 1.503.The liquid limit w_L is higher.The w_L of Zhanjiang clay is 58.17%～66.83%,and the statistical average is 62.33%.Compared with the natural moisture content of the clay,that is 49.27%,it is obviously much higher.The compression coefficient a_v of Zhanjiang clay is 0.26MPa^-1～0.5MPa^-1,and the average value is 0.38MPa^-1,which is moderately compressive clay.The natural moisture content,compressibility coefficient and unconfined compressive strength of the clay in Zhanjiang Formation have a good correlation with their porosity ratio;（2）At the same pore ratio e,the compressibility a_1-2-2 of the Zhanjiang Formation clay is far less than that of the general soft clay,and its unconfined compressive strength q_u is far greater than that of the general soft clay.（3）Consolidation undrained triaxial shear test study.The shear strength of the triaxial shear test is a broken line,indicating that the clay in Zhanjiang Formation is in an over-consolidated state.The internal friction angle φ_cu of the clay in Zhanjiang Formation is between 16.4°and 19.9°,with an average of 18.03°.The cohesive force C_cu of the clay in Zhanjiang Formation is between 25 kPa and 78 kPa,with an average of 51.89 kPa,but the coefficient of variation is large,up to 0.27.Therefore,it is not suitable to use the empirical value directly in engineering applications.（4）Experimental study on unconfined compressive strength.The sensitivity value S_t of Zhanjiang original clay is between 4.13 and 4.68,which is a high sensitivity clay.The unconfined test results statistics shows that the unconfined compressive strength of the Zhanjiang group clay is generally high,with an average of 152 kPa,distributed between135 and 162 kPa,corresponding to such high strength.The sensitivity is generally large,which fully reflects the strong structural characteristics of the clay in Zhanjiang Formation.（5）Experimental study on compression of undisturbed clay and remolded clay of strong structural clay in Zhanjiang Formation.The compression curve characteristics of natural undisturbed clay shows obvious segmentation,that is,there is an inflection point.when the stress level is low before the inflection point,the slope of the curve is small and gentle,and the slope of the curve after the inflection point is abruptly decreased,indicating that the clay sample is in the compression process.There is structural yield stress,which directly affects the deformation behavior and strength characteristics of natural clay.The compression curve of the reshaped soil sample can be approximated as a straight line,and the compressibility does not change much with the pressure.This is because the remolded sample has basically lost the influence of the pre-consolidation pressure and the structural strength of the clay.（6）Analyzing the strong structural genesis of the clay in Zhanjiang Formation from the geological point of view,including the regional geological evolution of Zhanjiang,the spatial distribution characteristics of Zhanjiang strong structural clay,the strong structural clay deposition process of Zhanjiang Formation,and formation mechanism of the strong structure of clay in Zhanjiang Formation,etc.