Research On Breaking Law Of Calcareous Sand Based On Resistivity Measurement Technology

There is a large amount of calcareous sand distributed in the South China Sea.The calcareous sand particles have many pores and are easily broken,which has mechanical properties different from common land sand.The particle breakage under the action of external forces directly causes the evolution of particle size,and its physical and mechanical properties will also change greatly.At present,most of the research on the particle breakage characteristics of calcareous sand is based on the screening method.Because calcareous sand particles are easily broken,particle breakage will inevitably occur in the screening process.In addition,the research of particle breakage during loading process is to stop the test at different loading strains and then screen,so the degree of breakage cannot be tested dynamically.Therefore,this paper uses resistivity testing technology to measure the basic physical material properties of calcareous sand through laboratory tests,and studies the resistivity influence characteristics of a single particle size group of calcareous sand undisturbed soil samples,as well as the influence of different influencing factors on particle breakage in the process of confined compression.Based on the change of resistivity of saturated calcareous sand in the process of confined compression,the empirical formula of relative breaking rate and resistivity of saturated calcareous sand was established.The main work and achievements are as follows:（1）Conduct SEM electron microscopy scanning test,XRD elemental analysis test,specific gravity test,relative density test and other laboratory tests on three kinds of calcareous sand to fully understand and understand the basic physical material properties of calcareous sand.（2）In order to verify the feasibility of the equipment,power history,contact resistance and contact area tests were carried out on three kinds of single-particle calcareous sand.Then,the influence of external factors on the resistivity of calcareous sand was investigated.The results showed that the conductivity of pore water increased with the increase of temperature,and the resistance decreased.In the range of saturation test,there is a power function attenuation relationship between the resistivity and saturation of three kinds of single particle size calcareous sand,and the relationship between structure factors and saturation and relative density is established by Archie formula.Furthermore,the particle size also has a certain influence on the resistivity of calcareous sand,and there are certain differences in the scatter plots obtained with different particle sizes,that is,under the same relative compactness,the resistivity of saturated calcareous sand increases with the increase of particle size,which is the same as that of saturated quartz sand.Finally,by comparing the resistivity of quartz sand and calcareous sand,it is found that under the same conditions,the resistivity of the two kinds of sand is similar with the change of saturation,but the resistivity of calcareous sand is lower than that of quartz sand.（3）In order to study the deformation and crushing characteristics of single grain size calcareous sand under confined compression,relevant tests were carried out on single grain size calcareous sand.The results show that:first,under different saturation conditions,the e-p curve in the early stage of compression is more sensitive to the initial load applied,which is steep,and then tends to be flat;For the samples with different initial relative density,the e-p curve has the same trend;With the increase of moisture content,the corresponding change of void ratio increases first and then decreased;In the saturation test range,under different initial compactness conditions,with the increase of consolidation pressure,the compression curve of single size calcareous sand gradually converges to a straight line,and the rebound is small when unloading;Under the condition of medium and low stress,the breakage characteristics and compression characteristics of calcareous sand particles with larger particle size are not significant,and the compressibility of calcareous sand particles increases with the increase of particle size.Secondly,by introducing plastic work W_pand normalizing the initial compactness and relative crushing rate,the empirical relationship between the crushing rate and the initial compactness of calcareous sand is established.There is a positive correlation between the particle size and the relative crushing rate B_r,and the breakage degree of calcareous sand with the same particle size decreased with the increase of saturation.（4）The main factors causing the change of the resistivity of calcareous sand in the consolidation process were analyzed,and the resistivity values of the three particle sizes of calcareous sand in the confined compression process at saturation were respectively measured.According to the above two chapters,the empirical formula between the resistivity of saturated calcareous sand and the breakage rate was established by using the structural factors,and the parameters were determined and the predicted resistivity was calculated by using the results of the breakage test of saturated calcareous sand particles of three sizes and the resistivity values under different loads.After comparing the measured resistivity with the predicted resistivity,it was found that the error was less than 1%and the fitting coefficient was also high.It is considered that the formula can be used to characterize the fragmentation of saturated calcareous sand particles.