Research On Electrical Resistivity Characteristics Of Loess In Process Of Grouting Reinforcement

With the advantages of simple construction and good strengthening effect,grouting method is often used to reinforce existing building foundation. But inthe consolidation process, it will generate a certain amount of additionalsettlement, thus affecting the quality of the project. So it is very necessary toresearch soil structure in the process of grouting solidified. It has become aresearch hotspot that through studying electrochemical properties to analysis themicrostructure of materials，the internal structure change of soil can be reflectedby the electrical parameters if soil is viewed as porous electrochemical system.Through grouting solidified loess，with electrical resistivity method anddirect shear test, the changes of additional deformation and resistivity of soilwhich were injected different kinds of slurry (sodium silicate solution, sodiumchloride-sodium silicate mixed solution, calcium chloride-sodium silicate mixedsolution) were tested, and before and after the grouting loess shear strength weremeasured. Electrical resistivity parameters-solidify time relationships, electricalresistivity-electrical current frequency relationships and additional deformation-solidify time relationships were revealed. Changes in soil structure were analyzed combined with changes in resistivity parameters of soil in groutsolidify process, and the effects which using different slurry to solidify loesswith the change of shear strength were compared. The results show:(1) Whether it is the resistivity of the vertical or horizontal resistivitydecreases as the curing time increased and ultimately stable. The reasons for thisphenomenon are the increasing water content, saturation and conductive cathode.According to the vertical and lateral resistivity decreasing amplitude, thetime-dependent resistivity process can be divided into three stages: steep dropstage (0~100min), slowly descending stage (about100~200min) and stable stage(after200Min).(2)AC resistivity method was used to measure the resistivity in this test,and the relationship between loess resistivity (vertical and horizontal) andcurrent frequency was showed: When the current frequency is lower than50kHz, the resistivity decrease rapidly with increasing current frequency; when thecurrent frequency is higher than50kHz, the resistivity remained stable withincreasing current frequency. Therefore, when the current frequency is lowerthan50kHz, the small changes of frequency can have a dramatic impact on testresults of resistivity; so the frequency range of50kHz~1MHz was suggested.(3) In the grouting solidified process of loess(sodium silicate solution,sodium silicate-sodium chloride mixed solution, sodium silicate-calciumchloride mixed solution), with increasing time, the average structure factor andaverage shape factor firstly decrease and eventually remained stable, anisotropy coefficient firstly increases and eventually remained stable. Combined with thephysical and chemical reaction of loess in the solidify process and comparedwith lateral and vertical resistivity changes with increasing time, The curveswhich average structure factor, the average shape factor and anisotropiccoefficients over time can be divided into three phases: collapsibility stage,replacement stage and consolidation stage.(4)Before and after the grouting loess shear strength values werecompared and found: The shear strengths of loess after grouting are higher thanthe values of loess without grouting, so slurry can change the engineeringcharacteristics of soil. Changing the concentration of the sodium silicate solution,the content of sodium chloride and calcium chloride in mixture will have animpact on grouting soil strength. The best ratios of slurry in this experiment areas follows: best concentration of sodium silicate solution is25%, optimal massratio of sodium silicate-sodium chloride is3%, and optimal mass ratio ofcalcium chloride-sodium silicate is9%.(5)It produces a certain deformation of additional settlement on soil duringgrouting process, and the additional settlement is smaller than collapsibility butcannot be ignored, we should pay attention to it in engineering practice.