| Soft clay strength has always been hot and difficult problems in geotechnicalengineering. With the rapid development of urban construction, there are more andmore excavation,underground tunnels projects in a number of projects,many of theseprojects are constructed in pre-consolidation pressure and unloading circumstances.However,these unloading projects usually use the strength index of loading tests whendesign.However,loading and unloading are two distinct processes,the study of soft claystrength characteristics on unload is a great sense of construction.In this paper,doing unconfined compressive strength test,consolidated undrainedtriaxial test and direct shear test on loading and unloading,refer to the basis on a largenumber of domestic and international references.Summary,analysis and comparison thetest results,reveal the strength characteristics of structural clay.This article carry out specific work and the main research results are as follows:1.With doing unconfined compressive strength test,drawing the figure of originalclays unconfined compressive stress-strain curves and reconstituted clays unconfinedcompressive stress-strain curves, and get the sensitivity value,s tbetween2.22to2.95,the sensitivity value is middle.Judging zhanjiang clay soil is middle sensitivityvalue.2.With doing undrained triaxial consolidation test, get the curves of original claysunconfined compressive stress-strain,and get the strength index(value c and value)of unconfined compressive stress-strain. From the strength envelope we know, thestrength envelope of zhanjiang soft clay is not a linear but a broken line,that is tosay,its value c and value is variable,value c is smaller and value is larger withhigh confining pressure,on the contrary,value c is larger and value is smaller withlow confining pressure.3.Under different pre-consolidation pressure,unloading shear strength index andloading shear strength index are not the same yet.Under the same verticalpressure,unloading shear strength index of soil are higher than loading shear strengthindex.that,the value c and value of unloading is higher than the value c and value of loading.4.Consolidation fast shear strength on unloading and consolidation fast shearstrength on loading are not the same,the unloading route is no longer the originalroute,the unloading route is non-linear distribution,and above the loading line.5.Through the laboratory tests we know that,when unloading ratio is less than thecritical unloading ratio,unloading ratio and strength retention ratio are linearrelationship.After soil reach the limit unloading ratio, unloading ratio continues toincrease and shear strength basic tend to a constant value,the soil that between criticalunloading ratio and limit unloading ratio,strength retention ratio is decay rapid with theunloading ratio increasing. |
