Test Study On Consolidation And Creep Characteristics Of Nanning Expansive Soils

Structures built on expansive soils such as municipal engineering, speedways,express railways and retaining walls will be unstable and damaged gradually with time,moreover,long-term settlements of foundation,ground settlements and deformation of tunnel in construction have relationship with its consolidation and creep characteristics,which has been successfully reported by many engineering cases and research on those constructions within the zone of expansive soil(EPS). EPS is widely distributed around the world,which frequently causes a great amount of engineering accidents and brings great economy loss to many countries. However , special studies on consolidation and creep characteristics of expansive soil have not been reported up till now. So,it's very essential and urgent to carry out systematical research on EPS. Based on present domestic and international research on consolidation and creep characteristics in soft soils and comprehensive analysis,this dissertation, supported by the National Natural Science Fund,Hunan Province Natural Science Fund and Key Financial Aid Project of Hunan Education Department , contributes many efforts to work toward consolidation and creep character of EPS from Nanning. By means of combining the research with experiments in-doors , model tests, theoretical analysis and numerical analysis,the research work have been accomplished with the following achievements:1) Based on one-dimension oedometer tests,deformation law of saturated EPS with time and consolidation strain on the condition of preloading and no preloading, controlling of different loading ratios,the way of step-loading,and holding each load level for 8 days have been studied. The results are as follows:â‘ Curves of void ratio versus log time are different under different loading ratios,and preloading or no preloading condition. To those sampls without preloading,curves of void ratio versus log time present to be linear, moreover,slope of fitting equation is quite close when loading ratio is 1. Curves of void ratio versus log time linetype and variation amplitude of void ratio change with load increasing when load ratio is 2 and 3 respectively,while,to those samples with preloading,changing trends of the curves of void ratio versus log time are different on p < 200 kPa and p >200 kPa when loading ratio is 1,moreover,the bigger the loading ratio is, the lower the consolidation deformation is.â‘¡Loading ratio only effects curves of void ratio versus log load linetype. Curves of void ratio versus log load present linear without preloading under different loading ratios. Further more,corresponding functions of void ratio versus time and log load when loading ratio is 1, preloading is 200 kPa and without preloading , have been fitted respectively to describe test curves with good agreements.â‘¢Free swelling curves approximately undergo three stages,under different loading ratios and preloading and no preloading,which could well be described by hyperbolic relationship in single-logarithmic scale, meanwhile,effects of expansion ratio and stable value under different preloading and loading ratio were analyzed contrastively.2) By means of contrastive shear tests for saturated expansive samples and saturated red clay in Zhuzhou under different consolidating loads, effect of consolidating loads and compactness on EPS shear character are discussed,obtaining the following conclusions and results:â‘ Curves of shear stress with shear displacement logarithm for saturated EPS tend to be shear-hardening form and presents linear under the same consolidating loads,while,curves of shear stress with shear displacement seem to be shear-weak hardening under low vertical load level,and presents shear-strong hardening at high load level.â‘¡Corresponding functions of shearing stress versus shearing displacement,consolidating load and compactness of two samples are fitted respectively,further more, shear characteristics of two soils under different consolidating loads are theoretical analyzed,which is important for the design and construction.3) Based on one-dimension compression creep test for unsaturated EPS,law of strain with time,water content and consolidating loads have been described. The results are as follows:â‘ To those soil samples under low water contents,attenuation trend of the strains with time is to be found earlier under the load and different water contents,while to those soil samples under high water contents,6 hours later after being loaded,non-attenuation trend of the strains with time is to be found. Moreover,the greater the water contents,the more obvious the non-attenuation trend. Further more,constitutive formula of strain versus water content and time when loaded 50 kPa is fitted with high agreement.â‘¡To those soil samples under low initial loads,attenuation trend of the strains with time is to be found while to those soil samples under heavy initial loads,non-attenuation trend of the strains with time is to be found. Moreover,constitutive formula of stress versus strain and time when water content is 16 % is fitted with high accuracy.4) Murayama rheology model improved by hardening function and Finite Element Analysis software ADINA are used in numerical simulation of compression creep for unsaturated EPS,and the validity of new model is proved,and furthermore,several influence factors of time-effect deformation of EPS are discussed.