Experimental Research On Dynamic Properties Of Reconstituted Weak Expansive Soil

Expansive soil is a kind of high-plastic clay mainly composed of strong hydrophilic minerals with a high strength and a low compressibility.It is widely distributed in more than 20 provinces and cities in China.Weak expansive soil after treatment with waterproof and moisture can be used as the highway subgrade filler,while studies on its dynamic response characteristics are few.With the acceleration of urbanization,infrastructures such as expressways and railways are bound to span more expansive soil areas.It is of great significance to study the dynamic response properties of expansive soil.A dynamic triaxial test was conducted by GDS to investigate the effects of confining pressure,loading frequency,consolidation stress ratio on the dynamic properties of remolded weak expansive soil under step loading and single grade loading.The research contents and main conclusions are as follows:(1)The stress-strain backbone curve can be described by hyperbolic function.Under the same conditions,dynamic modulus of elasticity increases with the increase of confining pressure,consolidation stress ratio and decreases sharply at first then tends to be flat with the increase of dynamic strain.The reciprocal of elastic modulus has a linear relationship with dynamic strain.,the maximum modulus increases linearly with the increase of confining pressure,a Maximum dynamic modulus of elasticity regression model considering confining pressure is developed.Damping ratio decreases with the increase of confining pressure and consolidation stress ratio.Meanwhile,a model was developed for Dynamic modulus ratio,damping ratio versus strain by using the Darendeli model and empirical relation between damping ratio and strain.The relationship between damping ratio and dynamic modulus ratio under different confining pressure and consolidation stress ratio could be expressed by the modified Hardin-Drnevich model after normalization processing.(2)Based on the accumulated deformation of samples under different confining pressures,consolidation ratios and dynamic stress amplitudes,a prediction model for accumulated deformation of weak expansive soils is established.The accumulated strain curves of expansive soils can be divided into plastically stable,critical and destructive types according to the strain rate,and the criteria for judging the cumulative strain of weak expansive soil is given.The dynamic strength of weak expansive soil under different confining pressures and consolidation ratios are analyzed,and the dynamic strength of the soil decreases a lot when the consolidation ratio is over than 1.5.The dynamic cohesion cd decreases with the increase of failure vibration,and the dynamic internal friction angle ?d decreases slightly with the increase of failure vibration.(3)Morphological properties of hysteretic curves be quantitatively described by the three parameters,namely,the area S of the hysteretic curve,center offset distance d of adjacent hysteretic curves,and the degree of closure ?p;The results show that the S,d and ?p of the hysteretic curve of weak expansive soils increase nonlinearly with the increase of dynamic stress amplitude,While decrease with the increase of confining pressure,frequency and consolidation stress ratio.k decreases logarithmically with the increase of dynamic stress amplitude,and increase with the increase of confining pressure,loading frequency and consolidation stress ratio;Hysteretic curves of weak expansive soil are approximately parallel under single grade loading.?p?d?and S decreases nonlinearly with the increase of loading cycle,which reflects the phenomenon of cyclic creep.The step loading history has a little influence on the hysteretic curve of expansive soil.Results obtained can provide basic datum and reference for relevant projects.