Study On Static And Dynamic Characteristics Of Saturated Round Gravel Soil In Nanning Metro Area

Due to safety of the subway under long-term operation condition,the static,dynamic and long-term deformation characteristics of the strata under the reciprocating cycle load in the tunnel are the urgent subject to research.In this paper,the static characteristics of saturated round gravel soil are analyzed by means of large static triaxial test.After constant pressure consolidation under different relative density Dr,multistage dynamic loading were applied on the round gravel soil specimen.Considering different relative density Dr,different dynamic stress ratio ?d/?c under the subway operating load,the dynamic characteristics of saturated round gravel soil and long-term deformation characteristics were analyzed.Some meaningful research results were obtained.(1)The stress-strain curve of saturated gravel soil accords with the Duncan Chang model.With the increase of the relative density Dr,the stress-strain curve is developed from the hardening type to the softening type,and the internal friction angle ? is linearly increased.(2)According to the difference of dynamic stress ratio ?d/?c,the type of axial strain-cyclic number curves and volume strain-cyclic number curves of the saturated round gravel soil can be divided into hyperbolic curve and power curve.It's hyperbolic curve under relative low dynamic stress ratio,and power curve under relative high dynamic stress ratio.Both strain decreases with the increase of the relative density Dr.(3)The dynamic pore pressure u of saturated round gravel soil shows two trends with the change of dynamic stress.Under the lower dynamic stress ratio,dynamic pore pressure initiallyincreased then decrease and finally tends to be stable with the increase of cyclic numbers.The pore pressure is basically stable in the later period of cyclic loading,and the stable pore pressure when Dr = 0.5 is higher than the pore pressure when Dr = 0.3 and Dr =0.7,this phenomenon should be associated with broken characteristics of saturated round gravel soil.Under the relatively high dynamic stress ratio,the dynamic pore pressure increases sharply and leads to the failure of the specimen.(4)The relationship between the dynamic strain and the dynamic strain of saturated round soil is consistent with the two-line model under the relative low dynamic stress ratio.With the increase of cyclic number,the secant modulus of the stress-strain hysteresis loops initially decreased then increase and finally tends to be stable.The cyclic number at the turning point of the modulus correspond to the turning point of the hole pressure,the number of times is about 100 times.In the case of Dr=0.3 and Dr=0.7,the stable secant modulus of was close to and obviously greater than that of Dr=0.5.(5)Based on the variation of the modulus E,reloading modulus Ef and cumulative deformation of the saturated circular gravel soil,a method to simulate stress-strain hysteresis loops is presented.The basic research of nanning round soil in this paper can provide some reference for the construction,operation and maintenance of nanning metro.