Study On Dynamic Characteristics Of Expansive Soil Under Subway Loading

At present,special soil dynamics has become one of the hot spots in the field of soil mechanics,especially the expansive soil,which has attracted extensive attention of experts due to its complexity,repeatability and long-term potential hazards.Anhui Province is one of the most widely distributed regions of expansive soil in China.Hefei is vigorously building subway in order to speed up the construction of urban transportation infrastructure network.However,under the influence of the subway’s vibration load,the expansive soil would result in irreversible plastic strain,which will cause unequal stress on the upper structure and negatively impact the subway’s regular functioning as well as put the ground buildings(structures)in risk.In light of this,research into the dynamic properties of expanding soil under subway load is extremely important,which can provide theoretical basis for the safe operation of Hefei Metro in the later stage.This paper selects the expansive soil in the subway station near Hefei Xinqiao International Airport as the research object,and studies the influence of loading methods on the dynamic stress-strain hysteresis curve,dynamic pore pressure and dynamic strain of remolded expansive soil in Hefei area through the indoor dynamic triaxial test,and the effects of intermittent loading ratio,static deviating stress and cyclic stress ratio on the accumulative pore pressure and accumulative plastic strain of expansive soil were studied under the intermittent subway cyclic loading,and finally,a calculation model for the expansive soil’s cumulative plastic strain under the load of the Hefei subway is developed.The following are the primary findings of the study.(1)Intermittent application of subway load will not change the overall form of the cumulative plastic strain development curve,but has a great impact on the development trend of dynamic pore pressure.(2)The pore pressure development curve of remolded expansive soil in Hefei area is related to the intermittent loading ratio.The intermittent loading ratio is small,showing a "hyperbolic" distribution;When the intermittent loading ratio is large,it presents a "skewed distribution" distribution,and the curve obviously has a "single peak" characteristic.However,no matter which curve form,the existence of intermittent loading ratio has a significant weakening effect on the growth of accumulated pore pressure.(3)Under the condition of intermittent loading,the cumulative plastic strain development mode of remolded expansive soil in Hefei area is: rapid increase-slow increase-stable.With different intermittent loading ratios,the cumulative plastic strain development law is different in the following three aspects: the initial strain growth rate,the vibration times corresponding to the slow increase stage,and the cumulative plastic strain value when it tends to be stable.(4)Under intermittent cyclic loading,other factors such as static deviator stress and cyclic stress ratio can increase the cumulative effect of strain.However,for the cumulative pore pressure,the effect of cyclic stress ratio is limited.The law of increasing with the increase of cyclic stress ratio only applies to cases where the intermittent loading ratio is small.When the intermittent loading is relatively large,the cumulative pore pressure curve has an intersection point.Before the intersection point,the greater the cyclic stress ratio,the greater the cumulative pore pressure value;After the intersection point,on the contrary,the larger the cyclic stress ratio,the smaller the cumulative pore pressure value.(5)Based on the relationship curves between the accumulated plastic strain and the number of vibrations under different intermittent loading ratio,static deviating stress and cyclic stress ratio obtained from the test,a calculation model that correlates the accumulated plastic strain with the number of cycles in the saturated and remodeled swelling soil under the load of Hefei subway is proposed on the basis of the existing strain model,the accumulated plastic strain calculation model has certain reference significance for the design and safe operation of Hefei subway.Figure [35] table [7] reference [94]...