| The eluvial laterite of basalt is mainly distributed in yunnan,hunan and qionglei area,and it is also widely distributed.Compared with other types of laterite,the residual basalt laterite has a finer grain size and a higher clay content.The main mineral composition is kaolinite,bauxite,goethite and hematite,etc.The si-al ratio is very small and the pores are relatively large(up to2).The engineering geological characteristics of the eluvial laterite are different from those of other laterites and will affect the dynamic characteristics of laterite.In particular,in the natural state,the strength parameters of the residual laterite of basalt vary greatly due to the different water-bearing conditions.Kunming chenggong university town is located in the southeast of kunming city.The construction of urban construction,expressway,high-speed railway,civil aviation and other infrastructure in this area has been accelerated.In addition,this area is controlled by xiaojiang active fault zone,which is an area with frequent seismic activities and serious earthquake hazards.Therefore,it is urgent and important to study the engineering properties of laterite,especially the dynamic characteristics of laterite.In this paper,the engineering properties of basalt residual laterite are studied.The influence of confining pressure,consolidation ratio and water content on the dynamic characteristics of laterite was studied by using SDT-20 soil dynamic triaxial test machine on laterite movement of basalt residual in Chenggong University Town.Then,dynamic characteristics such as dynamic shear modulus and damping ratio obtained by dynamic triaxial test were used to analyze the seismic response of a typical two-storey,two-column and three-span subway station in the basalt residual laterite region by using GTS NX numerical analysis software.The obtained results have practical value and guiding significance for the seismic safety and stability evaluation of building structures and underground structures in Chenggong area of Kunming.At the same time,the dynamic characteristic parameters of the similar basalt eluvial laterite can be obtained by using the fitting formula without tests.The results show that the diaphysis curve of the eluvial laterite has gone through the elastic stage,the transition stage and the failure stage,and there is a strain turning point.Under the same dynamic strain condition,the greater the confining pressure and consolidation ratio,the greater the dynamic stress.The larger the water content,the smaller the dynamic stress.The reciprocal dynamic modulus increases linearly,and the diaphysis curve can be fitted by Kondner hyperbola.With the same other conditions,the smaller the confining pressure and consolidation ratio,the greater the reciprocal of the dynamic modulus.The smaller the water content,the greater the reciprocal of the dynamic modulus.Under the initial load,the dynamic shear modulus remains at a large value,and then decreases rapidly with the increase of the dynamic shear strain.When the dynamic shear strain reaches a certain fixed value,the dynamic shear modulus remains near a stable value as the dynamic shear strain continues to increase.Under the same dynamic shear strain condition,the dynamic shear modulus increases with the increase of confining pressure and consolidation ratio,and decreases with the increase of water content.The damping ratio increases with the increase of the dynamic shear strain.Whenγ_d<0.2%,the damping ratio increases significantly and the increase rate is faster.So the damping ratio is also going to go up,but the damping ratio is going to go down very quickly whenγ_d>0.2%.Under the same dynamic shear strain condition,the larger the confining pressure is,the smaller the damping ratio is.The greater the consolidation ratio and water content,the greater the damping ratio,and the smaller the influence of confining pressure on the damping ratio.The failure criterion of dynamic strength test is the axial deformation up to 5%.Under certain other conditions,the larger the confining pressure and consolidation ratio is,the greater the dynamic stress required to achieve the failure is,the closer the dynamic strength curve is,the greater the water content is,and the smaller the dynamic stress required to achieve the failure is.With the increase of the number of vibration,the internal friction Angle increases nonlinearly.At first,the increase speed is faster,then it gradually slows down,and finally the increase speed tends to 0.The increase of internal friction Angle is large and small.The dynamic cohesion is the largest when it is not vibrated.With the increase of vibration times,the nonlinear dynamic cohesion gradually decreases,and the decrease speed is fast at first,then the decrease speed is slow,and finally it gradually approaches to a non-zero number.It is concluded that the relation between dynamic cohesion and vibration order conforms to the relation of power function.Function fitting can also be carried out by using the relation between dynamic internal friction Angle and vibration order.It can be found that there is little difference between the dynamic strength index obtained by using the method of drawing moire circle by substituting the equivalent failure order and the dynamic strength index obtained by directly substituting the equivalent failure order into the fitting curve,so the fitting curve can be used as a method to calculate the dynamic strength index.One-dimensional free field analysis shows that the relative displacement of the soil layer above the railway station increases gradually with the decrease of the buried depth,and reaches the maximum value of 0.05m when approaching the surface.The seismic response analysis shows that the underground structure is inclined towards the X-axis,and the maximum horizontal deformation of the structure is 4.1cm. |
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