Characteristics Of Stratigraphic Wave Velocity Of Loess-Paleosol Strata In Hequ Area Of Shanxi Province

With the economic development of China,the construction process of engineering activities in the loess region is accelerated,and the engineering construction in the loess plateau region has become an important part of the development of the central and western regions.As a kind of special soil,loess is characterized by rich macropores,vertical joint development and strong water sensitivity.The wrong judgment of loess stratum structure will cause serious damage and loss to engineering construction as well as life and property.It is helpful to know the natural structure characteristics of loess stratum by using in situ measurement method to measure the wave velocity.In this paper,a typical Loess-paleosoil strata in Zhuangzi Village,Hequ County was selected to test the wave velocity and the sampling density of exploration Wells.Six boreholes and one exploration well were designed and constructed on the test platform.The average depth of the boreholes was 60 meters and the depth of the exploration well was 30 meters.The boreholes were divided into two groups.The first group was excited by conventional shear wave excitation.It was found that there were many interference compression waves in the shear wave shape,and the amplitude of positive and negative shear wave was inconsistent,which led to the difficult interpretation of the first arrival time.To solve the above problems,the second group used the shear wave hammer generating device to excise in an optimized way.The results showed that there was almost no clutter interference such as compression wave in the shear wave shape,and the forward and reverse shear waveforms were clear and identifiable at first arrival.According to the waveform information obtained by the optimized excitation method,the wave velocities of the loess formation are calculated.The results show that the wave velocities of both shear wave and compression wave increase step type with increasing depth in the tested depth range.According to the shear wave velocity,the loess-paleosoil strata can be divided into five layers,with the thickness of 13 m,11.3m,18 m,11.7m and 6m from top to bottom respectively,and the corresponding wave velocities are 279m/s,346m/s,422m/s,457m/s and 558m/s,respectively.According to the wave velocity of compression wave,the Loess-paleosoil strata can be divided into four layers,with the thickness of 13 m,14.7m,26.7m and 5.7m from top to bottom respectively,and the corresponding wave velocities are467m/s,638m/s,780m/s and 988m/s,respectively.Combined with the geological profile of the test site,it is found that the formation inclination Angle deduced from the boundary line of shear wave velocity is in good agreement with the actual formation,that is,the shear wave velocity can more accurately reflect the structural characteristics of loess strata.At the same time,the wave velocities of shear wave and compression wave are compared with the formation density.It is found that there is a correlation between the wave velocities of shear wave and compression wave and the dry density and natural density.