Laboratory Study On The Dynamatic Characteristics Of Cement Soil In Beibu Gulf Marine Sedimentary Layer

Cement mixing pile is an effective measure to improve the strength of soft soil foundation.However,due to the long-term seawater erosion and the influence of long period seismic waves caused by strong earthquakes in the far field,the dynamic characteristics of cement mixing piles will continue to evolve.For the study of land reclamation area of cement mixing pile dynamic evolution,this paper on the Beibu Gulf region a industrial park blown sand reclamation area,access to the region the submarine sedimentary facies soft soil and the cement deep mixing method for modified cement-soil as test object,and then the dynamic characteristics of the soil were studied by using a GDS dynamic triaxial apparatus,finally analyses the cement mixing ratio,confining pressure,curing ages and maintenance environment on the influence of soil dynamic deformation and dynamic strength characteristics.The main research results of this paper are as follows:(1)By means of dynamic deformation test,the variation rules of hysteretic loop curve,diaphysis curve,dynamic elastic modulus and damping ratio of cement soil samples under the action of different cement incorporation ratio,different confining pressures,different curing ages and different curing environments were studied.The results show that the increase of cement incorporation ratio,confining pressure and fresh water curing age is beneficial to improve the strength and stiffness of soil,increase the dynamic elastic modulus and reduce the damping ratio.At the early stage,seawater curing age tends to weaken the strength and stiffness of soil.When the age is long enough,it is beneficial to strengthen the strength and stiffness of soil,increase the dynamic elastic modulus and reduce the damping ratio.Among them,seawater and fresh water have the most significant influence on the dynamic deformation characteristics of soil-cement,and the confining pressure has the least influence.(2)According to the dynamic deformation test data,the Hardin-Drnevich hyperbola model was used to fit the soil-cement skeleton curve,calculate the maximum dynamic elastic modulus and maximum damping ratio variation rules under various test conditions,and fit the normalized formula.The results show that Edmax increases with the increase of cement incorporation ratio and freshwater curing age,the influence of confining pressure decreases gradually,and decreases first and then increases with the increase of seawater curing age.Ed/Edmax decreases with the increase of εd.When the εd is less than 0.04%,the attenuation rate of Ed/Edmax is large;when the εd is greater than 0.04%,the attenuation rate of Ed/Edmax is close to zero.(3)Through the dynamic strength test,the dynamic strength curve of cement soil samples under the action of different cement incorporation ratio,different confining pressures,different curing ages and different curing environments was studied.The results show that:the higher the confining pressure is,the more obvious the increase of soil-cement dynamic shear strength is;the higher the confining pressure is,the higher the growth rate of soil-cement dynamic shear strength is.With the increase of curing age,the dynamic strength curve of seawater under curing environment shows a trend of decreasing first and then increasing.Although the strength of soil-cement under seawater curing condition is weaker than that under freshwater curing condition in terms of the overall time,the strength enhancement of soil-cement in seawater environment at the later stage cannot be ignored.(4)According to the dynamic strength test data,using the mole-coulomb theory to find out the response strength parameters Cd and φd,and analyzed the damage cycle,curing age and curing environment on Cd and Φd.The results indicate that both Cd and ΦD of soil-cement decrease with the increase of the number of vibration weeks,and both Cd and Φd of soil-cement in seawater maintenance environment decrease first and then increase with the increase of curing age,while Cd and φd of soil-cement in freshwater maintenance environment continue to increase with the increase of curing age.