Experimental Study On Dynamic Characteristics Of Lightweight Sand-EPS Beads Soil (LSES)

Lightweight Sand-EPS beads Soil (hereafter as LSES) is a novel geo-material, with sand, cement, EPS beads as its basic soil, cement agent and lightweight material, respectively. After blended with water and then mixed and compacted under different content, these main ingredients turn up to LSES with various properties. Since inevitably subjected to dynamic loading in practical engineering, the deformation and strength characteristics of LSES under dynamic loading are quite worth to study. The main reseach contents of this dissertation are as follows:Basic properties of LSES(1) The method of laboratory sample prepararion for LSES is dicussed, and the hardening mechanism of LSES is also analyzed. Through a medical CT scanning apparatus, the meso-structure of LSES is studyed, and it is suggested that LSES is a structural geo-material based on the scaning result of samples under different ingredient contents. The main factors influencing the Original Structure of LSES is also proposed.Deformation characteristics of LSES under dynamic loading(2) Laboratory dynamic triaxial tests on EPS blocks and LSES are conducted using a multi-function triaxial test apperatus, and the respective stress-strain relationships are obtained. The effects of cement content, EPS-bead content, confining pressure and cycle number on the reduction behavior of dynamic modulus are discussed. Meanwhile, the effect of EPS beads on the dynamic deformation characteristics of LESE based on those of EPS blcoks.(3) Based on the reduction behavior of dynamic modulus, critical cyclic stress ratio of LSES is proposed, which classifies the modulus reduction curve into two catigories: smooth type and fast-dropping type. Numerous test results are analyzed to obtain an unified empirical formula of modulus reduction, quantitatively reflecting the effects of some fators, and the parameters corresponding to different ingredient contents are also suggested.Strength characteristics of LSES under dynamic loading(4) According to the strain acceleration curve, the dynamic failure criteria of LSES are expressed as stain and the main factors are analyzed. Though the dynamic strength tests, the effects of cement content, EPS-bead content and confining pressure on the dynamic stregnth curve are discussed.(5) By combining the fast-drop type modulus reduction curve and the empirical formula with mathematical method, the empirical expression of dynamic strength N_f is obtained, based on which the dynamic Moore Circles and dynamic strength envelopes are analyzed and the dynamic strength index under given cyclic failure number are obtained.(6) By analyzing the properties of ingredients in LSES, the differences between LSES and conventional unsaturated soil are discussed, and the dynamic strength theory of LSES is hereby studyed.Variation characteristics of LSES structure under dynamic loading(7) The structure theory of LSES is discussed in detail. Through CT scanning and dynamic triaxial tests, the variation characteristics of LSES structure under dynamic loading are analyzed. By comparing the state parameters of meso-structure and macro-structure, the dynamic deformation and stregnth mechanisms of LSES are studyed roundly.