A Constitutive Model Of Bonded Soil Based On The Micro-Mechanism Of Bonding-Breakage

The natural soil has many complex mechanical properties that are different from those of the remolded soil made in laboratory and the relevant study is a hot topic in geo-mechanics. It is said that"The establishment of mathematical model of natural soil is the key issue of geo-mechanics in the 21-th century."In this thesis, a series of experiments of artificial bonded soil in lab have been carried out and the study on the micro-mechanism of particle bonding-breakage has been performed. The main achievements in this thesis can be summarized as following.The experiments on artificially bonded soil and remolded soil with different void ratio and bonding strength have been conducted in various stress paths on triaxial and truly triaxial conditions. On the basis of the comparison between experimental results of artificially bonded soil and remolded soil, the mechanical properties of artificially bonded soil have been comprehensively analyzed and summarized. The effects of bonding and initial void ratio on the mechanical property of artificially bonded soil have been studied.Based on the micro observation with SEM and some assumption, a new method to partition the bonding element and frictional element in artificially bonded soil has been proposed according to the contact property between particles. A new breakage parameter has been defined clearly with bonding element volume in micro level. The basic equation of the breakage mechanics have been deduced by the basic integrating equation of discrete medium mechanics from micro to macro level. The breakage-developing rule has been deduced based on the law of balance of energy principle in macro-micro level.Based on the equilibrium equation of contact force between particles in micro level, the breakage condition of bonding has been discussed. With the analysis of the composition of the bonded contact force, the criteria of bonding breakage have been established. The detailed equations of this criteria in isotropic loading and triaxial loading have been proposed. Based on this study, the strength envelop of bonding element and artificially bonded soil have been deduced.In the frame of the breakage mechanism, the new binary media model has been established with the breakage developing rule and breakage criteria. This model considers the bonding element as elasto-brittle material and the frictional element as elasto-plastic material which can be described by the modified Cam-clay model. The number of parameters in this model is moderate and all of them have the defining mechanical meanings. The value of these parameters can be calibrated by the conventional triaxial test with simple stress path in laboratory. The comparison between the results of calculation with this model and the experiments in this thesis show that this model can simulate the main mechanical properties of artificial bonded soil in various stress paths.