Study On Mechanism And Prediction Of The Post-construction Settlement Of The High Rockfill Foundations In Mountainous Area

A large number of high-fill foundations are being built in the southwestern mountainous areas of China,which may lead some challenges,such as large amount of earth-rock excavation,the stability of slope filling and the deformation problem.Among them,the deformation problem is the most difficult,especially the prediction and control of post-construction settlement.In this study,the long-term deformation characteristics of the high-fill foundation are systematically studied through laboratory tests,field tests,constitutive models and finite difference calculations.Meanwhile,a two-stage backanalysis method with a modified objective function defined for the time-dependent backanalysis problem of the high-fill foundations.The main research conclusions are obtained:(1)A feasible test method for simulating the deformation characteristics of natural rockfills is proposed by means of 3D printing technology.The sandstone-like particles are uniform in nature and shape.Furthermore,the particles can be produced in specified size and be preset crack within the grain,even be colored(for tracking).These advantages can help the research on the microcosmic mechanism of particle breakage and size effect in the creep process.(2)Two types of laboratory tests were carried out based on 3D printing technology: 1)The uniaxial creep test results of a 3d-printed sandstone-like disc show that the breakage time of a single particle corresponds to the axial force level,the initial crack length-diameter ratio,and the angle between the axial force and the preset crack.The simplified creep calculation method based on this concept of single particle breakage was further derived.2)The confined creep test results of 3d-printed sandstone-like particle with and without the preset crack and natural limestone rockfills reveal that,within the vertical stress range,the three samples exhibited similar particle breakage patterns.That is,the entire breakage of particle is not significant,but the main factors causing creep are the angular breakage of particles and the static fatigue.(3)By analyzing the results of large-scale triaxial creep tests on different rockfills,the law between the parameters of the classical Burgers model and the stress state was found,the damage mechanism of Kachnov was improved and the damage threshold of rockfill are defined.Based on these,a rheological model to simulate the shear creep behaviors of rockfills is proposed.(4)A two-stage inverse analysis method for predicting settlement after high fill construction is proposed.In the first stage,the weighted average method is improved to quickly identify an initial optimal solution and to determine the first exploration region for the next stage.In the second stage,an adaptive response surface method is proposed to reduce the number of fitting response surfaces by directly describing the objective function as a second-order polynomial of the unknown parameters.Furthermore,the adaptive RSM can produce a faster convergence rate by adaptively considering the translation,contraction or expansion of the exploration region.Back-anlysis for a synthetic numerical example of given exact solution is used to prove the two-stage backanalysis method is more efficient compared with the other two methods.The two-stage back-analysis method is then used to predict and analyze the settlement of Maotai Airport and the large in-situ creep test Guizhou province.