Study On Design Method Of The Dynamic Strength And Its Application To The Full Weathering Granite Subgrade In Highway Subgrade

Subgrade and pavement mainly bear the vehicle loads under the transport conditions. The actual working state of the subgrade and pavement has difference from the static mechanical calculation system. The vehicle loads are moving loads. Specially the heavy trucks running on the irregularity pavement would produce large dynamic loads to the pavement and subgrade. Subgrade has fatigue characteristic and produces residual plastic deformation under cycle dynamic loads. The residual plastic deformation is decided by dynamic strength of roadbed filling and the actual level of dynamic stress. So, it is indispensable to study the dynamic characteristics of subgrade and pavement and the design theory of subgrade dynamic strength, which is the direction of development of the highway technique, this kind of research, has not only the important theoretical research value but also the practical application significance. In recently, completely decomposed granite is used as roadbed filling in some civil engineering, but there are few researches to nature of completely decomposed granite filling material used in road, say nothing of the report of the dynamic strength of the completely decomposed granite. Based on the a question for discussion of ministry of communications, "research on the dynamic characteristics and stability of subgrade of completely decomposed granite(Approbation No.95-05-05-19)", these problems are studied in this paper, and main research work of this dissertation can be summarized as follows:a) The vehicles load models are analyzed and summarized. The three models, including the vibration spring model, semi-sine model and motive semicircle model with concentrated load, are regarded as automobile load models. Vehicle-pavement-coupling vibration is simulated and analyzed with contact unit method, which makes the automobile load model more reasonable.b) A pavement and subgrade coupling motion equation is established. And the subgrade-pavement structure dynamic respond is systematically studied. The distribution of the dynamic strain and stress, the variation with velocityand subgrade strength is analyzed. The strain and stress curve with time is obtained. This research is conducive to the subgrade dynamic strength design.c) Through full size model experiment, the variation of the subgrade dynamic strain and stress and total deformation is discussed under the conditions of three subgrade soil including full weathering granite, cement stable soil and reinforced soil with geogrid.d) The design method and theory of dynamic strength that is firstly applied to full weathering granite subgrade is put foreword. The design norm of dynamic strength in this granite subgrade is also raised. Proceeding from the dynamic strength, the application limits of the full weathering granite and cement stable soil in express highway subgrade are determined.e) Using finite element method, the dynamic strain and stress is analyzed under various construction stages. The cause of pavement crack is delivered. In the light of influence factors of highway quality, two norm of subgrade strain failure are as follows. The one is the failure of subgrade itself. The other is that failure gradually begin when the deformation reaches to some limit value.f) The CBR and elastic modulus value from the Standard Specification for Design of Highway Subgrade is accordant with the norm from the dynamic subgrade strength. As designing the dynamic subgrade strength, engineering properties of the filled soil is not only related to CBR value, but also is controlled by dynamic subgrade strength.g) In laboratory test, the dynamic fatigue properties of the full weathering granite and cement stable soil is studied. The variation of dynamic strength and elastic modulus with the loading times, degree of compaction, cement and moisture has made. The design norm of the dynamic strength and modulus on which the full weathering granite and cement stable soil is used in express highway is raised. The design methods are defined.h) The engineering characteristics of the full weathering granite and cement stable soil are systematically studied. The relationship that the CBR value of the full weathering granite is related to liquid and plastic limit, degree of compaction, moisture content is established. The liquid and plastic limitand classification of soil are regarded as the main norm of application range of filled soil of the full weathering granite.i) Through the theoretical research and analysis of field measure data, the settlement is deeply studied in this granite subgrade. The prediction formula of settlement is put foreword.j) The reliability of this granite as filled soil is expounded and proved by theoretical and experimental study. The guidance of design and construction of this granite subgrade is edited. The guidance is successfully applied to Lingxiang-Changsha Express Highway's subgrade construction with full weathering granite. And there are many good result including economical, social and environmental aspects.