Experimental Study On Engineering Properties Of Coarse-Grained Soils

The coarse-grained soils have the some good engineering properties and have been applied widely in the engineering construction. The study on the stress-strain relationship of coarse-grained soils become important, especially the characteristics of deformation and strength in the static and dynamic load process. In this thesis, the large-scale static-dynamic triaxial apparatus with high accuracy is self-developed and the coupling static-dynamic test method is applied to investigate the engineering properties of the coarse grained soils under the complex stress condition.1. The large-scale static-dynamic triaxial apparatus with high accuracy is self-developed by introducing the latest technique for the mirco-strain measurement. The main features of the apparatus are as follows: (1)Installing the Local Displacement Transducer(LDT) and the inner load cell in the triaxial chamber, the test precision is increased by one order of magnitude. (2)By adopting the multi-scale displacement measurement method, the stress-strain relationship with the range of strain from 10-6 to 10-1 can be measured continued and accurately. (3)The static and dynamic load can be combined arbitrarily to obtain a complex loading sequence. Additionally, it also has the properties of high level of automatic, good structure, and easy to operate.2. According to the test results from CD test for six types of coarse-grained soils, the dependence of different static deformation modulus on the strain level (or stress level) are intensively investigated by applying the latest new technique in the process of measurement. Some useful conclusions are obtained.3. By applying the latest new technique in the process of measurement, the formula to estimate the maximum dynamic equivalent shear modulus and a reference range of modulus are proposed on the basis of the laboratory results of dynamic elastic module and the damping ratio for 13 types of rockfill. In this range, the normalized dynamic equivalent shear modulus and the dynamic damping ratio are related to the amplitude of dynamic shear strain. The dynamic parameters of rockfill material can be estimated according to the proposed formula and the reference range, in case the test data is not enough.4. Through the design and application of the coupling static-dynamic tests, a new approach to investigate the characteristics of deformation and strength for soil in static and dynamic load cases especially the characteristic of dynamic deformation.5. A series of coupling static-dynamic tests are performed to investigate the dynamic permanent deformation characteristics of coarse-grained soils. The whole procedure of permanent deformation of coarse-grained soils under drained condition, which is from the initial state with equal stress to the approaching shear failure state, is obtained. Based on the analysis of test data, the influence of the principle stress ratio on the occurrence and the development of dynamic permanent deformation is discussed. Meanwhile, the Eiichi-Taniguchi model is modified and a unified formula for dynamic permanent deformation with different principle stress ratio under drained condition is proposed.