Research Of Compaction And Engineering Properties Of Over Coarse-Grained Soil

The over coarse-grained soil has some good engineering properties. It used widely in many projects, especially in highway subgrade. But the prospective effect did not achieve in many projects because its compaction properties. The criteria for evaluation of compaction quality and the mechanical properties of over coarse-grained soil have not study clearly. All of the problems hindered its farther project application. In order to adapting the need of development, the compaction and the mechanical properties are study by means of field roller compaction test and indoor large scale triaxial test. The work will found a basis of the further study of over coarse-grained soil.1. The mechanical properties and the influence of water are study by means of large scale compression test and triaxial test. (1)The constrained modulus does not increase with the increase of vertical pressure simply. On the contrary, some test results show it reduces under a larger pressure. (2)On the condition of the experiment, the relations between stress and strain are weak strain softening or strain hardening. The form rest with the value of confining pressure. On the state of low confining pressure, volume shrink happens first and cubic dilation develops gradually with the increase of axial strain. And the sample varies from dilation to volume shrink with the increase of confining pressure. But the shrinkage degree decreases little by little till stability. (3)The shear strength of over coarse-grained soil shows nonlinear characters with the stress level. It decreases generally with the increase of confining pressure. (4)The water has important effects to the compression characters and the shear characters of over coarse-grained soil. It mostly makes the compression coefficient degree increase and the parameter of shear strength decrease.2. The field roller compaction tests are carried depending on the project of S325 highway. The optimal technological parameters and quality control specification of the given project are found by contrast tests which different technological parameters such as construction machinery, laying depth, compaction times and water ratio are fit together and various dectection methods such as compaction settlement, watering method and flexure are adopted.3. High grain breakage appears easily under common pressure. It affects the dilatancy and the shear strength of over coarse-grained soil greatly. Systemic study of grain breakage is discussed on the basis of the study of predecessor. Especially, grain breakage under the action of compaction and shear and the effects of grain breakage to the mechanical properties are discussed.4. The stress-strain relation and the characters of volume change-axial strain are sum up. The applicability of Duncan-Chang model to over coarse-grained soil is also discussed. And the constitutive model adapting to over coarse-grained soil is established by improving Duncan-Chang model. In order to validate the rationality of new model, the simulation is executed by model parameters which obtained from large scale triaxial test.