Study On A Determination Method For Compactness Of Subgrade Based On Duncan-chang Model

Highway is the basic industrial of national economy, and the subgrade is the baseof highway, and the important part of the whole highroad construction. In theconstruction of highway, the quality of the compactness of highway subgrade must becontrolled for improving the quality of subgrade construction. The method which canquickly and reliably detect compactness of highway subgrade must be established.The widely used method for detecting compactness of soil-rock mixture subgradeinclude water (sand) replacement method and wave method by now. However, thereare deficiency and limitations since the accuracy of these above methods is poor orthe efficiency is low, which are unable to meet the detection accuracy requirements ofhighway subgrade. Therefore, establishing the rational method for detectingcompactness of highway subgrade is the key problem to control the compaction effectof highway subgrade. In this paper study on this problem combined with relatedprojects has important practical values for theory and engineering.In order to set up a new testing method for compactness of highway subgrade,firstly, based on the intensive study on subgrade deformation and mechanicsmechanism under static penetration, the stress of the subgrade caused by staticpenetration is divided into two parts: isotropic stress and axial deviatoric stress, thenonlinear variation characteristics of the subgrade soil deformation is considered, theidea of step-loading and analysis of foundation settlement of the layer-wisesummation analysis theory are introduced, and the incremental generalized Hooke’slaw and the incremental Duncan-Chang constitutive model are developed, thereby，thesubgrade penetration load and displacement analysis model with the initial porosityratio, Poisson ratio, cohesive strength and angle of internal friction as the modelparameters is established. Secondly, on the basis of the static penetrationdisplacement analysis model mentioned above, the method of back analysis based onthe adaptive genetic simulated-annealing algorithm is recommended, according to thesubgrade static penetration load and displacement test curves, the testing method forcompactness of subgrade based on static penetration is set up, this method can notonly test the compactness of subgrade, but also test the other physical and mechanicalparameters of the subgrade soil(such as Poisson ratio, cohesive strength, angle ofinternal friction and so on), furthermore, this method has the fast and efficient testing characteristics because the static penetration test can move to the special purposevehicle to make the fast moving and testing come ture. Finally, by comparing with theother existing methods and the computation of an engineering example, it can provethat the proposed method is reasonable and feasible.