Study On Treatment Technology For Special Roadbed In Mu Us Desert

On expressway construction in the desert, there are many technical problems including problems not only on construction compaction, windbreak and sand fixation but also on special roadbed treatment. The technical problems also include the treatment of special soil mixed with animal and plant remains after corruption and aeolian sand and the treatment of aeolian sand weak foundation containing silt at low-lying stagnant water. In the earlier construction of (the half width) of National Expressway210-Yulin-Shaanxi-Inner Mongolia boundary which totally includes76km, we have encountered many special foundation treatment problems. There are marsh wetland, sludge soil foundation, peat soil foundation and animal waste soil foundation including more than20sties. There are also more than10kilometers roadbed foundation where underground water level is close to the surface level. In the subsequent construction of another half width (88km) of National Expressway210, there are4km river valley terrace deposition area, the strata primary consisting of fine sand with high water content, and the bearing capacity is low. There are53km lake basin beach land along the road and the groundwater has relatively shallow burial depth. When rainy season comes, the low-lying sites often gather water and form lake or wet land. The surface soils are alluvial sediments or lacustrine deposit silt clay and most of the foundation soils are have level layered structure. There are18km road mainly locate at lake basin beach land where underground water level is high with saline soil locally. Special geological sections distribute widely. Special roadbed treatment has become the key problems in the desert expressway construction.After investigating and collecting material of desert expressways at home and abroad for the research, and also building the base on the Yulin-Shaanxi-Inner Mongolia boundary expressway, the main research of the desert expressway special roadbed treatment technologies and findings are as follows:1、Through the indoor tests, the paper approaches the physical properties of aeolian sand and make the qualitative analysis of the engineering geolgy characters with different sediment percentage. Based on the compacting test of aeolian sand with different sediment percentage, the compacting properties and the compacting mechanism of aeolian sand with different sediment percentages are studied.2、According to the tests above, the variation range of mechanical properties for aeolian sand with different sediment percentages are revealed. Following these results, the choice of the biggest dry density is obtained. In view of the results obtained, the road-related performance of aeolian sand with different sediment percentages are judged systemically, and the range of sediment percentage fitting for roadbed material is achieved.3、In Yulin-Shaanxi-Inner Mongolia boundary Expressway, plate loading test was studied at6test sections which were selected to ascertain the bearing capacity of natural foundation and the improved soil foundation. Foundation treatment technique measures were put forward.4、The natural aeolian foundation and the improved aeolian foundation were studied by numerical analysis of nonlinear finite element method. The mechanical characteristics of aeolian sand foundation was discussed by analysing the bearing capacity and foundation deformation. When the soils strength parameters were close to the reality, the results of numerical analysis of nonlinear finite element method and plate loading test have consistency and the results of two methods approximate to each other. The soft ground was analyzed by finite element method, and the results show when the soft ground was treated, the engineering characteristics was significantly improved.5、Using case-based reasoning method to predicte aeolian sand roadbed’s final sedimentation, we can build a reasonable relationship between the former sedimentation of aeolian sand roadbed and current predicted sedimentation of aeolian sand roadbed. The predicteion of results were close to the reality, and it has wide applicability. In order to verify stress and displacement, we use transfer of matrix method calculated stress and displacement of aeolian sand roadbed.6、Optimization analysis of different processing for special roadbed treatment of Yulin-Shaanxi-Inner Mongolia boundary Expressway was made by the grey interval incidence degree decision-making. Through analysing every factor which affects the choice of engineering processing scheme, the engineering processing scheme’s maximum relating gray was calculated. The evaluation of the grey interval incidence degree decision-making method for multi-index system close to the actual result.