Discussions On Liquefaction Mechanism Of Saturated Fine Grained Soil Under Vibration And Prediction Of Settlement Deformation And Study On The Corresponding Treatment

Based on the project sponsored by the Shandong Traffic Science Foundation, Discussions on Liquefaction Mechanism of the Saturated Fine Grained Soil under Vibration and Prediction of Settlement Deformation and Study on the corresponding Treatment, the present study aims to investigate the liquefaction and inhomogeneous deformation of the Saturated Fine Grained Soil due to vehicles' vibration on express highway foundation, and to propose some proper measures to dispose the liquefaction of foundation.Express highways are widely applied in sediment area of Yellow River, but some of their surface crack and fail to work because of the liquefaction and inhomogeneous deformation of the Saturated Fine Grained Soil induced by variation of groundwater level and impaction of vehicles' vibration. Therefore, it seriously influences application and increases maintaining expenses. These become an practical problem to dispose. It is one point of the dissertation.According to aggregate analysis and profound discussion on liquefaction under vibration and deformation failure on the saturated fine grained soil in research area under vehicular dynamic load, a set of relation characteristic of dynamic stress-strain and a deformation failure model are established to predict liquefacient area and the process of deformation. Then foundation disposal measures be reached. These will service to foundation safety in construction of road and bridge. This is the other one point of the dissertation.The research area is chosen in area to build express highway in Yellow River delta,which can reflect the actual engineering geology characteristic. The characteristic of the saturated fine grained soil in Yellow River delta is obtained according to field drilling, sampling and indoor test. The chief components of the saturated fine grained soil are mild sandy soil and mild clay, moreover, there is a little silt and silty fine sand.The groundwater level is more shallow, attaining to leave the ground most shallowly roughly 10cm, moisture content is more bigger. The microstructural characteristic of the soil is elementary consistence. There are some granule on the surface of grain and the most of grain is ellipsoidal. The touch is extrusion contact between granules, and a little is chain link, and the great majority reports the framework form construction. Mineral characteristic, the majority is detrital mineral,the content of quartz is biggest, the next is feldspar and calcspar. Clay mineral is made of illite and chlorite and illite cover more than 50%. It has less component of kaolinite and montmorillonite It is investigated that the saturated fine grained soil in Yellow River delta has special characteristic. On the basis of field test, indoor experiment and numerical analysis, we discuss the liquefaction mechanism under vibration and predict settlement deformation and propose the disposal measures, the conclusions are drew following:1. Liquefaction occurs mostly in the crust layer, the pore water pressure increases rapidly and the strength of silt reduces under cyclic loading. Strength of silt increases in the up-down crust layer. The strength of silt recovers to natural strength gradually after the vibration. Pore water pressure jumps rapidly under the cyclic loading and dissipates gradually after the cyclic loading. The layer of liquefaction expands in depth with the increasing of cycle number. The variety of physical mechanic indexes of silt in depth under cyclic loading has observably otherness in the direct of grain size distribution, water content, density, pore ratio, saturation, cohesive strength, internal friction angle, compressibility, and so on. The change of soil intensity is induced mainly by the grain size, mineral and microstructure. The rule is different in different layer and reverse in liquefaction areas and close-grained areas.2. It is found that the coefficient of permeability of the foundation in Yellow Riverdelta declines firstly and then increases continuously with the increment of vibrational energy and the amplitude of the variation is more than 4 times of the original. The test of variation of the soil density under cyclic loading at the same time shows that it increases firstly and then declines. Therefore, the relationship is negative correlation between coefficient of permeability and vibrational energy.3. On the basis of the deformation failure field test under cyclic loading, the influence factors of liquefaction deformation failure include density, moisture content and weak area in soil, in addition, size and frequency of vehicles. And the key factor is weak area in soil. The critical load and limiting load of the natural soil observably decline after cyclic loading. The critical load decreases by 39% and limiting load decreases by 25% under cyclic loading.4. The result of dynamic triaxial test and resonant column test indicates that the general failure standard is not suitable for foundation soil in Yellow River delta. Moreover, the embryonic failure standard of liquefaction are that the ratio of pore water pressure is 0.65 in mild sandy soil and mild clay and 0.87 in silt.5. Under the cyclic loading of lOOkPa, the pore water pressure and deformation of foundation soil are analyzed by numerical analysis, the result shows that the surface soil is less prone to liquefy, but the deformation is large; the lower layer is much prone to liquefy, and the deformation is little. The variation velocity of deformation and pore water pressure is larger during the loading begin and diminishes after 180 days. The foundation soil almost stabilize after 360 days.6. On the basis of field test and numerical analysis under cyclic loading, the deformation prediction result of foundation soil is obtained, when the energy reaches 1270N/m2 ? N, the immediate settlement of foundation soil is obviously at the initial stage, and the deformation reaches 10cm. With the loading going on, the foundation soil becomes more and more close-grained, the deformation tends to uniform speed, the value is about 2cm.7. Based on the destroy states of in-situ roadway and inside and field test and experimental research, the main measures proposed to prevent the liquefaction of saturation granule soil in Yellow River delta area are drew: For the built roadway,the exogenous factors such as overspeed and overloading should be controlled; For the building roadway, the measures should be taken according to the local conditions such as dynamic compaction, lime-soil bedding layer and dry jet mixing pile.This thesis is from span-new visual angle to research the liquefaction mechanism, deformation prediction and disposal measures in Yellow River delta. The research method and the technology route all have the innovation: The deformation destroy research of saturation granule soil under vehicle loading in Yellow River delta haven't been done by the predecessor; Liquefaction and nonuniformity deformation of the saturation grained soil are studied under field cyclic test in stead of traditional simple, broach analysis; Model the process of vehicle loading induced the saturation grained soil liquefaction and deformation basing on numerical analysis methods, and then reasonable advices are proposed for foundation repairing. This research achievements possess the notable guidance meaning to the process of liquefaction and deformation prediction of express highway, has engineering practical meaning for foundation treatment and promote the study on foundation soil under vehicle dynamic loading in Yellow River delta.