Study On The Foundation Treatment Technology Of Seismic Liquefaction And Its Coexistence With Saline Alkali Swamp Of Delingha-Xiangride Expressway

The Delingha-Xiangride expressway is located in the northeast of Qinghai Tibet Plateau,belong to important part of "in-depth implementation of development plan of western development strategy of highway and waterway transportation"(referred to as the "western plan",2011-2020),the distance is 165 km.The investigation shows that the project was widely distributed along the saline soil,salt marshes and aeolian sand soil,liquefaction and other special foundation,along the soil with silt,silty clay particle content is extremely low,earthquake liquefaction of foundation soil characteristic is obvious,with the characteristics of soft soil foundation of saline marsh.These special soils bring challenges to design,construction technology,and operation quality safety of The Delingha-Xiangride expressway.The foundation treatment technology of seismic liquefaction and its coexistence with saline alkali swamp has become the key and difficult problem in the construction of Delingha-Xiangride expressway.Based on liquefaction foundation treatment design and construction of the project through the project,the reasonable discrimination method of the liquefied soil foundation are put forward,through the optimization design of ground treatment scheme is reasonable and feasible,put forward the related quality control index and standard method,and the formation of Qinghai Province earthquake liquefaction and the saline marsh symbiotic technology guide are put forward for design and construction of foundation.Delingha-Xiangride expressway subgrade was treated with impact roller compaction in the dynamic replacement in medium liquefied subgrade and gravel compaction pile in serious liquefaction subgrade.The field experimental detection and analysis of displacement of high-speed showed good results,the settlement was significantly reduced,the degree of compaction improve.The dynamic replacement treatment of medium liquefied subgrade is successful,bearing capacity increased into 300 kPa,the bearing capacity of the composite foundation is 160 kPa,meet the design requirements.During the construction of gravel piles,the vibration compaction process and the amount of gravel are the key to the quality control of gravel pile.The dynamic penetration test shows that the gravel pile and the soil between piles are above the requirements of medium density.The saline soil subgrade filler deformation and water salt migration test showed that salt expansion phenomenon under the action of load with in different soil samples under static load and dynamic deformation and shrinkage,dynamic replacement of composite foundation and gravel pile composite foundation can form a drainage channel in the saline soil containing groundwater,resulting in reduce of groundwater level in the soil,improving soil strength,with better reinforcement effect compared to the other two methods.According to the highway Dechamps silty sand and saline soil foundation treatments targeted at different ground treatment period of surface subsidence,soil pressure,and underground water level observation research.Foundation treatment effect is poor and lack of capacity are mainly due to the impact of foundation settlement,composite foundation pile body to pile between the effect of the soil is a nonlinear process,the pile-soil stress ratio for nonlinear changes,its value changes with the load gradually increased,eventually with the composite foundation pile and soil deformation coordination to bear load,the pile-soil stress ratio will stabilize.The test results show that the dynamic compaction replacement treatment of foundation pile soil stress ratio can be 2.5 ~ 2.7;gravel pile soil stress ratio can be 1.2 ~ 1.5.And with increasing of the density of pile,the stress ratio of pile and soil can be improved.