Study On The Effect Of Ground Water Level Variation On The High Sneed Railway Viaduct Foundations

As an important mode of transportation,high-speed railway plays a vital role in China's economic and social development.In order to meet the strict post-construction settlement requirements and save land resources,many high-speed railway lines use a large number of viaducts as the lower support structure.However,due to climate change and groundwater pumping,the groundwater level in many regions of China has been declining,which has brought serious problems to the foundation of high-speed railway viaducts.It has been reported that the drop of groundwater level will cause large settlement of high-speed railway viaduct piers,and its maintenance cost A lot of manpower and resources.At present,there are still few studies in this area.It is necessary to study the influence law of groundwater level variation on the pile foundation of high-speed rail viaducts.In this paper,the centrifugal model tests and finite element numerical simulation are carried out to systematically study the variation characteristics of single pile and piles of different lengths under the conditions of water level drop and water level circulation.The main research work and corresponding research results are as follows:(1)Centrifugal model test of continuous water level decline conditions was carried out to study the stress and settlement changes of single piles and piles of different lengths under the condition that the groundwater level decreased by 3 times.The results show that the drop of groundwater level will cause large additional settlement of the ground and pile foundation,which easily exceeds the post-construction settlement standard of high-speed railway piers.(2)The finite element method is used to simulate the centrifugal test of the water level drop condition,and the finite element model which is consistent with the test results is obtained.The finite element results show that the relative displacement of the pile side soil and the pile foundation determines the lateral frictional resistance distribution of the pile,the groundwater level decreases,the relative displacement of the pile and soil increases,and the negative frictional resistance and the lower positive frictional resistance increase.The closer to the pile foundation,the smaller the settlement of the soil,and the settlement of the soil around the center pile inside the group pile is the smallest.(3)Carry out the centrifugal model test of the water level lifting cycle condition,and study the stress and settlement changes of single pile and piles of different lengths under the condition of three times of groundwater level lifting cycle.The test results show that the groundwater level lifting cycle will cause the ground and pile foundation to settle continuously.In the first cycle,the settlement accounts for more than 80%and 70%respectively.The longer the length of the pile group foundation,the lower the settlement ratio in the first cycle,that is,it needs to be fully developed after repeated lifting cycles.When the water level rises,the long pile and the ground will rebound slightly,but the water level will be restored as a whole,and the accumulated settlement will not recover.(4)Under the action of the groundwater level lifting cycle,the axial force of the pile foundation changes continuously.When the water level returns to the previous position,the axial force of the pile foundation will also recover.