Indoor Model Test Research On The Effect Of Water Level Change On The Bearing Capacity And Settlement Of Pile Foundation

With the continuous development of our country’s urbanization and large-scale comprehensive transportation hubs,the urban land is becoming increasingly tight,and the comprehensive transportation system has developed and utilized underground structures in large quantities,thus making the scale of foundation pits continue to increase,the environment in which they are located is more complex,and the average depth of foundation pit excavation.As the depth and number of foundation pit projects increase,the degree of precipitation in the foundation pit will also increase,and the process of precipitation in the foundation pit will affect the pile foundation and soil deformation of adjacent buildings.The impact will also become prominent.In this paper,the deep foundation pit project of Chengdu North Station of Chengdu Metro Line 18 is used as the background,and the proportion of quartz sand and natural river sand is used as the model foundation soil material.For the related effects of soil deformation and pile top settlement,20 groups of indoor model tests were designed,and the pile body axial force,filling settlement,pile top settlement and other data of each group of tests were measured,and the test results were compared and analyzed.The end bearing capacity and lateral resistance of pile foundations and their effects on settlement in different water levels and the process of rising and falling water were studied,and the following results were obtained:(1)When the water level in the soil layer is low,the pile top load is jointly borne by the end resistance and the pile side resistance.As the water level increases,the pile top load is more and more borne by the end resistance.The side resistance of the pile decreases with the increase of the water level,especially for the rock-socketed section of the pile,the side resistance of the pile in the rock-socketed section plays an important role in sharing the load on the top of the pile,and the change of the water level affects the attenuation of the lateral resistance at the rock-socketed section.The influence is greater than other positions of the pile body.When the water level in the soil layer is high,the load on the top of the pile is mainly borne by the end resistance.low water level.(2)With the progress of the water lifting process,the pile top load is more and more borne by the end resistance;the sharing effect of the pile side resistance on the pile top load generally decreases,and the pile side resistance of the rock-socketed section has a significant effect on the pile top load.The load sharing of the pile top is reduced more than other positions of the pile body;at the same time,the lifting water process has no obvious effect on the settlement of the soil surface around the pile whose foundation soil material is quartz sand and the settlement of the pile top of the two piles.(3)When the pile top load is large,with the increase of the test water level of different test groups,the increase of the end resistance of the river sand foundation soil material group to the pile top load sharing is greater than that of the quartz sand material group;For the overall lateral resistance of the pile body,with the increase of the test water level of different groups,when the load on the top of the pile is large,the overall lateral resistance of the pile body in the river sand type foundation soil material group reduces the load sharing on the top of the pile more than the ratio.For the quartz sand material group,the contrast is more pronounced especially in the rock-socketed section.(4)In the case that the pile top load is more and more borne by the end resistance with the progress of the lifting water process: the increase of the end resistance of the river sand material group to the load sharing of the pile top is proportional to the proportion of the quartz sand material group.For the overall lateral resistance of the pile body,the ratio of the river sand type foundation soil material group to the quartz sand type material group also reduces the load sharing on the top of the pile;at the same time,for the settlement of each point around the pile,the river sand The soil surface settlement around the piles of the similar material group is also larger than that of the quartz sand material group.However,for the settlement of the pile top,different foundation soil materials of river sand and quartz sand have no obvious effect on the settlement of the pile top under the condition of rapid lifting water.