Field Test And Numerical Simulation Research On The New Waterproof Structure Of Foundation In Loess Area

With the comprehensive implementation of western development and “one belt one road” and urbanization strategy,the infrastructure in the loess area expand continuously,buildings are becoming more and more and the scale is more and more large.The loess of which the structure collapse rapidly after being wet under the gravity of overlaying soil layer or the interaction of gravity of overlaying soil layer and additional pressure is called collapsible loess.The loess area in our country is 63.53×104km2,3/4 of which is collapsible loess.It is crucial for the engineering construction in loess area to treat the foundation then avoid the damage to the engineering building brought by the collapsibility.<Code for building construction in collapsible loess regions(GB50025-2004)>stipulates in the generals principles 1.0.3 that foundation treatment should be implemented as the principle thing according to the requirement of engineering and the character collapsible loess when engineering buildings are built in the collapsible area,that means the foundation is evaluated by the collapsibility of all the collapsible loess when it is saturated.There is usually a big gap between this thought and the real engineering,the principle threat of loess foundation is not the full immersion of uniform soil layer,and the foundation will not reach to the fully saturated state.This code is formulated mainly based on the experience in the construction of civil and industrial fields,the railway and the high way industry still follow the design idea of foundation treatment as the principle thing in this code,which cause unnecessary investment.Immersion is the external cause of the deformation of collapsible loess,if reasonable measurements are taken to protect the loess foundation from the immersion,the foundation treatment could be weaken in order to save the engineering investment.This paper studies a new kind of foundation waterproof structure with additional waterproof wall through field test and numerical simulation based on the newly built Chuanda highway in the loess area of eastern Qinghai province,the mainly research contents and results are as follows:(1)Choose the ramp of GuShan service area of ChuanDa highway as the experimental spot,the grade of collapsibility of foundation is judged to be grade III,it is evaluated as loess collapsible under overburden pressure,the lower limit depth of collapsible loess is 10 m.(2)Build the test subgrade of 8m waterproof wall and 10.5m waterproof wall.The foundation is treated with “80cm lime soil cushion and 1.5m digging backfill”.3 rows of cement soil compaction pile are constructed as waterproof wall at the toe of slope,the cement content of cement soil compaction pile is 8%,and the diameter is 40 cm,the pile spacing is 80 cm,and compaction piles are arranged on equilateral triangle,the length of compaction pile in this two experimental spot is 8m and 10.5m respectively.(3)The subgrade in this test section is constructed in July 2015,and the water immersion begins in October 2015 which lasts for 30 days.The test results show that Foundation of 8m waterproof wall under the toe and the middle of the slope is infiltrated;the collapsible loess within 10 m depth of 10.5m waterproof test section is not infiltrated.The foundation within the depth of the waterproof in this two experimental foundations is not infiltrated,which means that the waterproof can protect the foundation from the immersion.(4)The results of settlement observation shows that there is a sudden change of the settlement in the toe and the middle of the slope in the 8m waterproof wall foundation,that means collapse deformation appears in the foundation because of the existence of residual collapsibility.Collapse deformation does not appear in the foundation of 10.5m waterproof wall.(5)Using the neural network toolbox in the MATLAB to inverse the deformation modulus of the different kind soil based on FLAC3 D software,then calculate the saturated infiltration coefficient of the loess based on the field experimental data,then carry out numerical simulation on the new kind of foundation waterproof structure(6)Using FLAC3 D software to simulate the Moisture variation characteristics of foundation under the waterproof wall of different design parameter,and then carry out the parameter optimization of the waterproof structure.