Research On Supporting Of Deep Foundation Pit Based On The High Sensitivity Of Soil

The sensitivity of soil is the ratio of unconfined compressive strength of undisturbed soil to its immediate testing after remodeling,sensitivity St is often used to measure the effect of soil structure on strength.That is the ratio of unconfined compressive strength of St=Qu/Qt to the undisturbed soil immediately after its remodeling.According to the sensitivity,the clay can be divided into low sensitivity(1<St≤2),sensitivity(2<St≤4),high sensitivity(St>4).Sensitivity of soil is higher,the structure is strong,the soil disturbance intensity decreased more obviously.High sensitivity clay soil has large water content and large pore ratio,it is sensitive to disturbance,load,immersion and other external conditions.For example,during the construction process of some silty clay foundation piles,the soil between the piles is stirred violently and the vibration is very violent,which makes the bearing capacity decrease obviously.Some excavation needs to be anchored by anchor or anchor rope during the excavation.When drilling with an anchor dry drill,the vibration of the drill will cause obvious disturbance to the surrounding soil,so that the retaining structure will be unstable and finally collapse.Many of the foundation pit supporting pile displacement,heave of foundation pit,deformation and other diseases,and even cause the accidents.The occurrence of these diseases is essentially related to the sensitivity of the soil.The engineering geological condition in Xiaodian District of Shanxi,Taiyuan province is poor,and it belongs to typical cohesive soil site with high sensitivity.Some of the silty clay site in pile foundation construction process,soil between piles due to mixing,vibration and disturbance of the longevity capacity substantially reduce the collapse of potholes.Some foundation pits are anchored by anchor while they are excavated,anchor stem and anchor rope are more in quantity.The foundation pit with smaller lateral spacing is more reliable than the surrounding anchor and the anchor pit with large lateral spacing,collapse has occurred.There are many displacement of pile foundation,large deformation of various diseases in or after foundation pit construction.Through long-term research and observation,the occurrence of these diseases in Xiaodian Taiyuan is due to the soil with high sensitivity.Based on geological investigation and foundation pit support of Shanxi science and technology innovation city,combined with a large number of indoor geotechnical tests,the stability of foundation pit is simulated by software,the particle composition of the soil with high sensitivity、soil characteristics and the risk coefficient of the targeted support scheme were simulated.The main work and achievements are as follows:1.A profound understanding of the microscopic properties of soil with high sensitivity has been made through field sampling of soil samples、perform particle analysis in a timely manner and direct shear,liquid plastic limit test and other soil tests.2.Understand the safety and feasibility of the construction plan by analyzing the engineering characteristics and software simulation of foundation pit support scheme.3.Some foundation pit support schemes for high sensitivity soil are proposed through consulting documents and repeated tests.