A Study On Supporting Design About An Expansive Soil Deep Foundation Ditch In Cheng Du

With economic development, more and more high-rise building constructed, aswell as the development and utilization of underground space, a large number of deepfoundation pit engineering arises at the historic moment, the complexity andimportance of deep foundation pit engineering is also increasingly exposed, becominga difficult and hot engineering. Especially in expansive soil areas, the particularity ofexpansive soil foundation pit often lead to a significant engineering problem inconventional foundation pit supporting, the reason is mainly for the expansive soilwith the swell, water shrinkage properties. Designers often did not attach enoughimportance to the characteristics of expansive soil, the soil pressure calculation aswell as the foundation pit supporting scheme selection would have significant errors.So for the expansive soil characteristics and excavation mode, has importantengineering significance.Taking a deep foundation of expansive soil based in Chengdu, in the calculationof earth pressure, through physical simulation of expansive soil earth pressure wasmeasured, drawn expansive soil earth pressure variation curve, showed the earthpressure and expansive change with the change of moisture content, which providedguiding significance in the foundation pit supporting design calculations.In terms ofexcavation, according to the characteristics of expansive soil foundation pitparticularity and the foundation pit engineering, using the fuzzy hierarchycomprehensive evaluation method, to determine the optimal foundation pit supportingscheme. At last, by using the domestic industry more generic rock rationale for deepexcavation retaining structure design software to study two aspects as the basis for thefoundation pit design calculations. At last, by using the domestic industry moregeneric rock rationale for deep excavation retaining structure design software to studytwo aspects as the basis for the foundation pit design calculations.This article main research content including3components.Firstly, earth pressureof expansive soil and expansive force with the moisture content change rules werestudied by using the indoor physical simulation experiment method. Secondly, usedanalytic hierarchy process and fuzzy comprehensive evaluation method effectively, to set up suitable support scheme optimization model for expansive soil of deepfoundation pit, and chose suitable support scheme for some expansive soil of deepfoundation pit in Chengdu. Last, combined the above two studies on the content,foundation pit supporting design of deep foundation pit is calculated by making use of7.0version of the software.The main findings include:(1) According earth pressure of expansive soilphysical simulation results obtained:1)expansive soil earth pressure distributiontrapezoid along the wall high meet Ken Lang earth pressure theory;2)Earth pressurechange in the overall situation of expansive soil with higher moisture content andhigher. In the early earth pressure increased by a big margin, the inflection pointoccurs when the moisture content of approximately36%, the earth pressure increasesignificantly weakened.3)Using the Rankine soil pressure theory to calculate the soilpressure of the ordinary clay which the water content was30%,the calculation resultis less than the soil pressure of the expansive soil which the water content was30%.According to the variation of the soil pressure of the general cohesive soil withmoisture content,contrast to the variation of the soil pressure of expensivesoil,proofing that the soil pressure of expensive soil is greater than the soil pressure ofthe general cohesive soil,but no linear relationship between the two.(2) According theindoor experimental results of expansive soil swelling force obtained:1)With theexpansion soil contiuous moistening, the expansion force whole curve downwardtrend;2) Pre-expansion force larger decline, turning point arrived when the moisturecontent is about26%, expansion force decline reduced;3) expansion force earlydecline was nearly linear.(3)Using the Multiple Criteria Decision to be preferred forexpansive soil deep excavation program, preferred model building process andpreferred results showed that:1）Constrained by characteristics of the expansive soil,the weighting factor of geological have significantly improved;2)Utilization of AHPand fuzzy comprehensive evaluation method to establish the optimization model caneffectively improve the objectivity, comprehensiveness and effectiveness of thepreferred model, making the preferred results more in line with requirements andmore reliable;3)The result of preferred support programs is the Piles supportingscheme for the deep foundation with expansive soil, this program has reachedexcavation safety and economy requirements, and to verify the correctness of thepreferred model.(4) Utilization the Software of Lizheng7.0for excavation designcalculations, design results showed that:1) The stage version of the software is themost practical and reliable design of shoring computing software;2)Using the results of FAHP preferred outcome as the Supporting the design of the expansive soil in deepexcavation;3）In the process of supporting design calculations，the earth pressurecalculation section, combined with the research of expansive soil in earth pressurevariation on the calculation of earth pressure values were corrected, the final pitdesign calculations to meet the pit engineering requirements;4）Checking the stabilityof the final design achievements for each segment pit，including，the overall stabilitychecking，the against overturning stability checking，the heave stability checking,theresults of checking are in line with the stability requirements.