The FEM Analysis Of The Deep Foundation Pit's Stability Under The Influence Of The Micro-arteasian

Foundations excavation is a complicated geotechnical engineering problem. It isrelated to lots of knowledge on Soil Mechanics and Water Mechanics. The magnitude ofthe water's influence is difficulty to compute, but it is very important to the foundationsengineering. The Soil around the foundation pit is composed of stress field, displacementsfield and also a complex seepage field. It can be known from many failure of foundationsthat many of them are direct or indirect to the groundwater.The scale of groundwater influence on foundations' stablity in Tianjin is not morethan 50 meters. Besides shallow groundwater changing with the seasons below the ground1-2 meters, there are silt and fine sand layers below the ground 15-30 meters, which werefounded the water in these layers expresses some characters of confined water. The waterin these layers is called micro-artesian. In the practising the micor-artesian has a greatinfluence on the stability of foundations. In the underground engineering it is devastating.The piping phenomenon in Nanlou subway station is just a typical example.In this artical, summarizing the micro-artesian's damaging to the construction, I willanalyse the stability of the foundation under the influence of the micro-artesian. I discussin detail the confined water seepage's influence on the foundation, especially the passiveearth pressure on the bracing. Using the software--PLAXIS, I analyse the bracingstructure's deformation and total stability of foundation soil. Moreover, I made a computerprogram for Limit Equilibrium Slope Stability Analysis. Using it, I compute the stabilityof foundation in static water pressure conditon and compare it with Plaxis' resultsconsidering micro-arteasian's influence. At last, I demonstrate the micro-artesian'sinfluence on the foundations basing on the project of Nanlou subway station. Throughcomputing the changing of water field and effective stress field, I confired my attitude andget the results which is very close to the real value.So we must pay attension to the confined water, aviding the appearence of incident.