Experimental Study On Unloaded Soil Of Deep Foundation Pit And Finite Elements Analysis

With the emergence of the high-rise construction and the underground project, the quantity of deep foundation pit excavation project rapidly increases. The underground space took one kind not yet develops resources arouse people's widespread interest;the deep foundation pit design and the construction question become the geotechnical engineering projects hot spot. The deep foundation pit success or failure that mainly is decided by the design when soil parameter with this construction model selection whether conform to the project actual condition, the process of foundation pit excavation materially is the process of the foundation pit peripheral soil unloading, under the unloading condition the soil project of nature with the applying loading condition have wide differences. Since long ago, the people adopt "applying loading" testing method definite soil parameter and constitutive model, to the design calculation structure excavation unloading soil is inappropriate obviously;carries on the foundation pit excavation with the conventional earth applying loading test parameter numerical analysis and the design calculation can have the big error inevitably. At present there have many research of the soil character under applying loading condition, the simulation of deep foundation pit excavation process triaxial test research institute are not common. Especially uses the truly triaxial simulation pit excavation peripheral soil the plane strain condition unloading process experimental study to be extremely fewer. Therefore, this article uses the normal triaxial and the true triaxial, simulation structure excavation soil unloading stress path, studies the pit excavation soil the project characteristic to determine the soil parameter and this construction model, to foundation pit design soil parameter with this construction model selection more conform to the project actual condition, this has the extremely vital significance theory and practice meaning regarding the pit excavation project numerical analysis and the optimize design.The paper mainly research content and achievement as follows:1. By way of analyzing the stress path of soil during the process of digging foundation pits there are two kinds of stress path of foundation pits being dug: The surrounding area of the foundation pit are called active area, with vertical load unchanged and lateral load removed;area inside the foundation pit are called passive area, with lateral load unchanged and vertical load removed. Pointed out this kind of stress way and the road building, construct model the dam soil body and so on, the applying loading project the stress path is completely different.2. Use the normal triaxial adopt Wuhan clay to carry on the simulation structureexcavation soil axial symmetry stress unloading and applying loading to experiment, to the applying loading and unloading soil body character conduction analysis research. Pointed out, leaves the stress path to have the intense influence to the hole excavated for building foundation pit soil body distortion. Under different stress way, does not give a thought to the stress way the influence, generally with adds the theory and the parameter based on the convention which Holland experiments obtains comes to the foundation pit for building foundation project to carry on the computationto be incompatible, Should perform to revise.Gain the unloading soil stress-strain relations still might use the Duncan-Zhang model to indicate, but the unloading module is smaller than the normal triaxial to applying loading module, deduced the foundation pit excavation soil unloading tangent module formula.3. For the pit excavation peripheral active area clay carried on under the plane strain condition with the truly triaxial to solidify undraining water applying loading and the unloading experiment, solidifies the draining water unloading experiment, to the experimental each kind of curve to take the analysis.(l) obtains the unloading undraining experimental test specimen stress - strain relations curve along with the solidify pressure increase by the strain hardening transformation to strain softening, and the true triaxial unloading draining water experiment obtained test specimen stress - strain relations curve strain still is hardening, intermediate principal stress has the appears influence to the soil stress-strain relations .(2) The same curves is encircling presses, It is cutting the initial stage, two curves differences are not apparently. Along with continuation which cuts soil body under draining water condition, because of hardens development. The showing draining water ultimate strength obviously is higher than undraining water .4. Under identical stress path, the test specimen stressful condition is different. The stress - strain relations curve of experiments is obtained to have the remarkable difference. It is relational curve changes steep, the ultimate strain changes slightly. Explained among the principal stress in is not equal to time the big principal stress perhaps the small principal stress. Therefore, the center principal stress has the remarkable influence to the soil body stress-strain relations.5. The true triaxial unloading undraining water the test specimen in to solidify the pressure to be low time. The pore-water pressure increase and the average stress increase approximately becomes the linear relations.Along with solidifies the pressure increase, the average stress reduces gradually at the same time.The pore-water pressure increase is bigger than the zero. The test specimen unloading to the certain degree. Also is the test specimen when solidifies the pressure is low displays fordilatation of nature, when solidifies the pressure high test specimen performance for to cutfirst shrinks dilatation again.6. Generalized shearing stress and the generalized shearing strain relations curve are drawn up under the draining water with undraining water, its curve shape is nearly like as the tradition stress-strain relations curve, presents the good hyperbolic curve relations. Further infers the expression of generally shearing modulus under the plane strain condition unloading soil.7. The construction relations of unloading soil under the plane strain condition with draining and undraining has been researched, obtains the construction relations under the undraining condition unloading soil, but the relations has not conform to the Lade-Duncan model Duncan-Zhang model, is situated between two curves under high surrounding pressure. But the construction relations of draining unloading soil with undraining conform to Lade-Duncan model very well.8. Uses this test result of simulation structure excavation process true triaxial unloading applying loading, using the ANSYS finite element procedure does not supports the deep structure excavation project example computation. Compared with uses the soil unloading to applying loading parameter obtained pit excavation horizontal displacement, the function on the pit excavation retaining wall earth pressure, earth subsidence of pit surround, rise of pit bottom difference, that will open for the next deep foundation pit excavation support in the structural design soil parameter choice to provide the guidance suggestion.