Research On Model Test Of Deep Excavation Bracing And Numerical Simulation With ANSYS

Deep excavation and excavation bracing is a traditional topic in rock and soil engineering, but with modern characteristics. With the emergence of more and more skyscrapers, it becomes more and more important to study the technology of deep excavation and excavation bracing. Many overseas specialists have conducted series of research in the field including theoretical calculations, design methodology, field trip and indoor model test and achieved a lot fruitful results. However, much more work is expected to do in this field due to the complex and uncertainty.Based on the research on deep excavation and excavation bracing home and abroad, this article has completed the following experiments: firstly, it designs a set of indoor model test equipments which solves some key problems in model tests such as small range soil pressure test, antifriction of resistance force on molding board and bracing sand and completes the model test on standard sand;Secondly, it establishes infinite element calculating model, and makes predictable analysis to the relative measurements of model test with ANSYS software, and raises the recommended value for the relative measurements of model box;finally, it analyzes its regular rules of ground sedimentation, soil mass displacement, soil pressure and anchoring force based on the calculations with ANSYS software.This article has completed a few tasks and made several conclusions. They are as the followings:1. It designs and fabricates a sheet pile wall model test equipments. They are a handy model experimental bench with sand sample elevator and sand sample loading unit, a model box made of glass fiber with steel frame suit for the intensity requirement and experimental observation, a molding board made of multi-layer composite material with a soil pressure sensor inside and so on.2. It solves the problem that excavation bracing frame moves freely under the condition that there is no side friction resistance. The reasons lie as the followings: first of all, in this model test, the periphery of the model box is made of slippery, transparent glass fiber;what's more, it adopts a technique to avoid the surface-to-surface touch between the side of excavation bracing frame molding boardand wall panel of model box, which not only ensures effective touch between excavation bracing frame molding board and model box, but greatly decreases friction resistance between them because the ball inset glides on the surface of model box.3. It takes advantage of the weight of experimental sand to obstruct successfully, which resolves the contradiction between obstruct sand and the requirement of zero side friction resistance. The following are the details: in model test, first, stick some obstructing films to the edge of molding board;then, the weight of experimental sand may force the obstructing films to attach to the wall panel of model box closely, accordingly, the air gap is blocked. All of the above may prevent sand from leaking and guarantees the model test.4. It is the first time to apply soil pressure mini-sensor made of Single Crystal Silicon, CYG0515, in the model test. And CYG0515 is used combined with DH3815N, a static strain testing system. The system is a highly intelligentized high-speed itinerant data collecting system, which can complete a series of tasks like automatic balance, sample collecting control, automatic correction, data saving, processing and analyzing. When the system is operated with high frequency soil pressure sensor like CYG0515, it may promote the sensor's testing ability so as to record minute soil pressure.5. It uses self-made sensitivity coefficient to mark the experimental equipment. With 10 CYG0515 sensors remarked in sand samples, all sensors' sensitivity coefficients suit for experiment can be obtained, which guarantees the accurate soil pressure value in the experiment. The process and results also demonstrate that the type of CYG0515 sensors has advantages such as small discreteness, eyeballs scattering around fitting straight line, high precision, high sensitivity, stable performance, no dead zone around low range section, short postponing time and so on.6. It sets up a mechanical model with cantilever sheet pile wall excavation bracing frame based on indoor model test aiming at cantilever sheet pile wall excavation bracing frame with ANSYS software. Secondly, it has conducted a lot analysis to the influences brought by the relative measurements of model box and the corresponding errors. According to the analysis, it recommends the relativemeasurements for models with different earth mass.7. With elastic-plastic ANSYS software, firstly, it works out the isopleth of excavation's vertical and horizontal movement. Secondly, it educes the vertical displacement curve of ground level on the supporting side and excavation side. Thirdly, it derives the horizontal displacement curve of ground level on the supporting side and excavation side. Finally, it develops the cloud atlas of active soil pressure, the isopleth of major principal stress and minor principal stress. The illustrative calculating results reveal the distribution rules of earth mass displacement and sedimentation, soil pressure and major principal stress comprehensively. On the other hand, it makes a tentative study on the different anchoring forces' effects on soil pressure, ground sedimentation and earth mass variation inside excavation bracing. And it concludes that the anchoring force F from sheet pile wall plays an important role in controlling supporting structure and earth mass's variation. So it's an effective way to reduce ground sedimentation, prevent wall displacement and cracks with appropriately designed anchoring force.8. As to deep excavation elastic-plastic ANSYS software is a very effective tool. It offers a simpler method to calculate and analyze the variation and stress of excavation bracing and earth mass, which is a reliable reference for the design and construction of deep excavation.