Study Of Soil Nailing Internal Force Test And Deformation Regular For Deep Foundation Pit Engineering In Baotou

The soil nailing wall retaining structure is the most widely used in pit supportingengineering， however， the theory of soil nail wall supporting design seriously laggingbehind the practice is still not perfect. Currently， the design theory is that soil nail tensileforce calculation and overall stability checking are conducted based on the imaginaryretaining wall， with experience of soil pressure (composite soil nailing wall offoundation pit supporting technology specification GB50739-2011) and Rankine soilpressure (construction of foundation pit supporting technology regulation JGJ120-2012)being used. The design results and the actual monitoring results have a big gap. Becausethe complexity，variability and regionalism of soil mechanics properties in pit engineeringlead to diversity of soil nailing internal force calculation， the design results are difficult tograsp， which is the important cause of the accident. It is important to monitoring inaccordance with the relevant provisions on excavation engineering.Based on construction of foundation pit supporting technology regulation(JGJ120-2012) and the composite soil nailing wall of foundation pit supportingtechnology specification (GB50739-2011)， the soil nail wall supporting of the deepfoundation pit in local as design object， was made a comparison and calculation，showing the difference of specification.According to "Construction of foundation pit monitoring technical specification(GB50497-2009)， the designed monitoring points were used to monitor soil nailinginternal force and foundation pit deformation (slope crest horizontal displacement andvertical displacement). The results reflecting the correctness of the design result andreliability， show the process of the soil nailing internal force change and slope crestdeformation of earthwork excavation， and supply a reference in the similar region.Finite element software FLAC3D was used to simulate the excavation process.Compared the simulated data with experimental data， it showed consistency of the earthpressure distribution. And earth pressure distribution is more close to that of buildingfoundation pit supporting technical regulations (JGJ120-2012).Conclusions are as following:1. Two provisions specifying different soil pressure， different soil nailing internal force is calculated. And the measured soil pressure is closer to that of construction offoundation pit supporting technology procedures (JGJ120-2012).2. The first soil nailing in the soil nailing is usually subjected to the most unfavorableloading. With the increase of the excavation depth gradually， supporting structure isstable， and the soil nailing internal force value gradually is in a certain range.3. For each soil nail， the maximum axial force of soil nailing is discovered in thelocation of the excavation face about2m， decreasing along the both soil nailing sides. Italso suggests that maximize soil nail axial force is the most dangerous.4. When the excavation reached the basement design elevation， soil nailing structuretends to be stable. Compared each row of soil nail axial force value， it is found that soilnailing maximum axial force was in the third row of retaining structure， which is inaccordance with monitoring data and the results of numerical simulation.5. With the increase of excavation depth， the horizontal displacement of theexcavation surface gradually increased due to the absence of the excavation slope lateralconstraint. The maximum horizontal displacement appears on the top of the foundation pit，and the maximum horizontal displacement has a tendency to slip down with the continuingof the excavation condition.6. The surface subsidence also increased gradually with the depth of foundation pit，and the maximum subsidence was on the foundation pit excavation. Excavation surfacesubsidence value is smaller from the farther place. Each of excavating the foundation pitslope crest will produce certain settlement. When supporting structure is stable， thesettlement also gradually is in a certain range.