The Analysis And Application Study Of Arch Effect In Bedding Rock Foundation Pit

These years the efficient utilization of underground space has become an main method to addressing the city congestion. With the construction of foundation pit enjoying a boom all over the country,the stability has become a focus of research in engineering field. The bedding stratified rock foundation pit is found widely but has poor stability and high risk to collapse. Because of these characteristics,it has become a urgent issue in the foundation pit slope project. At present, the management of bedding stratified rock foundation pit is always based on the engineering specifications, which ignored the beneficial effects of rock arch effect on the foundation pit’s stability, finally making the management plan too safety and wasteful. The main reason is that the generation mechanism of rock arch effect and its beneficial effect on foundation pit has not been completely figured out. Based on the previous studies, the paper made a further research on the mechanism of rock foundation pit. The research results are as follows:1 By the supporting of the sides’ rock,the decline force in the bedding slope will deflect to the arch direction,and turn into the axial stress which is conducive to the stability of slope, resulting a arch effect in the rock. The main cause of the unstable failure of arch rock is that the bending tensile stress exceeds the rock limit, which mainly manifested as tension rifting sliding failure in the middle of the span.2 On the basis of modifying the assumptions conditions, we changed the width formula selection method in the previous rock arch axis supporting and derived the new rock arch axis equation. Comparing the new rock arch axis equations with the old one combined with the engineering example, we can come to the conclusion that the new rock arch axis equation is closer to the actual engineering data and has stronger applicability.3 Based on the controlling variable method, a research focusing on the effects of rock strength and foundation excavation width on rock arch effect is conducted. When other conditions remain unchanged, the upper thrust that rock itself can withstand increases, with the rock strength increases, So the stress that the rock arch need to undertake gradually becomes smaller, leading that the rock arch effect of the consequentrock foundation excavation inside gradually weakens. When other condition is constant,with the foundation pit width increases, free surface of pit increases, and the thrust force that sliding consequent rock layers of upper part pit generate increases accordingly.Consequently, the stress generated by the transfer of the rock mass becomes greater,and the stress that the rock arch need to bear will gradually become larger, therefore the rock arch effect of the consequent rock foundation pit inside gradually increases.4 The generation mechanism of rock arch effect and effects of foundation pit width on rock were studied using the ANSYS software;The rock arch effect under the conditions of the soft zone and the effect of the weak zone were also researched using FLAC3 D.5 In the design of J1-J2 part foundation pit support of Gaojiulu Fubang center,the rock arch’s beneficial effects on bedding rock pit were considered, based on the new rock arch axis equation and numerical simulation. And a correspondent design scheme was given finally.