The Pile-anchor Supporting Internal Force And Deformation Analysis Method And Experimental Research Of Deep Excavation

As its outstanding mechanical performance, good structure stability and remarkable economic benefit, the pile-anchor supporting structure is commonly used as the main supporting structure in the present application of deep excavation engineering. The fact that the theoretical research on pile-anchor supporting structure of deep excavation lags far behind the engineering practice and it is also considered as one of the main causes of deep excavation accidents. There also exist some problems in the prior theoretical researches which should be considered:though the calculation of earth pressure should be the key point when calculating the internal force and displacement of pile-anchor supporting structure, most of the calculations haven't fully considered the effect of displacement of supporting structure on the earth pressure; second, the soil around deep excavation is assumed as a kind of ideal-undisturbed soil in the analysis and calculation of ground settlement. In fact, the supported soil is not ideal undisturbed soil, but the combination of undisturbed soil and damaged soil, because the process of excavation goes with the soil damage. So it is obviously unreasonable that the nondestructive material constitutive models are used to describe the mechanical properties of the damaged materials in the existing research. Third, some of the existing analysis and design software can't reflect the reinforcement effect of prestressed anchor in the overall stability analysis of the pile-anchor supported deep excavation slope. Though there also are a lot of researches based on prestressed anchor or excavation stability, systematic research on interaction and mutual influence between the prestressed anchor and excavation stability has barely been seen. Therefore, this paper attempts to analyze above problems by methods like theoretical analyses, numerical simulation, field test and monitoring. The main results are as below:(1) According to the Winkler model, equated the interaction of soil and pile to the anchor bolt with the spring, and the integral equilibrium nonlinear equation group of pile-anchor supporting structure is established. A hybrid model for calculating the internal force and displacement of pile-anchor supporting structure is established by taking hybrid method to calculate. Compared numerical calculation with experimental results in an actual engineering example, it shows that this method could well reflect the interaction between supporting structure and soil pressure during the process of excavation. The result also shows that the calculated curve is in good agreement with the measured curve of the pile, and it is more close to the measured results compared to numerical calculation. So, all cases show that the method is reasonable and feasible.(2) The soil damage model, damage evolution equation and soil damage constitutive relation are established, which considered the influence of the soil damage in the calculation of ground settlement. Based on the principle of ground loss method, the settlement calculation method of deep excavation pile-anchor supporting structure is given, which considered the effect of soil damage and the action between displacement and earth pressure. Compared the numerical simulation with the actual monitoring results, it shows that the soil damage has an obvious effect on the ground settlement of excavation, which makes the soil settlement increase and the settlement area move toward the excavation. In addition, as a result of overload outside the excavation, the amount of ground settlement greatly increases and the maximum settlement point moves toward excavation. It is necessary to consider the influence of the soil damage and the external overload in the calculation and analyses of the ground settlement. The correctness and reliability of the method has been verified by engineering examples.(3) Introducing the attached stress method, equating prestress which applied to anchor, to the additional stress in the soil, calculation model of deep excavation stability of pile-anchor supporting structure is established, which considered the action of the prestressed,. And then the calculation formula is derived. Contrast analysis shows that PLAXIS software, Lizheng software and the methods that "Technical specification building foundation excavations" standards put forward are all didn't embody the effect that prestress shows on stability safety factor. But the calculation results described in this paper reflected the effect of prestressed force and it also shows that the overall stability and the safety factor of the excavation are gradually increased with the increasing of anchor prestress. In addition, the anchor bolt is very important to the overall stability of excavation slope and the safety factor of the overall stability of excavation is greatly improved after applying prestress to the anchor bolt.(4) Based on actual project, an experimental program was conducted to analyze the variation of the anchor force, the internal force of supporting piles and pile lateral displacement of the deep excavation. And then the variation rule of the internal force of the pile-anchor supporting structure in the actual construction process is obtained. After comparing the calculation results of the method with the experimental results, and analyzed the cause of the difference, and then the correctness, rationality and reliability of the method is further verified.(5) In the construction process of deep excavation, the field ground settlement was monitored, and the variation shows that:ground settlement occurs mainly in the middle and later stage of excavation. Going with the process of the excavation, the field ground settlement outside of excavation continues to expand, and the maximum settlement point gradually moves away from the edge of excavation, and the maximum settlement is also increasing. Within a certain period after completing the process of the excavation, the ground settlement amount continues to increase, but the growth rate greatly reduces, and tends to be stable until the floor construction is completed. The prestressed anchor has a good controlling effect on the ground settlement. The soil settlement could be better controlled as a result of the prestressed anchor restrains the increase tendency of the soil displacement, especially within a certain area of excavation side.