Centrifuge Test Research On Pre-stressed Anchor Flexible Retaining System

In recent years, there are more and more super high-rising buildings and the rail transit is in its full swing, stricter demands are set on the deep excavation with the increasing shortage of urban space, what's more, the demands on deformation and stability of the excavation support system becomes more and more strict. Fortunately, the development of the pre-stressed anchor flexible system solved that problem well. Pre-stressed anchor flexible system is a new supporting method for soft rock and the soil better than hard plastic clay, and it has the advantages of saving space, economical, short construction period, easy construction. Extensive research has been done with the method of numerical simulation and theoretical analysis by many researchers, but these two method cannot give a quantified analysis of the anchored slope, so it is necessary to do a further research by centrifuge modeling test. In this article, centrifuge modeling test would be conducted on the drum centrifuge of DLUT with the supporting of the soft rock excavation of Dalian Shengli Plaza as the model sample. This paper is mainly focused on the following contents:Aiming to solve the problem that the rock material of the prototype is not easy to get and distributes uneven, the similar material which contents barite powder, mica film, gypsum, quartz and water is developed in this paper. Six factors was selected and every factor had five variable levels in the orthogonal design, and a set of specimen mold was made for the 25 mixing ratio tests in which the mass, dimension, tension and compressive strength, elasticity modulus was measured. Then sensitivity analysis was conducted to find out how the factors and levels of the material influenced on the physical-mechanical properties and regression equations were built by using multiple regression analysis on the experimental results. The results showed that physical-mechanical properties of the similar material of different proportions changed in a wide range, and the property of the extreme soft rock was simulated well and met the requirements of this subject. The density increased with the increase of barite powder content; compressive strength was influenced the most by water-binder and decreased with the increase of water-binder ratio which had a little influence on other properties; quartz content played a dominant role in the internal friction angel the material and the internal friction angel increased with the increase of the quartz content; the mica film made many discontinuity planes in the similar material and had great effect on the tensile strength and cohesion.In the centrifuge test, the dimension of the model was determined according to the characteristic of the drum centrifugal of DLUT, and then the model box,inspection box and weight balance box was manufactured. Aiming to simulate the steps of foundation pit excavation, a stepped excavation system which was attached three LVDTs was designed and lights and a sport camera was installed in the drum. Basing on these, centrifugal test of pre-stressed anchor flexible supporting system with different pre-stress was done with the steps of simulate consolidation, stepped excavation and acceleration to failure, and the deformation and failure states were observed. The results showed that the centrifuge test could simulate the force and deformation of the soft rock excavation anchored by pre-stressed anchor well; the pre-stressed anchors with appropriate pre-stress could effectively reduce the horizontal and vertical displacement of the crest, and the global stability of the excavation increased with the increase of anchor pre-stress; both tension crack and local slippage failure showed up during the experiment, the tension crack which started from the back of anchorage zone appeared before local slippage failure. It's obvious that the anchorage zone could be reinforced well by pre-stressed anchor.