Study On Loaded Mechanism And Design Calculation Theory Of Micropile Structures For Slope Stabilization

With the development of infrastructure construction, a large number of slope diseases are met in the railway, highway, dam and mine construction. Some slope diseases need to be cured hurry up, just as slope failure induced by rain, the road being cut off by landslide and especially so many slope failures caused by earthquake in Wenchuan on May 12th. These Slope failures are significant hazards to public and private infrastructure, and their maintenance and repair is difficult because the conventional stabilizing methods are too limited to use. Stabilization through the installation of micropiles may solve these problems much easily, which is a relatively new technique for stabilizing slope that has been used successfully in several instances in China and abroad. Micropile technology was evolved continuously since its introduction by Fernando Lizzi in the 1950s. Over the past 20 years, advances in drilling equipment and techniques have extended the applicability of micropiles techniques to slope reinforcement. However, designs for existing applications are immature and have, thus, generally been very conservative out of necessity.Based on case stories, the loaded mechanism of micropile structures and the design method of micropile structures in slope stabilizing are studied in detail by multiple method including site investigation, analytic solution, numerical analysis, modeling test, in-situ experiment and so on.(1) Based on the method of grouting, the micropile classification system is developed. The paper classifies the foundamental types of micropile structure in practice.(2) It presents the method for getting the internal force of single micropile and its bearing capacity.(3) Based on the p-y method, it presents a rational method for the analysis of micropile structure assuming the limit state is failure of the micropile in bending.(4) By numerical analysis, the soil-micropile interaction is silulated based on the explicit-finite-difference code, FLAC3D. The stabilizing mechanism of micropile, the bearing capacity of micropile structure and its effect factors, differential loading among different rows of micropile are analyzed.(5) Based on the model experiments, the bearing capacity and failure model under sliding force between common anti-sliding piles and micropile groups was compared. It was shown that, the micropile group had good anti-sliding ability. Taking 2 mm as the acceptable displacement value of structure in model experiment, the bearing capacity of micropile group was somewhat less than the common anti-sliding pile.(6) Based on the stabilization of DH1 landslide project, in-situ testing study on the mechanical behavior of micropile structure and displacement characteristics of landslide was carried out. The results were compared to a solution for micropile using p-y method. Based on the comprehensive study, it was shown that the stabilizing effect of micropile structure was active and use of analysis method in this paper in design of micropile structure is reasonable.(7) Some micropile structures were adopted in the practice engineering, and the design of the micropile structure was performed using the design approach described in this paper. Several case histories of micropile engineering were presented.