Research On Micropile Reinforcing Mechanism And Application Of Expansive Soil Landslides In Shallow Accumulative Layer

Once micropile has been used in landslide reinforcement, it immediately gains its concern form the academic and engineering circles because of its small pile diameter, quite large lenth-diameter ratio, and its small flexural rigidity, however, due to its short time application, its bearing mechanism and failure modes are not fully grasped in depth, especially the research on how to develop the roles of micropile reinforcement on landslide, and the ways in which composite structure of micropile works on anti-slide and reinforcement are not plenitudinous. Furthermore, there is not a relatively comprehensive theoretical system of micropile calculation and design method, which largely affects the application and promotion of micropiles. Therefore, it is really important to study on load of supporting, deformation, failure modes of micropile, design theory, engineering application technology and construction technology in line with practical engineering.South mountainous region of Shaanxi Province lies in Qinba mountains in China well known for its complex geological structure, rock mass crushing, and special climate, which make it to be a high incidence zone of geological disasters and the landslide prone and worst-hit areas in China. In total, there are7109geological disasters in the area including6353landslide disasters which accounts for89.4%of the total. Based on a statistical analysis of survey of3442landslide disasters, it is found that shallow landslide accounts for51%, middle type makes up for42%, deep slide7%, and part of expansive soil landslide. For this reason, Landslide disaster prevention has become an important task for local governments.Based on the project named "A study on the key technology of prevention and control of landslides in Southern mountainous region of Shaanxi Province", and with different types of landslides characterized by region geographical features and anti-sliding piles as the main research object, this paper first puts forward the categories of accumulative landslide under complex geological environmental conditions in south mountainous region of Shaanxi Province from six aspects such as thickness of landslide body, angle of landslide, size of landslide, lithology, stability and its formation mechanism. And then it carefully probes genetic mechanism for rainfall induced accumulative landslide, the formation of expansive accumulative landslide and its failure modes. Later, it systematically analyzes of load transfer of micropile strengthening accumulation of expansive soil landslide, load distribution rule, the stress, deformation characteristics and failure modes by numerical simulations, in-door physical model test and on-site monitoring test, summary of micropile engineering application. And it also analyzes the load-bearing characteristics of micropile under the influence of the factors such as different pile spacing, row spacing, anchorage depth, pile top restraint, and rainfalls, while its reinforcement mechanism, design principles and design techniques on expansive soil landslides are further discussed. Therefore, the research attaches theoretical and practical importance to design theory of micro pile treatment for landslide hazards in southern mountain areas and development of in-site construction technology.Major findings go as follows:1. This paper first presents the categories of accumulative landslide under complex geological environmental conditions in South mountainous region of Shaanxi Province, and then analyzes the development characteristics and factors of accumulative landslide, and also probes formation and failure mechanism of landslide caused by rainfall induced, and shallow expansive soil.2. By means of numerical simulations, physical model test, on-site monitoring test, a systematic study on the reinforcement mechanism of micropiles on the shallow accumulation layer of expansive soil landslide in mountainous areas in southern Shaanxi was made.3. Reasonable pile spacing, row spacing, pile-soil interaction and row pile load-sharing ratio, anchorage depth, even the effect of tie beam and analysis of sensitive factors combined with rainfall patterns have been studied, and the design on22accumulative landslides were made,3failure modes of micropile structure were put forward, then the design principle, design thought, design method and design processes of reinforcement of micropiles working on accumulative landslides of expansive soils in southern mountainous region of Shaanxi Province was first proposed.