Study On Caculation Theory For Anti-sliding Structure Of Micro-piles

Micro-pile is a type of small diameter bored pile of which the diameter is between 100 and 300mm.At first, micro-piles is considered as a whole structure to bear vertical loads. However, in recent 20 years, due to the development of micro-pile technology, the views on bearing capacity of micro-pile have been changed. It is gradually realized that single micro-pile is also able to resist lateral loads. It is helpful for engineers to apply micro-pile in supporting projects, especially in which the construction condition is constricted. As a result of the advantages of applying micro-pile, attentions are paid to micro-pile. and micro-piles are used in foundation pit supporting, slope controlling and reconstruction projects after earthquake. However, the theory on micro-pile applied in slope engineering falls far behind practice. In view of the research situation, it is an urgent task to start researches on anti-sliding mechanism of micro-pile composite structure.In this paper, on the basis of collecting research data on micro-pile at home and abroad, micro-pile is classified into different types. The micro-pile composite structure studied in the paper is one kind of micro-piles. The emphasis of this paper is laid on the anti-sliding mechanism of micro-pile composite structure. The design method of anti-sliding micro-pile composite structure is discussed by considering both model test and theory research. And a project case is designed on the basis of theories discussed in this paper. By deep studies in this thesis, following conclusions are drawn:(1) collecting data on application and theory calculation of micro-pile at home and abroad and classifying it into different types. The anti-sliding mechanism of micro-pile is analyzed and the design flow chart of micro-piles system is provided.(2) the two kinds of calculation formulas of landslide thrust is presented by considering two different safety coefficient definition. And it is considered more reasonable that the landslide thrust is calculated by defining safety coefficient as the ratio of shear strength and shear stress on the sliding surface. The distribution form of landslide thrust is discussed briefly. Then the spacing of micro-pile composite structure is defined and the theoretical calculation formula is deduced, the application condition of the formula is also discussed.(3) Taking 3×3 micro-pile group as an example, mechanical model is established by reasonable hypothesis and simplification, and two kinds of estimating methods are proposed, one of which is linear displacement method and the other of which is parabola displacement method. By use of the strong symbolic operation function of Matlab, the internal force expression of micro-pile above slip surface is proposed.(4) Model test is done to study the anti-sliding mechanism, deformation trend, distribution form of loads acted on micro-pile composite structure. The moment of micro-pile model is calculated by the data obtained from model test, thus analyzing the anti-sliding mechanism of micro-pile and load distribution.(5) Combined with the practical project, the internal force of micro-pile composite structure is computed by the two kinds of theoretical formulas respectively. And the reliability of two kinds of displacement hypothesis methods are verified by comparing the calculation results.