Research On Stress Mechanism And Anti-corrosion Of Micropile Composite Anti-slide Structure

Retaining structures are the indispensable mechanical control measure in slope engineering. Following intensive study for landslide hazardous, research international and domestic and disaster prevention and control are unprecedented actively. Based on perfection of existing facilities, the prevention is going to the direction of light type, small-size and economy development. Light retaining system and composite structure are come into sight of researchers. The anti-slide micropile composite structure is one of the most representative light composite retaining structures.Rely on "Research on Prevention Technology of Landsilde and High Slope along the Highway in Qinghai Plateau Special Condition" of Qinghai Provincial Communications Department, "Research on Disaster Mechanism and Prevention Technology of High Slope Composed with Red Bed Accumulation Body" of Sichuan Provincial Communications Department, and "Research on Force Mechanism of Small-size Steel Pipe Pile" of Ministry of Land and Resources, the paper conducted the research. The study decomposes composite structure to single pile with different tip restraint condition, and calculated the structure displacement and internal force by Winkler Elastic Foundation Beam Method, Bridge Pile Foundation Calculate Method and p-y Curve Method. The study conducted model experiments indoor and analysed deformation and force mechanism of composite structure by horizontal load, and also conducted static and dynamic numerical simulation analysis for its failure mechanism. The paper discussed micropile corrosion mechanism, conduced 4 anti-corrosion basic experiments, and classified project level environmental effects. At last, the paper developed a new type of anti-corrosion admixture MPC-I. Some conclusions are drawn below.1. Micropile can be classified by 5 aspects, which are loaded types, working mechanism, layout pattern, construction technology, strengthening use.2. While reinforce rock bedded slope, the micropile function mainly embodies resistance to shear. It's related to material properties, dip angle, cross sectional area, length of shear and so on. While reinforce soil slope, micropile in rock-soil make up the composite skeleton, and consist an organic whole. In this moment, pile-soil complexus and bending resistance capacity of composite structure provide reinforce mechanism. The soil pressure distribution is trapezoid approximately, and its point of resultant force at 0.381H apart from bottom. While reinforce landslide, shear and bending resistance performance provide anti-slide capacity, especially its unique tensile resistance;3. Without regard to torsion, the structure can be simplified as lateral loaded rigid frame, decomposes to single pile with different tip restraint condition. The paper calculated the the structure displacement and internal force by Winkler Elastic Foundation Beam Method, Bridge Pile Foundation Calculate Method and p-y Curve Method. Rely on the Winkler elastic foundation beam theory, improved solve method of lateral loaded single pile stiffness coefficientρi. The paper provided applicable condition for different calculate method;4. In the same condition of model test indoor, micropile bearing capacity is greater than anti-slide retaining wall, less than anti-slide pile. For single micropiles unit(3×3), soil pressure of micropile which loaded not directly is far less than lateral load, only about 10% of load. The distribution of soil load is greater in the middle than tips. The most area of pile is tensile near load. And the greatest moment is about 1/2 length of pile above slide face which loaded directly.5. The anti-corrosion basic experiments showed that cementation power of micropile and rock-soil can be increased by water cement ratio decreasing. Hardware cloth and synthetic fiber can improve distribution range and value of pressure stress, improve bending resistance performance, prevent wide and deep crack generate. The hardware cloth can also postpone the corrosion of the main bar;6. Base on the current codes, rely on the corrosion by engineering properties and environment, the paper classified 4 categories for engineering environment. That is freeze thawing environment, carbonization environment, chloride environment and chemical corrosion. In accordance with micropile reinforce characteristic, the project considered micropile as a general perpetual slope reinforce structure, and its service life is 50 years;7. According to weak-medium corrosion environment, the project developed a new type of anti-corrosion admixture MPC-I. The MPC-I 28d strength of pressure, break and tensile is 4.27%,40.53% and 19.74% greater than the same grade cement plaster. The results showed that MPC-I can increase basic physical mechanics index of the same grade cement plaster. Its backfin ratio reduced about 25%, indicate MPC-I can improve plaster toughness in a certain extent. MPC-I have obviously superiority than Portland cement plaster and sulphate aluminium cement plaster in economic effectiveness and social benefits.