Research On Reliability Of Isolated Shallow Foundation & Its Application In Engineering

With rapid economic and constructional development in China, all kinds of towering constructions have widely been built in various fields. Generally speaking, towering construction is paid more attention because of its following characters: very high, small cross-section, important role from lateral loads on its structure as well as its strong randomicity. On the other hand, shallow foundation owns more wide applicable scope and important research foreground because of its wide application and low cost, so the type of the foundation is often taken as the first scheme during the design. In order to meet the practical need of the project, the research subject in the paper is about the shallow foundation design of transmission line tower, mainly includes the following aspects: capacity of subgrade, overturn stability, punching capacity and concrete'endurance, and their design theory of degree of reliability, and the innovations about the subject are expounded in detail as followings: (1) The three-dimensional calculation formula of subgrade limit capacity is bought forward on the limit analysis method, in which the concept is very clear and the form is very simple. Its good practical value in engineering is validated by comparing with the recommended formulas in cods. And the three-dimensional formula is amended on the basis of comparing with the test data; the calculation result of the formula is very similar with the test data. On the basis of theory analysis and reliability, the amended three-dimensional calculation formula and general ones are analyzed by reliability method, and the amended three-dimensional calculation formula is compared with Han's formulation of subgrade capacity. (2) The factors effecting the incline and settlement of foundation are firstly researched in this part. The 3-Dimensional calculation formulation on lateral limit capacity of shallow foundation with short column under lateral load is brought forward by the limit analysis method, which takes use of the condition that the subgrade are yielded partly as curial condition. The value of the 3-Dimensional calculation formulation in engineering is validated by the practical project. The lateral limit capacity and related indexes are analyzed by the reliability method, and the reliability indexes of subgrade settlement are researched on the basis of analyzing and concluding the existing methods and models of calculation. 　(3) The settlement and capacity of subgrade are analyzed through numerical simulation by Ansys and 3D-FLAC. The results of numerical simulation are used to compare with the calculation of theory analysis, which are very close, so they show that the theory analysis and the induced calculation formulation in the paper are right and precise. (4) On the basis of the punching experiments and theory research, the following aspects are completed in the part: 1) the parameter ρis taken into account, and the effects of ratio of steel in motherboard of foundation on punching capacity are analyzed through experiments; 2) the effects of foundation claying on punching capacity are tested and analyzed by experiments; 3) The punching angle is amended on the basis of testing and analyzing the failure specimens, as well as the perimeter of cross area of failure with other'production; The calculation formulation of punching capacity on isolated foundation on the basis of the above aspects. And the degree of reliability of the calculation formulation is researched, and the related design indexes on punching capacity are analyzed. (5) First, the measures of improving the concrete'endurance and related strengthening principal have been analyzed and researched. The following contrastive experiments were completed, they mainly included the fowl lows: 1) anti-pervasion and corruption experiments; 2) anti-frozen & melted experiments; 3) anti-sulphate experiments; On the basis of the series of experiments and the research on degree of reliability, the principle of optimizing and choosing on the concrete of shallow foundation are put forward. (6) The former design of the new type of shallow foundation of transmission line tower from Sichuan Power Information Limited Co. is optimized through reliability design method on the basis of the above achievement of theory research.