Study On Antiseismic Design Method And Antiseismic Measures Of Tailings Dam

Tailings dam is a soil construction that encloses tailings and its using function,architectural technology and structure static and dynamic characteristics are different fromtraditional hydraulic structure. In recent years, Chinese economy and industry quicklyadvance. Tailings dam rapidly aggrandize along with the demand increase of mine rawmaterials. Basically, tailings dam falls into three basic construction types: upstream, centerline, and downstream. The upstream method is frequently the least expensive, occupyingplace less, technology simply, and it has been used on many dams in the past. However,earthquake disasters show that the upstream method is the most susceptible to excessivepost-earthquake deformation and liquefaction because loose saturated deposits may beincorporated in the mostly upstream zones. There are frequently earthquakes in China, andmoreover, tailings dam is almost permanent soil construction and must be done antiseismicanalysis in design, serve and after closure. Consequently, it is of great importance andurgency to study antiseismic design, stability, deformation, and antiseismic measures fortailings dam. The main research works of this dissertation are as follow:1. The traditional site liquefaction evaluation method usually uses a factor of safety asassessing standard and the specified safety factor is largely determined by engineer'sexperience, however, there is not a liquefaction probability. The paper firstly expatiates on themechanism of sand liquefaction and evaluation method of site liquefaction. Secondly, a limitstate function for site liquefaction is developed based on logistic regression analysis SPTdatum of 200 sets case histories of 23 earthquakes over the world. And then reliability theoryis introduced site liquefaction evaluation and testing datum statistics analysis is used inconjunction with the first order and second moment method to found the liquefactionprobability evaluation model of site. Finally, a bridge site as example is analyzed andcompared to design code's results. The calculation result analyses show the proposed modelreliability is higher. Comparing to the deterministic method of site liquefaction evaluation, itcan not only assess if liquefaction occur but also give liquefaction probability, so it is possibleto make antiseismic design based on risk analysis.2. The calculation process of tailings dam antiseismic design is very complicated in code,so it is necessary to advance a practicably simplified method of earthquake liquefaction andstability analysis. Combining the editing of Antiseismic Design of Special Structures, two-dimensional seismic response analyse are carded out for many 60m high tailings dams.Analyzing the calculative results, acceleration amplification ratio of the crest, damacceleration distributing coefficient and stress reduction coefficient are concluded and thenthe simplified procedure for calculating the cyclic shear stress ratio is founded. Based on theinfluence factors analysis of tailings resistance, the formula of cyclic resistance ratio inChinese design code is simplified. The simplified liquefaction evaluation method only needsmall physical-mechanical properties datum of tailings and degree of seismic intensity andavoid making a lot of soil mechanical tests and numerical calculation to assess liquefaction oftailings. According to the relationship between sand liquefaction resistance factor and excesspore pressure ratio, a simple formula of excess pore water pressure is proposed and applied inSweden slope stability analysis method for tailings dam, and that to overcome the risk forignoring excess pore water pressure in traditional pseudo-static method. The specialities ofantiseismic design code for tailings dam in China and Japan are compared and then usingsimplified method to make antiseismic design for height less than 60 m and within 8 degree ofseismic intensity is proposed.3. Taking a tailings dam as example, dam seismic response, permanent deformation, andthe development process of excess pore water pressure are studied using the finite elementmethod. After comparing the effects of three antiseismic measures, such as falling soakageline, drainage by setting stone column and reinforcing with fibre, a synthetically antiseismicmeasure that is composed of fibre-reinforced in child dam, forcing buttress out of starter damand densification foundation is proposed. It is found that the synthetically antiseismicmeasure produces better antiseismic effect.4. By using the finite element code ALID (Analysis for Liquefaction-InducedDeformation), liquefaction-induced flow deformation of No. 1 Mochikoshi talings dam underdifferent conditions is estimated. Some measures, such as falling soakage line, settingstabilizing column, forcing buttress out of dam and densification foundation are analyzed toassess the effect on restraining liquefaction-induced deformation of tailings dam. Looking ateconomy and the convenience of construction, two synthetical measures, namely densificationfoundation and at the same time forcing buttress out of dam and falling soakage line, areproposed. It is found that the synthetical antiseismic measures can reduce theliquefaction-induced deformation of dam to considerable amount.5. Taking a tailings dam as example, the time history of acceleration, safety factor andslippage in different earthquake excitations are studied and then the effect of reinforcement toimprove dam stability and reduce slippage are analyzed, using the analyse method of slopeseismic stability and slip that is proposed by Watanabe. With inputting horizontal accelerationaugment, it is found that the variety value of horizontal equivalence acceleration and safety factor, exceeding acceleration and lasting time as well as slippage will be aggrandized.Reinforcement with fibre can improve the mechanical properties of tailings and stability ofdam and reduce slippage. Adding fibre space and reducing fibre intension can minish damsafety coefficient.