Stress State Analysis Of A Prestressed Concrete Liner Based On Monitor Data

Xiao Langdi sediment tunnel liner is the first case using double-looped unbonded prestressedly concrete lining around the hydraulic structure. This new type of structure is more simple construction and also good at anti-permeability cracking compared with traditional bonded prestressed concrete lining. During the construction period, the sediment tunnel liner instrumented with concrete strain meters, reinforcement meters, zero stress meters, anchorage load cells, joint meter, convergence meters and piezometer, totally 160. The tunnel were built from March 1998 to June 1999, at then reached to the full operating conditions. During the past twelve years, the instruments collected a lot of monitoring data. In this paper, the development of concrete stress and concrete creep over prestressing process for Xiao Langdi sediment tunnel liner were investigated based on the monitoring data of instruments. In the operational period, also research in the influence of various temperature and water pressure to the tunnel.By establishing a reasonable tensioning program and data collecting program, the total strain obtained from monitoring data were separated into elastic strains, concrete creep and the strain due to the prestress loss during the prestressing process. During the operation of the tunnel, the thesis reaches the stress and strain distribution in concrete with the methods of mathematical statistic analysis under different temperature and different water pressure conditions. Depending on the research, we may draw the following conclusions:(1) During the prestressing process ,the concrete creep account for 20% to 30% of the elastic strains . So the effects in the analysis of pre-stressed, it can't directly use the strain obtained from monitoring date when analysis the prestressing effect of the tunnel.(2) Concrete creep is linearly related to the existing stress and the loading time t, which can be expressed asε=ασt , the coefficientαis not a constant but a variable relating to the stress and constraint conditions.(3) The distribution of stress on average is uniform in the tunnel except the part around the boxouts after the prestressing process. The average stress in the end of the construction block is -8MPa, in the middle of the construction block is -6.7MPa. The middle part's stress is more uniform than the end part's. (4) Concrete compressive strain and temperature stress increase with increasing temperature, decrease with decreasing temperature during the operating. This rule is more obvious in the end of the construction block and the inside lining. In the analysis period, it has a maximum stress due to the temperature changes is-2.57MPa in the concrete, so must pay enough attention to the impact of temperature changes.(5) Concrete compressive strain decreases with the increase of head, with the decrease of head higher. Different parts of the concrete lining has different impact with the head changes, it have more influence on the end of the construction block than in the middle , on average the head is increased by 1m, reducing 0.32×10-6 pressure strain in the concrete.