特大圆形深基坑围护结构的内力变化规律

地下连续墙和内衬构成了阳逻长江公路大桥南锚碇特大圆形深基坑的围护结构。根据主筋的4种受力状况反演了围护结构的弯矩和轴力,发现了围护结构的内力具有如下规律:(1)内衬的弯矩在基坑开挖和内衬浇筑过程中出现周期性波动,内衬弯矩曲线出现周期性峰值。轴力多为压力,拉力很少且数值很小。(2)地连墙的弯矩变化规律与内衬迥然不同。随着内衬施工的进行,各深度处的弯矩和轴力变化曲线依次呈现"先大幅波动、后平稳变化"的趋势。轴力多为压力,且后期压力比初期大。(3)内衬浇筑和基坑开挖施工是导致开挖面地墙弯矩大幅波动的直接原因。其中,内衬混凝土水化放热产生一个正弯矩作用,使得上方各道内衬的内侧钢筋受压,而基坑开挖则使得其作用逐渐弱化。(4)温度升高在内衬中产生一个正弯矩作用,而温度降低使内衬中产生一个负弯矩作用。

The concrete diaphragm, along with concrete inner lining, functions as the bracing system of the super deep round foundation pit, which is used for the southern abutment foundation of Yangluo Yangtze River Highway Bridge. Upon amending theories previously used, a new theory of inverse analysis is developed, with which the internal force can be calculated on the basis of the measured stress of the main bars, which is classified into 4 cases rather than only one case. The back analysis result indicates that the internal force shows following regulations: first, the bending moment of inner lining wall changes periodically during concreting and excavation of the foundation pit. The axial force mainly behaves as pressure. Secondly, on the contrary to the regularity of inner lining wall, the development curve of the bending moment and axial force of diaphragm wall shows a trend of 'fluctuating firstly, and changing steadily afterwards'. Thirdly, the direct reason for remarkable fluctuation of bending moment of diaphragm wall is concreting of inner lining wall and excavation of the pit. The hydration heat of concrete of inner lining wall crates bending moment in the lining wall, making the inner main bars in upper inner lining wall to be compressed, whereas the following excavation decreases the action of the moment. In the end, the increase of weather temperature serves the same action as hydration heat, while the decrease of weather temperature does oppositely.