近海潮汐作用下深大基坑围护结构力学响应规律分析

Mechanical Response of Deep Foundation Pit Retaining Structure Under Offshore Tide

为更好探明潮汐环境下近海基坑围护结构力学响应问题,提出了以实测墙边地下水位数据为基础的模型边界潮汐地下水位振幅反演分析方法,分析了不同振幅潮汐作用下地下水渗流衰减规律,并进一步研究了不同振幅潮汐地下水作用下基坑围护结构的力学响应规律及响应机理。研究表明:基于地下水渗流衰减规律的潮汐地下水位振幅反演分析方法不用对实际近海区域地质构造信息进行详细考虑,即可得到包含基坑的小范围区域分析所需的边界地下水位,在近海工程潮汐影响分析中具有良好的应用价值;靠海侧地连墙与强透水层直接接触区域以及坑中坑钻孔灌注桩更多受余弦型潮波作用,两者水平侧移摆动随时间呈“类正余弦型”变化规律,而靠海侧地连墙其他区域和背海侧地连墙由于自身协同变形和受其他地层不同相位孔压的作用,呈前后不对称的“不规则槽型”变化规律;潮汐作用下,背海侧围护墙体侧移振幅沿深度增大逐渐降低,但靠海侧围护墙体侧移振幅、弯矩增量分布以及内撑轴力与地层透水性密切相关,特别在进行受较大潮汐影响工程的结构设计时,应尽量避免静力工况最大侧移位置和弯矩峰值位置与强透水层位置重合。

To explore the influence of offshore tide on the mechanical response of the retaining structure of foundation pit,the dynamic water level boundary input method is adopted to analyze the attenuation law of groundwater seepage under the action of tides at different amplitudes.Based on the measured groundwater level data near the retaining structure,the inversion method for tidal groundwater level amplitude at the numerical model boundary is established,and the mechanical response of the retaining structure of foundation pit under the action of tidal groundwater at different amplitudes are then studied.This study indicates that with the help of the inversion method for tidal groundwater level amplitude based on the attenuation law of groundwater seepage,the boundary groundwater level required for the small-scale regional numerical analysis of the foundation pit can be obtained without considering the geological information of the actual offshore area in detail,which has a good application value in the analysis of the tidal effect on offshore engineering.The direct contact area between the sea-side retaining structure and the strong permeable layer and the drilled grouting pile in the pit-in-pit are more affected by the cosine tidal waves,with the horizontal lateral swing of these two parts showing a‘sinusoidalcosine similarly’change rule with time.However,due to the self-collaborative deformation and the effect of pore pressure loads with different phases in other strata,the lateral time-history curves of the back-sea side retaining structure and the other regions of the seaside retaining structure show an asymmetric‘irregular groove’change rule.Under the action of tide,the lateral displacement amplitude of the retaining wall at the back of the sea gradually decreases with the increase of depth,but the lateral displacement amplitude,the bending moment increment distribution and the internal bracing axial force of the retaining wall at the sea side are closely related to the permeability of the stratum.Especially in the structural design of the project affected by large tide,the maximum lateral displacement position and bending moment peak position of the static working condition should be avoided to coincide with the position of the strong permeable layer as far as possible.