潮汐波动带偏载超深基坑变形控制数值模拟分析及工程实践

Numerical Simulation Analysis and Engineering Practice of Deformation Control of Ultra⁃deep Foundation Excavation Under Eccentric Load of Tidal Wave Zone

随着我国地下空间的持续开发,穿江越河及邻江邻河的地下工程项目越来越多,这类项目往往伴随邻山且邻水的工程特定环境,其深基坑工程变形机制和影响效力尚不明确,相关控制手段亦少有研究。依托杭州市某紧邻钱塘江的市政隧道工程,考虑潮汐波动影响对36.4m超深大偏载基坑变形进行了三维数值模拟分析,提出相应变形控制方法并进行工程实践。研究表明:通过依托工程基坑内外水位监测数据的理论分析和数值求解,建立基坑渗流场时空演化模型,得知潮汐水流进入土层边界时的水头衰减较大,在渗流路径中,水头变化较稳定,基坑附近地下水对潮汐循环荷载的响应有明显滞后性,基坑周围产生较高孔隙水压力。运用有限元软件采用修正Mohr-Coulomb弹塑性本构模型,建立偏载深基坑开挖及周围环境影响的数值模拟三维模型,为模拟潮汐波动带的影响,简化在基坑河流底部分别施加25kPa和65kPa均布荷载,得出相较于普通环境,潮汐动力影响下的基坑变形控制更应引起重视,通过三维数值模拟及工程实践,验证了超深基坑采用“1 200mm地下连续墙+5道混凝土支撑+2道钢支撑”的联合支护形式是一种有效的临近钱塘江超深基坑的支护对策。

With the continuous development of underground space in China,there are increasingly more underground engineering projects crossing or adjacent to rivers.Such projects are often accompanied by the unique environment of the project adjacent to the mountains and rivers,whose deformation mechanisms and influence effects of deep foundation pit engineering are not clear,and their relevant control methods are rarely studied.Based on a municipal tunnel project adjacent to the Qiantang River in Hangzhou,the seepage law of the tidal wave zone was systematically studied.The numerical simulation analysis of the deformation of the 36.4 m ultra-deep and large eccentric load foundation pit was carried out,the corresponding deformation control method was proposed,and engineering practice was carried out.The research shows that by relying on the theoretical analysis and numerical solution of the water level monitoring data inside and outside the foundation pit of the project,the spatial and temporal evolution model of the seepage field of the foundation pit is established.It is known that the head attenuation is large when the tidal water enters the soil boundary.In the seepage path,the head change is stable,the groundwater near the foundation pit has an obvious lag in response to the tidal cyclic load,and high pore water pressure is generated around the foundation pit.Based on the modified Mohr-Coulomb elastoplastic constitutive model,a three-dimensional model for numerical simulation of deep foundation pit excavation under partial load and its surrounding environment is established using ANSYS software.To simulate the influence of the tidal wave zone,it is simplified to apply a 20kPa uniform load at the bottom of the foundation pit river.It is concluded that,compared with the ordinary environment,the deformation control of foundation pits under the influence of tidal power should be given more attention.Through three-dimensional numerical simulation and engineering practice,it is verified that the combined support form of“1200mm underground continuous wall+5 concrete supports+2 steel supports”is an effective support countermeasure for an ultra-deep foundation pit near the Qiantang River.