基于连续-非连续单元法复合岩土体穿层预应力锚杆受力分析

CDEM-based Force Analysis of Pre-stressed Bolts Crossing Composite Rock-soil Strata

边坡工程施工过程中,采用预应力锚杆施加预紧力可约束岩土体开挖后应力重分布作用产生的过大变形,增强岩土体自身强度。针对某边坡工程中预应力锚杆穿过多层岩土体的荷载传递及锚固承载特征问题,基于连续-非连续单元法(continuum discontinuum element method,CDEM)数值模拟方法,考虑复合岩土体中岩土层理结构面之间的非连续以及块体-杆件耦合计算问题,建立二维边坡复合岩土体桩锚结构数值模型,揭示复合岩土体中穿层预应力锚杆的受力特征。研究结果表明:岩土层与锚固体极限粘结强度标准值越大,产生的轴应变越小,轴力传递效应越弱,锚杆轴力衰减率越高;张拉第二、三根锚杆时,其杆体作用在张拉第一根锚杆之后岩土层自平衡后的应力场内,岩土体结构面产生的错动以及剪切蠕变导致预应力快速损失,其损失率比第一根锚杆大3%~4%;该边坡工程中锚固角度在25°左右最优,既能控制水平向受力,也能防止坡顶沉降,桩锚结构整体稳定性较好。耦合复合岩土体建模-桩锚结构承载-参数优化,深入研究复合岩土体中穿层预应力锚杆受力及其参数影响规律,研究结果将指导复合岩土体中桩锚结构设计与施工。

During the construction of slope engineering,adopting pre-stressed bolts to apply pre-tightening force can restrain the excessive deformation caused by stress redistribution after excavation of the rock-soil mass,and enhance the strength of the rock-soil mass itself.Aiming at the load transfer laws and anchor bearing characteristics of pre-stressed bolts crossing multi-layered rock-soil mass in a slope project,the discontinuity between the rock-soil bedding structure planes in the composite rock-soil mass was considered based on the CDEM(continuum discontinuum element method)numerical simulation method as well as the block-rod coupling calculation problem.A two-dimensional numerical model of the pile-anchor structure of the composite rock-soil mass of the slope was established to reveal the stress characteristics of pre-stressed bolts crossing the composite rock-soil mass strata.The research results show as follows.The larger the standard value of the ultimate bond strength between the rock-soil stratum and the anchor,the smaller the axial strain,the weaker the axial force transmission effect,and the higher the axial force attenuation rate of the bolt.When the second and third bolts are tensioned,the rods act in the stress field caused by the self-balance of the rock-soil strata after the tension of the first bolt,and the dislocation and shear creep of the rock-soil structure surface will lead to quick loss of pre-tightening stress.The loss rate is 3%~4%larger than that of the first bolt.In this slope project,the optimal anchoring angle is about 25°,which can not only control the horizontal force,but also prevent the settlement of the top of the slope,and the overall stability of the pile-anchor structure is satisfactory.The composite rock-soil modeling,pile-anchor structure bearing,and parameter optimization were coupled,aiming at studying the force mechanism and parameter influencing law of pre-stressed bolts crossing composite rock-soil mass.The results will guide the design and construction of pile-anchor structure in composite rock-soil mass.