Effect of shield tunneling construction on bearing capacity of foundation of existing buildings and stability analysis of reinforced soil
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摘要: 针对目前盾构施工既有建（构）筑地基加固依靠经验，缺乏完善理论作为支撑的现象，有必要研究盾构掘进中、离开后既有建（构）筑地基承载力影响机理及加固后土体稳定性。为了解水泥土加固体的受剪工作状态，开展水泥土三轴试验，结果表明，当偏应力达到屈服之前，（σ1-σ3）-ε1关系近似直线，应变很小，且加固体与未加固土抗剪强度相差甚远，稳定性分析时，不考虑加固体位移及其外侧未加固土对剪力的分担。盾构掘进中，其周围土体受到挤压产生的剪应力，扩散至桩侧形成附加正摩阻力，基桩承载力提高；盾构离开后土体卸荷，桩侧产生负摩阻力，基桩承载力降低。盾构施工中加固体上段内侧受被动或主动土压力，外侧及下段受静止土压力，土压力差产生剪应力，潜在滑动界面产生拉、压应力，并导出加固后土体复合滑动面安全系数公式，通过工程实例验算加固体强度及加固后土体的稳定性。Abstract: The current foundation reinforcement of existing buildings (structures) in shield tunneling construction depends on experience and lacks perfect theory as support. To better this situation, this paper studies the influence mechanism of bearing capacity of existing buildings (structures) in shield tunneling and after leaving and the stability of soil after reinforcement. In order to understand the shear state of cement-soil reinforcement, the triaxial test of cement-soil is carried out. The results show that before the deviating stress reaches the yield point, the relationship of (σ1-σ3)-ε1 is approximately linear and the strain is very small, and the shear strength of the reinforcement is far from that of the unreinforced soil. In stability analysis, the displacement of the reinforcement body and the share of shear force of the unreinforced soil outside the reinforcement body are not taken into account. In shield tunneling, the squeezing of the surrounding soil to produce shear stress diffuses to the pile side to form additional positive friction resistance, and thus increases the bearing capacity of the pile. After the shield tunneling leaves, the soil unloads, the negative friction resistance occurs at the pile side, and the bearing capacity of the pile decreases. In shield tunneling construction, the upper part of reinforcement body is subjected to passive or active earth pressure, the outer part and the lower part are subjected to static earth pressure, the difference of earth pressure produces shear stress, the potential sliding interface produces tension and compression stress, and the formula of safety factor of composite sliding surface of soil after reinforcement is derived. The strength of reinforcement body and the stability of soil after reinforcement are checked through engineering examples.
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图 2 盾构施工纵向扰动分区
Figure 2. Shield tunneling construction longitudinal disturbance partition
图 3 盾构施工横向扰动范围与受影响建筑物关系
Figure 3. Relationship of transverse disturbance range and affected buildings in shield tunneling construction
图 4 盾构周围土体剪应力分布τ-r曲线
Figure 4. τ-r curve of shear stress distribution of soil around the shield tunnel
图 6 加固体土压力及加固后土体抗滑稳定计算示意图
Figure 6. Schematic diagram for calculating earth pressure and anti-sliding stability of reinforced soil
图 8 既有基础底板下注浆控制沉降
Figure 8. Grouting control settlement under the existing foundation floor
图 10 平和打包厂地基加固示意图
Figure 10. Sketch of foundation reinforcement in Pinghe Dabao Factory
图 11 开挖轮廓壁附加剪应力计算图
Figure 11. Calculation diagram of additional shear stress on excavation contour wall
表 1 土样的基本物理力学性质
Table 1. Basic physico-mechanical properties of soil samples
土层 容重γ/(kN·m-3) 相对密度ds 含水量wB/% 液限wl/% 塑限wp/% 压缩模量Es/MPa 粉质黏土 18.75 2.72 31.39 33.44 19.81 5.23 
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表 2 加固体剪应力计算
Table 2. Calculation of shear stress of reinforced body
施工阶段 上段长度/m 下段长度/m 被(主)动土压力/(kN·m-1) 桩外侧E0/(kN·m-1) 压力差/(kN·m-1) 平均剪应力/kPa 掘进中 11.8 8.5 1 627.2 601.6 1 025.6 176.8 离开后 11.3 8.7 443.6 566.0 122.4 21.1
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