工作井基坑开挖及吊装全过程土体应力路径研究

Research on Soil Stress Paths During Whole Process of Working Shaft Foundation Pit Excavation and Lifting

以济南市黄河隧道盾构始发工作井为研究实例,根据现场实际施工过程,即基坑分层开挖和吊装施工全过程,运用有限元分析软件ABAQUS进行数值模拟;分析不同区域、不同施工工况下土体单元的大、小主应力及大主应力轴旋转情况。结果表明:随着基坑开挖,坑内土体竖向卸荷,平均压应力不断减小,广义剪应力不断增大,大主应力轴产生顺时针旋转,旋转角变化范围为0°~89.39°,坑外平均压应力不断减小,而广义剪应力几乎不变,大主应力轴顺时针旋转角变化范围为0°~42.78°;在开挖到底后的吊装阶段,吊车正下方的土体单元大主应力旋转角产生较大的逆时针旋转,约为最终旋转角的0~1/4,而吊装对坑内土体的影响较小;吊车下方深1.3倍荷载宽度的三角形范围为吊装荷载的主要影响区,1.3~2.0倍深度范围为次影响区。

Taking the shield launching shaft of the Yellow River tunnel in Jinan city as research example,finite element analysis software ABAQUS was used to conduct numerical simulation according to the actual construction process on site,i.e.the whole process of layered excavation and lifting construction of the foundation pit.Lar ge and small principal stresses as well as rotation of large principal stress axises of soil units in different areas and under different construction conditions were analyzed.The results show that with excavation of the foundation pit,soil in the foundation pit vertically unloads,average compressive stress decreases continuously,generalized shear stress increases continuously,and the large principal stress axis rotates clockwise with rotation angle ranging from 0°to 89.39°.Average compressive stress outside the foundation pit decreases continuously,while generalized shear stress is almost unchanged,and the large principal stress axis rotates clockwise with rotation angle ranging from 0°to 42.78°.In lifting stage after excavation to bottom,the main stress rotation angle of the soil unit directly below the crane produces a larger counter clockwise rotation,which is about 0 to 1/4 of the final deflection angle,while the lifting has less influence on the soil in the pit.The triangle range 1.3 times of load width under the crane is the main influence area of lifting load,and the range 1.3 times to 2.0 times of the depth is the secondary influence area.