Internal forces of underground structures from observed displacements

This paper presents a method that provides a solution to the long standing problem of calculating internal force distributions based on displacement measurements of piles, retaining walls and tunnels. It is based on the principle of virtual work and therefore, analytically correct in the linear elastic range, and works without the need of any boundary conditions.The validation against multiple case studies, showcasing loading conditions including seismic, earth pressures, external loads, or sliding slopes in multiple ground conditions and construction processes, confirms its flexibility and applicability to any structure where displacements are observed. Although the validation presented here applies to bending moments and axial forces, the method is theoretically correct and applicable to other internal force distributions.     

Attenuation of blast vibration in tunneling using a pre-cut discontinuity

A pre-cut discontinuity, similar to the pre-splitting around a tunnel periphery, is introduced to investigate the attenuation of the wave propagation due to tunnel blasting. For this, two empty holes were drilled to support the sawing jigs and a wire sawing machine with embedded industrial diamond wire was used to cut an artificial discontinuity near the initial blasting holes at the tunnel face. The peak particle velocity with/without pre-cut was measured during tunnel blasting and the effect of the pre-cut method was quantitatively accounted for, although, due to limited time and unfavorable field conditions, the cutting depth was not able to reach the initial design depth. Numerical analysis was also performed in order to model the tunnel geometry and blasting procedure. For this, a commercial package called UDEC was used and the accuracy of UDEC was initially proven by an analytical solution of the reflection and transmission of the incident wave. Various parametric studies including sequential detonations were performed and the reduction factor of attenuation with ideal cut-off discontinuity was shown to be 50%. Future work will concentrate on the improvement of the wire sawing machine to reduce the cutting time and three dimensional modeling of the blasting effect will also be performed.     

高效磨削自动化装备重载荷进给单元轻量化设计研究

利用当前常用的有限元分析工具,对大体积质量重的高精度的磨削装备的主体结构的横梁进行拓扑优化设计和仿真分析,实现其轻量化,结果显示该设计不但能实现其轻量化,减少弯曲挠度,还能有效提高其动态性能.     

盾构施工对孔压扰动的三维流固耦合分析

如何对盾构施工过程中的孔压监测数据进行实时分析是工程实践中的难点问题。结合上海虹桥迎宾三路隧道工程,首先建立了包括各种盾构施工参数影响的分析模型,并将不同施工参数情况下超孔压计算结果与实测值进行了对比,验证了模型的合理性。之后分析了开挖面推力、注浆压力、掘进速度、开挖面水头、隧道埋深以及土体渗透系数等参数对隧道周围最大超孔压的影响,获得了最大超孔压拟合计算公式,与现场实测和解析解的对比说明三维流固耦合计算可更合理分析盾构施工对孔压的扰动。同时,较大的超孔压值对应于较大的地表沉降,因此可将实测孔压值与数值计算结果进行对比,从而进行施工参数的调整。在上海虹桥迎宾三路隧道工程试验段的施工过程中,现场监测数据表明可根据孔压监测值调整施工参数,最终减小地面沉降。     

冻土地区深基坑围护结构水平位移的监测及分析

作为我国第一条高寒地铁,哈尔滨地铁的修建对我国冻土地区地铁施工有着重大意义。明挖深基坑工程容易受地理环境的影响,尤其是冻融现象。本文通过对哈尔滨市地铁一号线烟厂站基坑围护结构水平位移的分析,阐述了冻土地区深大基坑的施工方式以及基坑围护结构受冻土影响的变化规律,这对我国今后冻土施工具有一定的借鉴意义。研究显示,影响基坑安全的因素存冻融现象、钢支撑架设、地面堆载、基坑开挖深度,其中冻融现象是影响季节性冻土地区深基坑安全性的重要因素。     

运营地铁隧道上方基坑施工技术及保护措施

结合上海东西通道工程研究了运营地铁隧道上方基坑施工的新技术.提出了基于时空效应和充分利用隧道抗弯刚度的“弹钢琴”开挖方法、三轴搅拌桩微扰动施工技术,最大限度减小了基坑施工引起的隧道隆起量.研究成果突破了现有技术随着穿越跨度和卸荷比的增加,隧道上浮量也不断累加的技术瓶颈.     

盾构机盾尾变形检测与有限元分析

为研究盾构机施工过程中盾尾的实时变形,提出一种有限元分析与应变检测相结合的方法,研发一种盾尾变形检测系统。建立了盾构机简化的三维模型,并依据盾构机在施工过程中,其壳体的受力与变形情况,通过有限元仿真得到盾尾应力与变形之间的本构关系,结合现场具体情况,确定了应变花的粘贴位置和数量。利用变形检测系统测量了盾尾 2 个截面上共 12 个区域的变形数据,并与现场全站仪测量数据进行了对比,两者之间的差别平均为 2.6 mm 。     

The impact of shallow cover on stability when tunnelling in soft soils

Reducing the cover of shallow (metro) tunnels can lower construction costs by lowering cost of the station boxes, increase safety and lower operational cost in the long-term. For bored tunnels there are normally minimal depth requirements stemming from design and construction. The aim of this paper is to investigate the effects of the cover-to-diameter ratio C/D to the stability of tunnelling process. Several models to analyse the tunnel stability were investigated and were applied for a case study in a typical Dutch soil profile with soft Holocene soil layers. The range of the support pressures in TBM machines, especially in EPB, when tunnelling in soft soil is derived for varied C/D ratio in different soil conditions. Based on the analysis results, some designing optimizations are proposed for shallow tunnels in soft soil.     

Advanced finite element analysis of a complex deep excavation case history in Shanghai

The construction of the North Square Shopping Center of the Shanghai South Railway Station is a large scale complex top-down deep excavation project. The excavation is adjacent to several current and newly planned Metro lines, and influenced by a neighboring Exchange Station excavation. The highly irregular geometry of this excavation greatly increases the complexity in 3D Finite Element modeling. The advanced numerical modeling described in this paper includes detailed structural and geotechnical behavior. Important features are considered in the analysis, e.g., 1) the small-strain stiffness of the soil, 2) the construction joints in the diaphragm wall, 3) the shrinkage in the concrete floor slabs and beams, 4) the complex construction sequences, and 5) the shape effect of the deep excavation. The numerical results agree well with the field data, and some valuable conclusions are generated.