Failure mechanism of large-diameter shield tunnels and its effects on ground surface settlements

A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.

Influence of secondary lining thickness on mechanical behaviours of double-layer lining in large-diameter shield tunnels

In large-diameter shield tunnels,applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining.The secondary lining thickness is a key parameter in the design of a double lining structure,which is worth being explored.Based on an actual large-diameter shield tunnel,loading model tests are carried out to investigate the effect of the secondary lining thickness on the mechanical behaviours of the double lining structure.The test results show that within the range of secondary lining thicknesses discussed,the load-bearing limit of the double-layer lining increases with growing secondary lining thickness.As a passive support,the secondary lining acts as an auxiliary load-bearing structure by contacting the segment.And changes in secondary lining thickness have a significant effect on the contact state between the segment and secondary lining,with both the contact pressure level and the contact area between the two varying.For double-layer lining structures in large-diameter shield tunnels,it is proposed that the stiffness of the secondary lining needs to be matched to the stiffness of the segment,as this allows them to have a coordinated deformation and a good joint load-bearing effect.

Shielded metal arc welding of cemented carbide to carbon steel

Electrode ENiFe-C1 and E4303 were selected to join the cemented carbide WC-20Co and carbon steel 45 by shielded metal arc welding process. Microstructure and bending property of the corresponding joints were analyzed. The results showed that the carbon steel electrode E4303 had no proper metallurgy condition for the arc welding of cemented carbide and carbon steel. The C and Ni content of the cast iron electrode ENiFe-C1 could meet the condition of preventing the formation ofη carbide,which was suit to the arc welding of cemented carbide and carbon steel,but the operation parameters needed to be optimized to minimize the slag inclusion. The alloy WC-20Co which did not fit for cold arc welding,by adopting the measure of being preheated at 723 K for 1 h before welding,and being kept at 723 K for 3 h after welding then followed furnace cooling could avoid the happening of crack in the WC-20Co base metal.

基于泥水盾构废浆的新型同步注浆浆液性能及影响因素初探

为响应我国生态文明建设要求,遵从绿色发展理念以及推进“双碳”战略目标的实现,针对泥水平衡盾构施工过程中产生的废弃浆液的处理及外运的高成本、易污染环境等问题,提出将废弃泥浆用作制备同步注浆浆液的解决办法。依托成都环线紫瑞隧道建设项目,通过室内试验方法研究浆灰比、灰砂比、粉灰比对基于砂卵石土地层泥水盾构废浆制备的新型同步注浆浆液的泌水率、流动度、凝结时间以及3,7,28 d抗压强度的影响规律,得出以下研究结论。(1)基于砂卵石土地层废浆制备的新型同步注浆浆液稳定性良好。(2)新型同步注浆浆液的凝结时间随着浆灰比、灰砂比的增加而增长,随着粉灰比的增加而减小;流动度随着浆灰比、灰砂比的增加而增加,随着粉灰比的增加而减小。(3)新型同步注浆浆液的3,7,28 d抗压强度随着浆灰比的增加而减小,随着粉灰比的增加而增加,随灰砂比的增大呈先增大后减小的变化规律,在灰砂比为0.8时,达到最大值。(4)经试验研究得出使用废浆以浆灰比2.5、灰砂比1.25、粉灰比0.75制备的新型同步注浆浆液3 h泌水率为0,凝结时间为7.25 h,流动度为23.3 cm,3,7,28 d抗压强度分别为1.2,1.5,2.7 MPa,各项性能均满足试验指标要求,将此配比方案应用于依托工程实际施工,能够满足施工现场的要求。此研究为泥水平衡盾构废弃泥浆再利用于同步注浆提供了有效支撑。

矿渣基地聚物流态盾构固化土的性能研究

为实现对地下工程中的高含水率盾构土资源化利用,探究地聚物材料固化盾构土的可行性,本文采用矿渣基地聚物固化盾构土,通过研究碱激发剂模数、矿物配比、碱激发剂掺量、温度对不同种类盾构固化土无侧限抗压强度和工程性能的影响规律,确定固化土配合比设计,在此基础之上研究地聚物掺量对固化土水稳性的影响,并采用SEM对盾构固化土进行微观分析,揭示其固化机制。结果表明,在试验拟定的水固比下,两种不同土质流态盾构固化土均有良好的力学性能和工程性能,矿渣基地聚物产生了无定形凝胶,增强了土壤颗粒之间的胶结及密实度,其中固化剂掺量为干土质量22%的盾构固化土在标养条件下的28 d无侧限抗压强度可达5.38 MPa, 40℃条件下可达8.08 MPa,水稳系数达0.98。

耐高温水泥基快中子屏蔽材料的制备与性能研究

以氢氧化铝、碳化硼、铝酸盐水泥等为原材料,采用压制方法制备了高氢含量快中子屏蔽材料,研究了该屏蔽材料的密度、力学性能、耐高温性能、尺寸稳定性、屏蔽性能。结果表明:虽然密度不高,但所制备的屏蔽材料具有较好的力学性能、耐高温性能、尺寸稳定性好、屏蔽性能好,且成本低廉,具有较好的应用前景。

Tunnel face stability and ground settlement in pressurized shield tunnelling

An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.

水溶蚀作用下水泥-水玻璃双液浆力学性能衰减机理研究

双液浆在富水环境中长期服役极易受到水溶蚀作用而力学性能大幅衰减。本文研究了配合比参数、养护制度对双液浆力学性能的影响,并结合多种微观分析手段,揭示了富水环境下双液浆性能衰减的作用机制。结果表明:10%、15%(质量分数)低含水率砂层中养护有利于早期强度发展,但后期强度逐渐衰减,而25%(质量分数)高含水率砂层中试块早期强度相比15%(质量分数)含水率砂层中试块降低了23.5%,但后期水溶蚀作用被大幅削弱,220 d抗压强度较90 d增加了15%;标准养护条件加速双液浆力学性能的劣化,试块强度分别较水中养护、绝湿养护降低了80.6%和91.0%;双液浆力学性能发展主要受水化反应及水溶蚀作用控制,早期阶段由水化反应主导,后期阶段由水溶蚀作用主导,力学性能的演变本质是两种效应相互叠加的结果;在富水环境中长期养护,基体外侧水化产物不断向外迁移溶出,在试块外层形成多孔结构包覆层,并成为内部结构中钠、硅酸根离子及水化产物的迁移通道,导致力学性能持续劣化。

玄武岩纤维膨润土水泥膏浆的注浆加固工程应用研究

岩溶塌陷是盾构法隧道工程穿越岩溶地层面临的关键问题之一,其不仅会对油气管道造成破坏,还会导致油气泄漏、破坏生态环境、威胁沿线居民生命财产安全等问题。针对湖南永州某地盾构法隧道穿越的岩溶地层溶洞发育特点,优选兼具良好流变性能和力学性能的玄武岩纤维膨润土水泥膏浆配方,开展玄武岩纤维膨润土水泥膏浆原位注浆充填加固实验,并通过钻孔取心和室内实验的方法检验了该注浆材料的加固效果,实验结果表明:钻孔取心获得的地层岩心密实,胶结强度较强,岩心采取率满足施工要求的80%;受地下水的影响,钻孔深度为6~7 m的注浆固结体28 d的无侧限抗压强度较小,平均为0.32 MPa,但试样较为完整;钻孔深度为7~8 m的注浆固结体28 d的无侧限抗压强度较6~7 m的注浆固结体增加了约5.36倍。采用玄武岩纤维膨润土水泥膏浆进行原位注浆充填加固的注浆固结体强度大于施工要求的强度指标,有效保障了岩溶地区盾构穿越工程的安全性。

Response of operating metro tunnels to compensation grouting of an underlying large-diameter shield tunnel:A case study in Hangzhou

Due to the shield tunneling underneath,long-term settlements may develop in the existing metro tunnels.The compensation grouting is applied worldwide to stabilize the settlement of ground and existing structures.Few field studies concerning large-diameter shield pass-ing tunnel from below have analyzed the interaction between the compensation grouting and the existing tunnel.This paper presents a case study on the response of the operating metro tunnels to the compensation grouting of an underlying large-diameter tunnel in muddy clay stratum.The tunnel deformations before,during,and after the compensation grouting were monitored and analyzed.The long-term tunnel settlements were mitigated and stabilized by the timely compensation grouting.Smaller settlement rates were observed during the grouting treatment,and the settlement was gradually stabilized three months after the grouting.The grouting holes at the tunnel invert were used initially for better grouting efficiency.The horizontal displacement and convergence developed during the grouting construc-tion and remained stable after the grouting process.Moreover,some limitations of the grouting treatment were discussed.The tunnel settlement in the section close to the center-line of the south-line tunnel cannot be prevented effectively.The differential displacement cannot be reduced by this grouting program.

泥水平衡盾构下穿海域施工技术应用

以深圳地铁12号线左炮台站~太子湾站区间下穿码头海域工程为例,阐述了泥水平衡盾构机成功下穿码头海域、断层破碎带及上软下硬地层的施工技术,主要包括风险辨识、盾构机选型、施工过程技术方案及风险预控措施等,通过对技术应用成果总结分析进一步说明了本技术具有科学性、安全性和高效性。因此,泥水平衡盾构下穿海域施工技术可供类似工程借鉴与参考。

碳纤维对水泥砂浆力学性能和电磁屏蔽性能的影响

具备优异力学性能和电磁屏蔽性能的碳纤维水泥基材料备受业内关注。文章通过制备不同碳纤维掺量的水泥砂浆,系统研究了碳纤维掺量、养护龄期及电磁波频率对砂浆力学性能和电磁屏蔽性能的影响。结果表明:0.6%碳纤维掺量的水泥28 d砂浆抗压和抗折强度最优,分别为48.19 MPa和7.7 MPa,高于对照组12.3%和5.5%。砂浆电磁屏蔽效能随频率增加呈现先增大后减小的趋势。0.6%碳纤维掺量砂浆屏蔽效能最大,为10.6 dB;继续增大碳纤维掺量,屏蔽效能峰值位点向18 GHz位点移动。碳纤维掺量从0增至0.6%,砂浆最大介电常数虚部从0.5增至32.6;碳纤维掺量继续增至1.0%,介电常数虚部从32.6降至24.9,降幅为23.6%。

石墨-水泥基复合材料的制备与性能

为提高水泥基材料的抗电磁干扰性能,制备了石墨–水泥基复合材料,测试了材料的电阻率、电磁屏蔽效能和力学性能。结果表明:对石墨–水泥基复合材料,在一定范围内,随掺入的石墨质量分数(下同)的增加,材料电阻率呈下降趋势。石墨掺入量为5%～10%时复合材料电阻率下降非常明显,超过15%以后,电阻率变化已不太明显;随着石墨掺量的增加,复合材料的电磁屏蔽效能也逐渐增大,石墨掺入量为15%时达到最大值,而抗折强度及抗压强度则随着石墨掺入量的增加有所下降。

水泥基功能复合材料研究进展及应用

介绍了国内外水泥基功能复合材料的研究进展及应用 ,重点对几种重要的水泥基功能复合材料 ,如导电、压电、介电、磁性、屏蔽等材料的组成、特性、工艺及发展状况进行了综述。

考虑黏度时变性的水泥浆液盾构壁后注浆扩散规律及管片压力模型的试验研究

对水泥浆液黏度时变性进行了试验研究,证实了工程常用水灰比范围内水泥浆液服从宾汉姆流体特性;不同水灰比浆液黏度均随注浆时间增大而大幅度增加。根据试验结果,考虑注浆过程中水泥浆液黏度随时间的变化,对盾构壁后注浆水泥浆液的扩散规律及因注浆而造成的管片压力进行了推导及分析。计算表明:相同注浆时间条件下,水泥浆液扩散半径及注浆对管片产生的压力值均随注浆压力的增大而增大。考虑浆液黏度时变性后,扩散半径、注浆对管片压力值等均较不考虑浆液时变性时减小,且随注浆压力的增大,浆液黏度变化对管片压力值的影响更加明显。相同注浆压力条件下,浆液扩散半径及对管片产生的压力值均随注浆时间的增长而增加,但注浆前期增长速度较快,而后逐渐减缓。研究成果对于盾构壁后注浆工艺选择及参数设计具有较大的指导意义。

碳纤维对水泥基复合材料电磁屏蔽性能的影响

本文根据电磁屏蔽原理,对掺有短切碳纤维(CF)的水泥基复合材料的电磁屏蔽性能进行了实验研究。结果表明:碳纤维水泥基复合材料在频率为9KHz^1.5GHz范围内具有良好的屏蔽效果。同时分析了碳纤维对水泥基复合材料屏蔽性能的影响机制。

用铀裂变室研究反射中子测量技术

在自行设计的水泥屏蔽体中，用铀裂变室研究了反射中子测量技术。在不同实验系统上，测量了铁球壳表面不同位置上中子引起的绝对裂变反应率分布。实验总误差为３．９％。

土压平衡盾构施工穿越砂层渣土改良试验研究

针对地铁隧道采用土压平衡盾构施工穿越砂层时表现出的非适应性开展了渣土改良及现场试验研究,通过对比渣土经不同配比膨润土泥浆改良前后的抗剪强度、渗透性及塌落度,得到了合理的膨润土浓度及泥浆掺入比.研究表明:当砂层采用浓度为1∶10膨润土泥浆改良后,渣土的塑性及流动性得到有效提高,抗剪强度及渗透性大幅降低;控制泥浆体积掺入比为1∶5进行掘进施工时,盾构机刀盘内外温度及磨损程度明显降低、排土顺畅且推进速度提高.研究成果对于解决土压平衡盾构穿越砂层时土压难以平衡、排土不正常、刀盘扭矩过大及磨损过快等问题具有参考价值.

盾尾注浆硬性浆液固结变形数值计算模型构建

为了更为合理地评价盾构壁后注浆控制地层变形机制,采用自制的硬性浆液固结变形试验装置,对水泥胶结作用影响硬性浆液的固结过程进行了试验研究。在此基础上,分析并建立了能够反映水泥胶结作用的硬性浆液固结变形模型,编制了相应的数值计算程序,并通过试验验证了该模型的合理性。硬性浆液固结变形数值计算模型的构建对于提高盾构施工模拟精细度将起到一定的推动作用。