Pressure from surrounding rock of three shallow tunnels with large section and small spacing

With the increasing traffic demand, the closely built three or more tunnels with large section play a significant role in the tunnel construction. However, the interaction among tunnels has important influences on the security and economy of tunnel engineering, and the calculation of pressure from the surrounding rock during the excavation is one of the problems that need to be solved urgently. Based on the practical engineering of three tunnels, the load model of three tunnels was proposed in consideration of the interaction and excavation sequence between tunnels. In comparison with the load model of single tunnel, the construction mechanical characteristics of the three tunnels were analyzed. The results show that the rock pressure of three tunnels calculated by the current tunnel design code is not reliable, and the interaction force increases with the spacing between tunnels.

Similar simulation study on the deformation and failure of surrounding rock of a large section chamber group under dynamic loading

Large and super-large section chamber groups in coal mines are frequently affected by dynamic loads resulting from production activities such as roadway driving and blasting.The stability of the surrounding rock is poor,and it is difficult to control.In this paper,a similar simulation test was used to study the deformation and evolution laws of the surrounding rock of a triangle-shaped chamber group under different dynamic loads.The results showed that under dynamic loading,the vertical stress of the surrounding rock of the chamber group increased in an oscillatory form.The maximum stress concentration coefficient reached 4.09.The damage degree of the roof was greater than that of the two sides.The deformation of the roof was approximately 1.2 times that of the two sides.For the chamber closer to the power source,the stress oscillation amplitude of the surrounding rock was larger,and the failure was more serious.The force of the anchorage structure showed a phased increasing characteristic;additionally,the force of the anchorage structure on the adjacent side of the chambers was greater than that on the other side.This study reveals the deformation and failure evolution laws of the surrounding rock of large section chamber groups under dynamic loading.

Application of 3D-computed tomography angiography technology in large meningioma resection

Objective:To discuss the role of 3D-computed tomography angiography(3D-CTA) technology in reducing injuries of large meningioma surgery.Methods:3D-CTA preoperative examinations were done in 473 patients with large meningioma(simulated group).The images were analyzed by 30 post-processing workstation.By observing the major intracranial blood vessels,venous sinus,and the compression and invasion pattern in the nerve region,assessing risk level of the surgery,simulating the surgical procedures,the surgical removal plan,surgical routes and tumor blood-supplying artery embolisation plan were performed.Two hundred and fifty seven large meningioma patients who didn’t underwent 3D-CTA preoperative examination served as control group.The incidence of postoperative complications,intraoperative blood transfusion and the operation time were compared between these two groups.Results:Compared with the control group,the Simpson’s grade 1 and 11 resection rate was 80.3%(380/473),similar with that of the control(81.3%,209/257).The incidence of postoperative complications in 3D-CTA simulated group was 37.0%which was significantly lower than that(48.2%) of the control(P【0.01). The intraoperative blood supply for simulated group and the control was(523.4±208.1) mL and (592.0±263.3) mL,respectively,with significant difference between two groups(P【0.01).And the operation time[(314.8±106.3)]min was significantly lower in simulated group than that in the control[(358.4±147.9) min](P【0.01).Conclusions:Application of 3D-CTA imaging technology in risk level assessment before large-scaled meningioma resection could assist in the rational planning of tumor resectin,surgical routes,and is helpful in reducing injuries and complications and enhancing the prognosis of the patients.

High prestress truss cable support principle and its application in large cross section coal roadway

With the enlarge of cross section of roadway, the radius of plastic area and broken area increase, and the tensile stress and shear stress distributing in roof coal-rock layers relevantly increase, which induce support effect not obvious for ordinary bolt（cable）. While bounding point and support structure of the truss cable is in vertex angle of roadway, and supplies coal-rock layers in bounding area with the horizontal and vertical pressure, so it settles the support problems in large cross section coal roadway. From the point of view of mechanics, gave emphasis on the invalid mechanics of ordinary bolt （cable） in large cross section coal roadway and supported mechanics of prestress truss cable. The author successfully used this technique in Wuyang Mine, and had the huge economic efficiency and the social benefit.

Intelligent optimization of the structure of the large section highway tunnel based on improved immune genetic algorithm

As in the building of deep buried long tunnels,there are complicated conditions such as great deformation,high stress,multi-variables,high non-linearity and so on,the algorithm for structure optimization and its application in tunnel engineering are still in the starting stage. Along with the rapid development of highways across the country,it has become a very urgent task to be tackled to carry out the optimization design of the structure of the section of the tunnel to lessen excavation workload and to reinforce the support. Artificial intelligence demonstrates an extremely strong capability of identifying,expressing and disposing such kind of multiple variables and complicated non-linear relations. In this paper,a comprehensive consideration of the strategy of the selection and updating of the concentration and adaptability of the immune algorithm is made to replace the selection mode in the original genetic algorithm which depends simply on the adaptability value. Such an algorithm has the advantages of both the immune algorithm and the genetic algorithm,thus serving the purpose of not only enhancing the individual adaptability but maintaining the individual diversity as well. By use of the identifying function of the antigen memory,the global search capability of the immune genetic algorithm is raised,thereby avoiding the occurrence of the premature phenomenon. By optimizing the structure of the section of the Huayuan tunnel,the current excavation area and support design are adjusted. A conclusion with applicable value is arrived at. At a higher computational speed and a higher efficiency,the current method is verified to have advantages in the optimization computation of the tunnel project. This also suggests that the application of the immune genetic algorithm has a practical significance to the stability assessment and informationization design of the wall rock of the tunnel.

Stability Analysis of Large Section Rocky Tunnel Support Structure

In order to study the stress characteristics of the initial support and secondary lining of the large section tunnel and to solve the problem of secondary lining cracking during operation. Taking the large section tunnel in Zihong village, Qi County as the research object, a numerical simulation method was used to establish a finite element model of the large section tunnel. So as to simulate and analyze the stress characteristics of the support structure of this tunnel. Through the simulation of the initial support and second lining of this large section tunnel in terms of displacement, stress, plastic zone damage and anchor shaft force, the results show that as the excavation progresses, the stress and displacement on the surface of the newly excavated tunnel profile is faster, especially at the side walls and arch footings, the stress and displacement values are slightly larger than other characteristic points, but the final values are stable and converge, and are basically consistent with the field monitoring results, which indicates that this support system is basically in stable state. Therefore, during the tunnel excavation and support process, special attention should be paid to the stability of the sidewalls and footings, and the results of this study will be of great practical significance for tunnel construction and maintenance.

Crack elongation and its width of large depth reinforced concrete beams

In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.

Simulation of the RCS Range Resolution of Extremely Large Target

The high frequency hybrid technique based on an iterative Physical Optics(PC)) and the method of equivalent current (MEC) approach is developed for predicting rangeresolution of the Radar Cross Section (RCS) in the spatial domain. We introduce the hybrid highfrequency method to simulate range resolution of the extremely large target in the near zone. Thispaper applies this method to simulate the range resolution of the two 1 m X 1 m plates and the ship.The study improves the speed of simulatingthe range resolution of the extremely large target and isprepared for the application of the extrapolation and interpolation in the spatial domain.

Dynamic plastic response of clamped stiffened plates with large deflection

Study on the dynamic response, and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity. The finite element method (FEM) and the finite strip method are usually adopted in their analysis. Although many useful conclusions have been obtained, the computational cost is enormous. Based on some assumptions, the dynamic plastic response of clamped stiffened plates with large deflections was theoretically investigated herein by a singly symmetric beam model. Firstly, the deflection conditions that a plastic string must satisfy were obtained by the linearized moment-axial force interaction curve for singly symmetric cross sections and the associated plastic flow rule. Secondly, the possible motion mechanisms of the beam under different load intensity were analysed in detail. For structures with plastic deformations, a simplified method was then given that the arbitrary impact load can be replaced equivalently by a rectangular pulse. Finally, to confirm the validity of the proposed method, the dynamic plastic response of a one-way stiffened plate with four fully clamped edges was calculated. The theoretical results were in good agreement with those of FEM. It indicates that the present calculation model is easy and feasible, and the equivalent substitution of load almost has no influence on the final deflection.

Taxonomy and phylogeny of the section Chaetoceros(Chaetocerotaceae,Bacillariophyta),with description of two new species

Chaetoceros Ehrenberg is one of the most diverse genera of planktonic diatoms.The species in section Chaetoceros are characterized by cells and setae having numerous chloroplasts and being widely distributed.However,the delimitations of some species are problematic because of limited morphological information in the classical descriptions.Monoclonal strains of the section Chaetoceros were established,morphological features were studied using light and electron microscopy,and the hypervariable D 1-D 3 region of the nuclear ribosomal large subunit gene was sequenced to address phylogenetic relationships.Fifteen species belonging to the section Chaetoceros were recorded,including two new species,C.hainanensis sp.nov.and C.tridiscus sp.nov.Chaetoceros hainanensis was characterized by straight chains,narrowly lanceolate to hexagonal apertures,sibling setae diverging in nearly right angles,stipule-shaped spines on terminal setae and arrowhead-shaped spines on intercalary setae.C.tridiscus had short straight chains,narrowly lanceolate apertures,arrowhead-shaped spines and circular poroids arranged in a grid pattern on terminal and intercalary setae.The phylogenetic analyses revealed six groups formed by 19 species within the section Chaetoceros,which was found to be monophyletic.The subdivision of the section is still not well understood.The morphological characters within each group varied considerably and molecular information on more species are needed to enrich the phylogenetic profiling.

Dynamic evolution in mechanical characteristics of complex supporting structures during large section tunnel construction

The shallow tunnelling method(STM)often uses temporary supports to divide large section tunnels into several closed or semiclosed sections so as to share the upper load.The complex support system composed of primary and temporary supports can ensure safety during tunnel construction.Based on the large section tunnel of Beijing Subway Line 12,the mechanical characteristics of support system by the double-side-drift method(DSDM)during excavation and demolition were analyzed through numerical simulation and monitoring.The study showed that the middle cave excavation was the most critical stage of the DSDM,during which the load on the supporting structure increased significantly.The temporary vertical support bore most of the new load during middle cave excavation.During the demolition stage,the load was redistributed,which caused arch settlement and section convergence.The removal of the temporary vertical support exerted the greatest impact in this process.The lateral temporary inverted arch changed from axial compression to axial tension after the middle and lower caves were excavated.Based on the mechanical characteristics of the support system,some engineering suggestions were proposed for large section tunnel construction.These research results can provide reference for the design and construction of similar large section tunnels.

桩-震陷土层耦合作用下变截面单桩动力响应

为研究不同类型地震波作用下大直径变截面钢管混凝土复合单桩的动力响应规律,依托厦门第二东通道翔安大桥工程,通过室内振动台试验,选取地震动强度为0.15g的5010波、1004波、Kobe波及El‐Centro波,研究大直径变截面钢管混凝土复合单桩的桩身加速度、水平位移、弯矩及桩基损伤等变化规律。试验结果表明:不同类型地震波由于其频谱特性不同,大直径变截面钢管混凝土复合单桩的动力响应特性存在差异;桩顶加速度最大值、桩顶水平位移最大值、桩身弯矩最大值均在1004波作用下最大,在Kobe波作用下最小;桩身弯矩最大值均未超过桩基设计抗弯承载力;在地震力的作用下对桩基础的抗弯承载能力进行设计时,应重点考虑软硬土层的分界面处抗弯能力。

大截面变化率铝合金异形管整体液力成形工艺设计与优化

目的针对某大截面变化率空心构件成形难的问题,采用液力成形的方法进行成形并对其生产工艺进行优化。方法首先针对目标零件,通过压扁截面处对称及圆截面处对称2种不同的对称方式设计了A型结构和B型结构,通过有限元模拟对比了同一加载路径下2种不同结构的成形特点,选取了成形效果较好的A型结构进行成形工艺研究,建立了A型结构的成形分区图,继而根据成形分区图进行了正交试验设计。结果在同一种加载路径下,A型结构成形的目标零件最大减薄率明显小于B型结构成形的目标零件最大减薄率,且在成形过程中,B型结构压扁特征处易出现褶皱或起皱趋势,而A型结构压扁特征处壁厚分布更加均匀,A型结构成形效果优于B型结构成形效果。优化后的工艺参数如下:压制压力为2 MPa、初始压力为7 MPa、成形压力为15 MPa、轴向进给为13 mm,成形零件最大减薄率为15.9%。结论经成形分区图指导设计的正交成形试验结果均符合设计要求,成形分区图的设立对成形试验的设计具有指导作用;采用优化后的工艺参数获得了较好的试验效果,可为工业生产提供指导。

大断面管幕箱涵顶进引起地表变形的解析解答

研究大断面管幕箱涵顶进全过程对土体变形和周围环境的影响,对于事前预测变形并控制施工扰动影响具有重要意义。基于Mindlin解答、修正Sagaseta公式等经典理论解答,分别考虑由正面推进力、摩擦力和土体损失等因素引起的地表变形,提出考虑三者共同作用下的大断面管幕箱涵顶进引起的地表变形计算方法。建立管幕箱涵顶进作用下土体受力模型,采用Mindlin解答分别给出正面推进力和摩擦力引起的土体变形计算公式;基于当层法原理提出由土体损失引起的横向地表沉降计算公式。根据各影响因素的相对独立性,将各因素引起的土体变形量叠加,从而得到一种适用于大断面管幕箱涵顶进施工,可综合考虑多种施工因素和土体三维变形的理论解答公式。通过工程实例验证公式的合理性,研究成果可为实际施工变形预测提供参考。

不同开挖工法下超大断面隧道受力变形分析

超大断面隧道具有洞身扁平率低、洞口边缘围岩变形大等特点,导致施工步序繁多,持续时间长等问题。因此,选用合理的开挖工法是保证隧道安全施工的重要手段。本文依托江西省首座超大断面隧道工程,采用ABAQUS软件模拟了不同开挖方式开挖下隧道围岩及支护结构的受力变形规律,同时结合现场监测数据进行对比和验证。结果表明:三台阶七步开挖法开挖时释放的围岩支护应力最大且易形成应力集中,应及时完成初期支使洞口快速封闭;3种开挖工法下产生的最大主应力均出现在拱脚位置,应及时在此处加强稳定性支撑;CRD法(cross diaphragm)施工引起的围岩扰动最大而双侧壁导坑法扰动较小,因此双侧壁导坑法更适合超大断面隧道施工。研究结论可为超大断面隧道施工方案的选取与优化提供指导。

地震作用下大断面偏压双线黄土隧道初期支护内力及变形响应研究

为研究西北黄土高原地区大断面偏压双线黄土隧道的初期支护结构在地震作用下的内力和变形响应特征,依托宁夏境内某大断面偏压双线黄土隧道,以工程地质勘察报告和设计资料为基础,选取Kobe波作为地震动输入,利用有限差分程序FLAC 3D建立三维数值分析模型,通过分析初期支护结构的内力和变形以研究其地震动力响应特征。研究结果表明:地震过程中左线和右线隧道拱肩位置的受拉侧会发生变化,左线隧道拱腰和右线隧道拱肩、拱脚和仰拱位置的轴力会发生拉压变化。地震作用下左右线隧道峰值弯矩和峰值轴力的最大值均在拱脚,应加强此位置的抗震设计。静载作用下左、右线隧道边墙弯矩分布不对称,且左线隧道更明显。地震作用下,左线和右线隧道的最大弯矩和最大轴力分别出现在左拱脚和右拱脚,且左线隧道(偏压侧隧道)动力响应更为剧烈;右线隧道整体变形明显大于左线隧道,地震作用下左右线隧道变形均增大且整体向右倾斜,左线和右线隧道的最大位移分别在右拱肩和右拱腰处,位移值分别为34.98 mm和39.11 mm。综合结构内力和变形响应分析,地震作用下左线和右线隧道的拱脚位置易出现结构损伤,且左线(偏压侧)隧道拱脚位置更易损伤。

大断面黄土隧道下穿地表建筑物沉降分析及对策

依托西延高铁某黄土隧道下穿地表建筑物工程实例,采用理论分析、数值模拟等手段,对大断面黄土隧道下穿地表建筑物施工中地表沉降范围及对策进行研究。结果表明:基于随机介质理论,隧道两侧的地表沉降范围可划分为强、弱、无影响区,隧道施工对地表强影响区范围约等于隧道埋深,弱影响区范围约为隧道埋深的2倍;在开挖面到达办公楼正下方时办公楼沉降值约占总沉降值的70%;穿过办公楼后,沉降速率趋于收敛,隧道施工中接近地表建筑物要加强施工质量,保证地表结构安全;隧道通过地表建筑物后,地表沉降趋于收敛,但沉降值仍不断增大,隧道穿越地表建筑物后,应持续开展建筑物沉降变形监测,掌子面二衬紧跟,保证地表建筑物结构安全;大断面黄土隧道下穿地表建筑物时,采用三台阶临时仰拱(腰梁)法、锁脚加强、初支加强等措施后,可保证隧道施工安全,相关措施可为相类似工程的施工提供借鉴意义。

矩形大断面顶管施工技术在地铁通道建设中的应用研究

为提高矩形大断面顶管施工安全水平和效率,应采取优化顶管机配置、加强沉降监测、止水补强等措施。合理的顶管机配置可以应对地铁工程复杂地质环境的施工挑战,有效降低顶管施工风险,保证地铁工程结构的施工安全。通过止水补强、沉降监测等措施,动态监控顶管施工全过程,提高施工安全和质量。以北京地铁17号线的望京西站1号换乘通道顶管施工项目为例,深入分析了工程特点,总结矩形大断面顶管施工风险及应对措施,进而探讨顶管施工技术要点,希望可为同类项目施工提供有益的技术参考。

王家岭矿末采段动压传播规律及围岩控制研究

以王家岭煤矿18102工作面末采段为研究对象,采用数值模拟和现场观测的方法分析了推进过程及采厚对支承压力的影响,进而分析支承压力对大断面回撤通道6.6 m×5.1 m的影响。结果表明,随着工作面的推进回撤通道两侧支承压力呈倍数增加,采厚越大回撤通道两侧支承压力越大。其中距回撤通道合理距离为主要因素,最终确定为30 m。采用高强锚杆索支护后表面位移观测结果,在工作面末采期间,两帮移近量153 mm,顶底板移近量184 mm,顶板离层量8 mm。该案例丰富了大断面回撤通道的围岩控制成果,可为类似条件下大断面回撤通道支护提供借鉴。

深部大断面硐室开挖顺序及支护参数优化

为解决深部大断面硐室开挖稳定性问题,采用数值模拟的方式开展深部大断面硐室开挖顺序及支护参数优化研究。建立了大断面硐室分布开挖模型,依据“先顶后帮”“先帮后顶”“帮顶同掘”的原则并参照工程现场中综掘机截割方式,设计16种模拟开挖方案。分别针对5种不同支护类型进行效果分析,并依据模拟结果对支护参数进行优化。结果表明:综合考虑塑性区变化、围岩收敛及开挖器具等因素,认为采用“先顶后帮”的断面开挖方式具有较小的扰动,并确认了最佳的开挖顺序。锚杆锚索和混凝土砌碹可以有效增加硐室的稳定性和承载能力,但硐室帮部、中间部位及底板中间部位仍存在变形,需要适当提高锚杆锚索的支护密度,并辅以注浆加强。