Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Spontaneous caving and gob-side entry retaining of thin seam with large inclined angle

Based on the research method of combining simulation analysis with field testing by distinct element process UDEC, we have analyzed the roof deformation and failure laws and roadway support technology of gob-side entry retaining in a thin seam with a large inclined angle. The results show that during exploitation in seams with large inclined angle, rotational subsidence of the main roof under the gob area is small and can maintain balance, so there is no need to provide artificial permanent support resistance for the main roof near the upper side to control rotational subsidence. Obstructed by the dense scrap rail,waste rock from the immediate roof caving slides from the upper gob area to the lower area and fills it,which strikes a balance between the immediate roof under the goaf after it fractures into large pieces and filling waste rocks.

AN ANALYSIS OF THE LARGE DEFLECTION OF AN ELASTIC-PLASTIC CANTILEVER SUBJECTED TO AN INCLINED CONCENTRATED FORCE

Based on the Plastica theory (see ref. [12]), the large deflection of an elastic-perfectly plastic cantilever subjected to an inclined concentrated force at its tip, before the unloading in the plastic region occurs, is analyzed in this paper. The emphasis of the analysis is put on the effects of the angle of inclination of the concentrated force upon the deformed shape, the load-deflection relationship and the length of the plastic region. Both analytical and computed results are given.

Mechanism and practice of rock control in deep large span cut holes

Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pre- stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control prin- ciples and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.

Analytical study on pretensioned bolt-cable combined support of large cross-section tunnel

To study the mechanical responses of large cross-section tunnel reinforced by pretensioned rock bolts and anchor cables, an analytical model is proposed. Considering the interaction between rock mass and bolt-cable support, the strain softening characteristic of rock mass, the elastic-plastic characteristic of bolt-cable support, and the delay effect of installation are considered in the model. To solve the different mechanical cases of tunneling reinforced by bolt-cable support, an analytical approach has been put forward to get the solutions of stress and displacement associated with tunneling. The proposed analytical model is verified by numerical simulation. Moreover, parametric analysis is performed to study the effects of pretension force,cross-section area, length, and supporting density of bolt-cable support on tunnel reinforcement, which can provide references for determining these parameters in tunnel design. Based on the analytical model, a new Ground Response Curve(GRC)considering the reinforcement of bolt-cable support is obtained, which shows the pretension forces and the timely installation are important in bolt-cable support. In addition, the proposed model is applied to the analysis of the Great Wall Station Tunnel, a high-speed railway tunnel with a super large cross-section, which shows that the analytical model of bolt-cable support was a useful tool for preliminary design of large cross-section tunnel.

CFD-Based Numerical Analysis of a Variable Cross-Section Cylinder

Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.

Investigate the nonuniformity of low-energy electron beam with large cross-sections

Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.

恶劣综采工况条件下的采煤机摇臂散热设计研究

简述了在采煤机设计过程中对恶劣综采工况中工作倾角较大、煤岩硬度较硬、截割功率大且结构紧凑限制条件下的摇臂热功率的计算,分析了该工况中摇臂简化为复杂齿轮箱思路下的热功率计算、散热途径和热平衡点,提出了摇臂内部结构改进及增加外置冷却装置的散热设计方案,并验证了满载试验条件下摇臂截割热平衡温度不超过90℃的方案可行性。

杭州电竞中心结构设计重难点概述

杭州电竞中心内圈主体结构采用钢框架-支撑结构,外圈采用“大倾角梭形斜柱+多段钢折梁框架”,是集承重与抗侧力于一体的结构体系,屋盖采用车辐式索承网格自平衡结构形式。详细介绍了地下结构、中央场馆结构的设计要点,门厅处利用建筑造型空间设计为多段钢折梁与跨层桁架相结合的结构形式;室内二层至三层楼面设计一浮空弧形人行桥,截面形式为薄壁钢箱梁,桥宽2.2m,跨度57m,采用“上挂下支”的稳定结构形式。对整体结构进行了静力弹性、动力弹塑性、振动台试验、典型节点有限元、整体稳定以及局部稳定等系列分析与试验。结果表明:结构在静力荷载和地震作用下强度和刚度均满足规范要求;典型节点极限承载力为荷载设计值的4.17倍;结构整体稳定性安全系数为3.79;斜柱局部稳定安全系数为2.52。合理的设计保证了结构的安全、经济和实用性。

大倾角钢箱提篮拱桥总体设计

考虑施工技术、经济性和景观效果等方面,陕西蔡家坡渭河特大桥主桥采用(35+210+35) m大倾角钢箱提篮拱桥。该桥采用摩擦摆和环向钢丝绳阻尼支座综合减隔震约束体系,以降低结构的地震响应。拱肋为单室等宽钢箱截面,采用主、副拱肋2条悬链线,主、副拱肋共面,设计为横向内倾20°的大倾角,在提高桥梁景观效果的同时,又有效提高了结构的整体稳定性;拱肋设钢-混结合段连接拱脚与混凝土拱座。桥面系采用自重较轻的正交异性钢桥面板结构。吊杆采用抗拉强度1 860 MPa的环氧柔性钢绞线。基础采用Φ2.5 m的钻孔灌注群桩,以抵抗软弱地质条件下荷载的竖向及水平作用力。该桥总体采用先梁后拱的施工方案。整体及局部有限元分析结果表明,桥梁结构力学性能均满足规范要求,设计安全可靠。

西安国际文化传播中心大跨斜幕墙支承结构设计

西安国际文化传播中心大跨斜幕墙支承采用竖向张弦桁架结构体系,结构造型独特新颖。对其结构选型和受力特点进行了重点介绍。采用MIDAS Gen软件建立有限元模型,进行非线性静力及抗震分析计算,同时采用ANSYS软件对考虑几何与材料双重非线性的结构整体稳定性进行了详细分析,探讨了安全系数取值等。分析结果及实际使用效果表明,幕墙支承满足正常使用的各项要求,并具有良好的抗震性能。

大倾角煤层抗剪锚杆设计与测试

为了减少大倾角煤层斜梯形巷道变形破坏,设计了新型抗剪锚杆,分析了锚杆工作原理及锚杆参数。以东峡煤矿为工程背景,采用物理模拟、数值模拟和现场监测相结合的研究方法,对大倾角斜梯形巷道抗剪锚杆支护进行了研究。结果表明,在加载中,原支护模型在4.9 MPa即发生破坏,而抗剪锚杆支护模型在7 MPa发生破坏,原支护试验顶板下沉量较大,其变形量及变形速度远大于抗剪锚杆支护试验;抗剪锚杆能有效控制巷道顶板离层,离层量为21~129 mm,抗剪锚杆能够承受的极限破断载荷为155 kN,能有效控制深部围岩的变形。

倾斜薄层炭质板岩隧道围岩大变形特征及其卸荷破坏防控对策研究

针对云南香丽高速公路11座典型倾斜薄层炭质板岩隧道,通过围岩变形监测、离散-连续耦合数值分析手段,研究了围岩大变形特征和卸荷变形破坏机制,并提出了相应防控对策。结果表明:(1)倾斜薄层炭质板岩隧道围岩变形受开挖卸荷和施工扰动影响大,围岩变形具有量值大、速率快、持续时间长的特点,拱部沉降大于水平收敛,为围岩卸荷大变形,整体呈现出非对称的空间分布特征;(2)围岩变形破坏随台阶施工进一步发展,上台阶开挖后,洞身左拱肩围岩出现弯折破坏,形成初始卸荷区域,具有显著的非对称特点,随着中、下台阶施工步序推进,左拱肩围岩的弯折破坏进一步发展,隧道拱部与右拱肩的围岩也逐渐产生朝向左侧的剪切滑移破坏,最终导致拱部卸荷破坏区域的整体扩张;(3)地层预加固是控制倾斜薄层炭质板岩隧道围岩变形的主要有效手段,同时可结合降低施工扰动、优化支护时机与参数等方面对围岩变形进行综合处置。

三面围合的人字结构——北京N公寓结构设计

基于某大跨斜连体三塔结构项目,采用多软件对比小震弹性分析、时程分析以及大震动力弹塑性分析方法,对其进行了斜连体传力路径分析、斜连体超限高层结构计算分析、斜连体防连续倒塌验算、斜连体与塔楼连接薄弱部位关键节点有限元分析。分析结果表明,斜连体传力路径可靠,斜连体及与塔楼连接关键传力节点在大震下不屈服,整体结构满足大震下的变形和承载力要求。故本项目结构布置合理,结构体系安全可靠。

基于MATLAB大采高液压支架稳定性仿真研究

针对液压支架存在失稳等重大安全隐患,以某型大采高液压支架为研究对象,对支架前倾、后仰、侧翻、滑移4种失稳进行分析,运用MATLAB仿真的方法对不同采高、底座宽度、极限倾角、煤层倾角、加载载荷下的支架重心高度等进行仿真分析和研究。研究结果表明:随着支架极限倾角的增加,支架重心高度呈现逐渐减小的趋势;随着支架底座宽度增加,支架重心高度呈现逐渐增加的趋势;随着采高高度的增加,最大、最小煤层倾角呈现逐渐减小的趋势;随着支架底座宽度增加,最大、最小煤层倾角呈现逐渐增加的趋势;随着加载载荷增加,煤层倾角呈现逐渐减小的趋势。该研究为液压支架稳定性、安全可靠性提高等方面提供理论基础。

深部构造区大倾角工作面回撤致冲机理及防治技术

深部构造区大倾角工作面回撤期间冲击风险较高,为研究回撤期间致冲机理及防治技术,以潘西煤矿6199工作面为背景,采用理论分析、数值模拟,结合现场数据开展研究。结果表明:工作面受多因素影响处于复杂高静载环境,上部基本顶尖角区剪应力集中明显,工作面液压支架撤离,上覆岩层压力向工作面前方转移,局部超过极限载荷可能发生高静载加载型冲击,基本顶破断及断层活化产生动载,可能诱发动静载叠加型冲击;根据回撤前矿压数据,前方岩层活动较为剧烈,工作面微震预警事件发生前后支架阻力升高,存在基本顶破断及断层活化可能,冲击风险较高。基于回撤致冲机理提出卸压-支护协同防冲技术,即通过弱化高静载影响,降低动载产生可能性,辅助提高顺槽支护强度、控制工作面顶板降低回撤期间冲击风险;工作面回撤期间矿压监测数据无明显升高,卸压-支护协同防冲技术效果较好。

大倾角煤层智能化监测监控装备研发与应用

通过对大倾角工作面的功能配置、监测办法、工艺匹配等问题分析,以采煤机记忆截割、液压支架跟机自动化和可视化远程监控为基础,以智能控制软件为核心,实现了在地面或巷道集控中心对综采设备的智能监测与集中控制,确保工作面截煤、推溜、移架、运输、除尘等智能化运行以及工作面连续、安全、高效开采。通过对支架功能精准监测,配合智能化开采工艺手段,实现了大倾角综采自动程序操作,跟机率达到80%以上。

环境对大型激光陀螺仪的影响研究综述

基于萨格纳克效应的大型激光陀螺仪被认为是精确监测地球自转的合适传感器,可用于潜在的地面科学研究和重大工程应用,如世界时UT1精密测量,地球固体潮观测、旋转地震波探测、广义相对论预言引力磁效应等领域。激光陀螺的灵敏度随环形腔尺寸增大而提高,其运行的长期稳定性受环境变化的影响。本文从激光陀螺仪工作原理出发,梳理了温度、倾斜、气压和风等环境变化对大型激光陀螺仪灵敏度和稳定度的影响,分析说明监测环境因素变化对其输出的萨格纳克频差修正和处置方法,为提高大型激光陀螺仪应用性能提供相关指导。

超大截面钢筋混凝土外倾斜柱施工技术

随着建筑业的发展,人们对建筑行业的追求不再拘泥于适用性、耐久性的传统需求,为打破传统方形建筑的格局,越来越多的异形建筑、异形结构被应用在建筑设计中,斜柱作为异形构件,被广泛应用于新型建筑设计。结合工程实例,从测量放线、钢筋绑扎、模板加固、支撑体系及混凝土浇筑等方面详细阐述了超大截面钢筋混凝土外倾斜柱施工工艺,成功解决了相关施工难题,可为类似工程提供参考。

改进的模糊层次分析法在缓倾斜厚大矿体开采方案优选中的应用

确定合适的开采方案是矿山企业必须考虑的重要问题,影响因素较多。针对山东某金矿矿体地质赋存特征及开采技术条件,在制定初步开采方案的基础上,采用改进的层次分析法和模糊数学理论优选开采方案。综合考虑影响开采方案选择的主要因素,建立了影响因素层次结构模型,基于改进的层次分析法即三标度法计算出开采方案各评价指标的权重,采用线性函数法和二元比较排序法实现决策指标的标准化及确定隶属度矩阵,进而构建了模糊数学综合评价模型;最后针对缓倾斜厚大矿体,利用模糊数学理论,得出待选开采方案的综合优越度分别为69.5%、67.6%和65.4%,从而确定上向分层胶结充填采矿法为最优开采方案。