Research on the bearing capacity characteristics of initial support for horseshoe-shaped tunnel prefabrication

In view of the limited theoretical research on the load model of initial support for horseshoe-shaped prefabrication,this study focuses on the Luochuan Tunnel on the Xi'an-Yan'an newly built railway as the research object to explore its load model,load characteristic curve,plastic zone,deformation,and critical thickness.Theoretical research and numerical analysis were conducted.The results indicate that under the same boundary conditions,the ultimate bearing capacity of the prefabricated assembly initial support is higher than that of the shotcrete initial support,resulting in larger ultimate deformation capacity of the prefabricated assembly initial support.Based on numerical calculations,the ultimate deformation and critical thickness of the prefabricated initial lining for single-and double-track railway tunnels are obtained when buried at depths of 200,500,and 900 m in rock masses of classes Ⅲ,Ⅳ,and Ⅴ.

Initial support distance of a non-circular tunnel based on convergence constraint method and integral failure criteria of rock

For deep tunnel projects,selecting an appropriate initial support distance is critical to improving the self-supporting capacity of surrounding rock.In this work,an intuitive method for determining the tunnel’s initial support distance was proposed.First,based on the convergence-confinement method,a three-dimensional analytical model was constructed by combining an analytical solution of a non-circular tunnel with the Tecplot software.Then,according to the integral failure criteria of rock,the failure tendency coefficients of hard surrounding rock were computed and the spatial distribution plots of that were constructed.On this basis,the tunnel’s key failure positions were identified,and the relationship between the failure tendency coefficient at key failure positions and their distances from the working face was established.Finally,the distance from the working face that corresponds to the critical failure tendency coefficient was taken as the optimal support distance.A practical project was used as an example,and a reasonable initial support distance was successfully determined by applying the developed method.Moreover,it is found that the stability of hard surrounding rock decreases rapidly within the range of 1.0D(D is the tunnel diameter)from the working face,and tends to be stable outside the range of 1.0D.

Double-layer Bayesian Classifier Ensembles Based on Frequent Itemsets

Numerous models have been proposed to reduce the classification error of Naive Bayes by weakening its attribute independence assumption and some have demonstrated remarkable error performance. Considering that ensemble learning is an effective method of reducing the classifmation error of the classifier, this paper proposes a double-layer Bayesian classifier ensembles （DLBCE） algorithm based on frequent itemsets. DLBCE constructs a double-layer Bayesian classifier （DLBC） for each frequent itemset the new instance contained and finally ensembles all the classifiers by assigning different weight to different classifier according to the conditional mutual information. The experimental results show that the proposed algorithm outperforms other outstanding algorithms.

A sparse algorithm for adaptive pruning least square support vector regression machine based on global representative point ranking

Least square support vector regression(LSSVR)is a method for function approximation,whose solutions are typically non-sparse,which limits its application especially in some occasions of fast prediction.In this paper,a sparse algorithm for adaptive pruning LSSVR algorithm based on global representative point ranking(GRPR-AP-LSSVR)is proposed.At first,the global representative point ranking(GRPR)algorithm is given,and relevant data analysis experiment is implemented which depicts the importance ranking of data points.Furthermore,the pruning strategy of removing two samples in the decremental learning procedure is designed to accelerate the training speed and ensure the sparsity.The removed data points are utilized to test the temporary learning model which ensures the regression accuracy.Finally,the proposed algorithm is verified on artificial datasets and UCI regression datasets,and experimental results indicate that,compared with several benchmark algorithms,the GRPR-AP-LSSVR algorithm has excellent sparsity and prediction speed without impairing the generalization performance.

The Belt and Road Initiative and Financing Constraint for Chinese Enterprises

In the context of China’s proactive implementation of the Belt and Road Initiative(BRI),unraveling the BRI’s effect on corporate behavior is of vital importance to China’s policymaking on overseas investment.With the BRI’s enactment as a quasi-natural experiment,this paper employs the difference in differences(DID)method to investigate the BRI’s effect on the financing constraint for Chinese enterprises.Our study finds that the BRI’s implementation has significantly reduced financing constraints for BRI enterprises,and the effect is more significant for emerging advantageous industries and export-oriented node cities.

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.

Abia State Telehealth Initiative: A Novel Ingenuity

In Nigeria, Universal health coverage has been sub-optimal due to limited access and inequality. This is worsened by poor health-seeking behavior due to out-of-pocket expenditure health system financing being practiced by a greater percentage of the population. However, leveraging on the increasing population of Nigerian’s using communication technologies provides a viable and robust platform for improving patient’s care. Consequently, tele-health initiative provides a complementary approach to improving access to quality health and universal health system coverage. Tele-health initiative is Abia state’s input in progressing the Universal Health Coverage mandate of the Federal Government of Nigeria, anchored on the e-Health policy of Nigeria, after its adoption at the 58th NCH in Sokoto in 2016, of which Abia became the pioneer state for the Project. Abia state’s telecommunication market caters to almost 3.5 million active subscribers, making it the single largest provider of services in the state. Objective: The project is designed to ascertain the impact of the tele-health initiative on healthcare service coverage in Abia State. Methodology: This is a descriptive study with the quantitative and qualitative arm. The study was conducted in all the seventeen local government areas in the State. Result: 29,488 incoming calls were related to general health inquiries about basic information, counseling, and support that improved callers’ knowledge and attitude towards their health, concerns, and symptoms. Also, 66.8% of all calls (19,382) were for routine health information, complaints on mild everyday symptoms, chronic disease management, and follow-up care. About 29.6% of total calls (8751) were made by persons seeking information on socially stigmatizing topics and conditions.

从单一到多元:博士生职业发展多样化的现实需求及教育支持策略研究

博士生职业发展从单一到多元是社会发展的产物。从国内外现状看,博士生职业发展多样化缘于学术劳动力市场中精英学术岗位供需失衡、学术职位稳定性下降的“推力”与非学术劳动力市场中对高层次人才需求日益增长的“拉力”等现实因素的共同作用。然而,由于博士生学术身份固化下的择业取向单一、高校培养观念滞后下的教育支持单一、职业预期定向下的学生智能单一等问题,至今大多数博士毕业生依然囿于学术职位。本研究通过分析美国大学协会的“博士生教育倡议”项目实践,借鉴项目中试点高校通过理念更新、数据透明、机制革新、资源整合为博士生职业发展多样化提供教育支持的成功经验,针对我国博士生教育的实际情况,提出以“新定位”拓宽培养目标、以“数字化”打开求职渠道、以“强机制”助力个性化培养、以“广合作”推动资源整合等教育支持策略。

RocSupport在隧洞初期支护数值分析中的应用

不同地质条件下,泄洪输水放空隧洞开挖后的初期支护对减少围岩变形,保障施工安全有重要意义。采用RocSupport模拟了泄洪输水放空隧洞开挖及初期次支护过程,分析了不同地质条件下(Ⅳ、V类围岩)的围岩稳定性,得出V类围岩收敛变形效率较快,应及时支护并考虑预留变形量,为设计成果进行数值校核,确保初期支护措施的可靠性。

基于拉丁超立方抽样的高大模板支撑体系承载力有限元分析

目的研究不同缺陷构配件下高大模板支撑体系承载性能的变化,为高大模板支撑体系的布置、构配件的搭配及使用提供指导,以预防和减少其在实际工程中的坍塌事故。方法基于拉丁超立方抽样,考虑构配件缺陷对三种搭设参数模板支撑体系承载性能的影响,随机取线性屈曲分析中一阶屈曲承载力的0.1%~0.2%作为假想水平力,对构配件性能缺陷进行有限元分析,探究不同搭设参数下支撑体系承载力及失稳模式。结果SPR对承载力的影响大于D和t,并且双因素耦合对承载力的影响大于单因素。立杆步距的变化对支撑体系承载力的影响大于立杆间距。随着影响因素耦合数量的增加,步距对支撑体系承载性能的影响也会随之增大。结论支撑体系搭设过程中将存在缺陷的构配件使用时分散排布,可以防止高大模板支撑体系整体失稳倒塌。

“躺平”还是“奋进”?组织支持感对基层干部主动性行为的影响

如何治理“躺平”干部,让他们主动作为是当今基层政府在提升治理水平中亟需解决的一个现实问题。基于社会交换理论和自我决定理论探究组织支持感对基层干部主动性行为的影响,以及公共服务动机、组织认同在其中的作用机制。通过对江西省454名基层干部的调查发现:组织支持感能够显著激发基层干部主动性行为;基层干部公共服务动机与组织认同在组织支持感与基层干部主动性行为间发挥链式中介效应。因此,激励基层干部主动作为,应当营造有利“奋进”的基层工作环境,加强公共服务动机的建设,重视基层干部组织认同感的培养。

软土地层隧道围岩分区初期支护技术研究

软土地层通常具有较低的承载力和较高的压缩性,隧道开挖过程中极易发生变形和坍塌。为了控制围岩的变形和破坏,确保施工安全,提出软土地层隧道围岩分区初期支护技术。通过合理规划围岩压力监测点,采集压力数据;利用简化的锚杆、钢架及岩体结构面,构建初期支护本构模型;计算锚杆与钢架的最佳间距和长度,并以此为依据设计复合支护结构,实现围岩分区初期支护。结果表明:所提方法隧道沉降位移较小、塑性区分布面积较小。体现了支护技术的有效性,具有较好的应用价值。

父母自主支持对大学生生涯适应力的影响:主动性人格和个人成长主动性的作用

为了探讨父母自主支持对大学生生涯适应力的影响及其作用机制,采用父母自主支持量表、主动性人格量表、个人成长主动性量表、生涯适应力量表对961名大学生进行问卷调查。结果发现,父母自主支持不仅可以直接影响大学生生涯适应力,还可以通过主动性人格的单独中介作用、个人成长主动性的单独中介作用、主动性人格与个人成长主动性的链式中介作用间接影响大学生生涯适应力。

非线性块系岩体动力响应及在巷道防冲支护中的应用

随着煤矿开采深度的增加,冲击地压灾害日趋严重,亟需采用新方法、新理论加以防治.摆型波是在深部岩体工程中发现的新型非线性波,其使岩体出现相对分离和相对压实的不同运动状态,与冲击地压灾害的发生密切相关.针对岩体中软弱结构层的非线性变形特征,引入双曲线模型建立块系岩体中摆型波传播的非线性动力模型,研究软弱层的物理力学性质(最大闭合量、初始刚度和阻尼)对块系岩体动力响应的影响.进一步,基于块系围岩与支护系统互馈作用的理论模型,在无初始地应力和考虑初始地应力的情况下研究巷道支护系统的刚度、让位能力和阻尼耗能作用对巷道顶板动力响应的影响,分析支护系统的受力情况,为新型防冲吸能巷道液压支架设备的吸能让位行为提供理论依据.研究结果表明:基于双曲线模型建立的块系岩体的非线性动力模型能够限制岩块间软弱层的最大变形量.冲击载荷越大,增大软弱层最大闭合量时岩块的加速度降低程度越显著.增加支护系统刚度,增强支护系统让位能力和阻尼耗能能力,均可有效降低巷道顶板的加速度幅值,减轻巷道围岩对支护系统的冲击力,有效保护巷道结构.

深大竖井开挖稳定性数值模拟分析

依托芷铜高速椿木山隧道通风竖井工程,针对竖井施工对围岩造成的扰动影响以及初期支护受力情况进行数值模拟分析,探明了竖井开挖中围岩最危险区以及初期支护参数的合理性,并根据分析结果提出相应的加固或处理措施。结果表明:竖井施工对围岩造成的扰动较小,围岩不会出现明显的塑性区,揭示了在开挖并施作初期支护后,围岩具有一定的稳定性;随着开挖深度的加大,岩体最大应力也在增大,在竖井底部达到最大值3.36 MPa,地表沉降曲线呈现出明显的V形特征,中间沉降量大,越远离中部开挖区,沉降量越小;不同性质的围岩过渡区会出现应力突变,在实际操作中应加强围岩过渡区的支护与监测频率。

基于数据驱动的液压支架初撑后承压效果即时预测技术

采煤工作面实际生产中,受顶板条件、采动、液压支架姿态影响,液压支架初撑后立柱压力可能发生变化,进而影响支架初撑后承压效果。液压支架在初撑后出现的承压失效可能导致煤壁片帮、架间冒漏、支架前倾、倒架等问题。目前智采工作面液压支架初撑力调控策略大多是直接判断升柱时立柱压力是否达到额定初撑力,缺乏考虑初撑后立柱压力变化引起的承压效果判断。针对上述问题,提出了一种基于立柱压力数据驱动的液压支架初撑后承压效果即时预测方法。将液压支架初撑后3 min内的立柱压力历史数据状况分为6种典型工况,并根据初撑后承压效果的不同将6种典型工况分为有效承压或失效承压;通过相关性分析,确定了影响支架初撑后承压效果的5个特征因素;对立柱压力样本进行有效承压或失效承压人工标注,并进行特征提取,将特征值分别输入决策树、随机森林、支持向量机、K最近邻(KNN) 4种不同算法建立预测模型,经过对比分析,随机森林模型预测准确率最高,达到95.60%,基本满足模型应用的准确率要求;建立了基于随机森林的液压支架初撑后承压效果即时预测模型,在此基础上开发了液压支架初撑后承压效果即时预测系统,并部署到煤矿现场应用,经过连续25 d的运行,该系统采集到液压支架初撑后3 min内的立柱压力后,可在5 s内输出液压支架初撑后的承压效果,预测结果与实际操作记录对比准确率为82.48%,说明该系统具有较高的承压效果预测准确性。

西南山区某浅埋铁路隧道初期支护变形侵限治理措施研究

西南山区某浅埋铁路双线隧道主要穿越全风化、强风化玄武岩,在隧道支护过程中发生多次变形侵限,最大变形达205 mm,给施工造成极大困难。为解决施工中存在的地表沉降、隧道变形及初期支护侵限问题,文章基于隧道支护结构的破坏特征,分析了隧道产生变形侵限的原因,确定隧道变形侵限段的临时支护形式,采用交叉中隔墙(CRD)法开挖,并采用隧道锚管径向注浆加固围岩、钢架支护等加强支护措施。通过实施以上技术方案,隧道顺利完成了对变形侵限的处理,并取得了较好的加固效果,可为类似隧道的施工处理提供借鉴和参考。

铁路隧道初期支护混凝土爆破累积损伤特征

依托京张高铁草帽山隧道工程,开展爆破振动监测及声波测试。爆破振动监测结果表明:隧道初期支护对应的质点峰值振动速度满足萨道夫斯基公式。声波测试结果表明:随着爆破次数的增多,爆破累积损伤逐渐增大。但随着爆破距离的增大,累积损伤的增量却呈逐渐减小的趋势。通过数据分析及曲线拟合的方式分别得到爆破施工对应的累积损伤范围(R_(cr))及临界爆破振动速度(PPV_(cr))。数值分析结果显示,累积损伤范围(R_(cr))与对应的临界爆破振动速度(PPV_(cr))之间存在良好的指数函数关系,通过设定相应的爆破振动速度阈值可以达到定量控制爆破损伤范围的目的。

300 m^(2)级5车道隧道九硐室施工力学特性数值计算

针对深圳侨城东路宝鹏大型地下互通式立交涉及的300 m^(2)级5车道超大断面隧道,开展施工技术方案及结构受力研究.首先,提出一套“分硐室开挖+衬砌加强支护”的超大断面隧道九硐室开挖施工技术.然后,结合隧道几何尺寸及支护方案,建立Midas三维有限元数值计算模型探究5车道超大断面隧道开挖施工动态力学响应特性.最后,提取隧道各分部结构应力云图,统计特征测点应力及位移监测曲线.研究结果表明:施工期间需采用超前小导管+管棚注浆措施对围岩进行预加固;现场需通过双侧壁导坑+双临时横撑构成九硐室开挖工法,并采用双层初期支护+加强加厚二次衬砌支护方案;现场开挖施工后结构应力与位移呈现快速增加趋势,而后隧掌子面不断前移各统计曲线逐步趋于平稳;围岩压力峰值可达2.01 MPa,拱顶位置超前小导管内力值最大为10 kN,两侧拱腰位置管棚内力最高为20 kN,拱腰及拱脚位置钢拱架内力最大为113 kN,拱肩位置锁脚锚杆内力在第66开挖施工步达到18 kN;初支结构测点应力峰值为2.4 MPa;初支拱顶、拱肩部位沉降峰值分别为12.4、6.8 mm;管棚、锁脚锚杆等结构联合支护效果明显.

矿山法隧道初期支护中栓钉型钢与喷射混凝土界面黏结滑移本构模型与试验研究

[目的]为探明矿山法隧道初期支护中栓钉型钢与喷射混凝土界面黏结滑移本构关系。[方法]以栓钉长度、直径和布置形式为变化参数,设置4组不同工况,进行腹板带栓钉的型钢-喷射混凝土短柱推出试验,分析其破坏模式、荷载-滑移特性和承载力等。[结果及结论]栓钉试件的破坏模式受栓钉数量和强度影响,分为拉裂破坏和胀裂破坏两类;典型的平均黏结强度-相对滑移曲线可分为无滑移段、曲线上升段、曲线下降段和水平残余段;室内试验证明栓钉直径和布置形式是影响承载能力的主要因素;根据受力机制建立带栓钉的型钢与喷射混凝土界面的黏结滑移本构模型,并经室内试验和数值模拟双重验证,表明提出的黏结滑移本构模型精度较高。研究结果可为矿山法隧道型钢与喷射混凝土支护结构设计提供理论支持。