Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

The Freeze-Sealing Pipe-Roof(FSPR)method,which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge,is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions.When the FSPR method is used to construct shallow burial submerged tunnels,the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel,and its waterproof performance needs to be further investigated.In this paper,a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation.The results show that excavation has a weakening effect on both sides of the frozen wall,with a greater effect on the inner side,and a positive temperature appears in the local area inside the jacked pipe.The concrete fill in the jacked pipe obviously improves the freezing efficiency,and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m,i.e.,the design requirement.In practice,the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel.The study serves as a technical reference for the design and implementation of similar projects.

Reduction of Undercuts in Fillet Welded Joints Using Taguchi Optimization Method

This project work focuses on the reduction of weld undercuts using the Taguchi method. The phenomenon of weld undercuts constitutes a major problem for the welding industry. When undercuts occur, and particularly when such cuts are deep, it has a negative impact on the weld as it lowers the integrity and quality of the weldment. Therefore, efforts are made globally to reduce the depth of such weld undercuts to the barest minimum. Several optimization methods have been adopted;however, in this study, the Taguchi method is applied. “The smaller the better components” of the Taguchi method is applied. From the results obtained from applying this Taguchi method, the optimum process parameters obtained are A2-B1-C2, which are a voltage of 20 V, a current of 180 A, and a welding speed of 130 mm/s, required to form an undercut of 0.03 mm. Whereas the existing process parameters used by the company are A1-B3-C, which make an undercut to a depth of 0.09 mm. It is concluded that the use of Taguchi method has been able to reduce the depth of undercut as shown in this study. A step-by-step approach is presented in the study.

Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young＇s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper. Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including △L, we finally extract Young＇s modulus from the measured resonance frequency versus effective length dependency and find that Young＇s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.

Effect of undercut defect on deformation behavior TC4 titanium alloy laser welded butt joint under static tensile loading

By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.

Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young’s modulus from the measured resonance frequency versus effective length dependency and find that Young’s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.

阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响

滑阀流道呈现一种非对称且变化的复杂流道,阀内形成湍流流动,致使阀芯表面受到不均匀压力作用,形成不平衡力,导致阀芯出现倾斜,增加阀芯卡滞的风险,影响滑阀正常工作。针对这个问题,研究了阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响。首先,简化了滑阀流道模型,采用数值模拟方法建立了滑阀瞬态流动分析模型;然后,基于伯努利效应,分析了不同偏心沉割槽时阀芯表面不均匀压力分布规律;最后,获取了不平衡力计算公式,研究了不同沉割槽偏心距对阀内流动特性、阀芯表面受力及径向不平衡力的影响。研究结果表明:采用偏心沉割槽结构减缓了出口段阀芯下表面区域的湍流程度,有效降低了阀芯径向不平衡力的大小;沉割槽偏心距为1.92 mm时,阀芯受到的不平衡力最小,相对于无偏心沉割槽,径向不平衡力在开度为0.5 mm时减小了77.63%,开度为1.5 mm时减小了50.18%,有效减缓了阀芯的倾斜程度。该研究结果对阀体沉割槽设计及阀芯不平衡力抑制方法的研究具有一定参考价值。

秘鲁邦沟铁矿自然崩落法矿岩崩落参数研究

自然崩落法开采过程中需要准确预测岩体的崩落行为,以保证安全生产作业。为了探究岩体崩落行为,通过数值模拟的方法深入分析自然崩落法矿岩崩落的时空演化规律,基于FLAC3D软件构建秘鲁邦沟铁矿实际地层三维模型,结合Burgers-Mohr本构模型,研究了矿岩初始和持续崩落拉底面积、矿岩持续崩落速度、全过程拉底地表沉陷以及矿岩崩落量等关键技术参数。结果表明:邦沟矿初始和持续崩落拉底面积分别在864~1350 m^(2)和5400~6534 m^(2);持续崩落速度为0.3112 m/d;全部拉底完毕后,矿岩崩落总量为63012万t,可满足设计产能需求。研究结果可为自然崩落法关键技术参数的研究提供新的思路和方法。

城市地下综合管廊浅埋暗挖法施工安全风险探讨

针对城市地下综合管廊浅埋暗挖法施工安全风险展开探讨,分析了地下综合管廊浅埋暗挖法施工安全风险因素,识别确定了浅埋暗挖法施工安全的致灾风险因素。基于此,构建了城市地下综合管廊浅埋暗挖法施工安全风险指标体系,指标体系包括技术风险因素、人员风险因素、环境风险因素、物料机械风险因素和施工管理风险因素5个方面,同时介绍了浅埋暗挖法施工安全风险评价贝叶斯网络模型;并提出了城市地下综合管廊浅埋暗挖法施工安全风险的关键问题。

岩石地区浅埋暗挖地铁车站支护结构设计初步研究

青岛地区地基多为岩浆岩类硬质岩石。以青岛地铁江西路站为例,利用工程类比法结合数值计算法,对其进行支护结构设计,并对计算结果进行了分析,提出了可行性设计方案。指出了针对青岛特殊地层条件下浅埋暗挖地铁站的支护结构型式、模型、设计方案优化等关键技术问题,以期为岩石地区浅埋暗挖法进一步推广应用提供理论依据。

厦门翔安海底隧道CRD法施工数值分析

厦门海底隧道属国内首建,出口端地层软弱、易膨胀、随挖随塌,稳定性差,施工难度很大。根据该地段的地质条件,设计六种不同的开挖与支护工况,利用数值法分别模拟这六种开挖过程的地层三维变形状态,分析和总结其变形、失稳规律,优化隧道开挖和支护方案及其工艺,提出了实用且可靠的施工措施和建议,有效地指导了施工,解决了施工技术难题。为同类工程建设提供了理论依据和实践经验。

岩体崩落机理的数值模拟研究

利用三维有限元法对铜矿峪铜矿５号矿体和程潮铁矿岩体崩落机理进行研究，探讨了不同削弱工程对采场应力分布的影响，得出了岩体削弱后的崩落机理，同时对初始拉底面积进行分析。

航天器迎风面不同位置原子氧掏蚀效应的数值模拟研究

Kapton作为基底的热控涂层被广泛应用于航天器的外表层设计中。近地轨道航天器的飞行方向与航天器表面法线之间的夹角(在本文中简称为ANI)对原子氧掏蚀效应有较大的影响。文章利用Monte Carlo方法研究了航天器迎风面(即0°≤ANI≤90°处)上ANI与掏蚀效应之间的关系。结果表明,束流和撞击能量不变时,ANI的增加会引起原子氧掏蚀空腔发生同向倾斜,空腔的深度不断减小,而宽度将急剧增加;当保护层厚度一定时,ANI的增加还会引起缺陷处入射的原子氧的反应率降低。

隧道工程浅埋暗挖法施工要点

明确了浅埋地下工程的基础概念,阐述了浅埋暗挖法的基本原理及发展方向,指出了浅埋暗挖法的施工原则。同时对浅埋暗挖各施工方法(全断面法、台阶法、中隔墙法和交叉中隔墙法、双侧壁导坑法、双CD法及特大断面的施工方法包括中洞法、柱洞法、侧洞法和桩柱法)的施工要点,适用范围及条件,优缺点进行了介绍和比较。最后总结强调了浅埋暗挖法施工要点。

表面缺陷对原子氧掏蚀效应影响的数值模拟研究

Kapton作为基底的热控涂层被广泛应用于航天器的外表层设计中,表面保护层中缺陷处所发生的掏蚀效应是近地轨道空间飞行时原子氧对此类热控材料作用的一种主要方式。文章通过蒙特卡洛方法研究了这些尺寸参数与原子氧效应之间的关系。结果表明,保护层缺陷的宽度直接影响进入缺陷内的原子氧的数量,空腔的“颈部”宽度与空腔最大宽度之比随着缺陷宽度增加,掏蚀深度的增加速度则随着缺陷的加宽而变小;保护层厚度主要对初次入射原子氧的入射过程有影响,加厚保护层可以减小原子氧的掏蚀深度和掏蚀空腔的宽度。这些结果可为原子氧防护层的设计提供参考依据。

注浆在地铁矿山法隧道中的应用

研究目的:随着我国城市轨道交通的快速发展,在城市地铁中按喷锚构筑法原理进行设计和施工的浅埋暗挖矿山法隧道越来越多,本文旨在分析在矿山法隧道中各种辅助施工措施的特点、适用条件。研究方法:通过对多个矿山法隧道的调查研究,对不同文地质条件、周边环境下的注浆措施进行分析对比和总结。研究结论:在城市地铁中的矿山法隧道,需根据工程的周边环境、隧道埋置深度、工程及水文地质条件、隧道断面尺寸,结合隧道施工的基本工法,选择合理的注浆参数,对地层及围岩进行必要的加固和止水,不但可以避免较多的施工风险,节约工程投资,而且还可以减少对周边环境的影响及破坏,满足工期的要求。

中深孔扩漏拉底方法在浅孔留矿法中的应用

锡铁山铅锌矿随着开采深度的下降,薄矿体逐渐增加,应用浅孔留矿法所占的比例越来越大。本文将浅孔留矿法形成底部结构的浅孔扩漏、拉底两步法改为中深孔扩漏拉底一步到位法。经过应用,证明这种方法提高了劳动生产率,降低了生产成本,取得了很好的经济和社会效益。

齿轮弯曲强度与沉切量关系研究

滚—磨工艺加工的齿轮,由于磨前滚刀有凸台,齿轮根部就有沉切。沉切量与磨前滚刀结构参数和变位系数及留磨量等参数有关。在磨前滚刀参数一定的条件下,对不同沉切量的齿轮分别用有限元方法计算了齿根拉应力和压应力,结果表明:沉切量与弯曲强度之间存在最佳的对应关系。

高强度梁类件回弹及补偿的二维截面法修正

针对现有的二维截面法预测、补偿回弹时无法有效地解决高强度汽车梁类件在成形后出现的纵向回弹及冲压负角问题,提出了修正算法对原算法进行修正及补充。修正后的算法充分考虑了各个关键截面的纵向回弹,针对迭代效率及精度,在补偿算法基础上引入了材料系数及能动系数来保证算法的合理性和可行性。根据侧壁角度回弹及卷曲回弹的不同变形模式,对补偿算法进行了考虑冲压负角的修正及补充。以某典型拼焊板汽车梁类件为例,对修正前后的二维截面算法进行了对比,实验结果证明了修正算法的可行性。

融雪剂融冰能力评价方法研究

为准确测试和区分不同融雪剂的除雪融冰性能,参考相关标准,通过分析国内外融雪剂融雪除冰试验条件及现存问题,确定了融冰试验、渗透试验、下切试验和振动融冰试验4种试验方法。将试验条件作为试验变量,根据测试结果显著性、数据重复性、融雪剂区分性3方面因素,确定了融冰能力、渗透能力、下切能力的试验方法、试验指标及最佳试验条件。结果表明:融冰能力测试结果随培养皿直径增加呈先增加后降低趋势,随冰样厚度和测试时间呈增加趋势;渗透深度测试结果随钻孔直径增大而降低,随测试时间增加逐渐增加,染色剂中荧光素钠盐染色效果较优;下切面积测试结果随加热棒直径和测试时间增加逐渐增大;3种融雪剂中氯化钙综合除雪融冰性能较强,同时改进的试验方法与SHRP试验方法对比,其融冰能力、渗透能力和下切能力试验标准差降低39%~94%,测试结果较为准确、可重复性较高、对融雪剂的区分性更强。这说明改进的试验方法不仅可以综合反映融雪剂融雪除冰过程,还能准确测定和区分融雪剂不同性能,对我国标准评价方法单一、与实际适用条件不符以及SHRP试验方法重复性较低的情况进行了补充与改善。

自然崩落法在中厚矿体中的应用研究

自然崩落法是一种高效率的地下采矿方法。我院在金山店铁矿对该采矿方法进行了卓有成效的试验研究，取得了圆满的成功。其试验矿秧的地质矿量达２８．４万ｔ，属建国以来规模最大的一次试验。本文主要论述了矿石的可崩性和应力状态的调查、分析与计算；崩矿过程的室内模拟实验；现场回采与放矿的生产试验。最后依据试验结果，对该采矿方法所取得的巨大技术经济效果作了评价。