江苏句容磨盘山地区茅西断裂的新认识

句容磨盘山高速公路隧道工程地质勘探中,发现龙王山组逆覆在浦口组之上,又被Q1-2砾石层不整合覆盖。据该现象所处的空间位置可以认为,该断裂即为茅西断裂,其活动时间应在K2p浦口组沉积之后,且有一组(至少两条)断裂组成。     

四川锦屏山-西昌地区地质条件与地质灾害发育情况

地质灾害发育程度与当地地质条件息息相关,地质条件又主要与出露的地层岩性、构造产状、地形地貌相关;地质灾害发育情况亦与气象条件和人类工程活动有一定关系.     

龙首山成矿带芨岭北东向深大隐伏断裂构造存在的佐证

龙首山成矿带是我国著名的镍、铁、铜、铀等多金属矿产地,北西向断裂作为铀矿控矿构造特征明显。为了查清芨岭北东向隐伏深大断裂是否存在,综合分析研究区的磁场、重力场和遥感影像特征,识别出芨岭北东向的深大断裂,认为该断裂属于早期的深大断裂,晚期复活错断了北西向断裂,北东向与北西向深大断裂交汇处是铀成矿的有利靶区。这一结论可能为该区深部找矿提供参考。     

断裂构造对山区公路隧道选线与施工的影响研究

断裂构造对于岩体的工程性质起着十分重要的作用。建设中的十漫 (十堰至漫川关) 高速公路,地处两郧断裂带穿越地区。结合该段最长的隧道——二道垭隧道左、右隧道不同围岩类别与特征,分析了两郧断裂带的影响。针对隧道不同围岩类别,探讨了不同的开挖和支护方法,并就其施工效率和成本进行了比较分析。研究成果表明, 断裂构造对隧道施工和稳定性有重要影响。高速公路选线应加强勘察,尽量避开断裂带,从而达到施工安全、迅速、经济的目的。     

关于吉林黄榆、吉昌地区石炭系磨盘山组穿时性的讨论

本文主要就吉林省永吉县至磐石市一带石炭系磨盘山组地层穿时的讨论,从沉积的石灰岩特征和所含生物化石特征阐述这套巨厚的石灰岩具有穿时特征,根据不同位置测量剖面及化石对比进一步验证了对这一问题的看法。     

四川西昌——攀枝花高速公路的酸水湾滑坡与线路选择

四川西昌-攀枝花高速公路的酸水湾隧道下穿巨型古滑坡,本文从其所处的地质构造背景分析入手,简述了滑坡特征及其对工程建设的影响,并与国内的地震破坏性统计资料对比后认为,该处位于磨盘山深大断裂东侧,次级小断裂比比皆是,滑坡连连,是潜在的危险地段,因此建议改线.建议路线既能避开危险地段,又能减少隧道长度.     

骊山山前断裂对西安地铁临潼线隧道的影响研究

以西安地铁临潼线穿越骊山山前断裂为研究背景,采用数值模拟方法,通过建立地铁隧道-断裂-地层三维有限元模型,研究了骊山山前断裂错动作用下隧道结构的变形受力特征,以此揭示了骊山山前断裂错动作用对西安地铁临潼线的影响机制以及重点设防位置,确定了地铁临潼线的设防范围,提出了相应防治建议措施。研究结果表明:断裂错动作用造成地铁隧道沿纵向发生弯曲变形,大致可分为3个变形区域:下盘稳定区、剪切拉张区和整体沉降区。断裂附近地层竖向应力和隧道拱底接触压力均表现为上盘减小而下盘增大,而隧道拱顶接触压力在上盘增大下盘减小。同时,沿纵向隧道顶部结构在上盘受压而下盘受拉,底部结构受力刚好相反,在上盘受拉下盘受压;隧道受剪区范围随断裂位错量变化基本保持不变,且最大值均出现在与断裂相交位置处。最后,综合确定了西安地铁临潼线跨越骊山山前断裂的纵向设防长度至少为80 m,并给出了跨断裂西安地铁临潼线的防治措施。研究结果可为西安地铁临潼线跨越骊山山前断裂带设计及其病害防治提供科学参考。     

深基坑开挖对武汉长江隧道影响数值模拟

以临近武汉长江隧道的华电集团华中总部研发基地基坑项目为研究对象,采用岩土、隧道结构专用有限元分析软件 MIDAS/GTS NX对该基坑施工过程中的9个施工工况进行模拟,得到基坑开挖完成后的地层、连续墙、隧道变形情况以及基坑开挖前后的隧道应力情况,并进行分析,得出模型的建立是合理可行的,且基坑开挖、支护变形带动坑外土体位移,引起临近基坑侧隧道产生水平位移最大值为4.17 mm;隧道的应力值与基坑开挖前的变化不大,在安全范围内。     

磨盘山水库坝基渗透稳定研究

磨盘山水库兴建遇到的主要地质问题是坝基渗漏及渗透稳定问题,将影响水库工程效益的发挥和大坝的安全运行,需采取适当的渗控工程措施。通过对坝基土颗粒组成及结构的分析,判别可能发生渗透破坏的类型,确定抗渗比降和允许比降。应用Visual MODFLOW进行水库坝区渗流场的三维渗流数值模拟分析,通过对18种渗控计算方案渗流场、渗流要素及防渗效果的统计分析,依据坝基土的允许比降,在安全、经济、合理原则的基础上,确定哈尔滨市磨盘山水库坝基渗控设计首选方案为：左岸防渗长度200 m、帷幕灌浆标准5 Lu。     

Analysis of the Influence of a Natural Fracture Network on Hydraulic Fracture Propagation in Carbonate Formations

A new experimental model has been designed to simulate the influence of a natural fracture network on the propagation geometry of hydraulic fractures in naturally fractured formations using a tri-axial fracturing system. In this model, a parallel and symmetrical pre-fracture network was created by placing cement plates in a cubic mold and filling the mold with additional cement to create the final testing block. The surface of the plates will thus be weakly cemented and form pre-fractures. The dimension and direction of the pre-fractures can be controlled using the plates. The experiments showed that the horizontal differential stress $\Updelta \sigma$ and the angle $\Updelta \theta$ between the maximum horizontal principal in situ stress and the pre-fracture are the dominating factors for the initiation and propagation of hydraulic fractures. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma \ge 2{\text{ MPa}}$ or $\Updelta \theta = 60^\circ$ and $\Updelta \sigma \ge 4{\text{ MPa}}$ , the direction of the initiation and propagation of the hydraulic fractures are consistent with or deviate from the normal direction of the pre-fracture. When the hydraulic fractures approach the pre-fractures, the direction of the hydraulic fracture propagation will be consistent with the normal direction of the pre-fracture. Otherwise, the hydraulic fracture will deflect and perpendicularly cross the parallel and symmetric pre-fracture network. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma < 2{\text{ MPa}},\,\Updelta \theta = 60^\circ$ , and $\Updelta \sigma < 4{\text{ MPa}}$ or $\Updelta \theta = 45^\circ$ and $\Updelta \sigma = 4 - 8{\text{ MPa}}$ , before the hydraulic fracture and the pre-fractures intersect, the direction of the hydraulic fracture propagation remains unchanged, and the pre-fractures open or dilate when the hydraulic fracture propagates to the intersection point, forming a complicated hydraulic fracture network with the propagation region of the overall hydraulic fracture network taking the shape of an ellipse. In this condition, the complexity level of the hydraulic fracture is controlled by the net pressure, the compressive normal stress acting on the pre-fractures, the shearing strength and the cohesion strength of the planes of weakness. The conclusions of this research are inconsistent with the formulation of the approach angle that has been widely accepted by previous studies. The principle of hydraulic fracture propagation is that it follows the least resistance, the most preferential propagation, and the shortest propagation path.     

2D Tunnel Numerical Investigation: The Influence of the Simplified Excavation Method on Tunnel Behaviour

Tunnel excavation is a three-dimensional (3D) problem. However, despite recent advances in computing resources, 3D models are still computationally inefficient and two-dimensional (2D) simulations are therefore often used. Modelling the tunnelling process in a 2D plane strain analysis requires a specific approach that allows a 3D tunnelling effect to be taken into consideration. As far as the urban tunnels are concerned, most cases reported in the literature have focused on estimating the applicability of these equivalent approaches that are based on the evaluation of the settlement that develops on the ground surface, without considering the influence of segment joints. The main objective of this study was to provide a 2D numerical investigation to highlight the influence of two equivalent approaches, that is, the convergence-confinement method (CCM) and the volume loss method (VLM), on the behaviour of a tunnel built in an urban area, in terms of not only the surface settlement but also the structural lining forces, taking into account the effect of segment joints. A technique that can be used to simulate the tunnel wall displacement process, based on the principles of the VLM, has been developed using the FLAC^3D finite difference program (Itasca in FLAC fast Lagrangian analysis of continua, version 4.0; User’s manual, http.itascacg.com, 2009). A comparison with 3D numerical results has been introduced to estimate the precision of these 2D equivalent approaches. The results have shown a significant influence of the tunnel boundary deconfinement technique and segment joints on the tunnel lining behaviour and surface settlements. The structural forces obtained by means of the CCM are often smaller than those determined with the VLM for the same surface settlement. Generally, the structural lining forces determined by the CCM are in better agreement with the 3D numerical results than the ones obtained with the VLM. However, in order to obtain an accurate estimation of the structural forces, the impact of the construction loads during tunnelling should be taken into account.     

小型溶洞对隧道稳定性的影响分析

根据钻探、物探资料,拟建南京地铁3号线滨江路站—五塘村站沿线穿越的灰岩地层中有数量较大的洞径为2～3m的小型溶洞。通过对该地区地质背景的分析发现,岩溶明显受断裂构造控制,溶洞发育规模小但数量多,对开挖后隧道的围岩稳定性有一定的影响。采用数值分析法研究了小型溶洞尺寸、与隧道位置关系等不同因素对隧道围岩稳定性的影响。计算结果表明,当溶洞尺寸和位置变化时,围岩塑性区也发生变化,塑性区面积随着溶洞尺寸的增大而增大。溶洞位于拱肩时塑性区面积最大,对围岩的稳定性影响大,位于拱腰时最小。隧道开挖后拱顶和拱底处最易破坏,相近条件下串珠状溶洞比单个溶洞的危害性要大。     

降云顶隧洞裂隙夹泥层爆破施工技术

裂隙夹泥层对爆破施工有着较大的影响。通过降云顶隧洞爆破施工的实践,分析探讨裂隙夹泥层对爆破施工的影响及应对措施。     

Effect of Tunnel Shape and Support System on Stability of a Tunnel in a Deep Coal Mine in China

Stability level of tunnels that exist in an underground mine has a great influence on the safety, production and economic performance of the mine. Ensuring of stability for soft-rock tunnels is an important task for deep coal mines located in high in situ stress conditions. The aim of this study is to investigate the effect of tunnel shape and support pattern on the deformation, failure zone and stability around a tunnel located in a coal rock mass in China and to select an appropriate tunnel shape and a support pattern to provide a stable stress-deformation condition around the tunnel. Using the available information on stratigraphy, geological structures, in situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces, a three-dimensional numerical model was built using the FLAC software to simulate the stress conditions around the tunnel in the coal rock mass. Analyses were conducted for several tunnel shapes and rock support patterns. Results obtained for the distribution of failed zones, and stress and displacement fields around the tunnel were compared to select the best tunnel shape and support pattern to achieve the optimum stability conditions. Also, a comparison is given between the numerical predictions and field deformation monitoring results.