Investigation of rock salt layer creep and its effects on casing collapse

Casing collapse is one of the costly incidents in the oil industry. In the oil fields of southwest Iran, most casing collapses have occurred in Gachsaran formation, and the halite rock salt layer in this formation may be the main cause for these incidents because of its peculiar creep behavior. In this research, triaxial creep experiments have been conducted on Gachsaran salt samples under various temperatures and differential stresses. The main purpose was to determine the creep characteristics of Gachsaran rock salt,and to examine the role of creep in several casing collapses that occurred in this formation. Results indicated that the halite rock salt of Gachsaran formation basically obeys the power law;however, its creep parameters are quite different from other halite rocks elsewhere. The time-dependent creep of Gachsaran rock salt exhibits strong sensitivity to temperature change;however, its sensitivity to variation of differential stress is rather low. The numerical simulation of the rock salt creep in a real oil well demonstrated the importance of creep and reservoir conditions on the safety factor of the tubing related to casing collapse.

Deformation mechanism and collapse treatment of the rock surrounding a shallow tunnel based on on-site monitoring

When tunnels are constructed at shallow depths in areas with poor geological conditions,such as portal sections,valleys and hillsides in regions with granitic bedrock,considerable excavation-induced deformation of the surrounding rock may occur,potentially resulting in tunnel collapses.The main reason for these problems is the lack of understanding of the deformation mechanism and evolution of the soft granitic rock surrounding the tunnel and the adoption of inappropriate construction technology and methods.This article analyzes the deformation mechanism of the rock surrounding a shallow tunnel based on in situ monitoring data as a case study and suggests that certain measures should be taken to effectively control the deformation of the surrounding rock and to minimize the potential for tunnel collapse.The results show that the deformation of the granitic soil surrounding the tunnel can be divided into three stages:the rapid deformation stage,the slow deformation stage and the stabilization stage.Appropriate construction methods should be carefully selected to ensure safety during tunnel excavation in the first stage.To avoid secondary disasters caused by tunnel collapses,three treatment measures may be implemented as part of safety management:enhancing the monitoring of the surrounding rock deformation,adjusting the construction methods and optimizing the support systems.In particular,accurate monitoring data and timely information feedback play a vital role in tunnel construction.Therefore,engineers with considerable engineering experience and professional knowledge are needed to analyze the monitoring data and make accurate predictions of tunnel deformation to ensure that reasonable measures are taken in the process of shallow tunnel excavation.

Analysis on Fracture Mechanics of Unstable Rock

Unstable rock is a kind of global geological disaster with high frequency. This paper, considering three kinds of combined loads which are gravity, fracture water pressure and seismic force, constructs a unstable rock mechanics model and it uses a fracture mechanics method to deduce the composite stress intensity factor of the type I - II. Based on the maximum circumferential stress theory, this article calculates the theo-retical fracture angle by triangle universal formula.

Earthquake-induced collapse mechanism of two types of dangerous rock masses

As the economy of China develops, an increasing number of key traffic projects have been undertaken in the west of China, where there are high, steep rock slopes. The collapse of dangerous rock masses, especially following a strong earthquake, is one of common geological disasters known in rock slope engineering. Therefore, it is important to study the collapse mechanism of dangerous rock masses induced by an earthquake and the analysis approach of its stability. This study provides a simple and convenient method to determine the collapse mechanisms of two types of dangerous rock masses(i.e. cantilever and upright) associated with the definition and calculation of the safety factor, which is based on the flexure theory of a constant-section beam by combining with the maximum tensile-stress criterion to depict the process of crack propagation caused by seismic waves. The calculation results show that there are critical crack depths in each form of the dangerous rock masses. Once the accumulated depth of the crack growth during an earthquake exceeds the critical depth, the collapse will occur. It is also demonstrated that the crack extension amount of each step is not a constant value, and is closely associated with the current accumulated crack depth. The greater the cumulative crack depth, the more easily the crack propagates. Finally, the validity and applicability of the proposed method are verified through two actual engineering examples.

Energy conversion and deposition behaviour in gravitational collapse of granular columns

The high-density gravitational collapse of granular columns is very similar to the movements of large collapsing columns in nature. Based on the development of dangerous columnar rock mass in fields, granular column collapse boundary condition in the physical experiments of this study is a new type of boundary conditions with a single free face and a three-dimensional deposit. Physical experiments have shown that the mobility of small particles during the collapse of granular columns was greater than that of large particles. For example, when particle size was increased from 5 to 15 mm, deposit runout was decreased by about 16.4%. When a column consisted of two particle types with different sizes, these particles could mix in the vicinity of layer interfaces and small particles might increase the mobility of large particles. In the process of collapse, potential and kinetic energy conversion rate is fluctuated. By increasing initial aspect ratio a, the ratio of the initial height of column to its length along flow direction,potential and kinetic energy conversion rate is decreased. For example, as a was increased from 0.5 to 4, the ratio of maximum kinetic energy obtained and total potential energy loss was decreased from47.6% to 7.4%. After movement stopped, an almost trapezoidal body remained in the column and a fanlike or fan-shaped accumulation was formed on the periphery of column. Using multiple exponential functions of the aspect ratio a, the planar morphology of the collapse deposit of granular columns could be quantitatively characterized. The movement of pillar dangerous rock masses with collapse failure mode could be evaluated using this granular column experimental results.

Stability of coal pillar in gob-side entry driving under unstable overlying strata and its coupling support control technique

Considering the situation that it is difficult to control the stability of narrow coal pillar in gob-side entry driving under unstable overlying strata, the finite difference numerical simulation method was adopted to analyze the inner stress distribution and its evolution regularity, as well as the deformation characteristics of narrow coal pillar in gob-side entry driving, in the whole process from entry driving of last working face to the present working face mining. A new method of narrow coal pillar control based on the triune coupling support technique (TCST), which includes that high-strength prestressed thread steel bolt is used to strain the coal on the goaf side, and that short bolt to control the integrity of global displacement zone in coal pillar on the entry side, and that long grouting cable to fix anchor point to constrain the bed separation between global displacement zone and fixed zone, is thereby generated and applied to the field production. The result indicates that after entry excavating along the gob under unstable overlying strata, the supporting structure left on the gob side of narrow coal pillar is basically invalid to maintain the coal-pillar stability, and the large deformation of the pillar on the gob side is evident. Except for the significant dynamic pressure appearing in the coal mining of last working face and overlying strata stabilizing process, the stress variation inside the coal pillar in other stages are rather steady, however, the stress expansion is obvious and the coal pillar continues to deform. Once the gob-side entry driving is completed, a global displacement zone on the entry side appears in the shallow part of the pillar, whereas, a relatively steady fixed zone staying almost still in gob-side entry driving and present working face mining is found in the deep part of the pillar. The application of TCST can not only avoid the failure of pillar supporting structure, but exert the supporting capacity of the bolting structure left in the pillar of last sublevel entry, thus to jointly maintain the stability of coal pillar.

Numerical analysis of seepage flow characteristic of collapse column under the influence of mining

Based on the importance of fractured rock mass seepage research, in order to analyze seepage flow characteristics of collapse column under the influence of mining, a method by embedding fractured rock mass flow solid coupling relationship into FLAC3D internal flow models is presented according to fluid-solid coupling theory and strength criterion. A calculation model of numerical analysis was established, and the influences of mining pressure and plastic damage to pore water pressure and seepage vector change rule were studied. The results show that collapse column is the main channel of confined water seepage upward. The impact is not big when the workface is away from the collapse column. But when the workface is nearing a collapse column, there will be a seepage channel on a side near the workface, in which seepage vector and head are comparatively large. With workface pushing through collapse column, the seepage channel transfers to the other side of the column. In addition, when the plastic damage area within the collapse column breaks through, a "pipeline flow" will be formed within the column, and seepage field will change remarkably and the possibility of water bursting will be greater.

Three-Dimensional Collapse Analysis for a Shallow Cavity in Layered Strata Based on Upper Bound Theorem

Layered rock strata are observed to be common during the excavation of tunnels or cavities,and may significantly affect the deformation and failure characteristics of surrounding rock masses due to various complex forms and mechanical properties.In this paper,we propose a three-dimensional axisymmetric velocity field for roof collapse of shallow cavities in multi rock layers,by considering the influences of roof cross-section shapes,supporting pressure,ground overload,etc.The internal energy dissipation rate and work rates of external forces corresponding to the velocity field are computed by employing the Hoek-Brown strength criterion and its associated flow rule.Further,the equations of the collapse surfaces and the corresponding weight of collapsing rock masses are derived on the basis of upper bound theorem.Furthermore,we validate the proposed method by comparing the results of numerical calculations and existing research findings.The change laws of the collapse range under varying parameters are obtained for the presence of rectangular and spherical cavities.We also find that the three-dimensional mechanism is relatively safer for engineering designing actually,compared with the traditional two-dimensional mechanism.All these conclusions may provide workable guidelines for the support design of shallow cavities in layered rock strata practically.

危岩崩塌防治技术体系及工程选型分析

危岩崩塌防治技术是保障危岩工程安全稳定的关键。通过对危岩崩塌防治技术的优缺点、适用条件、工程设置原则以及选型程序的分析,认为危岩崩塌防治技术可分为主动防治技术、被动防治技术和辅助防治技术,各项防治技术设计时应充分考虑其适用条件,按照工程设置原则采纳使用,适时选择多种技术组合方式的治理措施进行危岩崩塌工程防治;危岩崩塌防治技术选型应遵循查清危岩体基本情况→评价危岩体状态→选择危岩防治技术→分析防治技术选型结果的基本程序,确定危岩崩塌防治技术选型程序各环节的关键参数,以确定合适的崩塌防治技术。研究成果可为危岩崩塌防治工程设计提供理论依据和关键技术支撑。

应力波作用下隧洞顶板围岩块体失稳滑动解析理论研究

由于地质结构和开挖面的影响,隧洞围岩通常被切割成不同形状和尺寸的块体.其中,一些关键块体在开挖卸载后仍然保持稳定,但当受到应力波(如爆破振动和地震等)的干扰时可能会失去稳定性并滑动.基于应力波传播理论推导了隧洞围岩顶板矩形关键块体动力失稳滑动解析模型,在计算块体滑动位移过程中,考虑了块体间节理的不同闭合-张开模式,并采用线弹性模型和库仑滑移模型来描述节理的法向和切向行为.通过UDEC数值模型验证了解析模型的有效性和可靠性.随后,基于解析模型探讨了可能影响块体失稳滑动的参数.研究结果表明:在应力波作用下,隧洞围岩块体间节理面会闭合-张开,在张开过程中节理面的摩擦力会逐渐降低,甚至为零,块体间节理面的超低摩擦和无摩擦阶段对块体滑动位移的影响最大;当应力波垂直作用于围岩块体结构面且强度足以诱使节理面张开时,影响块体滑动位移较大的参数是节理面初始法向应力、应力波振幅、频率和块体岩性,单周期正弦应力波下块体滑动位移的变化在0.659~1.502 mm之间;其次为节理初始法向刚度、块体尺寸,块体滑动位移的变化在0.15~0.168 mm之间.

隧道岩体崩落灾害下施工人员疏散模拟方法研究

在隧道工程建设过程中,岩体崩落等安全事故属于常见的危险情况。为能够综合考虑到岩体坍塌这类动态危险障碍物对隧道内施工人员应急疏散的影响,选取某高原地区铁路隧道工程作为研究对象,运用元胞自动机理论(CA)构建了隧道内人员与动态危险障碍物(如落石)轨迹交互模型,并研发了岩体崩落时的人员疏散模拟方法。在此基础上,对隧道内不同岩体崩落灾害等级和范围下的应急疏散过程进行了分级分段的数值模拟和讨论。结果表明:开发的数值模拟方法能够准确地模拟出不同灾害等级下人群在岩体崩落时的疏散过程和伤亡情况;根据模拟结果可知,当发生同一等级的岩体崩落事故时,随着灾害范围的扩大,受伤人数增加,整体疏散速度变慢,从而导致疏散时间延长;同时,灾害等级也是影响施工人员安全的主要因素,灾害等级越高,坍塌岩块的密度越大,从而增加了临灾群体受伤和死亡的概率。该疏散模型为隧道灾害条件下施工人员应急疏散提供了参考依据。

某深埋TBM隧洞围岩地质变化区破坏特征与类型判别方法

某深埋TBM隧洞地质变化区开挖过程中岩爆和塌方交替发生,导致工期严重延误,严重威胁现场人员及施工安全。通过现场地质踏勘、微震监测和结构面统计,研究现场工程地质灾害与围岩岩性、地质条件的关系,建立基于岩性、地质及微震活动特征的地质灾害类型判别方法。结果表明,该隧洞破坏类型与围岩岩性有显著相关性,黑云母花岗岩洞段岩爆风险最高,混合花岗岩洞段次之,钾长石花岗岩与黑云母花岗岩围岩蚀变的洞段易发生塌方;岩性变化的交界面位置,破坏规模明显增大;破坏类型还与结构面密度相关,随着结构面密度减小,破坏类型由塌方转变为中等岩爆,进一步等级降低为轻微岩爆;微震特征分析表明,岩爆区域微震活动远大于塌方区域微震活动。当微震活动较低时,围岩破坏以塌方为主;当微震事件数>15,微震释放能>1000 J,围岩破坏以岩爆为主;当微震事件数>20,微震释放能>20000 J时,围岩可能发生中等岩爆。现场应用表明,该方法可准确预测掌子面前方潜在破坏类型,为类似工程灾害交替发生洞段的安全、高效施工提供参考。

岩溶地区危岩和岩质崩塌易发性评价研究——以广西贺州市平桂区为例

本文利用专家—层次分析法对岩溶地区危岩和岩质崩塌地质灾害易发性进行评价,以贺州市平桂区地质灾害详细调查成果资料作为依据,选取了地质灾害发育密度、地貌类型、坡度、植被指数、地层岩性、岩土体类型、覆盖层厚度、岩溶发育程度、地质构造、多年平均降雨量、居民地密度、路网密度、矿山开采强度13个影响岩溶地区危岩和岩质崩塌地质灾害易发性的地质环境因素,创建了岩溶地区危岩和岩质崩塌地质灾害易发性评价指标体系,再通过GIS的空间分析功能对岩溶地区危岩和岩质崩塌地质灾害易发性进行评价研究,评价结果对岩溶地区地质灾害的防治具有指导意义。

穿越碳质千枚岩破碎带隧道侵限及塌方的处治

基于316国道某穿越碳质千枚岩破碎带隧道侵限及塌方处治施工过程,根据现场侵限及塌方情况,分别对侵限段和塌方段进行处治。工程实践表明,采用“大管棚+小导管超前支护施工+空腔填充”技术进行超前支护对穿越碳质千枚岩破碎带隧道塌方进行处治较合理,施工效果良好,施工处于安全可控范围内。

基于地面三维激光扫描的南港危岩崩塌稳定性评价

崩塌是北京地区最为频发的突发地质灾害类型,因多分布于高陡斜坡,具有较高突发性和危害性,其勘查工作是长期困扰工程技术人员的难题。利用三维激光扫描技术对北京市门头沟区南港崩塌进行调查,结合点云数据和高清影像数据,构建崩塌三维空间模型,获取崩塌结构面和危岩体特征参数,评估危岩体稳定性和危害性。基于空间模型,自动识别及提取69组结构面信息,将其归纳为4组。利用4组节理面对坡体和危岩体的稳定性进行计算,结果表明,研究区易沿J1结构面发生倾倒式崩塌,易沿J2和J3结构面切割形成的楔形体发生滑移式崩塌。3处典型危岩体,在正常工况下1处为欠稳定,2处为基本稳定,在暴雨和地震条件下,1处为不稳定,2处为欠稳定。落石运动轨迹模拟分析显示98,6%的落石会撞击或经过居民房屋,直接威胁居民人身安全。

考虑割理面时煤层造斜段坍塌压力变化规律研究

在武威盆地太原组水平井钻进作业时,依据井史数据调研发现,煤层段卡钻、井径扩大、钻具掉落等井壁坍塌导致的井下复杂事故发生,严重制约了煤层气勘探开发的进程。由于煤岩交错割理性(面割理、端割理)弱结构面发育,使煤岩在造斜钻进时井壁破坏在力学上呈现为非连续性和非均质性。建立了考虑弱面的井壁坍塌数学模型。通过分析煤岩矿物成分、微宏观结构,确定煤岩井壁坍塌为力学机制占主导因素,得出割理导致的煤岩碎裂成块是井壁失稳的根本原因,建议在后续煤层钻井中优化井眼轨迹、优化钻井液性能进行井壁防塌,并引入煤岩井壁坍塌实时监测系统。

露天转地下挂帮矿崩落法开采边坡安全防控技术研究

露天转地下过渡期崩落法开采挂帮矿,会引起边坡的岩移和陷落,威胁露天矿的安全生产。以大孤山铁矿为工程背景,分析边坡岩移机理,得出挂帮矿持续冒落跨度为临界冒落跨度的1.25~1.65倍,第一分段进路布置在矿体厚度大于3.3l的位置,能够保证露天开采的安全。研究陷落散体所需的回采体积,得出回采体积先随着保安矿柱宽度的增加而减小,后又随着保安矿柱宽度的增加而增大,当保安矿柱的宽度为88.45 m时,所需回采体积最小。采用散体滑落试验,得出了防护坝设置在露天坑底的上一个台阶,保证了露天开采的安全。研究成果能够实现大孤山铁矿露天转地下过渡期的产能衔接和安全生产,对于矿山的未来发展具有重要意义。

基于沿空留巷技术的工作面过陷落柱工程实践

矿井采掘工作揭露陷落柱等地质构造时,往往会带来较多潜在隐患,可能导通含水层、造成瓦斯超限和形成支护难题等。针对6102工作面揭露大型陷落柱影响区的技术难题,矿方根据陷落柱产状及潜在的隐患情况,结合矿井较成熟的沿空留巷理论及经验,成功实施了基于沿空留巷技术的过陷落柱工程实践,在损失一定保护煤柱的代价下,确保了工作面安全快速跳过陷落柱影响区域,沿空留巷技术优势得到验证。

贵州碎屑岩分布区崩塌地质灾害发育特征及孕灾条件分析

碎屑岩分布区地质灾害以滑坡为主,而崩塌地质灾害往往容易被忽视。通过对碎屑岩崩塌孕育条件的分析,可以更好地指导碎屑岩分布区崩塌的防治工作。本文以云贵山崩塌为例,运用地面调查、遥感、数值模拟等技术手段,分析其地质灾害特征、运动特征及孕育条件。采用归纳分析的方法对碎屑岩崩塌孕灾条件进行了总结。结论显示,云贵山崩塌为小型崩塌,破坏模式多为倾倒式,影响范围112 m以内;陡峭的地形、硬岩夹软弱夹层组合、近水平斜坡结构、差异性风化是云贵山崩塌的主要孕育条件;碎屑岩崩塌孕灾条件中地形地貌、特殊岩性组合及软硬岩接触面的揭露情况对碎屑岩崩塌孕育的影响较大。

张家界天门洞危岩体监测方法建议

本文以张家界天门洞危岩体崩塌为例,针对危岩体崩塌监测与预警的国际难题,从天门洞危岩体形成崩塌的特点出发,在分析研究了天门洞高位、特高位危岩体的发育特征的基础上,提出天门洞危岩体崩塌监测可采用声发射技术的监测方法,确保景区游客和工作人员的安全。