• Title, Summary, Keyword: Rock reinforcement

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New reinforcement algorithms in discontinuous deformation analysis for rock failure

  • Chen, Yunjuan;Zhu, Weishen;Li, Shucai;Zhang, Xin
    • Geomechanics and Engineering
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    • v.11 no.6
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    • pp.787-803
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    • 2016
  • DDARF (Discontinuous Deformation Analysis for Rock Failure) is a numerical algorithm for simulating jointed rock masses' discontinuous deformation. While its reinforcement simulation is only limited to end-anchorage bolt, which is assumed to be a linear spring simply. Here, several new reinforcement modes in DDARF are proposed, including lining reinforcement, full-length anchorage bolt and equivalent reinforcement. In the numerical simulation, lining part is assigned higher mechanical strength than surrounding rock masses, it may include multiple virtual joints or not, depending on projects. There must be no embedding or stretching between lining blocks and surrounding blocks. To realize simulation of the full-length anchorage bolt, at every discontinuity passed through the bolt, a set of normal and tangential spring needs to be added along the bolt's axial and tangential direction. Thus, bolt's axial force, shearing force and full-length anchorage effect are all realized synchronously. And, failure criterions of anchorage effect are established for different failure modes. In the meantime, from the perspective of improving surrounding rock masses' overall strength, a new equivalent and tentative simulation method is proposed, it can save calculation storage and improve efficiency. Along the text, simulation algorithms and applications of these new reinforcement modes in DDARF are given.

Estimation of the Anisotropic Material Properties of Rock Masses with Permeation Grouting (그라우팅 강화터널의 설계 특성치 산정에 관한 연구)

  • Lee, Jun Seok;Bang, Chun Seok;Choe, Il Yun;Eom, Ju Hwan
    • Magazine of korean Tunnelling and Underground Space Association
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    • v.1 no.1
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    • pp.67-80
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    • 1999
  • The Grout-reinforcement technique which is widely used during the excavation of a shallow or an endangered tunnel can be classified into a couple of groups according to the properties and injection methods of the grout. The reinforcement design will, therefore, take a different approach based on the grouting method under consideration. However, the injection procedure is mainly performed by the experience of the foreman rather than engineering judgement , specifically the permeation grouting through the rock joints and its reinforcement effect Is not fully under-stood during the design stage, In this study, the anisotropic material properties of the grout-reinforced rock masses are derived from the concept of composite materials and the effect of intact rock, vertical grouting and permeation grouting is, therefore, fully accounted for. Through the parametric studies on the characteristics of rock joints, intact rock and grouting materials, various case studies have been considered. The results, illustrated via the design charts, can be directly used during the reinforcement design.

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A Case Study on Reinforcement Method of Cut Slope Expected Plane Destruction (평면파괴가 예상되는 사면의 보강대책에 관한 사례 연구)

  • Lee, Dong-Yub;Park, Choon-Sik;Kim, Beoung-Girl
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.1022-1028
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    • 2008
  • From the result of precise field investigation and stability examination for the rock slope, following results were acquired. 1. The weathering rock itself, existing fault zone and underground water complexly effect cut slope so that plane destruction may appear by fault zone. 2. The reinforcement force was decided by the result of limit equilibrium. 3. For rock cut slope, the Rock Bolt was judged as the most proper method to the cut slope as comparing/analyzing Rock Anchor, Rock Bolt and method after relaxing the slope.

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A case study on stability and reinforcement method of cut slope at quarry (채석장 사면의 안정성 검토 및 보강대책에 관한 사례 연구)

  • Park, Choon-Sik;Choi, Jun-Sam;Seo, Hyo-Sik
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.677-685
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    • 2009
  • From the result of precise field investigation and stability examination for the cut slope, following results were acquired. 1. The cause of the cut slope collapse seems that it came from complex actions such as the weathering rock itself, existing fault zone and crack from excessive blasting. 2. As a result of analysis, it is appeared that the cut slope can be in danger of plane destruction. 3. The reinforcement force is decided by the result of limit equilibrium analysis. 4. For reinforcement the method after relaxing the slope was judged as the most proper method to the cut slope as comparing/analyzing Rock Anchor, Rock Bolt and method after relaxing the slope.

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Modeling the Effect of Water, Excavation Sequence and Reinforcement on the Response of Tunnels

  • Kim, Yong-Il
    • Journal of the Korean Geotechnical Society
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    • v.15 no.3
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    • pp.161-176
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    • 1999
  • A powerful numerical method that can be used for modeling rock-structure interaction is the Discontinuous Deformation Analysis (D D A) method developed by Shi in 1988. In this method, rock masses are treated as systems of finite and deformable blocks. Large rock mass deformations and block movements are allowed. Although various extensions of the D D A method have been proposed in the literature, the method is not capable of modeling water-block interaction, sequential loading or unloading and rock reinforcement; three features that are needed when modeling surface or underground excavation in fractured rock. This paper presents three new extensions to the D D A method. The extensions consist of hydro-mechanical coupling between rock blocks and steady water flow in fractures, sequential loading or unloading, and rock reinforcement by rockbolts, shotcrete or concrete lining. Examples of application of the D D A method with the new extensions are presented. Simulations of the underground excavation of the \ulcornerUnju Tunnel\ulcorner in Korea were carried out to evaluate the influence of fracture flow, excavation sequence and reinforcement on the tunnel stability. The results of the present study indicate that fracture flow and improper selection of excavation sequence could have a destabilizing effect on the tunnel stability. On the other hand, reinforcement by rockbolts and shotcrete can stabilize the tunnel. It is found that, in general, the D D A program with the three new extensions can now be used as a practical tool in the design of underground structures. In particular, phases of construction (excavation, reinforcement) can now be simulated more realistically.

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Study on rock reinforcement process and the effect of produced strength right after rockbolt installation (록볼트의 타설 직후의 강도발현 과정 및 효과에 관한 연구)

  • Itoh, Jhun;Park, Hae-Geun;Kim, Dong-Wan;Kim, Jea-Kwon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.5 no.2
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    • pp.189-198
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    • 2003
  • For the huge section of tunnel, it is highly required to observe the role of each rock support and their effect of rock reinforcement in order to investigate more reasonable rock support structure. Especially for unstable tunnel situation with no shotcrete strength right after an excavation, sufficient investigation is needed for rock support structure. In this paper, we clarify the relations of compressive strength and material age, cohesion strength and material age, and cohesion stiffness and material age of grout with time-dependence through tests and numerical analysis simulation with trial rock mass considering hardening of bolt grouting material. By means of this process, effect of rock reinforcement for rockbolt is investigated right after an excavation and modelling and physical constants of young aged rockbolts are obtained. Additionally, the effect of rock reinforcement with hydraulic tensile friction bolt is examined right after an excavation, which grout effect is no need to be waited.

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Stability Analysis of a Subway Tunnel Excavated in Soft Rock (연약암반에 굴착되는 지하철 터널의 안정성 해석)

  • 이연규;서영호;이정인
    • Tunnel and Underground Space
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    • v.3 no.2
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    • pp.118-131
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    • 1993
  • In this study, the results of elasto-plastic analysis for a subway tunnel using finite element method are presented. To determine input data for the analysis we carried out rock mass classificaton, insitu test and back analysis using measured displacements. Tunnel convergence, extension of yielding Zone and support load are described. By comparing the results of four different reinforcement patterns, the influence of those patterns on tunnel stability is presented. As a result of the analysis we suggest a ratonal reinforcement pattern.

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Evaluation of Reinforcement Effect of Rock Bolts in Anisotropic Rock Mass Using Tunnel Scaled Model Tests (터널 축소모형실험을 통한 이방성 암반내 록볼트의 보강효과 검토)

  • Kim, Jong-Woo
    • Tunnel and Underground Space
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    • v.28 no.5
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    • pp.442-456
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    • 2018
  • Scaled model tests were performed to evaluate the reinforcement effect of rock bolts in anisotropic rock mass. For this purpose, two tunnel cases were experimented which had different tunnel sizes, rock strengths, anisotropic angles and coefficients of lateral pressure. The fully grouted rock bolts of the D25 deformed bar were modeled as the basting pins with bead and were systematically installed at the roof and the side wall of the model tunnel. As results of the first case experimentations, the unsupported model showed initial crack at the roof of tunnel, but the supported model with rock bolts showed initial crack at the floor of tunnel where rock bolts were not installed. The crack initiating pressure and the maximum pressure of the supported model with rock bolts were 11% and 7% larger than those of the unsupported model, respectively. Moreover, the effect of the existing discontinuities in anisotropic rock mass on the fracture behavior of tunnel was reduced in the supported model, and so the reinforcement effect of rock bolt turned out to be experimentally verified. As results of the second case experimentations considering different support patterns, the crack initiating pressures of models were larger and the reduction ratios of tunnel area according to applied load were smaller as the length and the quantity of rock bolts were larger. Therefore, it was found that the performance of the rock bolts turned out to be improved as they were larger.

A Study on Analysis for the Characteristics of Fault Zone at Mica-schist for Reinforcement of Large-Span Tunnel (대단면 터널 보강을 위한 운모편암 단층대 특성 분석에 관한 연구)

  • Chung, Hoi-Yong;Kim, Young-Geun;Park, Yeon-Jun;You, Kwang-Ho
    • Tunnel and Underground Space
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    • v.19 no.2
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    • pp.132-145
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    • 2009
  • Faults in rock mass have strong influences on the behaviors of rock structure such as rock slope, tunnel and underground space. Thus, it is very important to analyse for the characteristics of fault rocks in design for tunnel. But, due to the limitation of geotechnical investigation in design stages, tunnel engineers have to carry out the face mapping and additional geological survey during tunnel excavation to find the distribution of faults and the engineering properties of faults for support and reinforcement design of tunnel. In this study, various geological survey and field tests were carried out to analyse the characteristics of the large thrust fault zone through the large sectional tunnel is constructed in mica-schist region. Also, the distribution of structural geology, the shape of thrust faults and the mechanical properties of fault rock were studied for the reasonable design of the reinforcement and support method for the highly fractured fault zone in the large-span tunnel.

Experimental study on nano silica modified cement base grouting reinforcement materials

  • Zhou, Fei;Sun, Wenbin;Shao, Jianli;Kong, Lingjun;Geng, Xueyu
    • Geomechanics and Engineering
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    • v.20 no.1
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    • pp.67-73
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    • 2020
  • With the increasing number of underground projects, the problem of rock-water coupling catastrophe has increasingly become the focus of safety. Grouting reinforcement is gradually applied in subway, tunnel, bridge reinforcement, coal mine floor and other construction projects. At present, cement-based grouting materials are easy to shrink and have low strength after solidification. In order to overcome the special problems of high water pressure and high in-situ stress in deep part and improve the reinforcement effect. In view of the mining conditions of deep surrounding rock, a new type of cement-based reinforcement material was developed. We analyses the principle and main indexes of floor strengthening, and tests and optimizes the indexes and proportions of the two materials through laboratory tests. Then, observes and compares the microstructures of the optimized floor strengthening materials with those of the traditional strengthening materials through scanning electron microscopy. The test results show that 42.5 Portland cement-based grouting reinforcement material has the advantages of slight expansion, anti-dry-shrinkage, high compressive strength and high density when the water-cement ratio is 0.4, the content of bentonite is 4%, and the content of Nano Silica is 2.5%. The reinforcement effect is better than other traditional grouting reinforcement materials.