Classification of Factors Affecting the Performance of Fully Grouted Rock Bolts with Empirical Classification Systems

Empirical classification systems do not provide details of the factors that affect the performance of fully grouted rock bolts, as they are based on average values. Fully grouted rock-bolt patterns during tunnel-support design are a part of the composite support, and they are functions of rock-mass quality and tunnel span. Various fully grouted rock bolts are used in situ in different environments, along with other tunnel-support materials in static and dynamic environments during tunnel construction. The rock-bolt performances are evaluated through pull-out tests that follow ASTM standards. Several field pull-out tests were conducted on cement and resin grouted rock bolts. Under groundwater flow conditions, inflated steel tube rock bolts were tested and the results were compared with fully grouted rock bolts. Based on field experiments and previous studies, the factors that affect rock bolt performances are divided into five groups with respective sub-factors. Natural parameters cannot be controlled to ensure safety, economy, and stability in tunnels. The controllable factors, too, can be varied only within a practical range. In conclusion, the factors investigated here should be considered with the empirical support pattern of rock-mass classification systems for safe and economical design.

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Experimental Bond Behavior of Mortar Grouted GFRP Rock Bolt

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.261-263.1244 ◽

2011 ◽

Vol 261-263 ◽

pp. 1244-1248 ◽

Cited By ~ 1

Author(s):

Qi Neng Weng ◽

Yong Yuan ◽

Qian Guan Zhang

Keyword(s):

Rock Mass ◽

Concrete Block ◽

Rock Bolt ◽

Rock Bolts ◽

Engineering Structures ◽

Bond Behavior ◽

Gfrp Bars ◽

Pull Out ◽

Glass Fiber Reinforced ◽

Concrete Blocks

Bolts are widely used in slope engineering, tunnel and large cave supporting structures, as well as restoration of engineering structures. They can improve the strength and stability of ground, rock mass, and other structures. The traditional steel bolt has some disadvantages, such as easy corrosion, heavy weight, and difficult operation. Glass Fiber Reinforced Polymer (GFRP) is more resistant to chloride, stronger and lighter than steel. Those advantages make it a better alternative in some fields of engineering. To utilize GFRP bars as rock bolt, some aspects of its behavior, such as bond strength in mortar, bearing capacity, and bond stress distributing along its interface, have to be examined. This paper presents a research on bond behavior of GFRP rock bolts. A concrete block is used to represent rock mass in laboratory. Modified pull out tests were conducted on selected GFRP bars and compared with steel ones that were grouted with mortar in concrete blocks. Bond characteristics of mortar grouted GFRP rock bolts with diameter 16mm were mainly evaluated and other specs of bolts were also discussed.

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Inflatable rock bolt bond strength versus rock mass rating (RMR): A comparative analysis of pull-out testing data from underground mines in Nevada

International Journal of Mining Science and Technology ◽

10.1016/j.ijmst.2015.11.004 ◽

2016 ◽

Vol 26 (1) ◽

pp. 19-22 ◽

Cited By ~ 1

Author(s):

Chase Barnard ◽

Raj R. Kallu ◽

Sean Warren ◽

Rahul Thareja

Keyword(s):

Rock Mass ◽

Comparative Analysis ◽

Bond Strength ◽

Rock Bolt ◽

Underground Mines ◽

Rock Mass Rating ◽

Pull Out ◽

Testing Data

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Tunnel support design by comparison of empirical and finite element analysis of the Nahakki tunnel in mohmand agency, pakistan

Studia Geotechnica et Mechanica ◽

10.1515/sgem-2016-0008 ◽

2016 ◽

Vol 38 (1) ◽

pp. 75-84

Author(s):

Asif Riaz ◽

Syed Muhammad Jamil ◽

Muhammad Asif ◽

Kamran Akhtar

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Rock Mass ◽

Support Systems ◽

Classification Systems ◽

Geological Strength Index ◽

Support Design ◽

Element Analysis ◽

Tunnel Support ◽

Geological Conditions

Abstract The paper analyses the geological conditions of study area, rock mass strength parameters with suitable support structure propositions for the under construction Nahakki tunnel in Mohmand Agency. Geology of study area varies from mica schist to graphitic marble/phyllite to schist. The tunnel ground is classified and divided by the empisical classification systems like Rock mass rating (RMR), Q system (Q), and Geological strength index (GSI). Tunnel support measures are selected based on RMR and Q classification systems. Computer based finite element analysis (FEM) has given yet another dimension to design approach. FEM software Phase2 version 7.017 is used to calculate and compare deformations and stress concentrations around the tunnel, analyze interaction of support systems with excavated rock masses and verify and check the validity of empirically determined excavation and support systems.

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Mode of action and calculation of fully grouted rock bolts as reinforcement in stratified or jointed rock mass (In German)

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts ◽

10.1016/0148-9062(90)94637-9 ◽

1990 ◽

Vol 27 (3) ◽

pp. A168

Keyword(s):

Rock Mass ◽

Mode Of Action ◽

Jointed Rock ◽

Jointed Rock Mass ◽

Rock Bolts ◽

Grouted Rock Bolts

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Rock support in hydropower projects of Nepal: case studies

Journal of Nepal Geological Society ◽

10.3126/jngs.v34i0.31876 ◽

2006 ◽

Vol 34 ◽

pp. 29-38

Author(s):

Subas Chandra Sunuwar

Keyword(s):

Rock Mass ◽

Large Diameter ◽

Design Guidelines ◽

Rock Mass Classification ◽

Classification Systems ◽

Rating Systems ◽

Rock Support ◽

Support Design ◽

Tunnel Support ◽

Mass Classification

The principal objective of rock support is to assist the rock mass to support itself. One common example is where the rock support system (e.g. rock bolts and shotcrete) actually becomes integrated with the rock mass. Rock support strengthens the rock mass surrounding an excavation by creating a reinforced zone, which maintains the integrity of the excavated surface, possesses sufficient flexibility to allow for the redistribution of stresses around the excavation, and has enough stiffness to minimise the dilation (opening) of discontinuities. Rock mass classification systems are used worldwide as a basis for tunnel support design. The Q and Rock Mass Rating systems have been extensively applied in rock support design on most of the hydropower projects in Nepal. Generic design guidelines based on rock mass classification systems cannot provide suitable rock support for every site. Therefore some modifications are necessary to suite the site-specific ground conditions including local rock mass and geological hazards. There are relatively few tunnels excavated in the tectonically active Nepal Himalaya. Large diameter tunnels in Nepal are commonly lined with concrete whereas recently smaller-diameter tunnels are either shotcrete-lined or left unsupported. "Leaky" lining has been used in most of the projects to avoid the heavy reinforcement needed to withstand the occasional very high external water pressures.

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Studies of the composite system of rock mass and non-prestressed grouted rock bolts

Rock Bolting ◽

10.1201/9780203740507-7 ◽

2021 ◽

pp. 75-85

Author(s):

D. Wullschläger ◽

O. Natau

Keyword(s):

Rock Mass ◽

Composite System ◽

Rock Bolts ◽

Grouted Rock Bolts

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Reinforcement of Underground Excavation with Expansion Shell Rock Bolt Equipped with Deformable Component

Studia Geotechnica et Mechanica ◽

10.1515/sgem-2017-0004 ◽

2017 ◽

Vol 39 (1) ◽

pp. 39-52 ◽

Cited By ~ 11

Author(s):

Waldemar Korzeniowski ◽

Krzysztof Skrzypkowski ◽

Krzysztof Zagórski

Keyword(s):

Rock Mass ◽

Construction Materials ◽

Rock Bolt ◽

Loading Test ◽

Rock Bolts ◽

Disk Spring ◽

Static Loading Test ◽

Two Phases ◽

Rock Bolt Support ◽

Ultimate Loading Capacity

AbstractThe basic type of rock mass reinforcement method for both preparatory and operational workings in underground metal ore mines, both in Poland and in different countries across the world, is the expansion shell or adhesive-bonded rock bolt. The article discusses results of static loading test of the expansion shell rock bolts equipped with originally developed deformable component. This component consists of two profiled rock bolt washers, two disk springs, and three guide bars. The disk spring and disk washer material differs in stiffness. The construction materials ensure that at first the springs under loading are partially compressed, and then the rock bolt washer is plastically deformed. The rock bolts tested were installed in blocks simulating a rock mass with rock compressive strength of 80 MPa. The rock bolt was loaded statically until its ultimate loading capacity was exceeded. The study presents the results obtained under laboratory conditions in the test rig allowing testing of the rock bolts at their natural size, as used in underground metal ore mines. The stress-strain/displacement characteristics of the expansion shell rock bolt with the deformable component were determined experimentally. The relationships between the geometric parameters and specific strains or displacements of the bolt rod were described, and the percentage contribution of those values in total displacements, resulting from the deformation of rock bolt support components (washer, thread) and the expansion shell head displacements, were estimated. The stiffness of the yielded and stiff bolts was empirically determined, including stiffness parameters of every individual part (deformable component, steel rod). There were two phases of displacement observed during the static tension of the rock bolt which differed in their intensity.

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Laboratory Method for Evaluating the Characteristics of Expansion Rock Bolts Subjected to Axial Tension / Laboratoryjna Metoda Badania Charakterystyk Kotew Rozprężnych Poddanych Rozciąganiu Osiowemu

Archives of Mining Sciences ◽

10.1515/amsc-2015-0014 ◽

2015 ◽

Vol 60 (1) ◽

pp. 209-224 ◽

Cited By ~ 7

Author(s):

Waldemar Korzeniowski ◽

Krzysztof Skrzypkowski ◽

Łukasz Herezy

Keyword(s):

Rock Mass ◽

Laboratory Method ◽

Operating Conditions ◽

Rock Bolt ◽

Test Facility ◽

Geometrical Parameters ◽

Rock Bolts ◽

Axial Tension ◽

Rock Bolt Support ◽

Bolt Support

Abstract Rock bolts have long been used in Poland, above all in the ore mining. Worldwide experience (Australia, Chile, Canada, South Africa, Sweden, and USA) provides evidence of rock bolt supports being used for loads under both static and dynamic conditions. There are new construction designs dedicated to the more extreme operating conditions, particularly in mining but also in tunneling. Appreciating the role and significance of the rock bolt support and its use in Polish conditions amounting to millions of units per year, this article describes a new laboratory test facility which enables rock bolt testing under static load conditions. Measuring equipment used as well as the possibilities of the test facility were characterized. Tests were conducted on expansion rock bolt supports installed inside a block simulating rock mass with compression strength of 80 MPa, which was loaded statically as determined by taking account of the load in order to maintain the desired axial tension, which was statically burdened in accordance with determined program load taking into consideration the maintenance of set axial tension strength at specified time intervals until capacity was exceeded. As an experiment the stress-strain characteristics of the rock bolt support were removed showing detailed dependence between its geometrical parameters as well as actual rock bolt deformation and its percentage share in total displacement and deformation resulting from the deformation of the bolt support elements (washer, thread). Two characteristic exchange parts with varying intensity of deformation /displacement per unit were highlighted with an increase in axial force static rock bolt supports installed in the rock mass.

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Investigation of Load Bearing Capacities of Grouted Rock Bolts with New Auxetic Head Designs

Periodica Polytechnica Civil Engineering ◽

10.3311/ppci.16366 ◽

2020 ◽

Author(s):

Eren Komurlu ◽

Aysegul Durmus Demir ◽

Atila Gurhan Celik

Keyword(s):

Numerical Modelling ◽

Energy Absorption ◽

Experimental Studies ◽

Head Part ◽

Rock Bolts ◽

Load Bearing ◽

Ratio Effect ◽

Pull Out ◽

Drill Holes ◽

Grouted Rock Bolts

Within this study, new bolt heads were designed to be able to expand in drill holes as the load applied on the bolt shank increases. The heads of newly designed rock bolts include a conic part and split rings encircling them. To determine load bearing capacities of new rock bolts with varying angles of the conic parts and expansion properties, a series of deformation controlled pull-out tests were carried out by using bolt samples grouted in rock blocks. In addition to the experimental studies, numerical modelling analyses were performed to better understand the support properties of newly designed rock bolts. Because of a negative Poisson’s ratio effect supplied by the head part expansion with the tension of the shank, new bolt heads are suggested to be defined as auxetic. According to the results of this study, the new head designs significantly improve the load bearing and energy absorption capacities of grouted rock bolts.

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