Tunnel Support Testing

Roadway support inspection mainly conducts scientific testing and analysis on the initial setting force and working resistance testing, support strength and stiffness testing, structural component strength and weld quality testing, sealing performance and hydraulic system testing, stability and lateral force resistance testing, and geometric dimension and assembly quality testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Initial setting force and working resistance testing: Mainly measuring the initial support forces (initial setting forces) reached by the hydraulic systems after the installation of the roadway supports, as well as the actual resistances (working resistances) shown when bearing the surrounding rock pressures in the working states. These two parameters are the key indicators of evaluating whether the supports can effectively control the surrounding rock deformations and prevent the early roof separation, directly related to the timeliness and reliability of the support.

Support strength and stiffness testing: The support strength refers to the maximum support forces that the supports can provide per unit area, reflecting their load-bearing capabilities; the stiffness refers to the capability of the supports to resist the deformations under the loads. The testing needs to simulate the different loading rates and load distributions, to evaluate whether the mechanical properties of the supports under the complex stress conditions meet the design requirements.

Structural component strength and weld quality testing: The static load strength and fatigue strength testing are carried out on the main metal structural components such as the canopy beams, legs and bases of the supports. At the same time, the non-destructive flaw detection methods (such as the ultrasonic and magnetic particle flaw detection) are used to detect the key welds, ensuring that there are no defects such as the cracks, lack of penetration and slag inclusions, guaranteeing the overall integrity of the structures.

Sealing performance and hydraulic system testing: The sealing performance of the hydraulic cylinders such as the legs and jacks is emphatically checked, and their leakage amounts are tested under the rated pressures with the pressure holding. At the same time, the opening pressures, closing pressures and flow characteristics of the hydraulic components such as the safety valves and control valves are verified, ensuring that the hydraulic systems respond sensitively and are stable and reliable.

Stability and lateral force resistance testing: Evaluating the anti-toppling and anti-twisting capabilities of the supports under the horizontal loads or eccentric loads. Through the application of the lateral forces, the relative displacements between the canopy beams and bases of the supports and whether the structural components lose the stability are tested. This is crucial for ensuring the safety of the supports in the roadways in the geological structure zones or seriously affected by the mining activities.

Geometric dimension and assembly quality testing: Measuring the overall shape dimensions of the supports, fit clearances of the various connection components, and matching degrees of the pins and hole seats. Ensuring that the supports can be smoothly installed in place underground, with the reliable connections and no interference, meeting the requirements of the roadway cross-section designs.

Testing Scope

Hydraulic supports: Including the shield supports, chock-shield supports and sublevel caving hydraulic supports used for the roadway support of the fully mechanized mining faces in the coal mines. The testing covers the whole process from the factory delivery acceptance, underground installation and commissioning to the periodic strong inspection, ensuring that they adapt to the mine pressure laws of the working faces.

Bolt (cable) support systems: The testing objects include the resin bolts, pre-stressed anchor cables, steel straps, plates and supporting components. The testing scope involves the pull-out forces, pre-tightening torques, installation angles, anchoring agent curing effects of the bolts (cables), as well as the collaborative load-bearing properties of the whole support systems.

U-type steel yielding supports: For the arch yielding supports made of the U25, U29 and U36 section steels commonly used in the mine roadways, their ultimate load-bearing capacities, yielding properties (friction connector resistances), radial stiffnesses and deformation resistance of the supports are tested.

Concrete and shotcrete support: Covering the cast-in-place concrete roadway lining and shotcrete support layers. The testing contents include the concrete compressive strengths, support layer thicknesses, compactness, surface flatness and bonding strengths with the surrounding rocks, evaluating their overall support effects.

Metal trapezoidal supports and rigid supports: Including the trapezoidal or rectangular supports made of the mine I-beams and mine H-beams. The testing emphases are the node connection strengths, vertical and lateral load-bearing capabilities of the supports, as well as the deformation characteristics under the ground pressures.

Combined support systems: For the roadways using the composite support forms such as the "bolt + anchor cable + metal mesh" and "support + grouting", the testing scope needs to be extended to the interactions of the various support elements, load distribution relationships and the stability evaluation of the overall structures.

Testing Methods

Laboratory full support loading testing: On the large pressure testing machines, the center loading and eccentric loading testing are carried out on the supports according to the standards such as MT 312-2000. Through the transducer acquisition of the load-displacement curves, their initial setting forces, working resistances, yield loads and ultimate load-bearing capabilities are precisely determined. It is the core method of evaluating the comprehensive properties of the supports.

Underground online monitoring and mine pressure observation: The pressure transducers and displacement transducers are installed on the supports to monitor the working resistances and roof and floor convergence amounts in real time. Through the analysis of the change laws of the mine pressure data, the support effects are evaluated, and the basis is provided for the support selection and working face management. It belongs to the dynamic and in-situ testing.

Pull-out testing method: Mainly used for the quality testing of the bolt (cable) supports. The dedicated pull-out instruments are used to pull the installed bolts (cables) until reaching the design values or the failure, thereby testing whether their anchoring forces and installation qualities are qualified. The operation is direct and effective.

Non-destructive testing technology: The ultrasonic flaw detection (UT) is applied to detect the internal defects of the metal structural components; the magnetic particle flaw detection (MT) or penetrant flaw detection (PT) is used to detect the surface and near-surface cracks; the ultrasonic thickness gauges are used to measure the residual wall thicknesses of the structural components. These methods do not destroy the components, and are suitable for the periodic safety inspections of the in-service supports.

Sealing performance test bench testing: On the dedicated test benches, the high-pressure liquid injection, pressure holding and low-pressure stabilization testing are carried out on the hydraulic legs and jacks. Through the measurement of the pressure drops or the observation of the leakage conditions, the sealing properties of the hydraulic cylinders and valves are quantitatively evaluated, ensuring that the hydraulic systems have no internal or external leakage.

Geometric dimension and appearance inspection: The conventional measuring tools such as the callipers, tapes, angle gauges and laser distance meters are used, combined with the advanced technologies such as the three-dimensional laser scanning, for the comprehensive static measurement and recording of the geometric parameters, geometric tolerances and surface defects (rust and deformation) of the supports.

Testing Standards

Domestic Standards:

1. GB/T 25974, Powered supports for coal mine

2. MT 312-2000, General specification for powered support

3. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Large structural testing machine: Usually the microcomputer-controlled electro-hydraulic servo type, with the maximum loading capabilities of over 10000kN, equipped with the multi-channel data acquisition systems. It can simulate the complex load working conditions, and is the key equipment of carrying out the strength, stiffness and stability testing of the full supports and components.

Digital pressure transducers and acquisition instruments: Including the vibrating wire and resistance strain type pressure transducers, installed in the lower chambers of the support legs or pipelines, combined with the portable or fixed data acquisition instruments, realizing the long-term and continuous automatic monitoring and data storage of the underground support resistances.

Bolt pull-out dynamometer: Hydraulically driven, with the measuring ranges covering 50kN to 600kN, equipped with the digital display heads, which can precisely record the peak tensile forces. It is the necessary tool of the on-site sampling inspection of the bolt (cable) anchoring forces, requiring the portability, reliability and high precision.

Non-destructive testing instruments: Such as the ultrasonic flaw detectors, used to detect the internal weld defects of the structural components; the magnetic particle flaw detectors, used to detect the surface cracks of the ferromagnetic materials; the ultrasonic thickness gauges, used to measure the wall thicknesses of the worn components. These are the important tools of evaluating the structural health states of the supports.

Hydraulic system test bench: Integrating the high-pressure pump stations, precision pressure gauges, flow meters, temperature transducers and data recording systems, which can carry out the performance testing and setting of the hydraulic components such as the safety valves, control valves and legs, ensuring their accurate action pressures and good sealing.

Precision measuring tools and three-dimensional scanning systems: Including the conventional measuring tools such as the vernier callipers, micrometers, laser distance meters and total stations, as well as the high-precision three-dimensional laser scanners. The latter can quickly obtain the overall point cloud data of the supports, and precisely analyse the structural deformations through the comparison with the three-dimensional models, with the efficiency and precision far exceeding the traditional methods.