Development of a wireless system to measure the strain/deformation of rock bolts

In this study a smart set-up integrated with rock bolts was proposed to automatically monitor, record and analyse rock mass deformation. The proposed system which includes sensors and a wireless data acquisition system, rapidly and readily generates data sets along with customisable graphs, calculations and analysis in a cloud system and can be used in modern mining. To evaluate the developed technique, rock bolts were instrumented lengthwise using resistive strain gauges and then connected to the wireless data logger system. Elastic tensile tests as well as pull-out tests were conducted and the strain values along the rock bolts were successfully and accurately measured, recorded and uploaded to the cloud system

Finite element modelling of fully encapsulated cable bolts in laboratory large scale pull out test

Modelling cable bolts in numerical software is a challenging task. Cables are made from multiple strands wound together and when loaded, they tend to act in a way more complex manner than rock bolts. This study used laboratory data from large scale pull out testing of fully encapsulated cable bolts using cementitious grout. A finite element method was adopted and a series of engineering simplifications and assumptions were made to increase the efficiency of the model. The results were able to illustrate a better capability in modelling the bulbed cables compared to the plain cables. Also, the sensitivity analysis proposed that increasing cable diameter for a given hole size (decreasing grout annulus thickness) can increase the overall peak load value, similar to an increase in concrete confinement, grout uniaxial compressive strength, and bulb size

Shear behavior of clayey infilled rock joints having triangular and sinusoidal asperities

Rock joints govern an important role in the overall stability of rock slope which may be filled with infill material due to transported materials with water, weathering as well as joint shearing. There are two methods of testing rock joint shear behavior, one is Constant Normal Load (CNL), and another is Constant Normal Stiffness (CNS). The CNL is found suitable in slope stability where sliding mass can move freely without any restriction while CNS is suitable in underground excavation, pile socketed in rock and reinforced rock slope where the stiffness of boundary restricts dilation during the shearing process. This study investigates the shear behavior of clay infilled rock joints with triangular and sinusoidal asperities under CNL conditions. The pair of triangular and sinusoidal asperities is Type 1T, Type 2T and Type 1S, Type 2S respectively where prefix represent asperity height and suffix represent the type of asperity. Joint Roughness Coefficient () obtained from back-calculation of Barton equation using experimental data is 7, 9, 9 and 12 for Type 1T, Type 2T, Type 1S and Type 2S respectively. The direct shear test was performed on two campaigns, among these, was one of understanding shear behavior of infilled rock joints under various normal loads and another was the shear behavior of infill rock joints under various infill thicknesses. During the first campaign shear behavior of clayey infilled rock joint fewer than three different normal loads were tested. Likewise, in the second campaign shear behavior of clayey infill rock joint under three infill thickness were performed. Overall this study provides better insights into shear behavior clayey infilled rock joints having different joint morphology

SPT-CPT correlation in Southeast Queensland, Australia

Among the most popular in situ investigation techniques for identifying subsurface strata, cone penetrometer testing (CPT) and standard penetrometer testing (SPT) are employed in geotechnical engineering. In fact, both tests are adopted to correlate a wide range of geotechnical parameters in various design applications. The cost associated with conducting both in situ tests at the same locations often results in one method being chosen over the other. Hence, engineers have to corelate one of the tests’ parameters into the other test using empirical correlation in translating SPT blow counts (SPT-N) into CPT cone tip resistance (CPT-qc). However, disadvantages of this in situ test are that it does not directly quantify geotechnical parameters but uses correlations which are significantly influenced by soil properties. Also, many of correlations do not provide sufficient background on the statistical approach. This study investigates the conformity of the empirical correlations against local SPT-CPT correlation for different soil occurrences in Southeast Queensland (SEQ), adopting a linear regression model to validate the degree of the relationship. Seven soil groups were classified in SEQ, comprising cohesionless and cohesive soil. The results of the SEQ samples showed a strong liner relationship (r = 0.69 – 0.89) with at least 50% of data points coinciding with the regression line (R2 = 0.48 – 0.80). It follows that for some soil groups, the published correlation agrees well with the SEQ study, while others did not

Investigation of the effect of using fly ash in the grout mixture on performing the fully grouted rock bolt systems

This paper attempts to reveal the influence of using fly ash in the grout on the axial bearing capacity of fully grouted rock bolts. For this purpose, different fly ash contents, including 1% and 2%, have been applied with Stratabinder HS with a water-to-grout ratio of 30%. Also, after preparing and curing the required samples, the UCS tests were conducted to determine the influence of fly ash on the grout strength. Along with the UCS tests, several pull-out tests were examined by preparing and curing rock bolt samples with steel reinforcement rebars of 16 mm and steel pipes with a 50 mm length and 23 mm diameter. The results revealed that replacing a small amount of grout with fly ash could increase the strength of the grout. Also, the axial bearing capacity has risen by using fly ash in the grout mixture

Finite element numerical modelling of rock bolt axial behaviour subject to different geotechnical conditions

In rock bolting systems, grout acts as a medium to transfer initiated stress from the bolt to stable rock mass, and also to transfer the in-situ stress from surrounding rock to the bolt-grout interface. In this study interaction between the mechanical characteristics of the grout and rock bolt behaviour was investigated in different confining pressure conditions. First, the uniaxial compression strength of the grouts was experimentally determined, and then pull-out tests were carried out on rock bolts encapsulated using the same grouts to quantify the bonding behaviour. Numerical models using ABAQUS explicit finite element code were then applied to further analyse the effects of mechanical properties of the grouts and the confining stress on the behaviour of the rock bolting systems. The compression of the simulated results with the experimental tests showed that the proposed FE models simulate the axial behaviour of rock bolts efficiently. The results of the parametric study indicated that grout mechanical properties and the level of confining stress affect the ultimate bearing capacity of the encapsulated rock bolts and the force-displacement behaviour. The level of damage that occurred at the specimens due to pull-out load is also significantly influenced by these factors

The effect of changing confinement diameter on axial load transfer mechanisms of fully grouted rock bolts

This paper aims to study the effect of changing the confinement diameter on the axial load-bearing capacity of rock bolt systems. The diameter of the confinement is monitored in a fully encapsulated rock bolt at day 7 and 28 of grout curing. These particular times were considered critical to demonstrate grout strength when conducting pull-out tests on rock bolt samples. Following this, the samples were cast with a water-grout ratio of 36%, the internal diameters of encapsulation being 23 mm and 50 mm, and the encapsulation length at 50 mm. The results indicated that by increasing the confinement diameter, the rock bolt\u27s load-bearing capacity increased approximately 32% and 45% for days 7 and 28, respectively

Effects of rib distances on axial load transfer mechanisms of fully grouted rock bolts

Rock bolt systems are widely used for the reinforcement of underground coal mines after excavation. These systems consist of steel bolts installed in drill holes and encapsulated by resin or grout. The spacing between the rock bolt ribs is one of the factors affecting the axial load transfer mechanisms. Steel rebar with a 16 mm diameter, Stratabinder HS grout, and steel pipes with a diameter of 50 mm were used to simulate the rock bolt system. The distance between the ribs on the rebar was doubled for half of the samples to investigate the effects of rib spacing on the pull out capacity of grout encapsulated rock bolts. The water to grout ratio was set to 0.35. Pull-out testing of the samples with curing times 7, 14, and 28 days was carried out using the automated tensile testing machine at the Centre for Future Materials laboratory of the University of Southern Queensland. It was concluded that the ultimate load was increased when the spacing between the ribs was doubled. The results also showed curing time increases the ultimate pull-out load capacity

Investigating the axial and shear performance of fiberglass rock bolts

This paper primarily evaluates the axial and shear performance of fully grouted fibreglass- reinforced polymer (FRP) rock bolting systems. For this purpose, a FRP rock bolt with a diameter of 20 mm was selected for examination. To evaluate the axial performance, several samples with a double- embedment length of 150 mm and an exposed length of 200 mm were cast using an 80 MPa cementitious grout and cured for 28 days. Pull-out tests were then conducted at a controlled rate of 1 mm/min with a 1000 KN MTS apparatus to determine the pull-out performance of the FRP bolts. Furthermore, a comparative analysis involved testing a 20 mm fully grouted steel rock bolt with a 150 mm encapsulation length, was conducted. The results indicated that the axial bearing capacity of the FRP bolts varied between 84 KN and 110 KN, while the steel bar exhibited a capacity of 144.5 KN. The load-displacement curves analysis showed that steel rebar rock bolts absorb more energy during the debonding process compared to the FRP bolts. Along with pull-out tests, the shear behaviour of the FRP bolts was also determined by conducting single and double-shearing tests. With this aim, after casting the concrete blocks in a double-shearing box, three different pretension values were applied to the samples. The results showed that pretension values had a direct impact on the displacement values, while they did not have a direct impact on the peak shear force values. Additionally, the tensile properties of the FRP and the steel bolts showed a different behaviour in the uniaxial tensile test

Finite element simulation of fully grouted rock bolts behaviour across varied bore hole diameters

This paper introduces a finite element (FE) method to simulate the impact of confinement conditions on the axial load-bearing capacity of fully grouted rock bolts. The study utilises a combination of experimental and numerical modelling techniques. For this purpose, two different sizes of steel sleeves were used as confinements with a diameter of 23 mm and 50 mm. The samples were cured after embedding and grouting the bolt for 28 days. Subsequently, pull-out tests were conducted to assess the axial load-bearing capacity of the samples. The results showed a direct correlation between increased confinement diameter and higher values of ultimate pull-out capacities. In addition to the experimental tests, numerical models employing ABAQUS software were developed to simulate and analyse the debonding mechanism along the bolts. By defining the appropriate model geometry, materials properties, boundary conditions, and interactions, the simulation revealed that the debonding mechanism occurred at the bolt-grout interface. Eventually, a comparison between the load-displacement curves derived from the experimental tests and the numerical simulations highlighted the effectiveness of the numerical model in accurately representing the axial load transfer mechanism within the fully encapsulated rock bolts