Student– UNSW Mining Engineering The Influence Of Rock Size Sample On The Load Carrying Capacity Of Cable Bolts Under Confined Conditions Ibad Ur-Rahman Student– UNSW Mining Engineering

Introduction The objective is to develop a standardised methodology for an experiment to assess the load carrying capacity of cable bolts. Aimed at designing a system that compares the different size of sample effects on the performance of cable bolts under confined conditions

Background 1990- ‘Experimental and numerical investigations of cable bolt support system’ by Hossein Rajaie RDP-Howden electrohydraulic servo-controlled testing system was used with following characteristics 1000KN capacity Working stroke of 100 mm Pull out rate of 0.3 mm/s Pull out test performed under constant parameters; Embedded length Borehole diameters Sample diameters were varied; 100mm, 150mm,200mm,250mm and 300mm Preparation of sample (Rajaie,1990)

Rajaie’s Results Diameter of sample effected the load carrying capacity, as diameter increased the load carrying capacity also increased . Significant increase in load carrying capacity from 100mm to 200 mm sample stress distribution in cylinders affects the confining pressure on the grout and the cable grout interface Test standardised to 250mm in diameter Effect of diameter of sample on peak load ( Rajaie,1990)

Short comings of Rajaie’s Research Research is out dated Research performed on standard plain 7 strand wire cable bolt common at the time but newer technology been developed Bulbed and birdcage cable bolts are commonly used in the industry today, does Rajaie research remain true? Newer types of cable bolts are likely to induce higher lateral stresses during failure requiring larger rock samples to deal with the dilation generated by the bolt Research performed on samples in an unconfined state

Past UNSW Research 2013- ‘The Size effect of Rock samples used in anchorage performance testing of cable bolts’ by Matthew Holden Similar to Rajaie’s research Test involved using Bulbed cable bolts 16 samples were tested with 300mm length and diameters of 150mm, 215mm, 300mm and 400mm Bore hole diameter of 38mm Test Arrangement (Holden,2013)

Holden’s Results Two Types of Failures occurred: Type 1 where failure occurred at the grout/rock interface Type 2 where failure occurred at the bolt/grout interface. Shortcomings of research; Borehole contained un-realistic smooth wall Testing performed on samples under unconfined conditions

Methodology Sample length= 320 mm Diameters of samples; 150mm, 250mm,300mm,350mm and 500mm Sample borehole diameter= 42 mm Cable bolt used- Bulbed Sumo stand with indented wire Each sample was formed in 3 step process

Step 1-preparing samples Rock samples casted in molds Riffling effect created using 42 mm diameter PVC tube and 3mm diameter wire wrapped around it with 35mm in lay length UCS of cement =32 MPa

Step 2-Sample Curing Molds removed the following day after cement pouring Research In 2002 by A. Kılıc, E. Yasar and A.G. Celik showed that curing time had significant effect on pull out load. Samples left to cure for 28 days Curing time of sample vs. pull out load (Kılıc, Yasar and Celik , 2002)

Step 3-Grouting cable bolt into sample Cable bolts were grouted into each rock cylinder using slow set polyester resin. Setting time of resin 20-25 minutes Resin and oil catalyst mixed using electric mixer to combine the two components thoroughly and provide even distribution of catalyst. First resin was poured into borehole to a height 50mm below the top of the borehole, allowing for displacement of the resin after the cable bolt was installed.

Test Arrangements

Setting-up Test with Confinement Confinement of sample was achieved by adding metal plates to the sample. Metal plates designed specifically for each diameter leaving one centimeter gap between the sample and the metal plate Foams were added in between the two clamps to provide additional displacement for different level of confinement Micrometer torque wrench was used to tighten the screws to the specific torque required CONSTANT NORMAL STIFNESS

Results and Analysis The following tests were performed: size effect of rock sample on pull out load of cable bolt under unconfined conditions Size effect of rock sample on pull out load of cable bolts under confined condition with zero torque Size effect of rock sample on pull out load of cable bolts under confined condition with 40 N.m (30 ft.lb) Size effect of rock sample on pull out load of cable bolts under confined condition with 80 N.m (60 ft.lb)

Cable Bolt-Unconfined Rajaie’s Results (1990)

Cable Bolt- Zero Torque

Cable Bolt- 40 Nm Torque

Cable Bolt- 80 Nm Torque

Cable Bolt Results

Conclusion pull out tests found an increase trend in cable bolt pull out load capacity with size of the sample diameter. Also found that different level of confinement levels also influence the pull out load capacity, as the confinement increases so does the pull out load capacity of the cable bolt. Pull out test for cable bolts standardised to 350 mm diameter with a confinement pressure 40 N􏰀m