ABSTRACT:

Cable bolts are widely used as a principal means of support. The monitoring of the performance of reinforcement is critical in improving and optimizing reinforcement designs. This paper presents a case study where Stretch Measurement to Assess Reinforcement Technology (SMART) instrumentation was usedin conjunction with other observational, analytical, and numerical techniques to evaluate cable design performance and determine the nature of the failure mechanisms. This case study also provides an excellent comparative study of the in situ bond stiffness of plain strand and Garford bulb cable, as well as in evaluating the influence of faceplates on Garford cable's performance. Cablebolt design was optimized through a multifaceted design methodology and verified through field instrumentation. The changes in stope support design and cable bolting practice have resulted in significant cost savings.

RÉSUMÉR:

Les cables d'encrage sont amplement utilises comme methode principale de support dans les mines souterraines. Le contrôle de la performance du renforcement est crucial pour ameliorer et optimiser le concept de reforcement. Cette communication presente une etude de la technologie d'instrumentation SMART (Stretch Measurement to Assess Reinforcemnt Technology ou Mesure de l'elongation pour fin d'evaluer le renforcement); cette technologie est utilisee enparallèlle avec des techniques d'observations, d'analyse et de modelisationnumerique pour evaluer la performance du concept de renforcement et pourdetermmer la nature des rnecanismes de rupture. Cette etude de cas fournit parsurcroit un moyen ideal pour comparer la force d'adhesion de cable reguliers etdes cables Garford bulbes; aussi elle permet d'evaluer le rôle des plaques demetal sur la performance des cables Garford. Le concept de renforcement parcable fut optimiser par le bias d'une rnethodologie polyvalente et verifie àlaide d'instruments sur le terrain. Les modifications apportees à la conceptiondu soutènernent des chantiers miniers et à la procedure de renforcement par cable resultèrent en une diminution significative des coûts d'operation.

ZUSAMMENFASSUNG:

Die verbreitetste Tragermethode setzt Kabelbolzen ein. Die Überwachung der Stuetzungsleistung ist fuer die Verbesserung und Optimierung der Verstarkungskonstruktion entseheidend. Diese Arbeit stellt eine Fallstudie vor, in der DehnungsmeBung zur Beurteilung der Stuetzungstechnik (Stretch Measurement to Assess Reinforcement Technology [SMART]) in Verbindung mit anderen empirischen, analytischen und numerischen Methoden eingesetzt wurden, um die Leistungsfahigkeit der Kabelkonstruktion zu beurteilen und die Art der Ausfallmechanismen festzustellen. Diese Fallstudie liefert gleichzeitig eine ausgezeichnete.

1
INTRODUCTION

The benefits of cable bolt support in stabilising surface and underground excavations are well established and this support system is extensively used in the mining and civil engineering industries as a principal means of support. The monitoring of the performance of reinforcement around excavations is critical in assessing overall stability as well as in improving and optimising reinforcement designs. Hutchinson & Diederichs (1996), emphasise this in the verification portion of their cable bolting cycle. The verification process should involve an evaluation of the effect of cable bolts on rock mass stability, based on a combination of observation and instrumentation.

One of the major problems associated with the use of fully grouted cable bolts is the lack of a reliable method to monitor cable tension. In this paper, an innovative instrument will be described, that can determine the load distribution along fully grouted cable bolts. This instrument, the SMART (Stretch Measurement to Assess Reinforcement Tension) cable, allows strains along cables to be quantified; hence enabling loads to be Calculated. The instrument incorporates a miniature MPBX (Multiple Point Borehole Extensometer) within the cable, thereby avoiding interference with the cable:grout bond, as is the case with externally mounted gauges.

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