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Steel reinforced shotcrete lining (SRSL) support is the primary structure to maintain the stability and mobilize the self-bearing capacity of surrounding rock. However, the structural design of SRSL in underground excavation still relies on experience-based method and lack of quantitative mechanical analysis. This paper aims to propose a modified analytical model of support characteristic curve (SCC) that represents the mechanical behavior of SRSL structures in underground construction, through which the interface bond-slip behavior between steel arch and shotcrete layer is taken into consideration. Four-point bending test of SRSL composite beam was carried out to study the bearing mechanism and failure performance. Test results show that the shotcrete-steel interface is prone to slip failure which significantly reduces the overall strength of SRSL. The laboratory test is complemented by non-liner finite element parametric studies considering the bond-slip properties to clarify the design principles and to obtain the flexural stiffness of tunnel primary lining structures. Based on above studies, the simplified formulas for the SCC of SRSL is constructed. The research results provide a theoretical basis for the design and application of SRSL structure in related projects. [ABSTRACT FROM AUTHOR]

Block and panel caving methods are increasingly being proposed as an economical means for the excavation of ore deposits. The development of methods for predicting cave fragment size holds significant potential for reducing risk associated with cave mining projects. A fragmentation study was carried out for the New Afton B1 and B2 caves to generate fragmentation models that could be applied to future lifts. In part 1 of this paper, implications of fragmentation size for the mine are considered, whereas the effects on mill performance are addressed in part 2. Fragmentation measurements, from sieving and image-based methods, as well as historical logs of hang-up events are presented. Measurements showed that for the B1 and B2 caves, secondary fragmentation size, representing the size of material at drawpoints, is strongly related to faulting, height of draw and effects of the cave boundary. [ABSTRACT FROM AUTHOR]

Excavation methods for underground drivage should be cost effective and minimise damage to the periphery rock wall. Among the various methods of excavating systems the 'drill and blast' method is the most commonly used because of the low capital investment required, its easy manoeuvring and excavating capability and the flexibility of changing the excavation profile if ground conditions necessitate. The burn-cut method of blasting is cost effective and has a good advance rate compared to other conventional drilling patterns. This paper investigates how errors in the burn-cut method can be minimised and how the parameters influencing the progress per round of blast can be optimised. The importance of drilling accuracy, low burden and heavy charge concentration for the initial holes of the burn-cut method of blasting is discussed. This paper proposes a conceptual mathematical model to enable a better understanding of the burn-cut method of blasting. The model assumes that the process of breakage for the initial holes is a slabbing action and uses the concept of the deflection of a cantilevered beam (rock strata between charge and relief hole) to explain the importance of deeper relief holes. The results of an experimental study conducted in one of the tunnels in the Dul Hasti hydroelectric project in the Himalayan region are also discussed. [ABSTRACT FROM AUTHOR]

Stress relaxation is relevant to the design of both civil and mining excavations. While many authors refer to the adverse effect of stress relaxation on excavation stability, some present compelling empirical evidence indicating that stress relaxation does not have a significant effect. Establishing clear definitions of stress relaxation was critical to understanding and quantifying stress relaxation of the various types that have been referred to in the literature. This paper defines three types of stress relaxation – partial relaxation, full relaxation and tangential relaxation. Once clear definitions were determined, it became clear that the theoretical arguments and empirical evidence presented by various authors to support their respective cases are not contradictory; rather, the different conclusions can be attributed to different types of stress relaxation. In particular, when the minor principal stress is negative the intermediate principal stress has been identified as significantly affecting jointed rock mass behaviour. The aim of the study was to review and evaluate existing methods of quantifying the effect of stress relaxation around underground excavations and, if necessary, propose a new set of recommendations. An empirical stope stability model, that has been termed the Extended Mathews stability chart, was considered to be the most appropriate method of quantifying the effects of stress relaxation. A new set of guidelines to account for the effect of stress relaxation on excavation stability in the Extended Mathews stability chart has been proposed from a back-analysis of 55 case histories of stress relaxation. [ABSTRACT FROM AUTHOR]

Long-hole winze (LHW) blasting is a critical stage of production in underground sublevel open stoping; however, its influence on potential excavation damage is often overlooked. In addition, recent developments in uphole LHW practices are implementing longer firing lengths, sometimes exceeding 15–20 m on a single blast. This has the potential to increase the likelihood of blast-related damage. This paper introduces an empirical approach to determine long-hole winze firing heights to minimise near-field rock mass damage. The degree of damage is estimated from the amplitude of peak particle velocities induced by the LHW blasts. Modelling was conducted to evaluate the relationship between peak particle velocity (PPV) as a function of LHW firing heights and distance to a point of interest. A hypothesis was established and further verified with direct measurements from a comprehensive near-field vibration monitoring programme conducted at a large sublevel open stoping operation in Australia. An empirical model to estimate PPV as a function of a non-dimensional factor was established. The model is defined by the ratio of the distance to a point of interest and the LHW firing height. This model may be used to determine the recommended advance and firing phases of a LHW to minimise potential damage to open stope boundaries. [ABSTRACT FROM AUTHOR]

Many types of mining machines use pointed style picks in the excavation of weak and medium strength rock ranging from coal and evaporates to shales and sandstones. This paper explores the effect of the initial onset of pick wear on changes in the cutting performance as reflected by an increase in pick tip angle at varying depths of cut using two different rock types. Rock cutting tests were performed in Gambier limestone and Gosford sandstone at depths ranging from 5 mm to 20 mm using a pointed pick having tip angles of 70°, 90° 100° and 110°. The results reveal an increase in tool angle has a more pronounced effect on normal force with a three to four-fold increase compared to less than a two-fold increase in cutting force. Forces and specific energy were also found to increase with depth of cut over the range of tip angles. [ABSTRACT FROM PUBLISHER]

Because of several unforeseen actions such as the deep excavation and long-term consolidation of ground, the settlement and lateral displacement have become important parameters for shield tunnel. Due to lack of distributed characteristic, the traditional monitoring methods based on manual observation on some preset uniformly spaced points, probably ignore some local settlements or lateral displacements which may occur anywhere along a shield tunnel. According to an improved conjugated beam method (ICBM) which uses the distributed fiber optic sensors to monitor the deflection of statically indeterminate structure with a finite number of supports, this paper first extends the ICBM to monitor distributed deflection of statically indeterminate structure with infinite number of supports. Then a settlement and lateral displacement monitoring method for shield tunnels is proposed. Two experiments including a scale-down longitudinal concrete model and a long steel tube model are carried out to verify the monitoring accuracy of the proposed method. [ABSTRACT FROM AUTHOR]