加拿大巖爆支護(hù)手冊外文翻譯

本科畢業(yè)設(shè)計(jì) 英文翻譯 題 目 加拿大巖爆支護(hù)手冊 學(xué) 院 水 利 水 電 學(xué) 院 專 業(yè) 水 利 水 電 工 程 學(xué)生姓名 尹 剛 學(xué) 號 0943062172 年級 09級 指導(dǎo)教師 張 茹 二一三年六月三日四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 1 2.1Introduction Explicit analysis of each potential rockburst-damage mechanism and the interaction between the rockmass and the support system are complex tasks. This chapter provides a summary of the key items found in this handbook such that the practitioner is provided with guidance for support selection in burst-prone ground without undertaking all of the analytical steps necessary to complete a detailed design. For this summary chapter, details of the analysis procedures have been omitted, but they are described in subsequent chapters. Rockburst damage refers to damage that occurs around an excavation in a sudden or violent manner and is associated with a seismic event. Rockburst damage may not necessarily result in ejection of rock into the excavation, especially if the excavation is well supported. The damage mechanisms associated with different types of rockbursts vary from situation to situation (Kaiser 1993; Ortlepp and Stacey 1940). The first step in dealing with support selection for burst-prone conditions is to estimate the type of damage mechanism involved and the likely severity of the resulting damage. Also it is useful to understand the conditions that lead to or trigger a rockburst. 2.2 What causes rockbursts? For the purposes of hazard assessment and support design we distinguish between rockbursts that are triggered by remote seismic sources and rockbursts that are “self-initiated”. For self-initiated rockbursts, the location of the damage and the seismic event are the same. 2.2.1 Self-initiated rockbursts Self-initiated rockbursts occur when the stresses near the boundary of an excavation exceed the rockmass strength, and failure proceeds in an unstable or violent manner. The stresses generally increase as a result of nearby mining. In addition, the rockmass strength may degrade with time or with loss of confinement, leading to sudden failure. In either case the rockmass strength-to-stress ratio reaches unity and the rock fails. The failure process is sudden and violent if the stored strain energy in the rockmass is not dissipated in a gradual manner. This occurs when the stiffness of the loading system, i.e., the mine stiffness, is softer than the unloading stiffness of the volume of failing rock (Jaeger and Cook 1969; Brady and Brown 1993). 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 2 Another form of self-initiated rockburst is caused by a loss of structural stability. One example is the sudden buckling of a column or slab of rock. Structural instability usually leads to sudden failure but the conditions leading to failure are dependent on geometric considerations rather than the strength of the rock. 2.2.2 Remotely triggered rockbursts Rockbursts triggered by remote, relatively large magnitude seismic events (e.g., fault slip) are a common occurrence in some hard rock mines, particularly during the later stages of the mines life and where faults intersect stopes or large mined-out areas and sill pillars. A remote seismic event within a rockmass may create sufficiently high vibrations, and hence dynamic stresses,near an underground opening to initiate rockburst damage. The incoming seismic wave may lead to fracturing of rock near an underground opening, or lead to structural instability (buckling), or directly provide sufficient energy to eject rock due to seismic energy transfer, rockburst hazard assessment involves determining the peak particle velocities induced in the rock around underground openings close to the seismic source, i.e., generally within a few hundred metres (Chapter 5). However, meta-stable structures such as dykes and pillars may react to seismic events at larger distances ( 1000m). 2.2.3 Influence of mining stage The nature of the mining-induced seismic activity and the associated rockbursts occurring in a mine usually change throughout the mines life span. In some Canadian mines, significant 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 3 seismic activity may not occur until most of the ore has been mined and extraction ratios are high. Seismic activity occurring during the initial stages of a mines life is usually caused by high localized stress concentrations near drifts that are relatively isolated from each other. The magnitude of the seismic events associated with these failures is usually small (generally less than Nuttli magnitude 2 for Canadian mines). Strainbursts are often associated with localized stress raisers such as faults, dykes, and stiffer rock types. As the mine matures, multiple openings and numerous stopes are created. Strainbursts may still occur. However, now that larger volumes of rock have become highly stressed, sudden failure of rock pillars (e.g., sill pillars) may occur. When such pillars fail suddenly, significant stored strain energy is released from the hanging and footwall, and seismic activity with a moderate magnitude (around Nuttli magnitude 2) can occur. The maximum Nuttli magnitude for seismic events associated with pillar bursts in Ontario mines seems to be 3.5 (Hedley, pers. Comm. 1995). During late stages of a mines life, regional changes in the stresses are created, affecting large, mine-wide volumes of rock. This effect can initiate fault-slip seismic events with moderate to large seismic magnitudes (generally less than Nuttli magnitude 4 in Canada). Most importantly, these large events may be encountered where critically stressed faults intersect stopes, because a greater degree of freedom for movement along the fault has been created. Large seismic events may in tum trigger smaller localized rockbursts and seismically-induced rockfalls at multiple locations in the mine. 2.3 Rockburst damage mechanisms Based on our observations, rockburst damage is caused by one or more of the following mechanisms: Rock bulking due to fracturing Rock ejection due to seismic energy transfer Rockfalls induced by seismic shaking. These damage mechanisms are shown in Figure 2.1, and form the basis for discussion in the remainder of this handbook. Although combinations of the mechanisms shown in Figure 2.1 may occur, our investigations have shown that the occurrence of these mechanisms is relatively distinct. Note 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 4 that the focus here deals with the nature of the mechanisms actually causing the damage at the excavation, rather than the seismic event associated with the rockburst. Any one of the mechanisms shown in Figure 2.1 may be triggered by a number of different factors, such as a stress buildup or a remote seismic event, but this mechanism is triggered, it becomes the primary driving force behind whatever damage is caused to the excavation and the support system. 2.3.1 Rock bulking due to fracturing Rock increases in volume it fractures. This phenomenon is well known, and is reflected in the “swell factor” that measures the increase in volume of excavated rock compared to in-place rock. This phenomenon occurs whether the rock is fractured by explosives or by stress-induced failure mechanisms. The actual volume increase varies considerably, and is generally less for rock that is confined and remains in place after being fractured. Nevertheless, the underlying principle remains valid, i.e., fractured rock increases in volume. The volume increase, or bulking factor, can be controlled or at least partially suppressed by appropriate support measures. In the context of burst-prone ground, the phenomenon of rock bulking due to fracturing is 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 5 observed when the stresses near the opening suddenly exceed the rock strength and a zone of fractured rock occurs (Figure 2.1). If the fracturing occurs in an unstable and violent manner it is often referred to as a strain burst, and is perhaps the most common form of damage in both civil engineering and Canadian mining excavations in burst-prone ground. Highly stressed rock around an excavation or in a pillar is a prerequisite for this form of damage. Another form of bulking occurs when the rock around an excavation fails as a result of structural instability, for example, when a slab of loaded rock suddenly buckles into the excavation. In such cases, geometric effects will tend to magnify the bulking, leading to large bulking factors. Photo 2.1 shows rockburst damage to drifts supported with rockbolts and mesh, and with mesh-reinforced shotcrete and bolts, respectively. Damage was caused by bulking of the rockmass, which is reflected in the bagging of the shotcrete and mesh. In these cases, although the bulking rockmass bagged the shotcrete and mesh, the support system retained and held the broken rock in place. The bulking process due to fracturing may be self-initiated if mining-induced stresses exceed the long-term strength of the rock. In addition, the strength and stability of the rockmass may degrade with time or with changes in excavation geometry or with a reduction in confinement. All these factors can lead to sudden rock fracturing and ultimately cause rock bulking. Conditions leading to unstable rock fracturing are discussed in Chapter 6. Sudden rock fracturing and bulking may also be triggered by an incoming dynamic stress increment from a distant seismic source. In this case, although the triggering mechanism is different from the self-initiated case, once the failure is triggered, it will behave in a similar fashion to that outlined above. In other words, it does not really matter what triggers the near-field rock fracturing and bulking, whether it be self-initiated or triggered by a remote seismic event, the result is an increase of the rockmass volume. The failing rock tends to bulk in a relatively stable manner and often remains in place if adequately or if the rock fracturing consumes most of the liberated stored strain energy. This process is referred to as rock bulking without ejection. However, in situations where there is an excess of stored strain energy in the rockmass surrounding the excavation compared to the energy consumed in forming new fractures and deforming the fractured rockmass, then the excess energy can be transferred to the failing rock bulking with ejection. If there is sufficient excess energy, rock blocks may be ejected into the opening at relatively high velocities (Kaiser 1993). It is extremely difficult to predict whether rock will be ejected violently as part of the fracturing-bulking process. The only practical means to assess the violence of rockmass bulking 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 6 is based on observations underground. If there is a clear sign of ejection, i.e., if rock is displaced beyond its natural angle of repose, the ejection velocity must be high (e2 to 3 m/s). In such cases, the rockburst damage mechanism should be classified as bulking with ejection and the support should be chosen to dissipate kinetic energy. Ejection velocities in excess of 3 m/s may be observed if the released stored strain energy is focused on only part of the rock annulus or if energy is transferred from larger to smaller blocks. Analytical methods for estimating or predicting the occurrence of rock bulking and its extent are discussed in Chapter 6. However, there are no analytical methods that can be used with full confidence to give accurate and detailed predictions. Thus, observations of the nature of previous rockburst damage are needed to verify results from analytical considerations. In general, the primary evidence for rock bulking can be seen in the bagging or mattressing of mesh, as shown in Photo 2.1. Miners often refer to the bolts being sucked into the mesh indicating that the mesh has been tightly stretched due to the bulking of rock behind it. During rehabilitation of drifts, the thickness of fractured rock may be explicitly observed. An indication of the amount of bulking (or bulking factor) can be obtained by comparing pre-and post-damage opening dimensions. The combination of observations from previous rockbursts, together with the analytical methods outlined in Chapter 6, provide a basis for assessing whether or not rock bulking is the primary cause of damage. The wall movement resulting from bulking depends on the amount of bulking that occurs 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 7 and the thickness and areal extent of the failing rock annulus. If only a thin skin of rock is broken, the bulking effect will be relatively minor. If the fracture zone is relatively deep, then substantial closure movements must be anticipated. The rock bulking leads to several consequences. If support was installed, then the volume increase of the rock will load the support, and the support will, in turn, react against the bulking to confine the process. The outcome of this interaction may lead to failure of the support system. Alternatively, if the support system has adequate characteristics, it may succeed in suppressing most of the rock the rock bulking and achieve stability. Between these two extremes, the support system may simply deform enough to allow most of the bulking to occur, and the rockmass to re-establish itself in a new configuration confined by the support system. The action of rockmass bulking may seriously damage standard drift support systems. An ideal support system must be either strong enough to suppress this volume increase, or it must have sufficient ductility to allow the volume increase to take place without destruction of the support system. Other factors may magnify the destructive consequences of rock bulking. In particular, geometric effects, such as the lateral buckling of a series of slender rock slabs lying parallel to the excavation surface, may amplify the volume increase. From the perspective of the ground control engineer, faced with the task of selecting an appropriate support system, it is important to identify whether rock bulking is the dominant type of rockburst damage, and to identify whether it is associated with violent rock ejection in addition to a volume increase in the fractured rock. 2.3.2 Rock ejection due to seismic energy transfer Rock blocks may be violently ejected from the periphery of an excavation due to the transfer of seismic energy to the blocks from an incoming seismic stress wave as shown in Figure 2.1 (Wagner 1984; Roberts and Brummer 1988). This mechanism is considered to be a primary cause of rockburst damage in the deep mines of South Africa. In such cases, the kinetic energy in the ejected rock is clearly related to the energy transmitted from the seismic source or the peak particle velocity, which depends primarily on the magnitude of the source and its distance from the opening. In this regard, it is important to the excavation, and that the energy reaching the excavation from this secondary seismic source may be significantly greater than that from the primary, remote source. The ejection of rock blocks is most likely to occur in rockmasses that are well jointed or substantially fractured thereby allowing kinematic freedom for blocks of rock to move into the excavation. Naturally, damage to the support system will depend on the velocity and size of the ejected blocks, and thus the severity of damage is once again related to the thickness of the rock involved. A wide range of ejection velocities can be anticipated depending on the 四川大學(xué)本科畢業(yè)設(shè)計(jì) 英文翻譯 Canadian Rockburst Support Handbook 8 magnitude of the seismic energy and the mass of the ejected material. At low ejection velocities (between 0 and 3m/s), support systems can catch and retain the ejected rock such that the damage appears similar to rock bulking. Note however, the underlying cause of the rockburst damage seismic wave to kinetic energy of ejected rock. In contrast, rock bulking can be self-initiated without the presence of a remote seismic event. When an excavation is close to large magnitude seismic events, ejection velocities in excess of 3 m/s may occur. In cases where the mining environment has a low (soft) loading stiffness or in situations where the mechanism of rock bulking is combined with rock ejection, ejection velocities up to or exceeding 10 m/s may be experienced (Ortlepp 1993). In either case, it is important that the support has the ability to absorb energy. Observations from Canadian mines indicate that rock ejection caused solely by seismic energy transfer is relatively uncommon. Unfortunately, it is often difficult to distinguish rock ejection mechanisms from rock bulking mechanisms based solely on field observations. However, the damage mechanism should be classified as rock bulking without ejection, unless there are clear indications that blocks of have been thrown violently. In those cases where rock ejection is observed, support may be designed to protect against this phenomenon following the procedures outline in Chapter7. 2.3.3 Rockfalls induced by seismic shaking A seismically-induced rockfall occurs when an incoming seismic wave accelerates a volume of rock that was previously stable under static conditions, causing forces that overcome the capacity of the support system (Figure 2.1). Thus, the seismic shaking triggers the failure. However, gravity is a dominant force driving the failure, once it has been triggered. This mechanism is facilitated where deep seated fracturing has already loosened the rockmass, or where weak ge