加拿大巖爆支護手冊外文翻譯

1、<p>　　本科畢業(yè)設(shè)計英文翻譯</p><p>　　題 目 加拿大巖爆支護手冊 </p><p>　　學(xué) 院 水 利 水 電 學(xué) 院 </p><p>　　專 業(yè) 水 利 水 電 工 程　 </p><p>　　學(xué)生姓名

2、 尹 剛　 </p><p>　　學(xué) 號 0943062172 年級 09級　</p><p>　　指導(dǎo)教師 張 茹 　 </p><p><b>　　二Ο一三年六月三日</b></p><p>　　2.1I

3、ntroduction </p><p>　　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

4、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. F

5、or this summary chapter, details of the analysis procedures have been omitted, but they are des</p><p>　　Rockburst damage refers to damage that occurs around an excavation in a sudden or violent manner and i

6、s 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 type

7、s 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 estimat</p><p>　　2.2 What causes roc

8、kbursts?</p><p>　　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-in

9、itiated rockbursts, the location of the damage and the seismic event are the same.</p><p>　　2.2.1 Self-initiated rockbursts</p><p>　　Self-initiated rockbursts occur when the stresses near the bo

10、undary 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 wi

11、th 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 energ&

12、lt;/p><p>　　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 f

13、ailure but the conditions leading to failure are dependent on geometric considerations rather than the strength of the rock.</p><p>　　2.2.2 Remotely triggered rockbursts</p><p>　　Rockbursts trig

14、gered 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 mine’s life and where faults intersect stopes or

15、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

16、seismic wave may lead to fracturing of rock n</p><p>　　2.2.3 Influence of mining stage</p><p>　　The nature of the mining-induced seismic activity and the associated rockbursts occurring in a min

17、e usually change throughout the mine’s life span. In some Canadian mines, significant seismic activity may not occur until most of the ore has been mined and extraction ratios are high.</p><p>　　Seismic acti

18、vity occurring during the initial stages of a mine’s 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

19、 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.</p>

20、<p>　　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.

21、, 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

22、. The maximum Nuttli magnitude for seismic events associated with pillar</p><p>　　During late stages of a mine’s life, regional changes in the stresses are created, affecting large, mine-wide volumes of rock

23、. 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

24、 stressed faults intersect stopes, because a greater degree of freedom for movement along the fault has been created. Large seismic events may in tum trigg</p><p>　　2.3 Rockburst damage mechanisms</p>

25、<p>　　Based on our observations, rockburst damage is caused by one or more of the following mechanisms:</p><p>　　﹒Rock bulking due to fracturing</p><p>　　﹒Rock ejection due to seismic ener

26、gy transfer</p><p>　　﹒Rockfalls induced by seismic shaking.</p><p>　　These damage mechanisms are shown in Figure 2.1, and form the basis for discussion in the remainder of this handbook.</p&g

27、t;<p>　　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 that the focus here deals with the

28、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 differen

29、t factors, such as a stress buildup or a remote seismic event, but this mec</p><p>　　2.3.1 Rock bulking due to fracturing</p><p>　　Rock increases in volume it fractures. This phenomenon is well

30、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 fail

31、ure 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., f<

32、;/p><p>　　In the context of burst-prone ground, the phenomenon of rock bulking due to fracturing is observed when the stresses near the opening suddenly exceed the rock strength and a zone of fractured rock occ

33、urs (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 excavati

34、ons in burst-prone ground. Highly stressed rock around an excavation or in a pil</p><p>　　Another form of bulking occurs when the rock around an excavation fails as a result of structural instability, for ex

35、ample, 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.</p><p>　　Photo 2.1 shows rockburst

36、 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.

37、In these cases, although the bulking rockmass bagged the shotcrete and mesh, the support system retained and held the broken rock in place.</p><p>　　The bulking process due to fracturing may be self-initiate

38、d 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 confinem

39、ent. 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.</p><p>　　Sudden rock fracturing and bu

40、lking 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,

41、 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 seism

42、ic event, the result is an incr</p><p>　　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

43、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 consu

44、med in forming new fractures and deforming the fractured rockmass, then the excess energy can be transferred to th</p><p>　　It is extremely difficult to predict whether rock will be ejected violently as part

45、 of the fracturing-bulking process. The only practical means to assess the violence of rockmass bulking is based on observations underground. If there is a clear sign of ejection, i.e., if rock is displaced beyond its na

46、tural angle of repose, the ejection velocity must be high (>2 to 3 m/s). In such cases, the rockburst damage mechanism should be classified as bulking with ejection and the support should be chosen</p><p>

47、;　　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

48、 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 b

49、agging or mattressing of mesh, as shown in Photo 2.1. Miners of</p><p>　　The wall movement resulting from bulking depends on the amount of bulking that occurs and the thickness and areal extent of the failin

50、g 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.</p><p>　　T

51、he 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 ou

52、tcome 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 stabilit

53、y. Between these two extremes, the support system may simpl</p><p>　　The action of rockmass bulking may seriously damage standard drift support systems.</p><p>　　An ideal support system must be

54、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

55、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.</p><p&g

56、t;　　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 i

57、dentify whether it is associated with violent rock ejection in addition to a volume increase in the fractured rock. </p><p>　　2.3.2 Rock ejection due to seismic energy transfer</p><p>　　Rock blo

58、cks 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). Th

59、is 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

60、source or the peak particle velocity, which depends </p><p>　　The ejection of rock blocks is most likely to occur in rockmasses that are well jointed or substantially fractured thereby allowing kinematic fre

61、edom 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 thickn

62、ess of the rock involved. A wide range of ejection velocities can be anticipated depending on the magnitude of the seismic energy and t</p><p>　　At low ejection velocities (between 0 and 3m/s), support syste

63、ms 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

64、bulking can be self-initiated without the presence of a remote seismic event.</p><p>　　When an excavation is close to large magnitude seismic events, ejection velocities in excess of 3 m/s may occur. In case

65、s 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 (Ort

66、lepp 1993). In either case, it is important that the support has the ability to absorb energy.</p><p>　　Observations from Canadian mines indicate that rock ejection caused solely by seismic energy transfer i

67、s 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 r

68、ock 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 design</p><p>　　2.3.3 Rockfalls indu

69、ced by seismic shaking</p><p>　　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 overco

70、me 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 wher

71、e deep seated fracturing has already loosened the rockmass, or where weak geological structures exist tha</p><p>　　Seismically-induced rockfalls may involve large volumes of rock, especially in excavations w

72、ith wide spans. This damage mechanism is particularly important to consider at drift intersections or for wide span stopes. Photo 2.2 shows damage resulting from a seismically-induced rockfall in the top-sill excavation

73、of a stope. Furthermore, if the backs of drifts or stopes are only marginally stable prior to a seismic event, even a relatively remote seismic event may generate sufficient shaking to cau</p><p>　　Once agai

74、n, past observations of damage may provide a good indication of potential future damage. The occurrence of large gravity-driven rockfalls triggered by seismic shaking is generally evidenced by piles of rock on the floor

75、of a drift or stope. While the seismic event is the trigger, the resulting damage looks much the same as a fall-of-ground under static conditions. Techniques that can be used to design support against seismically-induced

76、 rockfalls are discussed in Chapter 8.</p><p>　　2.3.4 Summary</p><p>　　There fundamental rockburst-damage mechanisms have been identified:</p><p>　　﹒rock bulking due to fracturing&l

77、t;/p><p>　　﹒rock ejection due to seismic energy transfer</p><p>　　﹒rockfalls induced by seismic shaking.</p><p>　　In any given situation, it is important to identify which mechanisms a

78、re dominant, as the appropriate support response is different depending on the nature of the underlying are an important indicator of the potential future damage mechanisms. The procedures outlined in Chapter 6 to 8 may

79、be used to guide decisions regarding the damage mechanisms most likely to occur in a given situation. In Canadian mines, the most common damage mechanism is rock bulking, followed by seismically-induced rockfal</p>

80、<p>　　2.4 Severity of rockburst damage</p><p>　　Each of the rockburst-damage mechanisms discussed above may result in different levels of damage to an excavation and its support system. On the basis o

81、f field studies of rock damage and support damage levels, Kaiser et al (1993) defined various damage levels that were observed to occur in association with rockburst phenomena. The damage severity depended on many factor

82、s, including:</p><p>　　﹒failure potential near the opening ,i.e., the level of existing wall stress compared to the rockmass strength, which in turn depends on rock wall quality</p><p>　　﹒suppor

83、t effectiveness</p><p>　　﹒local mine stiffness</p><p>　　﹒magnitude of seismically-induced stresses, rock accelerations or velocities</p><p>　　﹒opening geometry, size and orientation

84、</p><p>　　﹒geological structure.</p><p>　　Despite the numerous factors affecting damage severity, our work has indicated that the single, most important factor characterizing damage severity is

85、the depth and lateral extent of the rock around the opening that is involved in the failure process, regardless of how this rock annulus was formed. In short, whether the damage mechanism is rock bulking, rock ejection,

86、or rockfalls, the mass or volume of the rock involved best quantifies the resulting level of rockburst damage. Thus ,for the pur</p><p>　　As described below, three levels of rockburst damage severity are def

87、ined. The thickness of the fractured or damaged rock annulus corresponded to each damage level is shown schematically in Figure 2.2. Damage level determination is usually based on observations of previous damage, where s

88、uch observations are available, plus the analytical methods outlined in subsequent chapters.</p><p>　　2.4.1 Minor damage</p><p>　　Damage of minor severity would commonly be described as rock spi

89、tting, spalling or shallow slabbing, as shown in Photo 2.3. Support would typically show clear signs of loading including moderate new bagging of mesh with a few broken wires. Minor damage would involve only a shallow sk

90、in of fractured or loose rock generally less than 0.25 m in thickness. For this situation the weight of rock involved in the failing ground is less than about 7 KN/㎡.</p><p>　　While this damage level is call

91、ed minor severity, it can lead to dangerous situations, particularly if it occurs when miners are in the immediate vicinity. Minor damage often occurs during the initial development of deep tunnels and drifts, or in high

92、ly stressed, moderately jointed rock at relatively large distance from fault-slip type seismic events. This is often the worst level of damage encountered in civil engineering excavations, but is very commonly encountere

93、d in most deep mining excavat</p><p>　　2.4.2 Moderate damage </p><p>　　Moderate damage implies that the rock is heavily fractured and may have displaced violently. Mesh will be bagged at its cap

94、acity as shown in Photo 2.1 and is often torn or pulled over rockbolt plates. Many holding elements will have failed but the volume of broken rock is limited such that drifts are still accessible. shotcrete would be heav

95、ily fractured.</p><p>　　Moderate damage is generally characterized by fractured or loosened rock of 0.25 m to 0.75 m in thickness (Photo 2.4). The exact nature of the damage will depend on the specific rockb

96、urst mechanism involved, for example, rock bulking versus seismically-induced rockfalls. For rock bulking. Deformation of the rock surface would generally be restricted to between 50 and 150 mm.</p><p>　　2.4

97、.3 Major damage</p><p>　　If a drift sustains major damage, it would be impassable due to substantial amounts of displaced rock. Most ground support components would be broken or damaged and shotcrete or othe