《原位锚杆载荷状态分析-毕业设计外文资料翻译.docx》由会员分享，可在线阅读，更多相关《原位锚杆载荷状态分析-毕业设计外文资料翻译.docx（21页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、英文原文ANALYSIS OF IN SITU ROCK BOLT LOADING STATUSD. H. S. ZouDept. of Mining Engineering, Dalhousie University, CanadaAbstract: Rock bolts are widely used in rock engineering for ground stabilization.The anchorage quality, the loading status and the bolt integrity are of most concern in the field. Ro
2、ck bolts performance is currently assessed by pullout or torque wrench tests. These methods are destructive or inaccurate and cannot provide all the required information. Consequently some research is directed to non-destructive testing methods. However, due to the complex ground conditions and the
3、loading mechanism of rock bolts, it is still a challenge to monitor the rock bolt performance in situ quantitatively and accurately. The tension distribution along a bolt for various types of bolts is often not well understood. The condition of the surrounding rock mass and the varying field stresse
4、s further complicate the problem. This article will thoroughly analyze mobilization of the anchoring force and distribution of the bolt tension for mechanically anchored, grouted, pre-tensioned and un-tensioned rock bolts. The terms load bearing capacity and anchorage quality of rock bolts will be c
5、larified. The effects of ground movement will also be examined with an insight into the future direction for rock bolt testing and monitoring.Keywords: rock bolt tension, non-destructive test, load capacity, anchorage quality.1. IntroductionRock bolts are widely used for ground support in rock engin
6、eering, such as in highway slopes, hydro dams, underground mine workings and open pit highwalls. Based on installation, rock bolts may be classified as mechanically anchored, fully or partially grouted (with resin or cement) and friction bolts. The grouted bolts may also have a bearing plate with in
7、itial tension. The primary function of rock bolts is to hold the rockmass together and increase or maintain the ground stability. In the field, the anchorage quality, the loading status and the bolt integrity are most concerned.At present the common practice of assessing anchorage quality is by pull
8、out test (Choquet 1991) and sometimes by torque wrench test (Seeber 1992). Both methods have limited capability and can not provide all the needed information. They are time consuming and destructive or inaccurate. Other researchers (Thurner 1988, Hirao et al 2001, Beard and Lowe 2003) have been try
9、ing to use non-destructive test technique to monitor rock bolts in the field. However due to the complex ground conditions and the loading mechanism in a rock bolt system, the technology can not be applied directly. It is still a challenge to monitor the rock bolt performance quantitatively and accu
10、rately. First of all, mobilization of the anchoring force and distribution of the bolt tension for various types of rock bolts are not well understood. The condition of the surrounding rockmass and the varying field stresses due to excavation activities further complicate the problem. In the followi
11、ng, the anchorage force and tension distribution together with other relevant issues will be discussed thoroughly.Since the anchorage of friction bolts depends on the random contacts between the bolt and the non-smooth borehole rock, the anchoring force is difficult to determine and it has little me
12、aning to predict its distribution at this point. Therefore the following discussions will be focused on the mechanically anchored and grouted bolts.2. Clarification of terminologyFor the clarity of discussions, some technical terminology relevant to rock bolting needs to be defined first:Anchorage:
13、the mechanism that bonds the bolt and the rockmass together. For mechanical bolts, it is the anchor at the hole bottom. For grouted bolts, it is the combination of the grout, the interface between the bolt and the grout, and the interface between the grout and the rock.Rock bolt failure: the failure
14、 of any component of the rock bolt system: steel bolt, anchorage or rock around the borehole. The failure of the bearing plate at the collar is excluded.Anchorage strength (Tas): the maximum tension tolerable per unit length of a grouted bolt before the anchorage fails.Anchoring force: the tension m
15、obilized at the anchored end of a mechanical bolt, or the total tension mobilized along a segment of a grouted bolt.Anchorage capacity (Tac): the maximum anchoring force of a bolt before the anchorage fails.Anchorage quality: the quality of anchor installation for mechanical bolts (measured by the a
16、nchorage capacity), or the quality of grouting for grouted bolts (measured by the anchorage strength and its consistency along the bolt). For grouted bolts, the anchorage quality is also called bond quality or grouting quality.Bolt tension (T): the actual tension in a bolt at a particular location.L
17、oad bearing capacity (LBC): the maximum tension tolerable by the rock bolt system.It is understood (Choquet 1991) that a rock bolt system may fail in any of the three components: the bolt, the anchorage and the rock. LBC is thus the smallest of the three corresponding property parameters of the syst
18、em: the bolt breaking force, the anchorage capacity and the tension at which the rock fails. The failure of rock often occurs in soft ground. This is not an engineering factor and will not be considered here. In hard rocks, LBC will mostly depend on the other two parameters. Failure of a bolt can be
19、 avoided by selecting larger diameter bolts or installing more bolts. For fully grouted bolts, the anchorage capacity increases with the length of the grouted segment and can exceed the bolt breaking force. Failure of a grouted bolt may not lead to the complete failure of the rock bolt system.3. Det
20、ermination of anchorage strength and capacityThe anchorage strength of a grouted bolt depends on the grout material and the grouting quality. Assume the grouting quality is the same around the bolt, the anchorage strength can be determined by the following equation: (1)where is the bolt diameter and
21、 is the grout shear strength, which may vary with the location,along the bolt.The anchorage capacity of a grouted bolt is the accumulated anchorage strength over the entire grouted length and is determined by integration: (2)where Lg is the grouted length. If the grouting quality is uniform througho
22、ut the length with equal anchorage strength, ,Equation (2) is simplified as: (3)It should be pointed out that the anchorage capacity may be determined over a segment of the grouted length in some cases. For both mechanical and grouted bolts,Tac can be determined by pullout test if the failure is thr
23、ough the anchorage. For grouted bolts, the average anchorage strength can then be determined by: (4)and the average grout shear strength by: (5)4.Eension mobilization and distribution in uniform mediaThe grout and the rockmass are assumed to be uniform and the ground movement is assumed to be distri
24、buted along the bolted section.4.1. Mechanically anchored boltA mechanical bolt is secured to the borehole at both ends of the bolt. An initial tension, To, may be applied by tightening the nut immediately after installation as illustrated in Figure 1. Figure1 Tension distribution in mechanical bolt
25、s Further tension is mobilized by ground movement between the anchor and the collar. The tension is uniform throughout the bolt except at the ends. Any geological structures or ground shear movement is not expected to alter the distribution pattern unless the bolt is sheared off the initial borehole
26、 position.4.2. Grouted bolt with bearing plateA bolt may be partially or fully grouted along the entire hole length. For the partially grouted bolt, there is a grout-free section, Lo, near the collar as shown in Figure 2. For the fully grouted bolt, due to the unevenness of the rock surface and the
27、size of the bearing plate, there is also a small segment near the plate free of grout, in the order of millimetres to centimetres.Figure2 Tension distribution in grouted bolts with bearing plate in uniform mediaFor grouted bolts, the mobilized anchorage strength and anchoring force are not uniform t
28、hroughout the grouted segment. From previous research and experiments (Tadolini 1990), it is understood that as an initial tension is applied to the head of the bolt, part of the anchorage strength is first mobilized near the collar and is distributed over a segment of the grouted bolt (Figure 2a, c
29、urve 1). The highest value is at the first grouting point. As the applied tension increases or as ground movement takes place in the grout-free section, the mobilized strength and the anchoring force increase in this segment (Figure 2a and 2b, curve 2). When the anchorage strength is reached, the mo
30、bilized strength will not increase in magnitude further but it extends further down the bolt (Figure 2a, curve3). The anchorage strength of fully grouted bolts in the field has been reported to be between 2.62 to 6.99 kN/cm of the grouted length depending on the diameter of the bolt (Karpin 1980).Th
31、e anchoring force is the total mobilized anchorage strength accumulated over this segment (Figure 2b) and it increases from zero at the first grouting point. Experiments showed that the distributions of the mobilized anchorage strength and the anchoring force may not follow a linear pattern as shown
32、 in Figure 2, a) and b). For fully resin-grouted bolts, the anchoring force can exceed the breaking force of the bolt.The anchoring force resists the applied tension. In the grout-free section, the bolt tension is uniform and equals the applied tension. In the grouted section, the bolt tension at a
33、location is the difference between the applied tension and the anchoring force. Its distribution is illustrated in Figure 2c. It needs to be pointed out that although the bolt tension varies in magnitude over this section, the percentage of the bolt tension seems to be quite constant at a location u
34、ntil the anchorage strength is fully mobilized.If ground movement takes place in the grouted section, the patterns of the mobilized anchorage strength, the anchoring force and the bolt tension will be similar to those of the grouted bolt without bearing plate (see the following section). If an initi
35、al tension is applied, the tension induced by ground movement will be superimposed on the initial tension (see Section 5).4.3.Grouted bolt without bearing plateWhen there is no bearing plate, the distribution pattern of the induced bolt tension in a grouted bolt will be quite different. Since there
36、is no initial tension, the bolt tension is solely induced by the differential ground movement. The tension distribution will be very complicated depending on the magnitude of differential movement and the separation line of the induced tension.In the field, the ground near the collar moves more than
37、 the other parts due to stress adjustment. The differential movement between two locations will induce a tension in the bolt. However the tension near the collar points to the opposite direction from the tension near the bottom. There is a separation line in between, as shown in Figure 3. In the fig
38、ure, the mobilized anchorage strength, the anchoring force and the bolt tension in the two parts of the bolt are illustrated. The mobilized anchorage strength and the bolt tension both reach peak values at the separation line (the former being capped at T as), and they decrease towards both directio
39、ns. On the right of the separation line, the anchoring force acts to resist the bolt tension from the left, and vice versa. Figure 3 shows two opposite non-symmetrical images. When the separation line gets close to the centre of the grouted segment, the two sets of images will approach a symmetrical
40、 pattern.Figure 3 Tension distribution in grouted bolts without bearing plate in uniform media5. Effects of field conditionsIn the field, the rockmass and the grout may not be uniform, the ground movement is not evenly distributed and geological structures (e.g., weak joint, fault, shear zone, etc.)
41、 may exist. Generally, the largest movement takes place at the borehole collar and it decreases down the borehole. If there is a geological structure, however, a large movement may take place at that location. These conditions may alter the distribution patterns of the mobilized anchoring force and
42、the bolt tension for grouted bolts. For mechanically anchored bolts the tension distribution pattern will not be affected by these conditions and the only change will be the tension magnitude.5.1.Geological structuresIf a geological structure exists in the grout-free segment, ground movement along t
43、he structure will simply increase the tension when a bearing plate exists with initial tension but not affect the distribution pattern shown in Figure 2. Obviously, it has not effect if there is no bearing plate.If such a structure occurs in the grouted segment, the associated ground movement is lik
44、ely the largest at that location. Severe shear may take place along these structures as well. For the grouted bolts without bearing plates, the location of such a structure may become the separation line of the bolt tension and a peak tension occurs in the bolt. The anchoring force and the bolt tens
45、ion will follow the same pattern as shown in Figure 3. For the pre-tensioned bolts with bearing plates, the tension induced by the structure will be superimposed on the initial tension. Figure 4 illustrates a typical distribution pattern. If there is more than one such structure, there will be more
46、such peaks in bolt tension.Figure 4 Effects of geological structure on tension distributionIt should be noted that to the left of the joint, the mobilized the bolt tension due to ground movement points to the opposite direction from the initial tension. If the joint is close to the collar and the in
47、duced tension overlaps the initial tension, it will reduce the bolt tension near the collar. This may result in a reduction of bolt tension in the grout-free section as shown in Figure 5. Otherwise, the tensions from the two sources will stand alone as separate loading systems.5.2.Non-uniform grouti
48、ngIf the grouting process is not properly controlled, it will result in poor grouting quality, such as low quality grout matrix and voids in the grouted section. Poor grouting will reduce the anchorage capacity. Voids in grout give rise to zero anchorage strength at that location and will change the bolt tension distribution. The effects may be complicated depending on the location of the void.Figure 5 Reduction of initia