高等巖石力學13章20131204.ppt

1、第13章 巖石開挖及穩(wěn)定措施,13.1 開挖過程,開挖是從巖體中移走材料從而形成空間。 兩個目的： 形成開挖空間； 獲得有價值的材料。 為了移走部分巖體，必須在原生裂隙基礎上產(chǎn)生新的裂隙。三個關(guān)鍵方面： 必須達到全應力-應變曲線的峰后區(qū)域； 原場塊體尺寸分布必須變?yōu)樗璧某叽绶植迹?通過何種方式輸入能量到巖體？,達到全應力應變曲線峰值后區(qū)域 峰值前后分別代表彈性、穩(wěn)定和塑性和破壞（破碎） 開挖邊界是兩種基本不同工程目的和材料性質(zhì)的界面； 巖體的抗壓、抗拉強度差異與最優(yōu)爆破方案的選擇 原位巖塊和開挖碎塊的尺寸分布 尺寸分布與轉(zhuǎn)換 與巖體開挖目的緊密關(guān)聯(lián) 能量輸入與開挖過程 用specific e

2、nergy表示來設計開挖能量輸入方式 兩種基本方式：爆破和機械,13.2 巖石爆破,應力波和氣體壓力作用,壓縮應力波在自由面處反射成拉伸應力波 然后是爆生氣體壓力為后續(xù)巖體破碎和崩解提供能量,爆破循環(huán) blasting rounds 爆破方案設計的基本原則：形成自由面,爆破循環(huán)的優(yōu)化包括： 嚴格控制鉆孔，保證正確的孔形； 使用高精度延時雷管，保證正確的起爆順序。 隧道掌子面的爆破循環(huán) 自由面不能垂直于炮孔 按順序起爆傾斜炮孔，即楔形掏槽wedge cut，以同心圓錐形式從掌子面中心向外圍順序起爆。,炸藥 其性能指標包括：強度、密度、爆速、敏感度、抗水性 其類型主要有：膠質(zhì)炸藥、半膠質(zhì)炸藥、銨油

3、炸藥、雷管 爆破規(guī)范、規(guī)程和爆破工程手冊,13.3 特殊爆破技術(shù),There may also be extra rock damage behind the borehole wall. For permanet rock face at or near the ground surface, an elegant form of blasting has been devised which takes advantage of the principles to minimize the damage to the rock. Pre-splitting: create the fina

4、l plane first For permanet rock face at depth, smooth-wall blasting Both of them produce a high-quality, high-strength and low-maintenance final surface.,1 預裂爆破（pre-split blasting）,Mechanism of pre-split blasting Initialy, the stress wave effect generates radial fractures with some bias towards the

5、plane of the blastholes, due to reflection from the nearest point of the adjacent blastholes. Second, there are dynamic and quasi-static effects of the gas pressure reinforcing this tendency. The gas travels along the fractures and causes further cracking in a manner similar to hydraulic fracturing;

6、 and The pressurized blastholes and radial fractures induce high elastic stress concentrations which contribute to failure of the rock along the plane.,成功預裂爆破的準則： 炮孔必須平行且局部共面 密集鉆孔 炮孔應該少量裝藥且炸藥與孔壁不耦合 同時起爆 確保良好的現(xiàn)場管理 影響預裂效果的因素： 爆破離自由面足夠遠； 非連續(xù)面與預裂面的夾角； 地應力。,2 光面爆破（ post -splitting or smooth-wall blasting

7、 ） 地應力的存在 初始開挖影響原場應力的大小和方向 開挖順序： First , an opening is created roughly which is close to the desired size and shape. Second, using similar blasting principles to those required for pre-split blasting, a smooth-wall blast follows.,13.4 機械開挖,隧道掘進機（Tunnel Boring Machines）,13.5 開挖對巖體環(huán)境的影響,巖體的加固與支護 （rock

8、 reinforcement and rock support） 開挖的三種主要效應： 原巖開挖使得開挖面附近巖體產(chǎn)生位移并運動（由于卸荷）； 在無支護開挖面上沒有正應力和剪切應力，因此開挖邊界一定是主應力面。 開挖邊界上，任何存在巖體中的前期水壓力將降為零（嚴格說降為大氣壓力）。,對于這三種效應，處理措施的共同點是：we should not blindly attempt to maintain the original conditions; rather, we should treat these effects as providing the opportunity to und

9、erstand the rock behavior and to develop the engineering sympathetically. 對于位移，工程需判斷其允許值；對于應力調(diào)整，設計合理開挖形狀；對于地下水，需了解并針對性控制。,13.6 穩(wěn)定措施 the stabilization strategy,Failure in excavation is due to blocks of rock moving into the excavation two approach philosophies can be considered for stabilizations: The

10、 block displacements are occuring because the rock mass is a discontinuum, and hence the rock is reinforced so that it behaves like a continuum. Direct support elements are introduced into the excavation in order to maintain block displacements at tolerable levels. The first is rock reinforcement, t

11、he second is rock support. Note that with rock reinforcement the engineering elements are inserted within the rock mass and with support they are inserted within the excavation.,開挖引起的變形和破壞，可以采用兩種對策： 巖體不連續(xù)導致巖塊的位移，因此加固巖體使其如同連續(xù)介質(zhì)； 在開挖處采用直接的支護結(jié)構(gòu)，以控制巖體位移在允許范圍內(nèi)。 前者為rock reinforcement，巖體加固是將engineering ele

12、ments 植入巖體中； 后者為rock support，是將他們置于開挖中。,這是一個巖體加固的實例。 Steel cables or bars grouted within boreholes are used in an attempt to minimize displacement occuring along the pre-exsiting discontinuities-so that the rock supports itself. An associated preventative measure is the spraying of concrete or cemen

13、t mortar onto the rock surface, in conjunction with the bolting in order to protect the surface and inhibit minor block movements.,這是一個采用結(jié)構(gòu)構(gòu)件支護的例子。 Steel arches or concrete rings are introduced to inhibit rock displacements at boundary of the excavation. These elements, which are external to the roc

14、k mass, provided load carrying capability, with the result that the rock does not totally support itself: the rock is supported. Support does not directly improve the instrinsic strength of the rock mass, but does alter the boundary conditions.,巖體的加固與支護的基本原理上的區(qū)別,13.6.1 巖體加固,由于加固植入體（reinforcing eleme

15、nts）的工作模式不同，分別介紹在連續(xù)巖體和不連續(xù)巖體中加固的差異。 連續(xù)巖體加固 連續(xù)巖體中采用加固措施能提高其固有強度，從而增強穩(wěn)定性，力學機理類似鋼筋混凝土。,A and E are the ratios of the cross-sectional areas and the Youngs moduli of the reinforcing element to that of the rock being reinforced, respectively. Note that the larger the ratios A and E, i.e. for an increased r

16、ock bolt density and lower stiffness rock, respectively, the larger the effctive confining pressure will be.,非連續(xù)巖體加固 與連續(xù)巖體加固不同的是，在不連續(xù)巖體中加固除了要提高巖體結(jié)構(gòu)特性（the rock structure properties）, 還要避免整塊巖石的大位移。 兩個重要因素： whether the blocks are free to move, given the geometry of the rock mass and excavation; and the

17、 character (quantity, length and orientation) of the reinforcement.,The tension anchor should be installed such that the block and the rock beneath act as a continuum, and block movement is inhibit. 無錨桿，坡面無粘性時，當坡角大于巖石表面摩擦角時，巖塊滑動。這是潛在破壞的第一準則。故針對錨桿的長度和直徑，他們必須保證桿體-漿體和漿體-巖體界面有足夠的粘接強度。錨桿直徑取決于錨桿材料的抗拉強度。 對

18、于錨桿方向和錨桿拉力，涉及因素較多。若只考慮使得錨桿中拉力最小，則最優(yōu)錨桿方向是錨桿與坡面夾角等于巖塊與邊坡的摩擦角。 The key point to be made is that, if the reinforcement inhibits block movement, and sufficient stress can be transmitted across the interface, then in principle the rock reinforcement has changed the rock discontinuum to a rock continuum.,1

19、3.6.3 巖體支護,The term rock support is used for the introduction of structural elements into a rock excavation in order to inhibit displacements at the excavation boundary. 連續(xù)巖體支護 平面CHILE材料，圓孔徑向位移,R is the radius of the opening, and are the far-field in-plane principal stresses, is the far-field anti-p

20、lane stress, is indicated in the margin sketch, and E and are the elastic constants.,The rock stabilization strategy can be based on the need to restrict the displacements as governed by the engineering objective. The ground response curve is a graph of the support pressure required to maintain equi

21、librium of the boundary at a given displacement value versus the displacement value. The ground response curves shown in following figure illustrate this relation for the cases of linearly elastic, stable non-elastic and unstable non-elastic behaviour. Because of the general nature of the ground res

22、ponse curve concept and te ability to study a variety of associated factors, it has become a widely used semi-empirical tool in the design of support for excavations.,In fig.(b), the same rock mass is excavated by different methods. Curve 1 represents the perfect excavation case, in which there is n

23、o disturbance of the remaining rock and there is no deviation from CHILE behaviour. Curve 2 may occur in a machine-driven tunnels, in which there is a slight disturbance to the remaining rock with the result of increased final displacement. Curve 3: high-quality blasting,more disturbance, displaceme

24、nt are increased yet further. All three of these curves intersect the boundary displacement axis which indicates that no support is required, providing the displacements are tolerable. Curve 4: poor-quality blasting,supporting is essential if stability of the excavation is to be maintained.,If support is re