洞室开挖稳定分析、如何建设隧洞外文文献翻译(四篇)

1、Tunnel Stability Analysis of Tunnel Excavation A spillway tunnel for an embankment dam is to be constructed in a poor quality sandstone. The excavated diameter of the tunnel is about 13m and the cover over the roof is 8m. The tunnel is to have a 1.3 m thick un-reinforced concrete lining and , after

2、placement of this lifting, a 28 to high portion of the rockfill dam will he over the constructed tunnel. The questions to be addressed are: (1) What support is required in order to excavate the tunnel safely under the very shallow cover? (2) Is the proposed top heading and bench excavation sequence,

3、 using drill and blast methods, appropriate for this tunnel? (3) How will the concrete lining respond to the loading imposed by the placement of 28m of rockfill over the tunnel? In order to answer these questions a series of two-dimensional finite element analyses were carried using the program PHAS

4、E. The first of these an alyses exam ined the stability and support requirements for the top heading excavation. The final analysis included the entire excavation and support sequence and the placement of the rockfill over the tunnel. The rock mass is a poor quality sandstone that, being close to su

5、rface, is heavily jointed. The mechanical properties assumed for this rock mass are a cohesive strength C=0.04Mpa, a friction angle of 40 and a modulus of deformation E =1334 MPa. No in situ stress measurements are available but, because of the location of the tunnel in the valley side, it has been

6、assumed that the horizontal stress normal to the tunnel axis has been reduced by stress relief. The model is loaded by gravity and a ratio of horizontal to vertical stress or 0.5 is assumed. A simplified version of the model was used to analyse the stability and support requirements for the top head

7、ing. This model did exclude the concrete lining and the bench excavations. The first model was used to examine the conditions for a full-face excavation of the top heading without any support. This is always a useful starting point in any tunnel support design study since it gives the designer a cle

8、ar picture of the magnitude of the problems that have to be dealt with. The model was loaded in two stages. The first stage involved the model without any excavations and this was created by assigning the material within the excavation boundary the properties of the surrounding rock mass. This first

9、 stage is carried out in order to allow the model to consolidate under gravitational loading. It is required in order to create a reference against which subsequent displacements in the model can be measured. The results of the analysie are illustrated in Figure 18.1, that shown the extent of yield

10、in the rock mass surrounding the top heading, and Figure 18.2 that shows the induced displacements around the tunnel. The large amount of yield in the rock mass overlying the top heading suggests that this excavation will be unstable without support. This view is supported by the displacements shown

11、 in Figure I8.2. The reader may be surprised that the displacement in the roof of the tunnel is only 26mm when the extent of the yield zone suggests complete collapse of the roof. It has to be remembered that PHASE is a small strain finite element model and that it cannot accommodate the very large

12、strains associated with the complete collapse of a tunnel. In examining Figure18.2 it is more important to look at the shape of the overall displacement profile than the magnitude of the displacements. A rock mass will not tolerate the differential displacements illustrated and progressive ravelling

13、 leading to ultimate collapse would almost certainly result from excavation of an unsupported top heading. A general rule of thumb used by experienced tunnellers is that an underground excavation will not be self-supporting unless the cover over the tunnel exceeds 1.5 times the span of the opening.

14、This is a typical situation that occurs when excavating tunnel portals are there are several options available for dealing with the problem. One of these options is to use a shotcrete lining to stabilize the rock mass above the tunnel. A finite element analysis of this option shows that a 50 mm thic

15、k layer of fully hardened shotcrete (uniaxial compressive strength of 30 MPa)is sufficient to stabilize the tunnel. The problem is how to get of shotcrete into an advancing tunnel heading. A second problem is whether the workers would have sufficient confidence in such a solution to work in the tunn

16、el. One project on which this solution was used was the construction of an 8 m span diversion tunnel for a dam. The rock mass was a very weakly cemented limestone that could be excavated by hand but which had sufficient strength that Scandinavian contractor on the project had used experienced tunnel

17、lers had complete confidence in tunnel was not on the critical path of the project it was marginally self-supporting. shotcrete for many years and the working under a cover of shotcrcte. and so construction The very The at a could proceed advance. A layer of occasional steel sets sufficiently slow p

18、ace to allow the shotcrete to set before the next un-reinforced shotcrete was the sole support used in this tunnel, with embedded in the shotcrete where ground conditions were particularly difficult. In the case of the top heading in sandstone under consideration here, the shotcrete solution was rej

19、ected because, in spite of the finite element analysis, the designers did not have sufficient confidence in the ability of the shotcrete layer to support the large span of blocky sandstone. In addition, the contractor on this dam project did not have a great deal of experience in using shotcrete in

20、tunnels and it was unlikely that the workers would have been prepared to operate under a cover of shotcrete only. Another alternative that is commonly used in excavating tunnel portals is to use steel sets to stabilise the initial portion of the tunnel under low cover. This solution works well in th

21、e case of small tunnels but, in this case, a 13 m span tunnel would require very heavy sets. An additional disadvantage in this case is that the installation of sets would permit too much deformation in the rack mass. This is because the steel sets are a passive support system and they only carry a

22、load when the rock mass has deformed onto the sets. Since this tunnel is in deformation of a dam, excessive deformation is clearly not acceptable because of the additional leakage paths which would be created through the rock mass. The solution finally adopted was borrowed from the mining industry w

23、here untensioned fully grouted dowels are frequently used to pre-support the rock mass above underground excavations. In this case, a pattern 3 mx3 m pattern of 15 m long 60 ton capacity cables were installed from the ground surface before excavation of the top heading was commenced. When these cabl

24、es were exposed in the excavation, face plates were attached and the excess cable length was cut off. In addition, a 2 m x 2 m pattern of 6 m long mechanically anchored rockbolts were installed radially from the roof of the top heading. The results of an analysis of this support system are illustrat

25、ed in Figure 18.3 and Figure 18.4 which show the extent of the yield zone and the deformations in the rock mass above the top heading. Comparing Figure 18.1 and Figure 18.3 shows that the extent of the yield zone is only reduced by a small amount by the enstallation of the support system. This is no

26、t surprising since some deformation of the rock mass is required in order to mobilize the supporting loads in the untensioned cables. This deformation occurs as a result of failure of the rock mass. Figure 18.4 shows that the displacements in the roof of the top heading have been reduced substantial

27、ly as a result of the placement of the support. However, a small problem remains and that is the excessive displacement of the rock between the rockbolt faceplates which are spaced on a 2 m x 2 m grid. Unless this displacement is controlled it can lead toprogressive ravelling of the rock mass. Only

28、a small surface pressure is required to control this ravelling and this could be achieved by means of a layer of mesh or shotcrete of by the installation of light steel sets. In this case the latter solution was adopted because of the sense of security which these gave for the workers in the tunnel.

29、 洞室开挖稳定分析 某土石坝工程在质量差的砂岩区开挖溢洪隧洞。其开挖直径13 m,顶部理深8rn。隧洞 有 1.3 m 厚的普通混凝土衬砌。衬砌浇筑后在隧洞上修建 28 m 高的土石坝出水口。 面临的问题是 : (1) 在浅部开挖时，为保证溢洪隧洞的安全所需的支护形式? (2) 在隧洞开挖时比较适用的是钻爆法施工，开挖过程中如何确定顶部上导洞和分步开 挖的顺序 ? (3) 混凝土衬砌与隧洞上 28 m 高的堆石荷载之间的作用是怎样的 ? 为解决上述问题，采用 PHASE2程序进行了一系列的平面有限元分析。首先对上导洞开 挖的稳定性及所需要的支护形式进行分析， 然后对全断面开挖、 支护顺序和堆石

30、对隧洞衬砌 的影响进行分析 岩体为质量差的砂岩， 近地表浅部节理发育。 其力学特性建议为 : 黏聚力 c=0.04Mpa. 内 摩擦角为40度，变形模量E =1 334MPa。没有现场地应力量测资料，由于隧洞位于谷坡， 可以假定垂直隧洞轴线的水平应力由于应力释放而减小，并且认为水平与垂直应力之比为 0.5，计算模型考虑自重荷载 . 一简化的计算模型可用于洞室顶拱稳定性分析和支护要求。 该模型不包括混凝土衬砌和 台阶开挖。 初始模型用来检查在没有任何支护情况下的上导洞全断面开挖的情况。该模型常用于隧 洞支护设计研究开始阶段，因为模型可以为设计者提供较清楚的将要处理问题的难度。 模型的加载分两个阶

31、段。 首先是没有开挖情况下的模型， 此模型是在开挖边界内用给定 岩石材料特性建立起来。 第一阶段实施是为了在重力荷载条件下对模型加固相对于模型其后 的位移可以量测到，则创建一个参考系是必要的。 分析结果如图 1 8.1 所示，图中显示了上导洞围岩的屈服范围;而图18.2则显示了旋隧洞 次生位移的情况。 上导洞洞顶岩体的大范围屈服说明在没有支护条件下的开挖是不稳定的。图18.的位移 也说明了这一点。 大家感到奇怪的是当屈服带的范围被暗示洞顶会全部坍塌时，隧洞顶部仅有26 mm 的 位移。但应记住PHASE“是一个关于小应变模型的有限元程序，并不适用于隧洞整体塌落的 应变工况。从图 18.2 可看

32、出，考虑整体位移形状远比位移量重要，而且岩体将不能承受图 所示的差异性位移， 上导洞不做支护开挖， 由于渐进式剥落 .最终导致洞石完全塌落是肯定。 经验丰富的隧洞建设者采用的经验法则是隧洞上部覆盖层厚度大于1.5 倍洞室跨度， 地 下开挖才可达到自承支护。 对所涉及的问题来说， 当开挖洞日有几种选取方案时， 上面情况 才会发生。 这些方案之一是采用喷混凝土衬砌来维持隧洞顶部岩体的稳定。这一方案有限元 分析表明，50 mm厚的充分硬化喷混凝土层（单轴压缩强度30MPa）对于隧洞的稳定已经足够。 问题是如何把充分硬化的喷射混凝土注人到前方的洞室端部。其次是施工者是否有信心来解 决隧洞的这一问题。

33、某工程在为大坝建一条 8m 跨度的导流洞时采用了喷混凝土衬砌。 围岩为弱胶结的灰岩。 可用手工掘进，但有足够的强度在一定程度上达到自承作用。斯堪的纳维亚（Scandinavian） 承包商在工程上采用喷混凝土技术已多年， 非常有经验的隧道建设者完全有信心在喷射过混 凝土的隧道中施工。 该隧洞并不是工程的关键隧洞， 建设者有充分的时间进行喷混凝土施工。 在隧洞中喷混凝土技术是常用的支护措施， 对隧洞地质条件特别差的地段， 采用预埋在喷混 凝土层中的钢拱架支护。 在砂岩中进行上导行洞开挖， 未采用喷混凝土方案， 尽管有限元分析结果表明是可以的， 但设计者没有充分的信心认为喷混凝土层可以对块状砂岩大

34、跨度洞室进行支护。除此以外， 大坝项目的承包商没有隧洞喷混凝土施工的丰富经验， 施工人员也不准备在仅有喷混凝土支 护条件下施工。 在开挖洞口时另一个通常采用的方法是在洞顶覆盖层较薄的地方用钢架来支护隧洞的 进口部分。在小型隧洞中常用此法，但本工程情况 13 m 跨度的隧洞需要高强度的钢架。另 一个不利因素是安装钢架时要预留有岩体较大的变形量。 这是因为钢架是一个被动的支护系 统，只有当岩体变形并与之接触时才可承重。 由于隧洞位于坝基中。过大然不能接受， 因为 过大的变形会增多渗漏通道。 最终采取的方案借鉴采矿工程的经验， 即对地下开挖以上的岩体一般采用非张拉注浆锚 索进行预支护。具体施工时，在

35、上导洞室开挖前，从地表安装装间距3m*3m、长15m、锚 固力 60 t 的锚索。当锚索在开挖面出露时，焊上面板并把多余的锚索切掉。此外，在洞室 顶部安装放射状间距 2mx2m、长6m的机械锚固的岩石锚杆。 支护系统的分析结果见图 18.3 和图 18.4，图中表明了屈服带的发展程度和上导洞之上 岩体的变形情况。 对比图 18.1 和图 18.3看出，在安装支护系统后， 屈服带范围有少量减小。 这并不奇怪， 因为岩体的某些变形要协调非张拉锚索的支护荷载，而且这些变形是岩体破裂的结果。 图 18.4 表明，上导洞顶拱的位移随着支护的安装显著地减少。然而 .仍存在一些小问题， 在岩石锚杆面板 （以

36、 2mx2m 的网格布设 ）之间的岩石仍存在较大位移。如果不对这些位移进 行控制，就可能导致岩体的渐进式剥落破坏。 控制岩体的剥落作用只需要很小的表面压力， 可通过挂网或安装轻型钢架喷混泥土来实 现。例中采用第二种方案，因为隧洞施工者对安全较为敏感。 How Tunnels Are Built After the general direction for a tunnel has been determined, the next steps are a geological survey of the site and a series of borings to obtain speci

37、fic information on the strata through which the tunnel may pass. The length and cross section of a tunnel generally are governed by the use for which it is intended, but its shape must be designed to provide the best resistance to internal and external forces. Generally, a circular or nearly circula

38、r shapes is choosen. In every hard rock, excavation usually is accomplished by drilling and blasting. In soft medium-hard rock, a tunnel-boring machine typically does the excavation work. In soft ground, excavation usually is accomplished by digging or by advancing a shield and squeezing the soft ma

39、terial into the tunnel. In all cases, the excavated rock or earth, called muck, is collected and transported out of the tunnel. In underwater tunneling, a shield is used to advance the work. Another method of building an underwater tunnel is to sink tubular sections into a strength dug at the bottom

40、 of a river or other body of water. Hard-rock tunneling Short tunnels through hard rock are driven only From the portals but longer ones usually are driven also from one or more intermediate shafts. Some long tunnels have been built with the aid of a small pilot tunnel driven parallel to the main tu

41、nnel and connected with it by crosscuts at intervals. The pilot tunnel not only furnishes addition points of access but also a route for removing muck and for ventilation ducts and drainage lines. Another method is the heading-and-bench system, formally used on most large funnel. because it required

42、 smaller amounts of power and permitted simultaneous drilling and mucking (removal of excavated material). The upper portion of the tunnel is driven ahead of the lower part which is called the bench. A separate crew is thus able to muck in the lower portion of the tunnel while the upper portion is b

43、eing drilled. With improvements in tunneling methods and machinery , the full-face method of attack, previously used only in small tunnels, came into common use in building large ones . This change was partly brought about by the jumbo, a movable platform on which numerous rock drills are mounted. B

44、y this device, a large part of the tunnel s face can he drilled at oneimte. The full face method became the commonest and fastest way to drive a tunnel. Soft-ground tunneling Some tunnels are driven wholly or mostly through soft material. In very soft ground, little or no blasting is necessary becau

45、se the material is easily excavated. At first, forepoling was the only method for building tunnels through very soft ground. Forepoles are heavy planks about 1.5 m long and sharpened to a point. They were inserted over the top horizontal bar of the bracing at the face of the tunnel. The forepoles we

46、re driven into the ground of the face with an outward inclination. After all the roof poles were driven for about half of their length, a timber was laid across their exposed ends to counter any strain on the outer ends. The forepoles thus provided an extension of the tunnel support, and the face wa

47、s extended under them. When the ends of the forepoles were reached, new timbering support was added, and the forepoles were driven into the ground for the next advance of the tunneling. The use of compressed air simplified working in soft ground. An airlock was built, though which men and equipment

48、passed, and sufficient air pressure was maintained at the tunnel face to hold the ground firm during excavation until timbering or other support was erected. Another development was the use of hydraulically powered shields behind which cast-iron or steel plates were placed on the circumference of th

49、e tunnels. These plates provided sufficient support for the tunnel while the work proceeded, as well as full working space formen in the tunnel. Under water tunneling The most difficult tunneling is that undertaken at considerable depths below a river or other body of water. In such cases, water see

50、ps through porous material or crevices, subjecting the work in progress to the pressure of the water above the tunneling path. When the tunnel is driven through stiff clay, the flow of water may be small enough to be removed by pumping. In more porous ground, compressed air must be used to exclude w

51、ater. The amount of air pressure that is needed increases as the depth of the tunnel increases below the surface. A circular shield has proved to be most efficient in resisting the pressure of soft ground, so most shield-driven tunnels are circular. The shield once consisted of sleet plates and angl

52、e supports, with a heavily braced diaphragm across its face. The diaphragm had a number of openings with doors so that workers could excavate material in front of the shield. In a further development, the shield was shoved forward into the silty material of a riverbed , thereby squeezing displaced m

53、aterial through the doors and into the tunnel, from which the muck was removed. The cylindrical shell of the shield may extend several feet in front of the diaphragm to provide a cutting edge. A rear section, called the tail, extends for several feet behind the body of the shield to protect workers.

54、 In large shields, an erector arm is used in the rear side of the shield to place the metal support segments along the circumference of the tunnel. The pressure against the forward motion of a shield may exceed 48.8Mpa.Hydraulic jacks are used to overcome this pressure and advance the shield, produc

55、ing a pressure of about 245 MPa on the outside surface of the shield. Shields can be steered by varying the thrust of the jacks from left side to right side or from top to bottom, thus varying the tunnel direction left or right or up or down. The jacks shove against the tunnel lining for each forwar

56、d shove. The cycle of operation is forward shove, line, muck, and then another forward shove. The shield used about 1955 on the third tube of the Lincoln Tunnel in New York City was 5.5 m long and 9.6 m in diameter. It was moved about 81.2 cm per shove, permitting the fabrication of a 81.2 cm suppor

57、t ring behind it. Cast-iron segments commonly are used in working behind such a shield. They are erected and bolted together in a short time to provide strength and watertightness. In the third tube of the Lincoln Tunnel each segment is 2 m long, 81.2cm wide, and 35.5 cm thick, and weighs about 1.5

58、tons. These sections form a ring of 14 segments that are linked together by bolts. The bolts were tightened by hand and then by machine. Immediately after they were in place, the sections were sealed at the joints to ensure permanent watertightness. Sunken-tube tunnels Where the riverbed subsoil is

59、firm and the river current is not excessive, shore-fabricated tunnel sections can be towed over a prepared trench in the river bottom and sunk into place to form a underwater tunnel. The first major prefabricated, floated. and sunken tunnel was the Detroit River Tunnel between Detroit and Windsor, O

60、ntrio. This vehicular tunnel was built in 19061910. The next important vehicular tunnel built by this method was the Posey tube, which was completed in 1928, It runs under a saltwater arm between Oakland and Alameda. Calif. Since then many other sunken-tube tunnels have been built under rivers and s