عنوان مقاله
حفر تونل های بزرگ در برابر سنگ های سخت
فهرست مطالب
مقدمه
پایداری نمای تونل
گزینه های تکیه گاهی و نگهدارنده برای زمین مچاله شونده
آبگردانی در ساخت تونل
پدیده مچاله شوندگی و ماشین های حفاری تونل
نتیجه گیری
بخشی از مقاله
پدیده مچاله شوندگی و ماشین های حفاری تونل
Dowden and Cass و Babendererde ماشین هایی را توصیف کرده اند که شیلد بیرونی از تعدادی تیغه تشکیل می شود که هر یک از آن ها برروی کوبه ها (چکش های تیرکوب) هیدرولیکی قرار گرفته اند به گونه ای که تیغه می تواندآزادانه در جهات محوری و شعاعی حرکت کند. ماشین با فرایند “” shuffle-shoe حرکت می کند که قابلیت سازگاری با مچاله شوندگی را دارد. ماشینی از این دست که در شکل 8 نشان داده شده است برای حفاری تونل آزمایشی Freudenstein در آلمان بکار گرفته شد.
کلمات کلیدی:
BIG TUNNELS IN BAD ROCK 2000 TERZAGHI LECTURE by Evert Hoek ASCE Journal of Geotechnical and Geoenvironmental Engineering Vol. 127, No. 9. September 2001, pages 726-740. The Terzaghi lecture was presented at the ASCE Civil Engineering Conference and Exposition To be held in Seattle, October 18-21, 2000 Hoek – 2000 Terzaghi lecture Page 1 of 15 Big Tunnels in Bad Rock By Evert Hoek1 ABSTRACT: Tunnels of 10 to 16 m span are frequently constructed for hydroelectric or transportation projects and many of these tunnels are excavated in rock masses of very poor quality. When the ratio of rock mass strength to in situ stress falls below 0.2, squeezing of the rock mass becomes a problem that can cause instability of both the tunnel and the face. A method for predicting squeezing conditions is presented and the practical options for pre-reinforcing the face and supporting the tunnel to deal with these problems are discussed. Two case histories are included to illustrate how these pre-reinforcement and support measures can be incorporated into a tunnel design. Brief discussions are also given on water problems in tunneling, the use of tunnel boring machines (TBMs) in squeezing ground and the construction costs for large tunnels in varying ground conditions. INTRODUCTION “Rock defects and loads on tunnel supports” by Karl Terzaghi (1946) was a landmark paper in tunneling literature and, for many years, it provided the basis for the rational design of tunnels, particularly those constructed in North America. There are still many valuable lessons to be learned from this work and it is recommended reading for anyone seriously interested in the practical aspects of tunnel design and construction. The “tunnel supports” discussed by Terzaghi were primarily steel sets and these were designed to support the “rock load” due to the weight of the broken ground resulting from the excavation of the tunnel. This concept is illustrated in Fig. 1 and Terzaghi developed a set of guidelines for estimating the rock load for different geological conditions. Fig. 1. – Terzaghi’s ground arch concept. Reproduced from “Rock defects and loads on tunnel supports” published in 1946. ___________________________________________________ 1Consulting engineer, 3414 Emerald Drive, North Vancouver, British Columbia, Canada V7R 3B5. Telephone + 1 604 988 3064, Fax + 1 604 980 3512, Email: ehoek@attglobal.net. An alternative tunnel support design method was developed in Europe and its origins can be traced to a paper by Fenner (1938). This method is based upon the development of a “plastic zone” in the rock mass surrounding a tunnel as illustrated in Fig. 2. The support pressure pi in Fig. 2 is that provided by the rock mass through which the tunnel is being advanced. At a distance of approximately one diameter ahead of the tunnel the rock mass is not influenced by the presence of the tunnel and the support pressure pi equals the in situ stress po, corresponding to point A on the ground response curve. As the tunnel advances the support provided by the rock mass diminishes and the rock mass responds elastically up to point B at which plastic failure of the rock mass initiates. The radius rp of the plastic zone and the radial convergence δ both increase as the support pressure decreases as illustrated in Fig. 2. Eventually, about two tunnel diameters behind the face, the support pressure pi provided by the face has decreased to zero and the radial convergence δ reaches its final value. Fig. 2: A tunnel model and ground-support interaction curve for the rock mass surrounding a tunnel.
