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PREDICTED AND OBSERVED GROUND DEFORMATIONS DUE TO TBM TUNNEL EXCAVATIONS ON THE IZMIR METRO PROJECT (STAGE 1)
Abstract and Figures
Stage 1 metro construction for the city of Izmir, which has the third highest population in Turkey, has been successfully completed. It included a 2.75 km tunnel excavated by tunnel-boring machine (TBM) using the earth pressure balance (EPB) method in soft ground conditions with shallow overburden. This paper revisits the surface settlement values predicted by the empirical approach, adds numerical analysis, describes the geotechnical instrumentation for field performance and then compares the observed deformations with empirically and numerically predicted ground deformations. INTRODUCTION With a population of 3.5 million, Izmir is the third biggest metropolis and one of the most historically significant cities in Turkey. The total length of planned rail transport in the Izmir Bay area is 45 km, according to the transportation master plan. The Yapi Merkezi – AdTranz Consortium has successfully completed Stage 1 of metro construction for Izmir Metropolitan under a design-and-build turnkey contract. With a total length of 11.5 km, the alignment's peak capacity will be 45,000 passengers per hour per direction in 2010. Total contract value was US$600m. The project includes 2.75 km of tunnels excavated by tunnel-boring machine (TBM) using the earth pressure balance (EPB) method. Yapi Merkezi subcontracted construction of the TBM tunnels to YAPTAG JV (Yapi Merkezi – Wayss & Freytag AG Joint Venture). Of the 10 stations on the project route, four are underground, and three are connected by TBM twin tunnels. The TBM tunnel alignment is situated in soft ground with shallow overburden, and crosses populated and historic built environment. The bore diameter of the completed TBM tunnels is 6.56 m. This paper compares the tunnelling-induced, observed ground deformations with values predicted by empirical methods and numerical analysis. It also describes the geotechnical instrumentation used for field performance and, finally, compares the observed deformations with empirically and numerically predicted deformations. PROJECT ALIGNMENT AND BUILT-ENVIRONMENT The 11.5-km-long project alignment was divided into its major elements: 1.7 km of mined tunnels, 1.4 km of TBM twin tunnels, 1.1 km of cut-and-cover tunnels, and the remainder was surface works. Konak, Cankaya and Basmane stations were constructed using the cut-and-cover method. Each station is approximately 200 m long, with excavation depths of 17 m, 20 m and 16 m respectively. These underground stations were connected by EPB-type TBM twin tunnels. Four
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چکیده
در تونل‌های مناطق شهری که بیش‌تر در عمق کم و در بستر خاکی حفر می‌شوند، فشار جبهه‌کار می‌تواند یکی از عوامل پیشگیری کننده‌ی نشست سطح زمین باشد. در پروژه‌ی خط 7 متروی تهران، تونل با ماشین حفاری مکانیزه از نوع متعادل کننده‌ی فشار زمین (EPB) حفر می‌شود. در این تحقیق با تمرکز بر روی چهار مقطع از این تونل، تاثیر فشار جبهه‌کار بر نشست سطح زمین مورد تحلیل قرار گرفته است. فشار جبهه‌کار در چهار حالت فشار اولیه، 5/1، 2 و 4 برابر فشار اولیه و فشار تزریق در 5 حالت بدون اعمال تزریق، برابر فشار جبهه‌کار، 5/0، 1 و 2 بار بیش‌تر از فشار جبهه‌کار با استفاده از نرم‌افزار اجزا محدود PLAXIS3D مورد ارزیابی قرار گرفته است. اعتبارسنجی نتایج با استفاده از ابزاربندی در سطح زمین و بر روی دو مقطع از تونل انجام گرفته است. مقایسه‌ی نتایج مدلسازی و نتایج حاصل از ابزاربندی بیانگر صحت روند مدلسازی است. برای حالت H2D است. همچنین نتایج نشان می‌دهد افزایش 4 برابری فشار جبهه‌کار، حداکثر سبب کاهش 5 میلی‌متری بیش‌ترین نشست می‌شود. بنابراین افزایش فشار جبهه‌کار، میزان نشست را کاهش می‌دهد اما این مقدار بسیار ناچیز است.
کلیدواژه‌ها
نشست EPB تونل متروی تهران ابزار بندی مدلسازی عددی
This paper presents a simplified method of adapting the settlement curve above the second tunnel to allow a more realistic prediction of the overall settlements above multiple tunnel constructions. The method is still based on the use of the error function curve and so can easily be incorporated into current software packages or spreadsheets. The method applies a modification factor to the soil within the zone of overlap between the predicted areas of disturbed soil above the tunnels. In clay soils it is shown that the ground settlements need to be modified by approximately 60% to take into account the prior disturbance from a first tunnelling operation. Although there is only limited good quality published case history data related to multiple tunnel constructions, the paper describes the good agreement obtained when the method is applied to several published results.
The prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi-empirical methods based on the Gaussian curve. However, the prediction of ground movements associated with closely spaced multiple tunnels, in particular side-by-side (sbs) tunnels, is not as well understood, and therefore simple predictive methods for this application are currently quite limited in terms of their accuracy. This paper describes results from a series of small-scale (1/ 50) laboratory model tests (conducted at 1g) carried out in Speswhite kaolin clay. These tests have been conducted to gain a greater understanding of the short- term ground movements associated with closely spaced multiple (sbs) tunnels. The observed ground movement results from these tests have shown many of the characteristics observed at full-scale in the published case studies. These results are compared to the commonly used Gaussian curve prediction method and demonstrate the potential inaccuracy in this approach for predicting ground movements associated with closely spaced multiple tunnels. A method that modifies the Gaussian curve approach is also applied to the laboratory data and shows improved predictions.
Izmir Metro System is planned as a high capacity system covering whole urban area according to master transportation plan. It will reach 45 km of double track in total when completed. The first stage of 11.4 km including backbone system between Ucyol and Halkapinar, workshop, depot area and Bornova branch were successfully constructed by Yapı Merkezi-Adtranz Consortium in less than four years. Due to the complex soil conditions, changing topography and dense urbanization, three different tunneling techniques were applied between Ucyol and Basmane Stations. This paper involves the results and evaluations of these different applications.
Measurements of settlement and ground movement made on tunnelling projects located, in the main, in built-up areas are reviewed. The ground conditions studied included stiff-fissured clays, glacial deposits and recently deposited silty clays, as well as cohesionless soils of low density, weak rocks and made ground. Many of the tunnels were driven in free air by use of shields, but compressed air was used in the weaker soils to maintain stability; the bentonite shield and chemical treatment of the ground were also used in loose sands. -from Authors
Discusses methods used for the analysis and prediction of ground movements caused by tunnelling. Emphasis is on transport tunnels. Single, twin and more complex tunnel configurations are considered. Estimation of trough width and ground loss, and long-term settlement are discussed. The effects on structures and environmental impact assessment methodology are outlined. It is concluded that analytical methods are well developed and applicable to engineering design, however, field data is deficient. (J.M.M.)
The geotechnical monitoring played an important role in guiding the tunneling applications during the construction of IZMIR LRTS (Light Rapid Transit System) 1st stage. The purpose of this paper is to review the deformation measurements and results gathered during the construction of LRTS 1st stage tunnels.The New Austrian Tunneling concept (NATM) was used for the construction of Ucyol–Konak conventional tunnels of the system. The EPBM (Earth Pressure Balance Method) concept used in the construction of Konak–Basmane precast segmental tunnels. Both tunneling concepts required monitoring of deformations during construction as well as for a period after its completion.
The stability of clay at vertical openings in walls and tunnels has been investigated. Laboratory experiments have shown that a cohesive soil flows through a vertical opening when the total overburden pressure exceeds about six times the undrained shear strength of the soil at the level of the opening. Field data collected from tunnels and pipes constructed in soft clays show that no difficulties have been encountered with soil flowing through openings in the tunnel lining or through the tunnel front when the net overburden pressure has been less than six times the undrained shear strength of the soil. Field data indicate, furthermore, that the force required to push a tunnel shield forward into a cohesive soil corresponds to approximately the sum of the overburden pressure and six times the undrained shear strength of the soil.
Vita. Includes bibliographical references (p. 146-148). Thesis (Ph. D.)--University of Illinois. Photocopy.
Prediction of Ground movements during the Construction of Istanbul Metro
- Yapi
Yapi Merkezi (1992), Prediction of Ground movements during the Construction of Istanbul Metro, Internal Report Yapi Merkezi, Istanbul