مخاطرات حفاري مكانيزه تونل در بافت فرسوده شهري

Mechanized tunneling hazards in urban area with old structures

يجاد فضاهاي زيرزميني و حفاري‌هاي تونل در زير مناطق شهري كه عمدتاً داراي سازه­هايي متراكم با بافت فرسوده و غيرمهندسي هستند حتي عليرغم استفاده از ماشين‌آلات حفاري پيشرفته با چالش­هايي همراه است. در اين مقاله، مخاطراتي كه در حفاري مكانيزه تونل‌ها با استفاده از ماشين حفار نوع سپر تعادلي در محيط­هاي شهري باعث آسيب­پذيري سازه­ها و ساختمان‌هاي مجاور مي­شوند مورد بررسي قرار گرفته­اند. خط يك متروي تبريز به طول 2/17 كيلومتر از ميدان ائل‌گلي آغاز و پس از عبور از مركز و بافت فرسوده شهري در كوي لاله خاتمه مي­يابد. حدود 8 كيلومتر از مسير به صورت تونل عميق با دو دستگاه ماشين حفار از نوع سپر تعادلي در حال حفاري مي‌باشد. بررسي مخاطرات حفاري در بافت شهري نشان مي­دهد ايجاد ترك‌هاي بزرگ و جزئي در ساختمان­ها به ترتيب حدود 13 و 31 درصد را بخود اختصاص داده و نفوذ فوم حفاري و دوغاب تزريقي از طريق حفرات مدفون با فرواني 11 درصد، از آسيب‌هايي هستند كه در زمان حفاري با آنها مواجه شده است. وجود حفره­هاي مدفون در شهرهاي تاريخي و با سابقه زلزله‌خيزي مثل تبريز از عوامل تشديد كننده آسيب­هاي حفاري تونل مي­باشد. بر اساس نتايج ابزار دقيق، بيشترين نشست در زمان عبور ماشين حفار اتفاق افتاده و مقدار آن با عمق افزايش پيدا مي­كند. نتايج اين مقاله مي­تواند در پيش­بيني و كاهش مخاطرات حفاري ساير خطوط متروي تبريز و يا شهرهاي مشابه نقش مؤثري داشته باشد.

Using of underground spaces for transportation have been inevitable with considering to population growth, energy saving and environmental polluting issues especially in metropolis and its need to have modern systems. Tunneling under urban environment which involves old residential building with high density, different infrastructures, monuments and unknown buried subterranean has a specific challenges in spite of using modern tunneling machines. There are different parameters which determine the influence to adjacent structures due to mechanized tunneling. Risk assessment procedures form a key component of pre-construction studies for underground projects. In this paper, main parameters which cause to hazards and damage to adjacent structures in tunneling by using of pressurized TBM (EPB) in urban areas have been presented and classified corresponding to their abundance on the Tabriz metro line 1. The project is 17.2 kilometers long which is includes 8 kilometers twin tunnel is part of metropolitan transportation development of Tabriz city. This line is consisted of 17 underground stations and passes underneath the historical city center. Mechanical tunneling of Tabriz metro line 1 twin tunnels with 6.88m in diameter is under construction by using of two EPB-TBM under special urban area including of old residential buildings, different infrastructures and geological challenges (mix faced condition, buried holes, disturbed ground during varies earthquakes, abrasive ground) and continuous needs for TBMs maintenance in hyperbaric condition. For evaluation of varies hazards on the Tabriz metro line 1 in the studied area, different events have been registered. In order to measurement of settlements in adjacent building, targets along the tunneling line on building walls installed and their movements have been monitored. The variation of displacement in depth were monitored via installation of extensimeter in the tunnel line. It was found that as well as surface subsidence and other parameters which accounting to tunneling risk assessment efforts, there are some hazards which could enhance the risks in tunneling works in urban area. As experienced in Tabriz metro line 1, presence of wells and unknown buried underground spaces could be enhance the tunneling influence and risks to the adjacent structures. It was conclude that cracks in building due to surface subsidence with 45 percent is the main hazard. The permeation and flow of foam (soil conditioner additives) and grouts to adjacent buildings via holes and unknown spaces with 11 percent was the other hazard which has experienced on the Tabriz metro L1. It was seen that maximum displacement occured during passing of first TBM in tunneling crown level.