برآورد كمينه‌ي فشار جبهه‌‌‌كار تونل‌هاي درون‌شهري با ماشين EPB به روش تحليلي و عددي مطالعه‌ي موردي: تونل خط 7 متروي تهران (قطعه ي شرقي- غربي)

Evaluating Face Minimum Pressure for Urban Tunneling using an EPB Machine and Analytical and Numerical Methods Case Study: Tunnel for Line 7, Tehran Subway (East-West section)

برآورد فشار بهينه براي نگهداري جبهه‌‌‌كار تونل‌هاي شهري از مهم‌ترين عوامل در راندمان ماشين حفاري فشار تعادلي زمين (EPB) است. اعمال فشار كمتر از حد تعادلي باعث نشست و بيشتر از آن باعث بالازدگي جبهه‌كار و سطح زمين مي‌شود. جهت برآورد فشار بهينه از پارامترهاي فيزيكي و مكانيكي خاك، ارتفاع روباره، سطح آب زيرزميني، پارامترهاي هندسي تونل و بارهاي ترافيكي و سازه‌‌يي به كمك روش‌هاي تحليلي و عددي استفاده مي‌شود. با روش‌ تحليلي جانسكز و عددي، فشار لازم براي نگهداري جبهه‌كار تونل خط 7 متروي تهران (قطعه‌ي شرقي- غربي) محاسبه و با يكديگر مقايسه شده‌اند. نتايج حاصل از نرم‌افزار PLAXIS3D با مقادير به‌دست‌آمده از روش‌ تحليلي، حدود 25-20 كيلوپاسكال اختلاف دارند. اين اختلاف به دليل نوسانات فشار آب است، كه در روش عددي منظور نشده است. بدين ترتيب نتايج حاصل از روش عددي تطابق خوبي با روش تحليلي استفاده‌شده دارد.

Tunnel face support during boring operations is gaining more interest as tunneling development expands towards geo-technically less appropriate zones with heavy traffic. Good tunnel face support is a pre-requisite for successful safe boring, and evaluating optimum pressure is an important factor in the performance of the Earth Pressure Balance (EPB) machine in urban tunneling. Applying pressures lower than equilibrium results in face subsidence, while higher than equilibrium causes an up-lift in ground surface, leading in either case, to operation disruption, floor subsidence and damage to nearby buildings. Optimum pressure for face support is evaluated here using analytical and numerical methods, and parameters such as soil physical and mechanical characteristics, height of over-burden, water table level, tunnel geometry, and traffic and structural loads. As the tunnel for line 7 of the Tehran subway (Eastern-Western piece) was excavated in an urban zone, in this work, the Jancsecz analytical method was used to measure the required pressure for the tunnel face support. The tunnel was bored using a 9/164m diameter ground pressure balancing machine. The final tunnel cover was tetragonal in geometry, 35cm thick and 1.50m wide, making an outside diameter of 8.85m for the tunnel. Data obtained for this study was obtained from 13 boreholes and 5 wells excavated deliberately along the tunnel. The flow direction of underground water about the tunneling zone was found to be north-east to south-west. Considering the average water level obtained from the boreholes, only 35% of the tunnel remains above water and 65% is below water level. To illustrate water pressure fluctuation, this was considered in the analytical method, but ignored in the numerical one, which employed PLAXIS 3D software. When comparing the results, a pressure difference of 20-25 kPa was noted, indicating acceptable conformance of the data.