مدلسازي عملكرد سيستم المان هاي مسلح كننده طولي فايبرگلاس جهت پايدارسازي جبهه حفاري تونل ها

در زمين­هاي ريزشي جهت حفاري­ ايمن سازه­هاي زير زميني، سيستم­هاي نگهداري متفاوتي مي­تواند استفاده شود. در چنين شرايطي پيش مسلح سازي با استفاده از داول­هاي طولي يكي از روش­هاي بسيار كارآمد است. مطالعه حاضر به مدل سازي عددي رفتار سيستم نگهداري فايبرگلاس مي پردازد كه در آن تغيير مكان جبهه مسلح شده بدست مي­آيد. تركيب اين سيستم با سيستم نگهداري شاتكريت بعنوان سيستم نگهداري اصلي تونل و سيستم پيش برش مكانيكي (پريكاتينگ) بعنوان يكي ديگر از روش­هاي پيش نگهداري تاج تونل نيز مورد مطالعه قرار گرفته است و نهايتا مقدار بار معادل وارده بر اين المانهاي طولي تعيين شد. اين تحقيق، در شرايط مختلف تنش محيطي درجا و در عمق­هاي متفاوت بر روي يك نوع خاك دانه­اي (سنگ خرد شده و بشدت ضعيف) انجام گرفته است.. با جمع بندي و پردازش نتايج، روابط تجربي براي تخمين تغييرمكان جبهه حفاري تونل­هاي حفاري شده در سنگ ضعيف و تنش داول هاي مسلح كننده بر حسب حفاري، تنش­هاي برجاي محيطي و همچنين چگالي (تعداد) داول­ها ارائه شده است.

For safe underground excavation, different supporting systems can be used in weak ground conditions. However, rock mass instability does not give opportunity to install an appropriate supporting system. Because, tunnel face collapses and moves suddenly toward into tunnel. Different approaches and methods has been developed to prevail over this condition including sequential excavation of tunnel face, grouting of unstable and loose zones behind the face, using inclined longitudinal elements above tunnel crown prior to excavation known as arch umbrella elements methods, installing a pre-cutting system, and pre-reinforcement of tunnel face by fiber glass longitudinal elements. These methods may be employed either alone or together according to the severity of the problem. Fiber glass dowels are one of the most efficient and economic methods of above mentioned approaches. Fast installation, flexibility in using with other supporting systems … are the other advantages of this pre-reinforcement. Although numerous studies have been conducted to evaluate and quantify the effectiveness of this method, some aspects such as evaluation of the tensile force induced in the dowels has not been studied. In fact, a correct dimensioning and evaluation can be obtained through three-dimensional numerical modelling. Hence, this paper studied numerically the behavior of the longitudinal fiber glass dowels installed uniformly at tunnel face along tunnel axis and may accompanied with the different supporting system i.e. with shotcrete layer as the main supporting system or with arch umbrellas or pre-cutting system as the other pre-support method. The analyses was carried out by FLAC 3D in different weak ground condition, say the class IV in Binyavsky category, subjected to three different in-situ stresses implying tunnel depths. As well, four lateral stress coefficient were chosen in the analyses. The fiberglass forces as well as tunnel center displacements are the output of this simulation. First of all, the obtained results from the numerical simulation in hydrostatic stress condition were verified by one of the previously presented analytical methods, then analyses were extended to non-hydrostatic stress condition. The results showed non-hydrostatic stress causes non-uniform stress and displacements in the face. As a result, the location of critical zones developed in tunnel face. It leads to employ more dowels on those zones. On the other hand, as lateral coefficient increases, the maximum stress of the dowels and strain of tunnel center increases. The maximum strain and stress occur at k0=2. However; critical zone can be developed at the tunnel crown at k0=0.5. Therefore, with increasing the lateral coefficient, critical zone moves toward the tunnel sides. As well, the best result for the dowels could be seen when they were accompanied with pre-cutting system. It is more highlighted to notice that using dowels in more deep tunnels subjected to great lateral stress (say very squeezing condition) is not sufficient (because they yield) but must be accompanied with other system. Finally, from the results of numerous analyses, mathematical formulations were presented to fast calculate the maximum stress of dowels and strain of the tunnel center in any different condition of weak ground condition