تحليل تنش قايم وارد بر مجاري مدفون در خاك مسلح

Analytical Evaluation of Pressure Acting over a Buried Conduit in Reinforced Granular Soil

در اين نوشتار، روشي تحليلي جهت تعيين تنش وارد بر مجاري مدفون در خاك با درنظرگرفتن اثر توام پديده‌ي قوس‏زدگي و اثر تسليح خاك با يك لايه‌ي‏ تسليح ارايه شده است. به منظور ارايه‌ي عملكرد اين روش، مطالعات پارامتري در خصوص بررسي نحوه‌ي تاثير عوامل مختلف در ميزان تنش وارد بر حفره و كارايي سيستم انجام شده است. نتايج نشان مي‏دهد كه استفاده از مصالح نرم با مدول كشساني پايين در محدوده‌ي بين 350 تا 700 كيلوپاسكال در بالاي حفره و افزايش ضخامت اين نوع مصالح روي حفره تا ميزان حدود عرض ترانشه، موجب عملكرد قوسي بهتر، كاهش تنش وارد بر حفره و افزايش كارايي سيستم مي‌‌شود. همچنين مقايسه‌ي نتايج حاصل از خاكريز غيرمسلح و خاكريز مسلح نشان مي‌دهد كه استفاده از يك لايه‌ي‏ تسليح با سختي كششي در محدوده‌ي بين 100 تا 2000 كيلونيوتن بر متر مي‏تواند سبب كاهش تنش روي حفره و در نتيجه افزايش كارايي سيستم شود. روش تحليلي موردنظر علاوه بر رفع محدوديت‏هاي موجود در روش‏هاي ديگر پژوهشگران، تطبيق قابل قبولي در مقايسه با آن‏ها در شرايط يكسان دارد.

Underground conduits, voids or buried pipes have been since ancient times for carrying oil, water, gas, sewage, slurry, and similar materials from one location to another. A conduit placed in a relatively narrow ditch is known as a ditch conduit, and it is often covered with locally available unreinforced earth fill. Designing a buried conduit covered with granular soil backfill requires that the vertical load acting on the conduit is estimated. A vertical load that develops above a buried pipe/ buried conduit often differs from free-field stress. The arching action of a granular soil mass overlying buried conduits can reduce the vertical pressure on them. Reduction in the load on the conduit occurs due to mobilization of the shear resistance along the walls of the ditch during settlement of the backfill within the ditch. However, in some cases, designers need more reduction in pressure acting over the conduit, which is possible by placing a geosynthetic layer within the soil backfill. This paper represents an analytical method to evaluate stress reduction on a buried conduit reinforced with a single reinforcement layer. Vertical pressure acting on the buried conduit is estimated, due to the simultaneous effects of soil arching action and the geosynthetic layer. A numerical example to evaluate vertical pressure over the conduit is explained. The effects of various parameters, such as tensile stiffness of reinforcement, elastic modulus of soft material, burial depth of conduit on the pressure over the conduit, and efficiency, are investigated and discussed. Comparison results of reinforced and unreinforced backfill shows the significant effect of reinforcement in decreasing stress acting on the conduit. This reduction is more highlighted when the depth of the buried conduit is increased. Comparisons of acting pressure on the conduit with the present approach shows satisfactory agreement with those obtained from other studies, under the same conditions, irrespective of unreinforced and reinforced backfill.