مطالعه‌ي آزمايشگاهي و عددي تاثير مسلح‌سازي خاك در ظرفيت باربري پي نواري در نزديكي ديوار حايل

EXPERIMENTAL AND NUMERICAL STUDY OF SOIL-REINFORCEMENT EFFECTS ON THE BEARING CAPACITY OF SHALLOW FOUNDATIONS NEAR THE RETAINING WALL

در اين پژوهش، يك مدل كوچك آزمايشگاهي براي بررسي رفتار خاك ماسه‌يي مسلح و ديوار حايل انعطاف‌پذير ساخته شده است. تغييرمكان افقي ديوار و ظرفيت باربري پي نواري در حالت‌هاي مسلح و غيرمسلح اندازه‌گيري‌ شده است تا اينكه تاثير تغيير در فواصل، تعداد، و عمق مسلح‌كننده‌ها و تغيير موقعيت پي نواري در اين پارامترها بررسي شود. در ادامه، مدل عددي با همان اندازه‌ي مدل آزمايشگاهي در نرم‌افزار PLAXIS ايجاد و نتايج به‌دست آمده با نتايج مدل آزمايشگاهي مقايسه شده است. در حالت كلي با به‌كارگيري و افزايش تعداد مسلح‌كننده با فواصل مناسب در ناحيه‌ي فوقاني خاكريز پشت ديوار، در مدل آزمايشگاهي و عددي، تغييرمكان جانبي سطح ديوار كاهش، و ظرفيت باربري پي نواري افزايش يافته است، به‌طوري كه مناسب‌ترين حالت براي اندركنش ديوار و پي نواري از لحاظ عملكرد در سه لايه‌ي مسلح و براي شرايط 12/0h/H= و 33/0d/H= ايجاد شده است. بررسي عملكرد مسلح‌كننده و خاك ماسه‌يي با مدل‌سازي فيزيكي با روش PIV و مدل عددي با استفاده از نرم‌افزار PLAXIS، حاكي از افزايش حجم گوه‌ي گسيختگي در عمق و در نتيجه افزايش ظرفيت باربري پي نواري در حالت مسلح است.

A comprehensive set of laboratory model tests were carried out to investigate the behavior of reinforced sand and flexible retaining wall under strip foundation loading. A model box with inner dimensions of 0.4 × 1m in the plane and 0.5m in height was used. One side of the test box was a transparent plexiglas plate for observation, and for photographing soil deformation and failure mechanism during the test. Three linear variable displacement transducers (LVDTs) were used to measure the horizontal displacement of the wall. The strip footing was made of a steel box; 0.399 m in length, 0.06 m in width and 0.03 m in thickness. The length of the footing was made almost equal to the width of the tank model in order to maintain the plane strain conditions. For modelling the flexible retaining wall, factory-trimmed aluminium of thickness 5mm was used. All tests were conducted with a wall height of 0.42 m and geotextile reinforcement. Displacement (Settlement) of the model footing was measured using two LVDTs, located on each side of the centre line of the footing. The sand raining technique was used to prepare the model backfill and the model footing was loaded using a hydraulic jack. Relationships between the bearing capacity and wall deflection versus geotextile parameters, such as depth of geotextile layer, number and spacing of geotextile layer and linear footing position to the wall face, were studied. A series of finite element analyses was additionally carried out using the PLAXIS program, and the results were compared with test results. Both experimental and numerical studies indicated that the bearing capacity increases with an increasing number of reinforcement layers, and the wall deflection decreases also with an increasing reinforcement layer. The use of multiple layers of reinforcement is beneficial only if the spacing between the reinforcement layers gives a better result for the bearing capacity and the wall deflection. Inspection of reinforcement and soil behaviour with the PIV (particle image velocimetry) method and the PLAXIS program indicate that increasing reinforcement layers causes a large, wide failure zone rather than unreinforced backfill. For the first, second and third reinforcement layer, the optimum spacing obtained 0.12H improvement in bearing capacity or wall deflection. However, this did not depend solely on the spacing of the reinforcement layers; the number of these layers and the footing location were also important. With the footing near the wall face (b/B=1.17), bearing capacity and wall deflection increased more than in the other cases. For two different footing positions, the wall deflection decreased as the geotextile number and spacing increased, and the bearing capacity reached maximum value at a depth of d/H=0.33.