ظرفيت باربري پي نواري واقع بر ماسه‌ي سست مقاوم‌ شده با لايه‌ي ماسه‌ي مسلح

Bearing Capacity of Strip Foundation on the Soft Sand Strenghtened with Reinforced Sand Overlay

به كارگيري لايه ‌يي از ماسه‌ي مسلح شده، روشي مناسب براي مقاوم سازي پي هاي واقع بر خاك هاي مسيله دار مانند ماسه‌هاي سست است. در اين نوشتار، رفتار مدل آزمايشگاهي پي نواري واقع بر ماسه‌ي سست و مقاوم سازي شده با لايه‌يي از ماسه‌ي مسلح ارايه شده است. در تمام آزمايش‌ها، ماسه‌ي بادي عبوري از الك 425/0 ميلي‌متري و با زاويه‌ي اصطكاك داخلي °29 به‌عنوان ماسه‌ي سُست استفاده شده است. در اين بررسي آزمايشگاهي، يك سري آزمايش به منظور بررسي اثر حالت و شكل مسلح سازي در ظرفيت باربري پي، به‌عنوان شاخصي از عملكرد آن، انجام پذيرفت. بدين منظور مسلح كننده ها با شكل‌هاي هندسي مختلف مانند هذلولي، عمودي، افقي، و تركيبي مورد استفاده قرار گرفت. بر اساس نتايج آزمايشگاهي، استفاده از تركيب مسلح‌سازي افقي و عمودي و يا مسلح سازي به شكل هذلولي مقعر، ظرفيت باربري پي نواري را در مقايسه با مسلح‌سازي افقي متداول به نسبت بيشتري افزايش مي‌دهد.

Based on experimental results, application of reinforced sand layer is an appropriate strengthening method in foundations on problematic soils such as loose sands. In this article results from the laboratory model studies on a number of strip foundation models laid on loose sand subgrade strengthened with reinforced sand layer using different reinforcement geometry are presented. For this purpose a series of tests were conducted on laboratory models to examine the effect of soil reinforcement on foundation bearing capacity. In the experiments, the soft soil that was selected was part of Yazd (a city in the center of Iran) dune sand that passed from sieve no. 40 (0.425 mm) and its friction angle was 29°. This type of sand moves away from loading area when a direct load is applied. The model scale effect was considered on maximum size of soil grain and the strength of reinforcement elements. Additionally, various geometrical profiles used for the reinforcement elements (e.g. hyperbolic shape), positioned vertically, horizontally flat or both. The results show that the efficiency of reinforcement was decreased by increasing the number of horizontal reinforcement layers and by increasing the depth of reinforcement. Based on the laboratory model test results, the bearing capacity of strip foundations were improved significantly in comparison to conventional horizontal reinforcement in the following conditions: 1. When reinforcement elements were used both vertically and horizontally in a specific configuration, the bearing capacity ratio (BCR) and the reinforcement influence factor (RIF) were resulted 16.6 and1.8 respectively. 2. When horizontal reinforcement element in the form of concaved hyperbolic shape was used, BCR and RIF were resulted 11.4 and 1.3 respectively. Applying vertical reinforcement under horizontal reinforcement produced more effective results when compared with the vertical reinforcement alone. This behavior can be attributed to the fact that as loading increase on the loose sand, it causes the soil moves away horizontally and as a result, the efficiency of vertical reinforcement is increased.