مدلسازي احتمالاتي-ژئوتكنيكي گودبرداري در حاشيه شهر قائن

Probabilistic and Geotechnical Modeling of an Excavation in the Outskirts of Qaen

عمليات گودبرداري يكي از فعاليت‌هاي پر خطر در ساختمان‌سازي به حساب مي‌آيد كه معمولاً به منظورهاي مختلف مانند رسيدن به سطح تراز مناسب خاك براي اجراي فونداسيون، يا احداث طبقات زيرين انجام مي‌شود. امروزه گزارش‌هاي متعددي از خسارات مالي و بعضاً جاني در شهرهاي بزرگ كشور منتشر مي‌شود، كه ناشي از عدم توجه به پايداري ديواره‌ي گود و نيز نگهداري مورد نياز آن است. در اين مقاله با استفاده از نرم‌افزارSlide، ابتدا به بررسي پايداري ديواره‌ي گود در يكي از نقاط حاشيه‌اي شهر قائن پرداخته‌شده و سپس بررسي و تحليل نگهداري ديواره‌ي گود با استفاده از روش ميخ‌گذاري‌ خاك در شرايط مختلف انجام شده است. اين پژوهش يك بررسي تقريباً كامل گودبرداري است كه با استفاده از تحليل برگشتي،تحليل حساسيت و تحليل احتمالي، در شرايط قطعي و احتمالاتي انجام شده است. طبق نتايج به دست‌آمده از اين مطالعه، خاك منطقه‌ي مورد نظر براي گودبرداري ناپايدار است و به كارگيري روش ميخ‌گذاري تا عمق مورد مطالعه (10 متر) و شيب‌دار كردن ديواره‌هاي گود، راهكارهاي مناسب براي رسيدن به ضريب ايمني قابل قبول هستند. در انتها چند روش مختلف كه داراي ضريب ايمني قابل قبول هستند براي اجراي گود پيشنهاد شده است. اين تحقيق الگوي جامعي را براي تحليل ديواره‌هاي گودبرداري ارائه مي‌كند كه براي اجراي گودبرداري در مناطق هم‌جوار نيز مفيد خواهد بود.

An excavation operation for the building purposes is a high-risk activity, which is done for different reasons, such as achieving an appropriate level of the earth for foundation or construction of basements. In this paper, using the Slide 6.0 program the stability of a pit wall in the outskirts of Qaen is investigated at first and then the pit wall stability after using soil nailing with various patterns is analyzed. Using back analysis, sensitivity analysis, and probabilistic analysis, this study presents a comprehensive model for analyzing pit walls, and will be useful for excavation operation in neighboring areas as well. Finally, several pit designs with acceptable safety factors have been proposed for pit excavation. Introduction Due to the growing trend of urban populations, the construction activities are increasing in central and marginal areas of cities. One of the basic concerns in these constructions is the stability of the excavated pit wall. The basic rule of judgment about the stability of a pit wall is the standard safety factor. In the traditional deterministic approach of safety factor calculation, any error or uncertainty in the soil parameters is directly reflected in the results. In recent years, the use of the probabilistic approach that provides additional measures related to the probability of failure and risk rate has become popular. In the probabilistic approach in addition to the mean safety factor, the probability of failure and reliability index are also obtained. Methodology and Approaches To perform a probabilistic analysis of a pit wall, strength properties of the soil layer and the soil density were defined as variable inputs. The coefficients of variation of these parameters according to laboratory experiments were selected. Normal and log-normal statistical distributions were used for the input variable parameters as recommended by USACE. For the efficient performance of the probabilistic analysis, Monte Carlo simulation was used. This way, and using the Slide 6.0 program, the stability of a pit wall in the outskirts of Qaen is investigated with various patterns of soil nailing as the supporting system. Results and Conclusions According to the results of this study, the soil is unstable for excavation operation and employing soil nailing technique and reducing the pit wall slope angle are appropriate steps to achieve a secure condition. Several safe pit designs have been proposed for excavating the pit.