Optimization of Sardasht Dam Sealing System Using UDEC Software

Document Type : Research Article

Authors

1 Dept. of Mining,Faculty of Engineering, University of Gonabad, Khorasan Razavi

2 M.Sc. of Mining Engineering. University of Gonabad, Khorasan Razavi

3 Associated prof., School of Mining, College of Engineering, University of Tehran,

Abstract

Summary
In this paper, the capability of foundation and support for the Sardasht dam is investigated. Finally, according to the results of numerical modeling in UDEC software, the diameter and distance of grout injection boreholes and dimensions and angle of seal curtain of the dam foundation dam have been suggested.
 
Introduction
The injection is a process whereby a cement slurry is pushed into rock formations through a borehole, thereby reducing the permeability and deformation of the rock mass and increasing its resistance. The rocks are almost impermeable and rock mass permeability is often a function of discontinuity systems. Due to the different and unpredictable behavior of rock masses, there is no specific law for determining the distance of injection holes and generally relies on the experience and judgment of the design engineer when deciding on the borehole distance. So, it is proposed to use numerical methods in predicting the radii of injection for grouting material and also determining the ideal spacing between adjacent holes. As the main results of this study, the optimum pattern for drilling sealing systems for different locations of the Sardasht dam was determined and compared to the empirical models using the discrete element method in UDEC. The optimum deviation angle of the holes was investigated, too.
 
Methodology and Approaches
The Sardasht dam is a trench with a clay core with a height of about 106 meters and a length of 280 meters. The total embankment volume of the dam body is estimated to be about 3 million cubic meters and the volume of clay core is about 516000 cubic meters. The water diversion system consists of two tunnel strings with an inner diameter of 7m and lengths of 627m and 682m in the right support and its height is about 46m. The right tunnel is used as the lower evacuator during the operation period. In order to investigate the in-situ condition of rock mass in Sardasht Dam area, rock mechanical parameters including rock mass quality index (RQD), specific gravity, uniaxial compressive strength, and geometry and resistive properties of discontinuities have been determined and measured. Then, the quality of grout injection in walls and foundation of the Sardasht dam was modeled, using numerical modeling in UDEC discrete element software.
 
Results and Conclusions
The results of this study show that the appropriate borehole spacing for the walls and the foundation should be taken as 3m and 5m, respectively. Also, the results obtained from the numerical modeling of the optimum injection pressure in the construction area of the Sardasht dam were determined for different depths. Based on the numerical modeling results in order to minimize water leakage from the Sardasht dam foundation, the optimum angle of curtain installation should be 17 degrees.

Keywords

Main Subjects

Full Text

1- مقدمه

تزریق فرآیندی است که به واسطه آن دوغاب سیمانی از طریق یک گمانه با فشار به داخل تشکیلات سنگی (خاکی) نفوذ کرده و در اثر آن نفوذپذیری و تغییر شکل‌پذیری توده سنگ کاهش یافته و مقاومت آن افزایش پیدا می‌کند. نفوذپذیری سنگ بکر در مقایسه با ناپیوستگی‏های موجود بسیار کم بوده و نفوذپذیری توده سنگ غالباً تابع سیستم‌های ناپیوستگی است. در مهندسی سنگ و زمین شناسی، از رفتار رئولوژیکی بینگهام در مدل‌سازی جریان دوغاب‌های سیمانی استفاده می‌شود[1]. تفاوت اصلی این مدل با یک سیال نیوتنی این است که در یک سیال بینگهام، سطح تنش باید از مقاومت برشی اولیه تجاوز کند تا جریان سیال آغاز شود. الگوی طراحی شبکه گمانه‌های تزریق بسته به هدف تزریق متفاوت است، اما معیار فاصله‌داری نهایی گمانه‌ها مستقل از آن است و به نفوذپذیری اولیه تشکیلات زمین شناسی، سیستم ناپیوستگی‏ها، ترکیب ماده تزریق، فشار تزریق و معیار اشباع‌شدگی بستگی دارد [2]. نظر به رفتار متفاوت و غیرقابل پیش‌بینی توده‌های سنگی، قانون ثابت و مشخصی برای تعیین فاصله چال‌های تزریق وجود ندارد و عموماً هنگام تصمیم‌گیری در مورد فاصله گمانه‌ها، به تجربه و قضاوت مهندسی طراح تکیه می‌شود. نتایج بررسی‌های لیو و سان نشان داد که مهم‌ترین عوامل پیچیدگی تزریق دوغاب در توده سنگ به عنوان یک فرآیند هیدرولیکی - مکانیکی ناشی از سه عامل اصلی تغییر شکل مکانیکی توده‏ سنگ در طول فرآیند تزریق، نفوذ دوغاب درون درز و شکاف‏ها و توسعه شکستگی‌های ناشی از تنش تزریق، است. مسیر نفوذ دوغاب در توده‌سنگ محدود به ناپیوستگی‏های ذاتی نبوده بلکه ترکیب این ناپیوستگی‏ها با شکستگی‌های هیدرولیکی در طول فرآیند تزریق، شبکه ناپیوستگی‏ها[i] را تشکیل می‏دهند [3-5]. روش‌های تجربی تعیین عمق نفوذ دوغاب، محدود به شرایط آزمایش بوده و راهکارهای تئوری بیشتر براساس تئوری محیط پیوسته هستند اما روش‌های عددی می‌توانند ابزاری مناسب برای مدل کردن جریان واقعی سیال در توده‏سنگ‏هایی با شکستگی‌های پبچیده باشند. بر این اساس همواره استفاده از روش‌های تحلیل عددی در پیش‌بینی نتایج تزریق در توده‏ سنگ مورد توجه محققین مختلف قرار گرفته‌است.


[i] Fracture Network

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Journal of Analytical and Numerical Methods in Mining Engineering
Volume 11, Issue 26
April 2021
Pages 23-34

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History

  • Receive Date: 17 December 2019
  • Revise Date: 02 April 2020
  • Accept Date: 04 July 2020

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