Search

Hydraulic fracturing can occur in the clay core of earth and rockfill dams if the vertical effective stress in the core is reduced to the levels that are small enough to allow a tensile fracture to occur due to hydraulic pressure of the seeping water. This situation may arise if the total stress in the core is reduced by the “arching effect” where the core settles relative to the filter or rock-fill shell of the dam. Water pressure increase in the core which occurs on first impounding of water, may reduce effective stresses further, and if they reach low enough values, a fracture will occur. The design of earth dams (especially those with thin vertical central cores) to resist hydraulic fracture is therefore of great importance, as there have been several dam failures in the past that have been attributed to the hydraulic fracture. In this paper, the behavior of Hyttejuvet Dam, which was thought to have failed due to hydraulic fracturing, is studied. 2D coupled consolidation finite element analysis of the construction and first impounding of the rockfill dam was carried out with elasto-plastic model (Drucker-Preger/Cap model) using ABAQUS software. The result of the analysis with respect to the pore pressure and settlement in some parts of the dam are compared with the measured data from the instruments in the dam. According to the result of the comparison, the appropriate model for predicting the behavior of Hyttejuvet Dam is obtained. Also different criteria are used to predict the hydraulic fracturing of the dam. By comparing the results of the study using these criteria, one may be able to predict the hydraulic fracturing mechanism in the clay core of the studied dam.

TOOBA deep excavation project was conducted in a densely developed area in the North West of Tehran, capital of Iran, to provide space for 4 basement levels for multiple buildings around the already functional TOOBA tower. TOOBA tower is located in the northern leg of the excavation boundary in a way that the northern side of the building abuts the excavation edge. Hence, this project involved excavation on 3 sides of the roughly rectangular plan of TOOBA tower to the depth of 16.5 meters below its foundation level. The necessity for constraining the deformations of the tower commended the construction of contiguous bored concrete piles around the building supported at 4 different levels with tieback and wailing system. A monitoring program for measuring the deformations of the tower and supporting system was also enforced during and after excavation. The three-dimensional nature of the retaining structure required careful design and construction procedure to avoid problems such as the intersection of the anchors. Each tieback was given a unique direction which was defined by 3 angles relative to the local x, y and z axes. Therefore, complicated forces were exerted on the wailing system and piles. The excavation procedure was ensued with no excessive deformations occurring in the building during or after the excavation. This paper considers some of the design and construction aspects of this successfully completed project.