Combination of Cement Deep Mixing (CDM) and Steel Sheet Piles for the Cofferdam Used in Construction of Deep Foundation Pit in Soft Ground in the Mekong Delta Coast

Cofferdam foundation is defined as a temporary structure which is used to prevent soil erosion in the construction area as well as to prevent water from entering the excavated area when excavation is to be done by digging deeper along the river bank or coast. Most of the works such as dams, locks, bridge footings and water intakes of thermal power plants have deep and wide foundation pits leading to very large cofferdam. In fact, the cofferdam for such works are usually made of specialized steel sheet piles and combined with shoring frames. The specialized steel sheet piles are not popular in the market meanwhile the shoring frame reduces the work space and increases the complication of construction works. Based on research and experience from projects in the Mekong Delta, the cofferdam for the deep and wide foundation pits made by combining between soil cement columns with common steel sheet piles is the reasonable solution. This solution not only does not need specialized steel sheet piles but also takes advantage of local materials, moreover, increasing the work space because it does not need a shoring frame. This paper is going to present the cofferdam used in construction of deep and wide foundation pits under the soft soil of the Song Hau thermal power plant by combining cement deep mixing (CDM) with common steel sheet piles.