"In December 1993, His Majesty the King gave advice on how to solve the decades-long cyclical problems of drought, flooding and soil deterioration suffered by farmers and other people of Nakhon Nayok province."

In December 1993, His Majesty the King gave advice on how to solve the decades-long cyclical problems of drought, flooding and soil deterioration suffered by farmers and other people of Nakhon Nayok province. He emphasized the importance of proper water management and he instructed the Royal Irrigation Department to look into solutions for the upper Nakhon Nayok River basin, which would provide the maximum benefit for both population and environment. His Majesty?s initiative is today realized through the completion of the khlong The Dan Dam-a modern engineering wonder that will bring water and life to the long-suffering people of Nakhon Nayok

The people of the Nakhon Nayok basin have long been subject to the vagaries of the Nakhon Nayok River, which rises from the slopes of khao Yai National Park and runs southwest. Eventually draining into the Prachinburi River and the Bangpakong River. The problem has always been too little water or too much. in Years of low rainfall, the flat and cannot store sufficient water for irrigation and the result i8s severs drought. Over the last 10-year period, the basin has experienc4ed its most severe drought, with a 97.3 percent drop in harvestable crops. In years of heave rains, flooding rages through the lfat plain causing massive destruction of property. In 1990, for example, flooding devastated over 300,000 rai of paddy, valued at over 456 million baht, To add to the woes, the alternate cycles of drought and folding cause an increase in soil acidity, In Kakhon Nayok province, more than 40 percent of the land suffers from high acidity causing and estimated 336 million baht in lost income annually.

His Majesty the king became aware of these problems many years ago. Following many personal site inspections on foot and by helicopter, His Majesty pinpointed the problems and suggested that adeguate surplus water retention and in improved drainnge and irrigation system would eliminate most of the problems experienced by the farmers, as well as businesses and industries along the Nakhon Nayok River. The solution was a damm and upgraded irrigation system that would provide controlled water supplies to 100,100 rai of farmland and that would facilitate storage of some 224 million cubic meters of water.

The Royal Irrigation Department took action on His Majesty?s ideas. Project feasibility studies and environmental impact assessments, for the dam were completed in 1996, and Cabinet approval for the project was granted the same year. Construction got underway in November 1999 by the CCVK joint venture, Construction will be fully complete in early 2005 and the dam operational. The reservoir behind the dam will fill with water throughout the 2005 rainy season.

?Dam is a median tool. In the year of plentiful water, store the excess. Do not use it because rain water is adequate for use. In the year of water shortage, use it to ease the dangerous threat from drought. Danger from floods will also be abated.

The Constrution

the kholong Tha Dan Dam is a Roller-Compacted Concrete (RCC) dam built on a solid rock foundation. Completed in early 2005, The dam is 93 meters high, with a length of 2,720 meters and an estimated RCC volume of 5,470,720 cubic meters, making it the bigtgest and longst RCC dam in the world, and Thailand?s largest dam.

The main construction works involved in the project are:

* Excavation and blasting of 1,550,000 cubic meters oif rock for the dam foundation.

* Blasting and crushing of 5,000,000 cubic meters of rock from the quarry in order to produce aggregates for the RCC and CVC (Conventional Vibrated Concrete).

* Drilling and grouting of drainage and grout curtains (total length of drill holed 397,000 meters.)

* Placing of 5,470,000 cubic meters of RCC as well as 558,000 cubic meters of conventional concrete.

Foundation Structures

Construction of the dam commenced with the rock excavation of the dam from approximately 29 meters above mean sea level down to about 19 meters above MSL. Rock excavation included underground drainage and grouting galleries of 3 meters diameter over a total length of 2 kilometers.

With pouring of the leveling concrete on the base rock foundation, work on consolidation grouting commenced. Consolidation grouting aims to fill voids, fracture zones and cracks below the surface of the excavation; to strengthen and watertight the superficial rock which has been subject to decompression and fracturing during the excavation work; and to fill shrinkage fissures at the rock/concrete interface.

First stage consolidation grouting undertaken over the whole area of the dam foundation consists of 9-meter-deep holes with 3-meter spacing. The second stage consolidation grouting, undertaken only at the toe and heel of the am, consists of 15-meter-deep holes.

Subsequently, the grout and drainage curtain will be achieved from the dam? control? gallery, The grout curtain consists of one row of 60-meter-deep grouting holes, which are necessary to control seepage under the dam foundation. The drainage curtain, which consists of 40- meter-deep holes spaced five meters apart, is needed to control the hydraulic gradient and to reduce the uplift pressure at the base of the structure,

RCC Work

The RCC technique was selected for the dam owing to its solidity, reduced construction time frame and relatively low cost, Common factors in The RCC approach are high-speed construction and a no-slump consistency that allows the mixture to be compacted by large vibratory rollers.

For the khlong Tha Dan project, lignite fly ash has been introduced as a cement replacement in order to reduce the amount of cement used, to save on material costs, to reduce the heat of hydration and to increase the workability of the mix, and the long-long-term strength development of the dam This concept also makes use of a byproduct of lignite combustion from the Mah Moh Power Plant in Lampang.The mix proportion used at khlong Tha Dan consists of 1,300 kg of course aggregate, 850 kg of fine aggregate, 60 -80 kg