Nierji Water Conservancy Project The Impermeable Construction Technique And Research

The rock-fill dam has been widely applied and well developed in the dam construction throughout the world. The embankment has characterized as:material explored nearby,the foundation deformation fitted well,simple construction techniques,and ease to organize the rapid mechanical construction. Nowadays techniques and equipment have improved rapidly. With the use of computer auxiliary design and the physical model application in the experiment,new layout schemes,new types of the dam and the structure have been explored to fit the complicated circumstances. At mean time,it is very important to study and adopt new dam construction techniques in the world,such as to focus on the wide application of the rock-fill concrete deck and rolled asphalt concrete core dams.The rolled asphalt rock-fill dam with concrete core is one of new impervious structures in the rock-fill dams. It has very high imperviousness with ability to fit the deformation and it is easy to organize the construction. Its permeability coefficient is normally lower than 10-7- 10-8cm/s. The asphalt concrete has very good flexibility to fit different kinds of settlements. If there were cracks,the asphalt concrete would be able to self-heal up with the act of the dam gravity. Besides that,the impervious asphalt concrete is much easier to construct than the impervious earth material. It has much more advantages in the wet seasons.The main dam is the rolled asphalt rock-fill with the concrete core in Nierji Project. The construction techniques and mechanics are approaching or even reaching the international advanced level in the asphalt concrete impervious deck of the recent completed Tianhuangping Pumped-storage hydroplant and the counter dam in the Yangtze River which is being built with the height of 104 m,the volume of asphalt concrete core of 5x104m3. The stability analysis for the seepage is one of the most important steps in the design of rock-fill dam. The wrong designs or doings of the dam body,seepage of foundation or by-pass seepage would cause the body or foundations to deform or even breach the dam. For example,after the collapse of Ditong Dam in Idaho,May 5,1976,it was found that it was not impervious very well,the impervious curtain was built poorly. When the seepage went through theimpervious curtain,the exit water from the pervious material of the downstream or the right side of dam through the foundation or certain line between the foundation and the dam caused contact scour and piping. The stability analysis in Nierji Project is simplified as the plane seepage analysis. The result shows that the profile of the main dam and the second dam and all the impervious rock fill material have no problem. The total seepage volume is 3.9092x106m3 per year. It occupies 0.037% of the average inflow of the reservoir,which is acceptable from the point of view of the water resources utilization.The construction techniques of the asphalt concrete core have developed very rapidly. In the construction techniques,it was developed from the handwork or qusi-mechnical construction into mechanical construction. The producing,processing and transporting of material,bathing,mixing and transporting of mixed asphalt,laying and rolling of mixed asphalt and transporting of material was archived by specialized machines. All the systems are under automatic control.