The RUBBER DAMS in Federally Administered Tribal Areas (FATA) Pakistan.
Rubber Dam is a flexible kind of dam that can be raised either to full or part heights and lowered fully to the bed of the river any time necessary. Invented in Europe as fabri-dam, Rubber Dam was initially developed in the USA in early 60s and has been used in many countries both in the west and the east. Japan, China and Bangladesh are the main producer-users of Rubber Dam now. The Chinese claims to have some 400 Rubber Dams in their country.
Rubber Dam consist mainly of a dam body or dam bag made of rubber reinforced with woven synthetic fabric, a system of anchorage of the dam bag with the foundation base usually built of concrete, a system of filling and emptying of the dam bag including safety control measures and the foundation including base floor, aprons, abutments and other protective works.
The fabric in the dam body provides the required tensile strength while the rubber acts as the adhesive and waterproofing element. The fabric reinforcement is usually in number of layers depending on the design strength requirements.
The dam bag needs to be anchored to the base floor usually constructed on the bed of the river adequately. The two types of anchor system that are usually used are - steel anchor bolts with clamps and concrete or wooden wedge blocks. Stainless steel bolts and nuts are preferable because these do not reduce strength due to corrosion or rusting.
However, stainless steel should be used with due consideration to its cost aspects. In concrete wedge block system, slots are kept in the concrete base floor and the ends of the rubber sheets are anchored into the slots by wedging down two pre- cast concrete wedge blocks. The slots and the concrete blocks should be in perfect dimensions and finish for quality anchorage. For low height dams of simpler hydraulic forces, wooden wedge blocks may be used if it is ensured that the blocks will be permanently under water.
Pumping in either air or water or both in combination can fill the dam bag. Air filling is preferred when quicker filling and emptying are desired. Water filling is relatively slow but ordinary water pumps and fittings can be used. Larger pumping capacity is provided when quicker filling requirement is anticipated. The pipes of filling -emptying system is embedded in the foundation floor and is connected to the pumps. The system usually includes safety measures against overfilling through overflow outlets and monitoring manometers.
The foundation of rubber dam consists of reinforced concrete floor with appropriate measures for control of under-seepage, uplift and scour. Adequate earth retaining and erosion and scour protection works are also to be provided.