Laserfiche WebLink
this task is completed and approved by the PROJECT MANAGER. Payment for this task will be <br /> made only for the unit price shown under Item 6 of the Bid Schedule. <br /> TASK 7 UNDERDRAIN CONSTRUCTION <br /> The PROJECT MANAGER may determine that it is desirable to construct an underdrain(s) <br /> where coal refuse is used as fill material in order to obtain the design slope on the north face of <br /> the Old Refuse Pile, or at some portions of the refuse disposal site. <br /> Underdrain Construction Requirements <br /> (1) The PROJECT MANAGER will identify the location of the underdrain in the field. This will be <br /> accomplished prior to beginning fill or disposal operations. Prior to beginning construction of the <br /> drain, the CONTRACTOR will remove any vegetation and topsoil existing within the underdrain <br /> corridor. Salvaged topsoil will be removed to the storage location agreed upon during completion <br /> of Task 2, Earth Work. <br /> (2) Excavation of the underdrain will begin after topsoil and vegetation salvage is complete. The <br /> excavation will typically be rectangular in shape, having vertical sides. In the case of <br /> constructing an under drain at a fill location at the Old Refuse Pile, excavation into the pile will <br /> be necessary. Excavation will occur for a horizontal distance of approximately five feet (5'). <br /> Excavation of coal refuse to natural ground level is required. Excavation will occur so that the <br /> under-drain has a minimum gradient of two percent(2%) parallel with the length of the <br /> underdrain. The minimum width of the excavation will be four feet (4') and the minimum depth <br /> below native ground surface at the upper most extent of the excavation will three feet(3'). See <br /> Figure 1, Typical Underdrain. Excavation will continue until the end of the drain is no less than <br /> ten feet(10') from the toe of the fill slope. <br /> Excavation of an underdrain at the disposal area will be identical to that described above, <br /> however, removal of rubbelized concrete or similar materials will be required, rather than <br /> excavation of coal refuse. <br /> (3)The base of the drain after excavation shall be compacted using a hand held compactor. <br /> (4) Upon completion and acceptance of the excavation, a geotextile fabric, such as Mirafi 140N <br /> or equivalent material pre-approved by the PROJECT MANAGER, will be placed within the <br /> excavation. The geotextile shall be placed so that it is not folded or wrinkled. Aggregate shall <br /> be carefully placed within the geotextile so as to avoid puncturing the fabric. Aggregate shall fill <br /> the trench to its full depth. <br /> Aggregate shall consist of durable rock materials, with an average size of no less than three <br /> quarters of an inch (3/4"), and no larger than six inches (6") as measured across the shortest <br /> axis of any one rock, shall be introduced into the excavated drain, so that the drain is filled from <br /> top to bottom and side to side for its length. See Figure 1, Typical Underdrain. Durable rock is <br /> defined as competent granitic or metamorphic rocks, excluding slightly metamorphosed <br /> sandstones, shales or other friable materials. The PROJECT MANAGER may reject material <br /> considered to be unacceptable. <br /> Upon completion of filling the lined trench with aggregate, the ends of the geotextile shall be <br /> wrapped over the top of the aggregate, so that the fabric overlaps itself by a minimum of twelve <br /> inches (12"). <br /> 14 <br />