Downstream Embankment Erosion Repairs

This action was awarded as an 8(a) Sole Source Set-Aside under the authority of section 8(a) of the Small Business Act. In accordance with these specifications the Contractor shall supply all plant, labor, materials, appurtenances, equipment, shop facilities, supervision, tools, staging, scaffolding and any other items necessary to complete the work for the Downstream Embankment Erosion Control Measures and Repairs at Galisteo Dam. 1. Placing Aggregate Base Course. a. The Contractor shall install a 4" lift of aggregate base course on designated 2000 ft. portion of downstream embankment access road. The Portion of road to receive base course is designated on Attachment 1 and labeled as "Re-grade Road." The existing unimproved road shall be graded to receive a uniform 4" lift of ABC that shall be compacted to 95% of maximum dry density. The Contractor shall insure that finished grade of the road shall be shaped to provide positive drainage from driving surface. See typical road and ditch sections on Attachment 2. b. The Contractor shall insure all other road segments on the downstream embankment designated in Attachment 3 are uniformly graded and shaped to ensure that storm/runoff water is adequately routed to the ditches tending that portion of road. 2. Grade, Shape, and Cut Ditches a. The Contractor shall insure that shape and grade right ditch of main downstream access road. The ditch shall be graded to divert flows towards low points identified in Attachment 4. b. The contractor shall install 90 plastic "V" ditch transition at low points identified in Attachment 4. The transition locations shall coincide with center line of culverts described in paragraph 3. c. The Contractor shall construct Gabion structures at the termination of turnout ditches. Government furnished Gabion baskets will be constructed using 4"-8" fractured rock and placed in such a manner as to protect the slope from excessive erosion from the channeled runoff. See (Attachment 5) d. All Gabions shall be anchored to the ground utilizing 1.33 lb./ft. tee posts. e. All rock required for gabions shall be the responsibility of the contractor. 3. Install Culverts with gabion/riprap a. The Contractor shall install government furnished 24" PE culverts at sag points to allow lined ditch on left side of road to channel runoff under the road to the downstream portion of the drainage system (Attachment 4). The locations noted on the attachment are approximate and may vary dependent upon field conditions. b. The centerline of culvert shall align with the 90 plastic "V" ditch transition and buried to such a depth as to allow a minimum coverage of 16 inches from the top of the culvert to the lowest point of the traveled surface on the road. c. The culvert grade shall be set at no less than 1% and no more than 3% fall across the road. d. The Contractor shall construct and place Government furnished Gabion baskets will be constructed using 4"-8" fractured rock at outfall of culverts to diffuse energy of runoff. Gabions shall be keyed into the embankment and act as a splash pad. Geo textile shall be installed between earth and gabion baskets. e. The Contractor shall place geotextile and rip-rap in runoff channels on slope between gabion structures and ditch at toe of slope. f. All rock required for gabions shall be the responsibility of the contractor. 4. Fill and Repair Existing Head Cuts a. The Contractor shall repair three (3) head cuts that have developed on the downstream slope of access road. b. The slopes of the repairs shall match existing embankment slope and be compacted to a minimum 90 percent of maximum dry density. c. All fill material required to fill-in repair areas shall conform to the definition of satisfactory soil material as defined in AASHTO M 145, Soil Classification Group A-2-4 or A-2-5. In addition, fill material must also be free from roots and other organic matter, trash, debris, frozen materials.