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SIGNET STL Project No. 0010771 7L-stfng Labs Page 10 Prior to pouring concrete, the sand should be thoroughly consolidated. The upper 2 inches of sand _ should be wetted during or just before the concrete pour to aid in concrete curing. The floor slab should be reinforced as a minimum with 6"x6"/10"x10" welded wire mesh or preferably #4 reinforcement bars at 24 inches on-center each way within the floor slabs middle-third. Thicker floor slabs with increased concrete strength and reinforcement should be designed wherever large vehicular loads, heavy concentrated loads, heavy equipment or machinery is anticipated. An average modules of subgrade reaction of 150 pounds per square inch per inch is recommended for design. The exterior slabs should be poured separately in order to act independently of the walls and foundation system. All fills required to bring the building pads to grade should be Engineered Fills. Lateral Earth Pressures and Retaining Walls Walls retaining horizontal backfill and capable of deflecting a minimum of 0.1% of its height at the top may be designed using an equivalent fluid active pressure of 30 pounds per square foot per foot of depth. Walls incapable of this deflection or are fully constrained walls against deflection may be designed for an equivalent fluid at-rest pressure of 60 pounds per square foot per foot of depth. Expansive soils should not be used for backfill against walls. The wedge of non-expansive backfill material should extend from the bottom of each retaining wall outward and upward at a slope of 2:1, horizontal to vertical, or flatter. The stated lateral earth pressures do not include the effects of ` hydrostatic water pressures generated by infiltrating surface water that may accumulate behind the retaining walls; or loads imposed by construction equipment, foundations or roadways. ` During grading and backfilling operations adjacent to any walls, heavy equipment should not be allowed to operate within a lateral distance of 5 feet from the wall, or within a lateral distance equal to the wall height, whichever is greater, to avoid developing excessive lateral pressures. Within this zone, only hand operated equipment ("whackers", vibratory plates, or pneumatic compactors) should be used to compact the backfill soils. Retaining and/or below grade walls should be drained with either perforated pipe encased in free draining gravel or a pre-fabricated drainage system. The gravel zone should have a minimum width of 12 inches wide and should extend upward to within 12 inches of the top of the wall. The upper 12 inches of backfill should consist of native soils, concrete, asphalt-concrete or other suitable backfill to minimize surface drainage into the wall drain system. The aggregate should conform to Class R permeable materials graded in accordance with Section 68-1.025 of the CalTrans Standard Specifications (January 1988). Pre-fabricated drainage systems, such as Miradrain, Enkadrain or an equivalent substitute, are acceptable alternatives in lieu of gravel provided they are installed in accordance with the manufacturers recommendations. If a pre-fabricated drainage system is proposed, our firm should review the system for final acceptance prior to installation. Drainage pipes should be placed with perforations down and should discharge in a non-erosive manner away from foundations and other improvements. The pipes should be placed no higher than six inches above the heel of the wall in the centerline of the drainage blanket and should have a minimum diameter of four inches. Collector pipes may be either slotted or perforated. Slots should be no wider than ''/cinch, while perforations should be no more than 'flinch in diameter. If retaining walls are less '� 1417 No. Market Blvd., Suite 1 • Sacramento, CA 95834 • (916) 568-5858 • Fax: (916) 568-5813