2000 TOWER ST ARTS AND SCIENCES BLDG 2018-01-02 MF Import

material. Alternatively, the wall drainage material may consist of clean gravel (gravel backfill for drains per WSDOT Standard Specification Section 9-03.12(4)) surrounded with a non -woven geotex+'le fabric such as Mirafi 140N (or approved equivalent). The zone of wall drainage material should be 2 feet wide and should extend from the base of the wall to within 2 feet of the ground surface. The wall drainage material should be covered with 2 feet of less permeable material, such as the on -site glacial till that is properly moisture conditioned and compacted. A 4-inch-diameter perforated drain pipe should be installed within the free -draining material at the base of each wall. We recommend using either heavy -wall solid pipe (SDR-35 PVC) or rigid corrugates polyethylene pipe (ADS N-12, or equal). We recommend against using flexible h4bing for the wall drain pipe. The footing drain recommended above can be incorporated into the bottom of the drainage zone and used for this purpose. The pipes should be laid with minimum slopes of one-half percent and discharge into the stormwaler collection system to convey the water off site. The pipe installations should include a cicanout riser with cover located at the upper end of each pipe run. The cleanouts could be placed in flush mounted access boxes. Collected downspout water should be routed to appropriate discharge points in separate pipe systems. Other Considerations Exterior retaining systems used to achieve grade transitions or for landscaping, can be constructed using traditional structural systems such as reinforced concrete, CMU blocks, or rockeries. Alternatively, retaining walls can consist of reinforced soil and block facing structures. In recent years, the latter structural system has proven to be an economically reasonable alternative to more traditional retaining wall systems. We can provide additional design recommendations for reinforced soil and 'block facing structures, if requested. SLAB -ON -GRADE FLOOR Subgrade Preparation We recommend that concrete slabs -on -grade be constructed on a gravel layer to provide uniform support and drainage, and to act as a capillary break. We expect that slab -on -grade floors can be supported on the native dense to very dense till and very stiff to hard advance outwash deposit. encountered in our borings or on properly compacted structural fill extending down to these materials. Prior to placmg the gravel layer, the subgrade should be proofrolled as described previously in the Earthwork section of this report. If necessary, the subgrade should be recompacted to a firm and unyielding condition. Design Parameters The gravel layer below slabs -on -grade should consist of G inches of clean crushed gravel, with a maximum particle size of 1 V2 incijes and negligible sand or silt. If the 12-inch-thick working pad layer is constructed and if areas contaminated with soil arc removed, then the working pad layer can be used as the capillary break layer described above. for slabs designed as a beam on an clastic foundation, a modulus of subgrade reaction of 200 Pei may be used for subgrade soils prepared as recommended above. 1 G c n F n g i n c e r s 15 File No. 5936-002-001040204