1530 51ST PL SW 2016-01-01 MF Import

Gcotcchnical Enginccring Evalu,...,,n Lcttcr Mosman Basement [verett, Washington NGA Pilc No. 8R6013 Dc;ccm6cr 17, 2013 Page 9 also recommend that watcrproofing be applied to thc cxicrior of thc retaining walls for the basement areas. Slab-on-Crade We do not know how exacdy the slab-on-grade was construcled. T�ically, we recommend a capillary break laycr underneath the slab Ihat is hydraulically connected to the footin,g drains. We also typicall� recommend that the slab subgrade be in a firm and unyielding condition pror to the placement o'r the capillary break, and that the slab is reinforced with a wire mesh or min� '-: ^bar reinforcement. 'in this case, it seems that [he existing slab was placed on a firm subgrzde, .t we are not aware that a�y capillary break material was placed beneath the slab, or if positive drainage from underneath the slab to the outside was attecipted. In any case, we understand that you do not wish to disturb the eaisting slab and to Ieave it as is, accepting any future risks associated with the slab. Such risks include dampness within the living space and/or settling or cracking of ihe slab. The drains that are recommended along the outside perimeter of the basement should reduce the potential for damp conditions to devclop withi❑ thc basement; howcver, thc drains alone will not eliminate suc6 potcntial. Structural Fill Gcoeral: Fill placed behind thc retaining wall, bencath foundations, slabs, or other settlement-sensitive structures should be placcd as structural fiIL SWctural fill, by definition, is placed in accordance with prescribed methods and slandards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include [he performance of a representative number of in-place density tests to documcnl the attainment of the desired degree of rclaNve compaction. . Materials: On this site all structural fills should consist of a good quality, gnnular soil, Gee of organics and other deleterious material, and be well gr�dul to a maximum size of about thrce inches. Structural fill materials should contain no more than five-percent fines (soil finer than U.S. No. 200 sieve, bascd on that fraction passing thc U.S. 3/4-inch sicvc). 'I'hc usc of the on-si!e soils as structura] fill is not recommendcd. We should be retained to evaluale proposed structural fill matcrial prior to placement. NELSON GEOTECHNICAL ASSOCIATES, INC.