244 HEATHER RD 2016-01-01 MF Import

d7/28!1997 14:15 2C�63E59?73 LITTEN EWGIt;EERIIJG PAGE Ei4 Mazk T. Otten, P.E. En�ineering Consultant There aze a wide variety of reinforced eanh walls,but tnost of these consist of gravel or sand backfill reinforced with metal strips or geomembrane fabrics. Reinforced earth wails are �eneraily covered with pre-cast concrete elements(such as Keystone or Allen Block). Crib walls can be coesweted from steel,concrete, or timber. Hollow cribs are formed out of the suuctural material, and then the space inside is�Ilzd with sand and gravel. Structura] walls include soldier piles msde from steel beams or concrete columns,piles with eatth de-backs, steel sheet piles, or reinforced concrete. Soldie�piles resist the lateral force of the soll prassure by using the downslope soil resistance on the underground portion of the piles. Tieback anc:hors are drilled into stronger soil upslope w�d below the slide zone. Stezl rods in the ancliors tie into the wall face to provide resistance to the lateral soil presswe. Structural walls aze generally the stzongest and safest to construct,but cost the most. StAbilizntion Optioas It appears that Giles assumed tliat the objective was to stabilize the slopes. They recomcnended that horizontal drains 150 to 200 feet long be drilled from the west slope startins ]00 vertical feet below the house. The horizontal drains they recommend would improve the stability of the slope; however, drains this deep may not effectively drain neat-surface groundwater in thz fill placed in tho weat yard. The piling wall described by Giles in t}tere Yard Stabilization section would be one method of protectin�part o£the yard from fu�ther sliding and would protect tha house. In my upinion, it would be difficult and expensive to attempt to prevent fiuther slidins on the entire west slope. 'fhe overaU slope from the creek to the house is about 30 degrees('_'14 feet vertical to 376 feet horizontal). Based on my expericnce and design oFsimilar slopes,the dense and hard glacia! soils on the slopz should bz stable for e design life of 50 to 10 years. However, due to groundwater seepage forces, aurface erosion and creek erosion, future surficisl sliding should be expected. In my opinion,the house can be protected without attempting to prevent surficial movement on die west slope. Tn order to protect the house,the soil in the yazd needs to be stabilized. Slope stability cwi be improved several methods, as summarized below. One option tn protect the bouse and to improve khe yard stability,wauld be to lower the elevation of die wast yard below the slide scarp by 3 to 8 feeL This would require excavation and off-site disposal of the loose silty sand fill. Tl�is could be done widt tenaces sepazatzd by relatively low w�alls, so that the yard area would be nearly the same as it is now, but would siniply be lower in elevatiou. 3 7/j$f97 07:SLTRDOC