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� May 7, 2001 � ( <br /> Rockery—Pete Peters Residence <br /> L&A Jcb No. 1058 <br /> Page 3 <br /> cover and subjected to stormwater erosion, the Advance Outwash deposits on a slope can very <br /> gradually become unstable and slough to a flatter inclination. The Advance Outwash deposits in <br /> their native, undisturbed sta!e can provide very good foundation support with little settlement <br /> expected for light to moderate residential structures. <br /> SUBSURFACE CONDITIONS <br /> We probe tl�e surficial soils in the azea where the proposed rockery is to be constructed by <br /> manually pushing a probe baz, made of a 0.5-inch-diameter by 4-ft-long steel rod fit with a cross <br /> bar, into the ground to get an indication of the density of the soils. The probe bar could generally <br /> penetrate to about 2.5 to 3.5 feet. The ground probing results indicate that the unweathered <br /> glacial till is at relatively shallow depths overlain by a layer of weathered till not significantly more <br /> tban 3.0 feet thick. <br /> ROCKERY STABII.ITY <br /> A rockery by nature is not an engineered retaining wall, such as a reinforced concret,� wall. <br /> Although a rockery wall can provide some degree of retention capability, its main function is tc <br /> serve as a protective facing to shield the earthen banks behind the rockery from naxural <br /> weathering and erosion process. To aclueve a satisfactory rockery, the earthen banks behind the <br /> rockery must be stable by themselves. <br /> If rockei}�is used to line a cut bank, the cut bank itself should be able to remain stable over long <br /> term. If rockery is used to line a fill embankment, the fill embankment should be constructed of <br /> suitable material and compacted to a certain density requirement to ensure its stability. The fill <br /> embankment should be over-built a few feet, then cut back to where it is to be lined by rockery to <br /> ascertain the density and stability of the nearly vertical cut bank. Altecnatively, the SIl <br /> embankment can be built short of the rockery with a sloping face, ihen lined with the rockery with <br /> space between the rockery and the sloping face filled with rock spalls. <br /> i <br /> S <br /> i <br /> LIU&ASSOCIATES,INC. 3L <br /> // <br /> a <br /> { <br /> L <br />