Detailed Soil Survey of the Mount Revelstoke Summit Area.

42TABLE 7.GUIDES FOR ASSESSING SOIL LIMITATIONS FOR ROADS AND PARKING LOTSThis guide applies to soils evaluated for construction and maintenance of roads and parking lots havingsome kind of surfacing, commonly gravel . They consist of : (1) underlying local soil material (either cutor fill) called the subgrade ; and (2) gravel surface . They also are graded to shed water and have ordinaryprovisions for drainage . The roads are built mainly from the soil at hand, and cuts and fills are limited,usually less than 6 feet . Excluded from consideration in this guide are highways designed for fast-movingheavy trucks .Properties that affect design and construction of roads are : (1) those that affect the load supporting capacityand stability of the subgrade ; and (2) those that affect the workability and amount of cut and fill .The AASHO and Unified Classification, and the shrink-swell potential give an indication of the trafficsupporting capacity . Wetness and flooding affect stability . Slope, depth of bedrock, stoniness, rockiness,and wetness affect the ease of excavation and the amount of cut and fill to reach an even grade .Soil limitation ratings do not substitute for basic soil data or for onsite investigations .ItemsAffectingUseone to SlightDegree of Soil LimitationModerateevereSoil drainage Rapidlyl, well and mod- Imperfectly drained. Poorly and very poorlyclassl erately well drained . drained .Flooding None . Once in 5 years . More than once in 5 years .Slope 0 to 9% (AD) . 9 to 15% (E) . More than 15% (> E) .Depth to bedrock More than 40 inches . 20 to 40 inches . Less than 20 inches .Subgrade2 (Str .)a. AASHOGroup index30 to 4 . 5 to 8 . more than 8 .b . Unified GW, GP SW, GM, SM, C1 (with PI5 less than CL (with PI5 15 or more),soil classes and GC~+ and SC4. 15), ML, SP . CH, MH, OH, CL, Pt .Shrink-swell Low (PI5 less than 15) . Moderate (PI5 10 to 35) . High (PI5 greater than 20) .potential6Susceptibility Low (Fl, F2)6 . Moderate (F3)6 . High (F4)6 .to frost heave7Stoniness8 Stones greater than 5' Stones 2 to 5' apart . Stones less than 2' apart .apart .Rockiness8 Rock exposures greater Rock exposures 300 to Rock exposures less than 100'than 300' apart and 100' apart and cover 2 apart and cover greater thancover less than 2% of to 10% of the surface. 10% of the surface .the surface .1 . For an explanation of soil drainage classes see the System of Soil Classification for Canada (C .S .S .C .,1970), pp . 215-216 .2 . This item estimates the strength of a soil as it applies to roadbeds . When available, AASHO GroupIndex values from laboratory tests were used ; otherwise the estimated Unified classes were used . Onunsurfaced roads, rapidly drained, very sandy poorly graded soils may cause washboard or rough roads .3 . Group Index values were estimated from information published by the1962), pp . 23-25 .4 . Downgrade to moderate if content of fines (lessthan 200 mesh) is greater than about 30% .5 . PI means plasticity index.6 .Inherent swelling capacity is estimated as low when the plasticity index is less than 15, medium whenthe plasticity index is 10 to 15 and high when the plasticity index is greater than 20 (Tarzaghi andPeck, 1967) . Gravelly and stony soils may not exhibit shrink-swell as estimated by the plasticityindex because of dilution of the fines with coarse fragments . In these situations decrease a severelimitation to moderate and a moderate limitation to slight .7 .Frost heave is important where frost penetratesportable by capillary movement is sufficient tobility classes are taken from the United Statesreproduced from the above article.below the hardened surface layer and moisture transformice lenses at the freezing front . The suscepti-Army Corps of Engineers (1962), pp . 5-8 . Table 11 is8 . See also definitions for rockiness and stoniness in the System of Soil Classification for Canada (C .S .S .C .,1970), pp . 213-214 .