Pobierz pełny numer 1/2010 S&E - Structure and Environment - Kielce

ROAD SUBGRADE EMBANKMENT DEFORMATIONwith asphalt and cement-concrete pavements at thecarriageway and shoulders, with good grassy turfsat the slopes. Particularly often these deformationsoccur in the first 1-3 years of grade level service.The possible schemes of local deformationdevelopments are presented at the Figure 2. In allcases there are slip lines of the definite coat massif ofsoil in the coating surface of the slope:The condition of the slope stability is the balanceor excess of restraining forces over the shear forces.Stability coefficient is:, (1), (2)where: γ – soil density; Zi – running coordinate ofthe active zone capacity of the slope perpendicularlyits surface; tgψ Zi– coefficient of soil shift of theactive zone h at depth Zi; tgφ n, C n– correspondinglycalculated values of angle of repose and soil cohesionat depth Zi; α – rate of slope.а)b)c)Fig. 2. Development scheme of shear deformations on thefill slopes [6]: а) due to identity element; b) inplane slipwith uplift; c) destruction of the whole slope in the belt ofweathering on the circular cylindrical surface; 1 – face ofslope; 2 – capacity of the active zone ha; 3 – shift surface;4 – assumed blocks; 5 – retaining prism in uplift zone2.1. The water and it role in losing stability of the slopeThe analysis of the complex of restraining forceshowed that, the main role in the loss of local soilstability on the slopes is played by water, whichcauses decreasing of angle of repose and cohesionbetween the particulates and dynamically effects thesoil grains.Structural cohesion С nin graded materials takesplace only in case of high density and soil compactnessand predominantly in case of low homogeneity ongrain-size classification and is predetermined, mainly,by interlocking grain arrangement [9].Table 1. Dependence of cohesion and angle of internalfriction of soil from its porosity [9]Cohesion С (МPа) and angle ofType of refuse stoneinternal friction j (grade) with theporosity factor e0.45 0.55 0.65 0.75Gravel and coarse sand0.02 0.01 – –43 40 38 –Sands of average coarseness0.03 0.02 0.01 –40 38 35 –Fine sand0.06 0.04 0.02 –38 36 32 28Dust sand0.08 0.06 0.04 0.0236 34 30 26Note: Upper line – cohesion, lower – angle of repose.The water gets into the soil on the slopes as a resultof percolation in case of storm event and snow melting.In winter the soil of grade level freezes (after thetemperature fall below -5°С). Isothermal curve of zerotemperature falls lower and lower from the surface of33