Soil And Rock General Soil Characteristics Trafficability – ability of soil to support weight of vehicles under repeated traffic –Controls traffic on unimproved access roads –Also gives measure of how earthmoving equip will operate –Primarily function of moisture conditions and soil type Loadability – how difficult to excavate and haul a soil –Granular – high –Compact cohesive - low /home1/o/misc/lhmi/Friends/kevin/

Soil And Rock Unit Soil Weight –Pounds /cy –Depends on soil type, moisture content, degree of compaction –Relation between soil weight and bearing capacity So soil weight is used as a measure of compaction Soil weight is also a factor in hauling

Soil And Rock Moisture Content(%) = (moist wt – dry wt)/dry wt X 100 Soil sample 120# Dry weight 100# MC = ( )/100X100 = 20%

Soil ID Boulders Cobbles – over 3” diameter Gravel 1/4” – 3” diameter Sand 0.7mm (200 sieve) – ¼” diameter Silt – 0.7 mm Clay less than 0.002mm Organic Matter decaying organic matter Soils classified using these types

Soil Classification Systems Unified System –All material #’’+ removed –Separates soils into two main groups- Fine grained and coarse grained –Table 2-2, Figure 2-1 AASHTO System –7 classes of soil –Based on suitability of soil for subgrade –Table 2-3 –Table 2-4

Soil Volume Change Characteristics Soil Conditions –Bank – material in natural state before disturbance – Bank cubic yard –Loose – material that has been excavated or loaded loose cubic yard –Compacted – material after compaction compacted cubic yard

Soil Volume Change Characteristics Swell –Soil increases in volume when it is excavated Soil grains are loosened and air fills voids So 1 unit of soil in bank is smaller than the soil once it is excavated Swell(%) = ((weight/bank vol)/(weight/loose vol)- 1)X100 Soil wt = 2800#/cy in bank Soil wt = 2000#/cy loose Swell = ((2800/2000)-1)X100 = 40%

Soil Volume Change Characteristics Shrinkage –Soil decreases in volume when it is compacted Air is forced out of soil So 1 unit of soil compacted is smaller than the soil in the bank or once it is excavated Shrinkage(%) = (1-(weight/bank vol)/(weight/compacted vol))X100 Soil wt = 2800#/cy in bank Soil wt = 3500#/cy compacted Swell = (1-(2800/3500))X100 = 20%

Soil Volume Change Characteristics Load and Shrinkage Factors –Need a common unit of measure for earthwork (get rid of calculations ) –Can use any of the three measures Called pay measure in contract Load factor = 1/(1+swell) Shrinkage factor = 1- shrinkage

Spoil Banks Material removed from excavation –Longer than wide – spoil bank – triangular x section –Conical – spoil pile –To determine the size of the bank or pile need swell and angle of repose for soil –Angle of repose = angle that soil on side of bank naturally form Varies with moisture content and type Table 2-6

Spoil Banks Spoil bank –Vol = X sect area x length –B = (4V/(lx tan R))^1.2 –H = (B x tan R)/2 –B – base width –H height –L length –R angle of repose –V volume

Spoil Banks Spoil pile –Vol = 1/3  D/2)^2 X H –D = (7.64V/tan R)^1/3 –H = D/2 x tan R –D – diameter of base –H height –R angle of repose –V volume

Estimating earthwork 3 types of excavations –Small pit –Trench –Large areas Roadways –Find cut and fill using cross sections –Mass diagram

Estimating earthwork Pit Excavations –Area X average depth –Depending on size and ground may break into several geometric shapes to get volume –Give bank volume

Estimating earthwork Trench Excavations –V = x sectional area X length –Take x sections every 50 feet and compute volumes between x sections

Estimating earthwork Large Areas –Use a grid to find volume