Soil And Rock General Soil Characteristics Trafficability ability

Soil And Rock • General Soil Characteristics • Trafficability – ability of soil to support weight of vehicles under repeated traffic – Controls traffic on unimproved access roads /home 1/o/misc/lhmi/Friends/kevin/ – 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

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 = (120 -100)/100 X 100 = 20%

Soil ID • • Boulders Cobbles – over 3” diameter Gravel 1/4” – 3” diameter Sand 0. 7 mm (200 sieve) – ¼” diameter Silt 0. 002 – 0. 7 mm Clay less than 0. 002 mm 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)X 100 • Soil wt = 2800#/cy in bank • Soil wt = 2000#/cy loose • Swell = ((2800/2000)-1)X 100 = 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))X 100 • Soil wt = 2800#/cy in bank • Soil wt = 3500#/cy compacted • Swell = (1 -(2800/3500))X 100 = 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 = (4 V/(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 p(D/2)^2 X H – D = (7. 64 V/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