Chapter 2 Soils Investigation

1. Chapter 2Soils Investigation

2. Soil Deposits • Soil grains come from weathering of bedrock • Physical weathering – granular soils • Chemical weather – creates clay • Soil is either residual or transport • Residual is result of weathering of existing bedrock • Depth is greatest in hot humid climates • Transported have been moved from original location • Amounts increase at farther distances from tropics • Canada and northern us mostly transported soils

3. Transported Soils • Moved by • Gravity – landslides – same grains but usually less dense • Wind – fine sand and silts – deposits in mounds or dunes • Water – carries soil grains – stream velocity will determine where soil types are deposit • Glaciers – deposited all types of soil as they advance and resides

4. Field Investigation Techniques • Purpose of Soil investigation is to determine • Allowable bearing capacity for foundations • Water resources • Estimate infiltration and seepage rates • Information required in soilds investigation • Depth thickness and properties of each soil layer • Location of groundwater table • Depth to bedrock • Before field investigation preliminary information can be found • Geological and agricultural soils maps • Aerial photographs • Area reconnaissance

5. Subsurface investigation • Geophysical methods seismic or electrical • Useful indicators of depth to the water table and bedrock • Probing or jetting with a stream of water • Test pits or trenches • Suitable for shallow depths only • Hand augers • Suitable for shallow depths only • Boring test holes • Typical way to investigate soils

6. Number of test • One story building • 30 to 60 m apart to a depth of 6 -10m with one deeper hole to check the deeper soils • Four story buildings • 15 -30m apart to a depth of 10-15m with some holes to a depth one and one half times the width of the building and at least one deep hole to bedrock • Highways • Test holes every 300m apart to a depth of 3m

7. Standard penetration test • Sampler 60cm long with a 50mm outside diameter is driven by a hammer with a mass of 63.5kg and falling 75cm – the sampler is first driven 15cm to be sure that it is below the bottom of the test hole – then the number of blows required to drive it another 30cm is recorded as the N value • Most common strength test done in field • Values obtained are affected by the depth of overburden – espically in sandy soils • To correct this value N=N’ x (1x100/po)1/2 is used • Example page 83 • Chart page 83

8. Other field test to determine strength • Vane • Vane is shoved into soil and torguq is applied until it twists – gives shear strength or cohesion ofo cohesive soils • Cone • Simple cone is driven through soils – with the number of blows required for each foot or meter being recorded – indicates the depth of fill or the dept to layer changes

9. Pressuremeter test • New test to replace standard penetration test Page 86 and 87

10. Field log • Sample number, depth and type • Field test depth and results • Depth to layer changes • Field soil description • Type of soil grains • Moisture conditions • Consistency or density • Seams and stratification • Other distinguishing features

11. Laboratory Tests • Page 90 table 2-4 • Approximate soil strength from field test is can be determined using table 2-5 on page 91