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18 Cards in this Set
- Front
- Back
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Ground investigation provides (7)
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1) type of foundation req (shallow or deep)
2) info to make allowable load capacity of foundation 3) data/lab tests for settlement predictions 4) location of groundwater table 5) identify and solve construction problems 6) identify potential problems concerning adjacent property 7) identify environmental problems |
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Three stages of ground investigation (3)
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1) Desk studies
- survey maps - air photographs - previous records - libraries - discussion w/ locals 2) Preliminary Investigations - carried out on site w/ no major expenditure - confirm/revise desk study - add info via. limited sub-surface exploration program 3) Detailed Investigation - bulk of expenditure - detailed sub-surface exploration |
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Test pitting, sampling and lab test of collected samples. Advantages and Disadvantages.
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Excavation by hand or w/ excavator
Adv. - cost effective - detailed stratigraphy - large quantities for testing - large samples obtained - field testing in pit Disadvan. - depth limit to 6m in clays - req. for side supports - deep pits uneconomical - below groundwater and through rock difficult and costly - too many pits scar site - time consuming - limited to depths above GWL |
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Commonly used drilling and sampling methods, disturbed samples taken (3)
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Auger boring. Practical for 35m
Rotory drilling; Wash boring; Percussion drilling. Practical for 70m Test pits and open cuts. Usually less than 6m. These are applicable for all soils. Penetration testing used in conjunction with these methods, intervals of 1 to 1.5m. |
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Commonly used drilling and sampling methods, undisturbed samples taken (3)
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Auger drilling; rotary drilling; percussion drilling; wash boring. Depth depends on equipment. 50-100mm diameter or thereabouts.
Test pits. Usually less than 6m. Hand trimmed. |
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What are "hollow-stem augers" and their advantages and disadvantages?
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- Outer spiral continuous flight with separate inner rod which blocks base of hole while auger is advanced
- Auger forced into ground with inner and outer rotating together - Samples gathered by removing inner rod and plug from base of auger Adv. - Widely available - Quick - Provide casing Disadvan. - Depth 30m, reduced w/ hard-to-drill materials - High hydrostatic pressure causes problems w/ sand heaving. Add water to augers. - For fissured clay powerful rig required |
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What is "percussion drilling" and what are it's advantages and disadvantages?
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- Casing first by hammering (china 3000 years)
- Lifting and dropping of heavy tool to break or crush soil until slurry forms - Bailer used to remove slurry Adv. - Simple operation and maintenance - Suitable for wide variety of rocks - Possible above and below water table Disadvan. - Slow, compared with other methods - Equipment can be heavy - Water needed for dry holes |
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What is "washboring" and what are it's advantages and disadvantages?
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- Casing driven with drop hammer
- Soil loosened/removed using water or drilling mud jetter under pressure - Water leaves hole w/ loose soil through pipe - Water reaches ground allowed to settle Adv. - Simple to use - Possible above and below water table Disadvan. - Water required for pumping - Unconsolidated rocks only - Boulders prevent further drilling |
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What is "rotary drilling" and what are it's advantages and disadvantages?
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- Rapid rotation of drill bit mounted on drill rods
- Cuts and breaks material at bottom of hole - Pump drilling fluid (water mixed w/ bentonite) and up annulus and drill rods - Fluid stabilises wall and cools drillbit Adv. - Drills most rock formations - Water and mud support drilling - Fast - Possible above and below water table - Possible to drill >40m Disadvan. - Costly - Water required for pumping - Problems with boulders - Careful operation and maintenance |
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Why are samples required..? (2)
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- Carry out soil classification test
- Determine soil engineering design parameters: STRENGTH COMPRESSIBILITY PERMEABILITY |
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Samples should be..? (3)
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- Representative of ground from which they are taken
- Large enough to represent, (i) particle sized (ii) fabric (iii) fabric (iv) fissuring (v) fracturing - subjected to little disturbance where strength and compressibility tests are planned |
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Types of samples (2)
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Undisturbed soil:
- High quality - Blocks or driving tubes to gather samples - Permeability, compressibility, shear strength tests - Difficult to obtain in sand Disturbed soil samples: - Taken from cuttings from drilling - Used for classification tests |
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Factors that make an undisturbed soil sample hard to obtain (8)
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1/ Unloaded from the in situ confining pressures
2/ Volume displacement of the tube 3/ Friction on the sides of the collection device 4/ Unknown changes in the water content 5/ Loss of hydrostatic pressure 6/ Handling and transporting 7/ Quality of attitude of drilling crew 8/ Hot or cold days |
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Factors affecting the disturbance degree of undisturbed sample (4)
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1/ Area ratio
2/ Cutting edge taper angle 3/ Inside clearance 4/ Sampler driving methods |
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What does increasing area ratio give (2) and what does the permissible area ratio depend upon (4)?
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Increasing area ratio:
- Increased soil disturbance and remoulding - Increased penetration resistance Permissible area ratio dependant upon: - Soil type - Soil strength - Soil sensitivity - Purpose of sampling Reasonable area ratio ~ 10% |
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Why would you have a cutting edge taper angle?
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The practical need for a large area ratio can be compensated for by the use of a small cutting edge taper angle.
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What is the purpose of the inside clearance?
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Inside clearance should gives the soil sample room for partial swelling and lateral stress reduction but not allow the loss of the sample when withdrawing the sample tube.
It reduces the adhesion between the soil and the inside of the sample tube which may prevent further soil entering the tube. |
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SPT split spoon properties (5)
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- Thick-walled
- Obtaining disturbed samples - Threaded on both ends and split lengthwise. Driving shoe / head hold together - Spring basket-type sample retainer - Driven with weight hammer |
