Drilling Techniques

Question 1

What are the advantages and limitations of Test Pits?

Answer 1

Advantages:

• quick and cheap
• visual inspection and grab samples

Limitations:

• Depths of 4-5m
• no soil strength info

Question 2

What is the cost of Test Pits and how many can be done in a day?

Answer 2

~$1500/day, 5-10 test pits per day

Question 3

What are the advantages of using the solid-stem auger?

Answer 3

• relatively cheap
• simple to do
• provides soil samples
• reaches depths of 15m in soft soil
• can be used in conjunction with SPT or DCPT to provide strength info

Question 4

What are the limitations of using the solid-stem auger?

Answer 4

• limited depth
• doesn’t work in hard soils
• soil may become disturbed or will cave when changing to SPT attachment

Question 5

How much does a solid-stem & hollow-stem augers cost and how many holes per day?

Answer 5

~ $3000/day, 3-5 test holes

Question 6

What are the advantages of using the hollow-stem auger?

Answer 6

• relatively cheap
• depths of 15m in soft soils
• less potential for soil disturbance

Question 7

What are the limitations of using the hollow-stem auger?

Answer 7

• Slower than solid-stem auger
• can’t penetrate hard soils
• does not provide samples except where SPT’s are performed

Question 8

What are the advantages of sonic drilling?

Answer 8

• can penetrate hard/dense soils
• reaches depths greater than 50m
• can perform SPT but there may be disturbance
• provides a continuous core sample

Question 9

What are the limitations of sonic drilling?

Answer 9

• relatively expensive

- ground disturbance may affect SPT values

Question 10

How much does sonic drilling cost and how many holes per day?

Answer 10

~$7-10K/day. 1 or 2 test holes per day.

Question 11

What are the advantages of the Cone Penetration Test (CPT)?

Answer 11

• more accurate strength info than SPT

- can reach depths greater than 50m in ideal soft soils

Question 12

What are the limitations of the Cone Penetration Test (CPT)?

Answer 12

• no soil sample

- cannot penetrate dense ground

Question 13

How much does the Cone Penetration Test (CPT) cost and how many holes per day?

Answer 13

~$4000 and 2-3 holes per day.

Question 14

What are the advantages of the Dynamic Cone Penetration Test (DCPT)?

Answer 14

• provides continuous soil strength information

- auger carries rig, so no need to mobilize additional equipment

Question 15

What are the limitations of the Dynamic Cone Penetration Test (DCPT)?

Answer 15

• less accurate than CPT
• does not provide samples
• cannot penetrate dense earth

Question 16

What is the main advantage of the Shelby Tube?

Answer 16

Obtains a high quality “undisturbed” sample

Question 17

What are the limitations of the Shelby Tube?

Answer 17

• only used for soft to firm fine-grained soils

- usually costly and requires specific protocols to protect the samples during transportation

Question 18

Compare Index Tests to Direct Measurements

Answer 18

Index tests - general characteristics can be calculated through relationships, past experience and judgement (i.e. particle size)
Direct Measurement - measures properties (i.e. strength, compression) but requires an undisturbed sample

Question 19

What is the Split-Spoon sampler?

Answer 19

• A thick-walled tube that is hammered into the soil
• provides disturbed samples
• It is the most common method of collecting samples