18 Questions
What is the purpose of driving the sampler into the soil using hammer blows in the Standard Penetration Test?
To create a borehole for sampling
Why is the first 15 cm drive in the SPT considered as seating load and ignored?
To account for the initial compression and disturbance of the soil
Why are split spoon samples taken at intervals of 1.5 m during soil sampling?
To prevent disturbance in deeper layers during sampling
What parameter is determined by taking the average N-value from each 1.5 m in the Standard Penetration Test?
Final SPT N-value
In the 2V:1H method, what does '2V' represent?
Vertical effective stress
What is a key advantage of using site investigation techniques like the Standard Penetration Test?
Identifying potential foundation issues
What is the purpose of using test pits in site investigation?
To visually inspect subsurface conditions in their natural state
In foundation engineering, what is the maximum depth limit for test pits?
18-20 feet
When is auger boring considered suitable for site investigation?
Only in cohesive soils below the groundwater table
What is the function of hollow stem augers in site investigation?
To use for sampling or conducting tests
Which technique permits sampling/testing on exposed surfaces during site investigation?
Test pits
What is the main advantage of using test pits over boreholes during site investigation?
Permits visual inspection of natural conditions
What is the primary objective of wash boring in foundation engineering?
To create a borehole by using a casing and drilling with water or mud.
What is the main difference between mud rotary drilling and core drilling?
Mud rotary drilling uses a core barrel with a drill bit, while core drilling is used for rock cores.
Which method involves grinding the soil by lifting and dropping heavy chisels or bits?
Percussion Drilling
What tool is commonly used for obtaining rock cores in foundation engineering?
Tricone drill bit
In wash boring, how is soil loosened and removed from the borehole?
By jetting water or drilling mud under pressure and allowing it to settle at ground level.
Which site investigation technique involves hollow drill rods with a rotating drill bit and continuous pumping of drilling mud?
Mud rotary drilling
Study Notes
Standard Penetration Test (SPT)
- 1.5 m are drilled using a drilling machine
- The sampler is driven into the soil by hammer blows to the top of the drill rod
- Standard weight of the hammer is 622.72 N (63.48 kg), and for each blow, the hammer drops at a distance of 76.2 cm
- Number of blows required for a spoon penetration of three 15 cm intervals are recorded
- First 15 cm drive is considered as seating load and is ignored
- Number of blows required for the last two intervals are added to give the SPT N-value at that depth
Site Investigation and Borehole Depth
- Site investigation is necessary for a structure of 100 m length and 70 m width
- Soil profile is required to determine the approximate depth of borehole
- Assuming a uniform pressure of 200 kPa on the surface of the soil and γw = 10 kN/m3, the approximate depth of borehole can be calculated
Methods of Boring
- Test Pits: permits visual inspection of subsurface conditions in natural state
- Maximum depth limited to 18-20 ft
- Especially useful for gravelly soil where boreholes may be difficult
- Sampling/testing done on exposed surfaces
- Auger Boring: simplest method of exploration and sampling
- Power-driven or hand-operated
- Maximum depth of 10 m
- Suitable in all soils above ground water table but only in cohesive soil below ground water table
- Hollow stem augers used for sampling or conducting Standard Penetration Tests
- Wash Boring: uses a casing driven with a drop hammer and a hollow drill rod with chopping bit
- Soil is loosened and removed from the borehole using water or a drilling mud jetted under pressure
- Also known as mud rotary drilling (soil) or core drilling (rock)
- Percussion Drilling: grinding the soil by repeated lifting and dropping of heavy chisels or drilling bits
- Water is added to form slurry of cuttings
Test your knowledge on the Standard Penetration Test (SPT) used in foundation engineering. Learn about the process of driving a sampler into soil using hammer blows and understand the significance of the results obtained.
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