A standard penetration test has been conducted on a coarse sand at a depth of 16 ft below the surface. The blow counts obtained in the field were as follows: 0-6 in. (4 blows), 6- 12 in. (6 blows), and 12-18 in. (6 blows). The tests were conducted using a USA-style donut hammer in a 6 in. diameter boring using a standard sampler with the liner installed. The vertical effective stress at the test depth was 1500 lb.ft’. Determine N1.
A standard penetration test has been conducted on a coarse sand at a depth of 16 ft below the surface. The blow counts obtained in the field were as follows: 0-6 in. (4 blows), 6- 12 in. (6 blows), and 12-18 in. (6 blows). The tests were conducted using a USA-style donut hammer in a 6 in. diameter boring using a standard sampler with the liner installed. The vertical effective stress at the test depth was 1500 lb.ft’. Determine N1.
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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![### Standard Penetration Test in Coarse Sand
**Context:**
A standard penetration test (SPT) was conducted to assess soil properties in coarse sand at a depth of 16 feet below the surface. The SPT is a widely used method for estimating the density and mechanical properties of subsurface materials, typically in geotechnical engineering and soil mechanics.
**Procedure and Results:**
- **Testing Depth:** 16 feet below ground level
- **Blow Counts (N-values):**
- 0-6 inches: 4 blows
- 6-12 inches: 6 blows
- 12-18 inches: 6 blows
- **Total Blow Count:** The sum of the blow counts is 4 + 6 + 6 = 16 blows.
- **Equipment Used:**
- **Hammer Type:** USA-style donut hammer
- **Borehole Diameter:** 6 inches
- **Sampler:** Standard sampler with liner installed
- **Soil Condition:**
- **Vertical Effective Stress:** 1500 pounds per square foot (lb/ft²)
**Objective:**
Determine the corrected blow count, \( N_{60} \) which accounts for the overburden pressure and hammer energy efficiency adjustments.
**Explanation:**
The **Standard Penetration Test (SPT)** measures the resistance of soil to penetration by a standard sampler driven into the ground by a series of hammer blows. The number of blows required to drive the sampler a certain distance (typically 18 inches) is recorded as the blow count (N-value). This value helps in evaluating soil properties such as density, strength, and compaction.
To calculate the corrected SPT N-value, known as \( N_{60} \), adjustments are made to the raw N-value to account for factors like:
1. **Energy Efficiency:** Different hammers and procedures might deliver energy differently to the sampler. The correction factor typically used is 0.6 for a donut hammer.
2. **Overburden Pressure:** The effective stress at the test depth influences the resistance of the soil.
To determine \( N_{60} \):
\[ N_{60} = N \times (E_r / 60) \]
where \( N \) is the raw N-value (cumulative blow count for the last 12 inches of penetration), and \( E_r \) is the hammer energy ratio, assumed to be 60%](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F24dbfb66-daf6-4b8e-a748-b5c870ef5592%2Fdd1dd9ed-fc45-4ca3-aa4c-e5ff6e0a875e%2Fh59n0et_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Standard Penetration Test in Coarse Sand
**Context:**
A standard penetration test (SPT) was conducted to assess soil properties in coarse sand at a depth of 16 feet below the surface. The SPT is a widely used method for estimating the density and mechanical properties of subsurface materials, typically in geotechnical engineering and soil mechanics.
**Procedure and Results:**
- **Testing Depth:** 16 feet below ground level
- **Blow Counts (N-values):**
- 0-6 inches: 4 blows
- 6-12 inches: 6 blows
- 12-18 inches: 6 blows
- **Total Blow Count:** The sum of the blow counts is 4 + 6 + 6 = 16 blows.
- **Equipment Used:**
- **Hammer Type:** USA-style donut hammer
- **Borehole Diameter:** 6 inches
- **Sampler:** Standard sampler with liner installed
- **Soil Condition:**
- **Vertical Effective Stress:** 1500 pounds per square foot (lb/ft²)
**Objective:**
Determine the corrected blow count, \( N_{60} \) which accounts for the overburden pressure and hammer energy efficiency adjustments.
**Explanation:**
The **Standard Penetration Test (SPT)** measures the resistance of soil to penetration by a standard sampler driven into the ground by a series of hammer blows. The number of blows required to drive the sampler a certain distance (typically 18 inches) is recorded as the blow count (N-value). This value helps in evaluating soil properties such as density, strength, and compaction.
To calculate the corrected SPT N-value, known as \( N_{60} \), adjustments are made to the raw N-value to account for factors like:
1. **Energy Efficiency:** Different hammers and procedures might deliver energy differently to the sampler. The correction factor typically used is 0.6 for a donut hammer.
2. **Overburden Pressure:** The effective stress at the test depth influences the resistance of the soil.
To determine \( N_{60} \):
\[ N_{60} = N \times (E_r / 60) \]
where \( N \) is the raw N-value (cumulative blow count for the last 12 inches of penetration), and \( E_r \) is the hammer energy ratio, assumed to be 60%
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