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**What Is SPT Test**?

**The Standard Penetration Test (SPT Test**) is one type of **in-situ soil test** and It is conducted to determine the **geotechnical engineering **properties of **subsurface soils**, especially for cohesionless soil.

**SPT Test** is most widely used to check various **parameters and properties of soil on the construction site**. For any building foundation, design and construction **soil testing** are essential.

The test is extremely useful for determining the** bearing capacity, density, and angle of shearing resistance of any soil.** It can be used to determine the properties of **cohesive **and **cohesionless **soil. The **Standard Penetration** **Test ASTM D1586-11**

## Significance Soil Penetration Test

**By performing an SPT test we can find out,**

- Angel of
**shearing**resistance of**cohesionless soils**. - The relative
**density**of**cohesionless**soils. **Unconfined**compressive**strength**of**cohesive**soils.

**Purposes of Standard Penetration Test**

**The spt test is conducted mainly for two purposes,**

- Soil
**sample**to identify the type and**nature**of the**soil**at various**depths**. - To
**determine**penetration**resistance**of soil at**various depths**this is used for geotechnical design**purposes**.

**Standard Penetration Test Equipment**

**Following are the equipment used for the spt test,**

**1. Drilling Equipment**

We can use any **drilling equipment **which provides a **good **and clean **borehole**, which is at least** 5mm** larger than the **Split Spoon Sampler**.

**2. Split Spoon Sampler**

This is a **thick**–**walled **sample tube. The **split spoon sampler **has an outer **diameter **of it is **50.8 mm** and an **inside diameter **is **35 mm** with a length of around **650 mm** (26 inches).

This **tool **has an assembly of a steel tube, **coupling**, driving shoes, a **check valve**, and **venting ports**. The **split spoon sampler **collects only disturbed soil **samples**.

**3. Drop Hammer**

This **tool **is used to **drive **the **sampler **into the **borehole**. The mass of it is **63.5 kg** (140 lb).

**4. Driving Head (Anvil)**

It is **used **to stop the **hammer **on a **certain **point.

**5. Guiding Rod**

The **Guiding rod **just guides the **hammer **to the anvil.

**Standard Penetration Test Procedure**

**Spt Test procedure on site as follows,**

### 1. **Dig Starting Bore Hole**

First, dig the **starting **borehole with **boring equipment**.

Before **conducting **the test, we have to decide the **total depth **of **penetration **bore and **depth interval **to carry the test and **collect **the **sample **the same.

Let’s take **borehole **depth up to** 10m**. (Generally, depth of bore is up to **groundwater **table or up to **hard strata **below ground surface.)

We can decide the **intermediate **test depth of every **1m. **So, SPT is **conducted **at every one meter of **boring **below ground level and soil **samples **are **collected **at the same **depth**.

**2. Assemble the Sampler**

Once the **boring **of the hole is **done **up to **desired depth **(1 m depth we decided) **remove **the drilling tools from the **borehole **and clean all the **disturbing materials**.

After that fit the **soil sampler **named as **split spoon sampler **with the **drilling rod **and **lower **it into the **borehole**.

Now, the rest **split spoon sampler** attracted with **drilling **rod at **bottom **of the **drilled borehole **of undistributed **soil**.

**3. Assemble Equipment**

As we place the **sampler **rest on the **bottom **of the **borehole**, it’s time to conduct the **SPT test**.

Keep ready test **equipment **the Hammer, Anvil, and **guiding rod **and **assemble **them with each other **properly**.

Mark the **distance **of **150mm** on the drilling rod to observe **penetration details**.

**4. Conduct SPT Test**

**Firstly **drive the **drop hammer **on the bottom of a **borehole **by blows from the slide **hammer with a mass of 63.5 kg** falling through a **distance of 750 mm (30 in)** at the rate of **30 blows per minute**.

Now, Count the **number **of blows **required **to reach or **drive depth of 150 mm (6 in).**

**Similarly**, again **drive sampler **in soil and **count **the blows needed to **penetrate **the **second **and **third **150 mm (6 in).

In this test, the **total sum **of the number of blows **required **to drive the sampler **150mm** (6 in.) of **penetration **is termed the “**standard penetration resistance” or the “N-value“.**

If the **sampler **is driven less than** 450 mm **(total), then the **“N-value” **shall be for the **300 mm of penetration (if less than 300 mm is penetrated, then the **report should specify the number of blows and the depth penetrated).

If a number of **blows **are required to drive the **sampler **to a depth of **150 mm excess of the value 50**, it is **considered **as a refusal and the test is **discontinued**.

The **entire **sampler may sometimes sink under its **own weight **when a very soft sub-soil stratum is **encountered**. Under such **situations**, it may not be **necessary **to give any blow to the **sampler **and “N-value” should be **indicated **as **zero**.

The **Test **shall be made at **every change **in the stratum or at **intervals **of not more than **1.5 meters** whichever is less. The test may be **made **at lesser intervals if **necessary **or **specified**.

**5. Soil Sample Collection**

Now, **collect **the **soil** **sample **from the **borehole**,

- Take out a
**spilt sampler**from the**borehole**. - Carefully,
**separate**the split spoon sampler from the**drilling rod**and**remove**any**excess**soil from the**bottom**, also**drain water**if it contains. - Slowly open the
**one side**of the**split spoon sampler**to expose**fresh material**and any**stratification**. - Record the
**length**, composition, color,**stratification**, and condition of the**sample**. **Remove**soil specimen from**split spoon**sampler and**pack it in a plastic bag.**

**How to Find Bearing Capacity of Soil from SPT Test Result**

**The following are the step to find the bearing capacity of soil from SPT Values or standard penetration test calculation.**

**Step: 1 Take Average of Penetration Value**

Make **necessary **correction **SPT values** and take an average of **corrected **SPT **values **from the base level of **foundation **to a depth equal to 2 times the **width of the foundation.**

**Step: 2 Find our Angle of Shearing Resistance**

**Find out **the angle of **sharing **resistance by **correlating **the above **SPT values** from a **given graph**.

**Step: 3 Find out Effective Surcharge**

**Find out** the value of effective **surcharge **by multiplying the **effective **unit **weight **of **soil **with the depth of the **foundation **i.e.

**q = ϒ*Df**

Where,

**q = Effective surcharge at foundation base level, in kgf/cm2**

**ϒ = Unit weight of soil, in kgf/cm3**

**Df = Depth of foundation, in cm**

**Step: 4 Find out Bearing Capacity Factor**

**Calculate** the corresponding values of **bearing capacity **factors (i.e. Nq & Nϒ) by correlating the **values **of angle of **shearing resistance **from the table **given below**. For any **intermediate value **of ‘ϕ’, make linear **interpolation**.

### **Step: 5 Find Out Shape Factor**

**Calculate shape factors (i.e. sq & sϒ) using the formula given below.**

Where,

**B = Width of foundation, in cm**

**L = Length of foundation, in cm**

**Step: 6 Find Out Depth Factor**

**Calculate depth factors (i.e. dq & dϒ) using the following formula.**

**dq=dϒ=1 (for ϕ < 100)**

**dq = dϒ = 1+0.1(Df/B)(Nϕ)1/2 (for ϕ>100)**

**Nϕ is calculated using the following formula**

**Nϕ = tan2[(π/4)+(ϕ/2)]**

**Step: 7 Calculate Inclination Factor**

**Calculate inclination factors (i.e. iq & iϒ) using the formula given below**

Where,

**α = Load inclination to the vertical in degrees**

**ϕ = Angles of shearing resistance in degrees**

**Step: 8 Calculate Correction Factor**

Find out the **correction **factor for the **location **of the water table **using **the **following formula**

**W’ = 0.5+0.5[Dw/(Df+B)]**

Where,

**W’ = Water table correction factor**

**Dw = Depth of water table, in cm**

**Df = Depth of foundation, in cm**

**Step: 9 Calculate Bearing Capacity of Soil:**

**Calculate net ultimate bearing capacity by using the below equation.**

Where,

**qd = It is Net ultimate bearing capacity of foundation (kgf/cm2)**

**q = Effective surcharge at base level of foundation, in kgf/cm2 (Refer step-3)**

**Nq & Nϒ = Bearing capacity factors (Refer step-4)**

**sq & sϒ = Shape factors (Refer step-5)**

**dq & dϒ = Depth factors (Refer step-6)**

**iq & iϒ = Inclination factors (Refer step-7)**

**W’ = Correction factor for the location of the water table (Refer step-8)**

**B = Width of foundation, in cm**

**ϒ = Foundation soil bulk unit weight, in kgf/cm3.**

## Standard Penetration Test Lab Manual

**Free download standard penetration test lab manual from below link,**

**SPT Test Report**

**Free download standard penetration test lab report** or **spt test report format from below link,**

**You May Also Like:**

**Specific Gravity of Soil Test with Sample Report****11 Soil Stabilization Methods & Their Use****Water Content of Soil Test – Procedure, Result & Report****Bearing Capacity of Soil & Suitability of Foundation**

## FAQs: SPT Test

### Soil Penetration Test

**The Standard Penetration Test (SPT**) is one type of **in-situ soil test** and It is conducted to determine the **geotechnical engineering properties of subsurface soils**, especially for cohesionless soil. **SPT Test** is most widely used to check various **parameters and properties of soil on the construction site**. For any building foundation, design and construction **soil testing** are essential.

### Standard Penetration Test Equipment

**SPT Test required following equipment,**

Drilling Equipment

Split Spoon Sampler

Drop Hammer

Driving Head (Anvil)

Guiding Rod

### Standard Penetration Test Procedure

**SPT test procedure as follows,1. Dig Starting Bore Hole** up to 1m first..

**2. Assemble the Sampler:**Fit the soil sampler named as split spoon sampler with the drilling rod and lower it into the borehole.

**3. Assemble Equipment:**Keep ready test equipment the Hammer, Anvil and guiding rod and assemble them with each other properly.

**4. Conduct SPT Test**: Firstly drive the drop hammer on the bottom of a borehole by blows from the slide

**hammer with a mass of 63.5 kg**falling through a

**distance of 750 mm (30 in)**at the rate of 30 blows per minute. Count the numbers of blow required to reach or

**drive depth of 150 mm (6 in).**

**5. Soil Sample Collection**: Now, collect the soil sample from the borehole,

### What Is n Value

The **number of blows** required by **hammer to dig 30 cm depth** in **SPT test** is known as **N- Value of Soi**l. The measured** N-value **is also called **standard penetration resistance of the soil. **

### SPT Test IS Code

The standard penetration test conducted as per **IS -2131:1963**

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Abhik GhoshThe Standard Penetration Test ASTM E1105, is not the right reference, Standard Penetration Test ASTM D1586-11 is the right reference for the code, please he a look at it.

Thanking you.