Standard Penetration Test (SPT) for Drillers

British Drilling Association
30 Mar 202315:44

TLDRThe Standard Penetration Test (SPT) is a critical method for assessing soil characteristics, essential in structural design. This video outlines the equipment, calibration, and procedures for conducting an SPT, emphasizing the importance of proper maintenance and adherence to standards (BS EN ISO 22476-3). It details the use of specific hammers, drill rods, and the process of penetration recording, highlighting safety and accuracy in testing.

Takeaways

  • 🔨 The Standard Penetration Test (SPT) is a method used for sampling sands, developed in the early 1900s and now has a dedicated standard (BS EN ISO 22476-3).
  • 🏗️ The SPT requires a 63.5 kg weight dropped from a height of 760 mm onto an anvil, with the entire assembly not exceeding 115 kg.
  • 🛠️ Two common types of equipment used in the UK are the automatic triphammer (standard drop hammer) and the hydraulic hammer.
  • 🔩 The correct size of drill rod should be used, with an ideal AB-sized rod of about 50 mm diameter and a weight not exceeding 10 kg per meter.
  • đź’ˇ Proper maintenance and safety checks of the SPT equipment are crucial, including daily inspections and refraining from using damaged or poorly maintained equipment.
  • đź“Ź The straightness and verticality of the test string affect the test results, and a centralizer or top clamps can help maintain alignment.
  • đź“ť Accurate recording of test depth, borehole depth, casing depth, water level, and rod markings is essential for reliable results.
  • 🔩 The seating drive and main drive increments should be recorded, with refusal noted if penetration is not achieved within specified blow limits.
  • 🔄 In strong materials where the hammer bounces on impact, the test should be terminated immediately, and the refusal depth noted without recording an N value.
  • 🔄 For design purposes, the energy ratio of the hammer must be determined and recorded, with recalibration required at least every 12 months.

Q & A

  • What is the Standard Penetration Test (SPT)?

    -The Standard Penetration Test (SPT) is a method developed in the early 1900s for sampling sands and later evolved into a test used for determining the ground's material characteristics across various materials.

  • What is the dedicated standard for carrying out the SPT?

    -The dedicated standard for carrying out the SPT is BS EN ISO 22476-3.

  • What are the two common types of equipment used for SPT in the UK?

    -The two common types of equipment used for SPT in the UK are the automatic triphammer (also known as a standard drop hammer) and the hydraulic hammer.

  • What is the weight and height specification for the SPT hammer?

    -The SPT requires a 63.5 kilogram weight to be dropped over a 760 millimeter height onto an anvil.

  • What is the maximum weight allowed for the entire SPT assembly?

    -The entire SPT assembly should not weigh more than 115 kilograms.

  • What is the ideal size for the drill rod used in SPT?

    -The ideal drill rod for SPT is an 'N'-sized rod of around 50 millimeters diameter, with a weight not exceeding 10 kilograms per meter.

  • How often should the straightness of the rods be checked?

    -The straightness of the rods should be checked at least every 20 tests.

  • What is the purpose of using a centralizer or closing the top clamps during the SPT?

    -Using a centralizer or closing the top clamps helps to keep the rod centrally aligned within the borehole, preventing side-to-side movement or wobbling of the drill string for more consistent and reliable results.

  • What should be done if the SPT hammer is poorly maintained or not functioning correctly?

    -If the SPT hammer is poorly maintained or not functioning correctly, it should not be used and should be replaced or immediately refurbished.

  • What is the significance of the N-value in the SPT?

    -The N-value represents the number of blows required for the test to achieve a 300 millimeter penetration, and it is used to help define the ground's material characteristics for structural and foundation design purposes.

  • How often should the energy ratio of the SPT hammer be determined and recorded?

    -The energy ratio of the SPT hammer should be determined and recorded at a minimum every 12 months.

Outlines

00:00

🔨 Introduction to Standard Penetration Test (SPT)

This paragraph introduces the Standard Penetration Test (SPT), a method developed in the early 1900s for sampling sands. It explains the evolution of SPT into a widely used test with a dedicated standard, BS EN ISO 22476-3. The video aims to examine the requirements set by the standard regarding equipment, calibration, maintenance, pre-test checks, test procedure, and reporting. It emphasizes the importance of using the correct equipment, such as a 63.5 kg weight dropped from a 760 mm height onto an anvil, and the types of drilling machines that can be used for SPT. The paragraph also discusses the significance of the test in determining the ground's material characteristics, which are crucial for designing structures and foundations.

05:03

đź›  Equipment and Maintenance for SPT

This paragraph delves into the specifics of the equipment used for SPT, including the types of hammers (automatic triphammer and hydraulic hammer), drill rods, and the importance of their proper weight and size. It highlights the need for regular inspection and maintenance of the equipment, especially hydraulic hammers, and the safety measures to be taken while using the SPT hammer. The paragraph also addresses the potential issues with poorly maintained equipment and the impact on test results. It stresses the importance of using straight rods and the methods for checking rod straightness, as well as the proper use of centralizers to ensure consistent, reliable results.

10:04

đź“Ź Conducting and Recording the SPT

This paragraph outlines the process of conducting and recording a Standard Penetration Test. It details the steps involved, starting from checking the borehole cleanliness and measuring its depth, to lowering the test string and marking the rods with increments. The paragraph explains the procedure for the seating drive and the main or test drive, including the number of blows required for each increment and how to record refusals. It also describes the actions to be taken if self-weight penetration or bouncing occurs. The paragraph concludes with the proper handling of the hammer and test string after the test, the use of SPT split spoons and cones for different materials, and the importance of accurate recording and labeling of test results and samples.

15:05

đź“‹ Final Remarks and Guidance on SPT

In the final paragraph, the video script provides a summary of the key points discussed about the Standard Penetration Test. It reiterates the importance of understanding the process, using well-maintained equipment, and following the standard procedures for accurate results. The paragraph also mentions the necessity of having the hammer's energy ratio determined and recorded, especially for SBT equipment used for design purposes. It advises on the frequency of calibration and the signs of a poorly operating or maintained hammer. The video ends with guidance on how to obtain further information or assistance and extends well wishes to the viewers for their SPT endeavors.

Mindmap

Keywords

đź’ˇStandard Penetration Test (SPT)

The Standard Penetration Test (SPT) is a widely used geotechnical field test that measures the resistance encountered by a drill string when driven into the ground by a standard drop hammer or hydraulic hammer. It is essential for determining soil conditions and is critical for the design of foundations and structures. In the video, the SPT is discussed in detail, including its methodology, equipment used, and the importance of following the dedicated standard, BS EN ISO 22476-3, for accurate results.

đź’ˇAnvil

An anvil is a heavy block of metal that is used in the SPT to absorb the impact of the dropped weight. It is a crucial component of the test assembly and must be securely attached to the drill string. The anvil's function is to transfer the energy from the falling weight to the drill string, thereby penetrating the ground. The video emphasizes the importance of using a manufacturer's approved role or cell lock pin with rubber dampeners on both sides of the cell lock pin to ensure the anvil's proper attachment.

đź’ˇDrill Rod

A drill rod is a long, cylindrical tool used in drilling operations to transmit torque and weight from the drilling machinery to the drill bit. In the context of the SPT, the drill rods must conform to specific weight and size requirements, with an ideal diameter of around 50 millimeters and a weight not exceeding 10 kilograms per meter. The drill rods play a vital role in the SPT as they are the means by which the test weight is delivered to the anvil.

đź’ˇHydraulic Hammer

A hydraulic hammer is a type of equipment used in the SPT that operates using a chain-driven mechanism to lift and drop the test weight. It is commonly found on rotary and dynamic sampling machines. The hydraulic hammer's function is to apply the necessary force to drive the drill string into the ground, and it is an alternative to the standard drop hammer. The video discusses the proper use and maintenance of hydraulic hammers, emphasizing their importance in achieving accurate SPT results.

đź’ˇPre-test Checks

Pre-test checks are the initial inspections and preparations conducted before starting the SPT to ensure the equipment is functioning correctly and safely. These checks include verifying the calibration of the equipment, inspecting the drill rods for straightness and compliance with weight standards, and confirming the cleanliness of the borehole to the specified test depth. Pre-test checks are crucial for the accuracy and reliability of the SPT results.

đź’ˇTest Procedure

The test procedure refers to the series of steps followed during the SPT, which includes the seating drive, main drive, and recording of the number of blows required for each increment of penetration. The procedure is critical for obtaining consistent and reliable data about the soil's resistance to penetration. The video provides a detailed explanation of the test procedure, highlighting the importance of following the correct sequence of actions and accurately recording the results.

đź’ˇRefusal

In the context of the SPT, 'refusal' occurs when the drill string is unable to achieve the specified penetration depth within a set number of blows. For the seating drive, refusal is recorded if 25 blows fail to achieve 150 mm penetration, and for the main drive, refusal is noted if 50 blows do not result in 300 mm penetration. Refusal indicates that the soil is highly resistant, and this information is essential for understanding the ground's material characteristics.

đź’ˇN Value

The N value is a numerical result obtained from the SPT, representing the average number of blows required to achieve each 300 mm penetration during the main drive. It is an important parameter used in geotechnical engineering to assess soil conditions and design foundations and structures accordingly. The N value is calculated by adding up the blows for each increment and is used to characterize the soil's resistance to penetration.

đź’ˇDynamic Sampling Machine

A dynamic sampling machine is a type of drilling equipment that is specifically designed for soil sampling operations. It is used in conjunction with the SPT to collect disturbed samples from the ground. The machine typically includes a hydraulic hammer and other mechanisms to facilitate the drilling and sampling process. The video discusses the use of dynamic sampling machines in the SPT, including the attachment of the hydraulic hammer and the collection of samples in split spoons.

đź’ˇCalibration Report

A calibration report is a document that verifies the accuracy and performance of the SPT equipment, specifically the energy ratio of the hammer. It is essential for ensuring that the SPT results are reliable and can be used for design purposes. The report is typically completed at least every 12 months and includes an assessment of the hammer's drop height, weight, and the straightness of internal components. The video emphasizes the importance of regular calibration reports to maintain the integrity of the SPT equipment.

đź’ˇDriller's Log

A driller's log is a detailed record of the drilling process and the results obtained from the SPT. It includes information such as test depth, number of blows per increment, N value, casing depth, and water level. The driller's log serves as a critical document for geotechnical engineers and other stakeholders to analyze the soil conditions and design structures accordingly. The video outlines the importance of accurately recording all relevant data in the driller's log or data collection program.

Highlights

Standard Penetration Test (SPT) is a method developed in the early 1900s for sampling sands.

The SPT became a standardized test in the late 1940s and is used for all materials today.

The dedicated standard for SPT is BS EN ISO 22476-3.

SPT requires a 63.5 kg weight dropped over a 760 mm height onto an anvil.

The entire SPT assembly should not weigh more than 115 kg.

Two common types of equipment used in the UK are the automatic triphammer and the hydraulic hammer.

The ideal drill rod for SPT is an 'A' sized rod of around 50 mm diameter.

It's crucial to check the SPT hammer's safety, correct usage, and maintenance.

Hydraulic hammers should be inspected daily, and automatic hammers should be part of a daily machine inspection scheme.

The test results can be affected by variables such as equipment maintenance, driller's skill, and the straightness of the test string.

A centralizer or closing the top clamps can help keep the rod centrally aligned within the borehole.

The straightness of the rods should be checked at least every 20 tests.

The test string should be lowered to the base of the borehole with at least 450 mm above the datum point.

The seating drive and main drive are key parts of the SPT procedure, with specific increments and blow counts recorded.

If the main drive meets refusal, the depth penetrated is recorded but no N value is noted.

In strong materials, if the hammer bounces on impact, the test should be terminated immediately.

When a split spoon is used, a small disturbed sample is obtained and should be properly labeled and recorded.

The driller's log must have boxes for recalling all relevant information such as test depth, self-weight penetration, and the N value.

SPT equipment used for design purposes must have the energy ratio of the hammer determined and recorded.

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