Spt soil test

Types of spt soils tests

The Standard Penetration Test (SPT) is a common in situ geotechnical soil investigation technique to obtain soil samples and determine the soil strata's consistency, features, and bearing capacity. It is part of a soil exploration series carried out by contractors, construction companies, and geotechnical engineers to discover the soil's capability to support a proposed construction project. The decision on what kind of foundation should be used for a construction project is influenced by the results from the SPT soil test.

SPT soil testing apparatus comprises a drive assembly with a hammer and anvil system, a split spoon sampler, a drive head, extension rods, and a coupling system. The Drive assembly is fixed into the soil at the required depth using a hammer that weighs about 63.5 cm and drops from a height of 1.5 m. This is repeated until the last two strikes penetrate the soil further into the ground. The depth at which this occurs is recorded as the N-value, and it is further analyzed to determine whether the soil is cohesive, granular, or mixed, its level of liquefaction, and the SPT boundary lines.

While SPT soil tests

may provide critical information about the soil, they also have some downsides. Getting continuous soil samples at regular intervals can be pretty expensive, and some experts have pointed out that the SPT's correlations and assumptions are not accurate representations of the soil's behavior. Several alternatives are available for the SPT soil test, like the Penetration / Cone Penetration Test (CPT), Vane Shear Test, Weigh Boring Test, Field Pump Test, Pressure Dilatometer Test, etc. These may or may not have the same economic implications and limitations as the SPT test.

Specifications and maintenance of SPT soils tests

SPT soil test specifications

• Depth: The SPT soil test's depth varies with the geographic area and soil conditions. Typically, the SPT soil test examines the soil up to 15 m in depth from the ground surface. For further research, other techniques can be employed in conjunction with the SPT.
• Sampling: In the SPT soil test, disturbed soil samples are collected for laboratory analysis. These samples help determine soil characteristics, such as soil composition, consistency, and moisture content.
• Strike blow: In SPT, the soil resistance is measured by striking the soil sampler with a hammer weighing 63.5 kg (140 pounds) dropped from a height of 76 cm (30 inches). The number of blows required to drive the sampler 30 cm (12 inches) into the soil is recorded as the SPT.
• SPT N-values: The blow count of the SPT soil test is usually normalized as N-values. SPT N-values help classify soil types and assess their engineering properties. The N-values are affected by many factors, including soil composition, gradation, moisture content, and density.
• SPT correlation with soil parameters: The SPT N-value is correlated with various soil parameters such as soil shear strength, soil bearing capacity, soil consistency, etc. These correlations provide an empirical basis for assessing the engineering properties of the soil, which is helpful for foundation design and stability analysis.

Maintenance

• Coating: It is important to regularly clean and maintain the coatings on testing instruments and equipment to ensure their effectiveness and protect against corrosion and wear.
• Calibration: The accuracy of test results can be ensured by regularly calibrating and maintaining testing instruments and equipment to meet the required standards and tolerances.
• Cleaning: To avoid cross-contamination or interference, cleaning and decontaminating the testing site's surfaces and equipment is essential before and after conducting tests. Soil samples should also be handled with care and preserved properly to maintain their integrity and prevent contamination.
• Record-keeping: It is good practice to keep records of soil test results, equipment maintenance, and any calibration performed for future reference and quality control purposes.

Scenarios of SPT soil tests

• Civil engineering

  In civil engineering, SPT data are important in determining the solidity, stability, and load-bearing capacity of soil for constructing buildings, bridges, and roads. They help in ensuring that structures are built on safe and appropriate foundations.

• Environmental assessments

  SPT soil tests help in pollution detection and risk appraisal in environmental contexts by determining the kind and position of pollutants in the soil. This is crucial for the design of suitable remediation strategies and for protecting human health and the environment.

• Geotechnical investigations

  SPT tests provide data for soil classification, shear strength, consolidation parameters, and other geotechnical properties. Such information is vital for designing foundations, retaining structures, slopes, and other geotechnical engineering solutions.

• Mining

  In mining operations, SPT tests can assist in evaluating soil properties and determining the stability of slopes and excavations. This helps in ensuring safe mining practices and managing environmental impacts.

• Landfill construction

  SPT tests can help in assessing soil stability and settlement characteristics when constructing landfills. The data obtained from the tests aid in designing landfill systems that minimize environmental risks and control settlement behavior.

• Hydraulic engineering

  SPT tests are significant in hydraulic engineering for determining soil parameters related to hydraulic structures such as dams, levees, and bank revetments. The soil profile and its engineering properties obtained from SPT testing are crucial for the stability and safety of these structures.

How to choose SPT soil tests

When purchasing SPT soil test equipment, it is important to look at several parameters and make a well-informed decision.

• Procurement

  The first step in selecting an SPT testing apparatus is to identify reliable manufacturers, dealers, and suppliers of this tool. Conducting thorough research to find individuals who sell quality products can make purchasing this device simpler.

• Device catalog

  Once procurement sources have been identified, it's important to go through the catalog of devices they offer, especially the SPT soil test device. At this point, it's crucial to consider various models of the SPT device, which are usually presented with their distinguishing features and benefits.

• Quality assurance

  It's important to ensure the quality of the SPT soil test device by considering its characteristic features. Other than the model and manufacturer, customers need to ensure their selected SPT device is durable and reliable. Thus, it must provide lengthy service and exact soil test results. A good way to know about a device's quality is to look at the reviews written about it online.

Q&A

Q1: How do SPT hammers work?

A1: The SPT is performed by dropping a 63.5 kg weight through a height of 3.05 m onto the sampler. The sampler is then driven into the ground using the blows of the hammer.

Q2: What is the difference between SPT and CPT?

A2: The standard penetration test (SPT) is a dynamic test. On the other hand, the cone penetration test (CPT) is a static pressure measurement test. As a result, SPT soil tests are generally faster than CPT. However, the CPT test provides more detailed soil information.

Q3: What types of soil can SPT provide samples from?

A3: The SPT can be conducted in cohesive and granular soils. Additionally, it can be performed in gravel, water, and hard rock.

Q4: How are SPT results interpreted?

A4: Knowing the parameters of the soil is very important for the stability analysis and calculation of the foundation. The number of blows recorded for each strata is referred to as a straight N value. It is used to estimate soil density and bear capacity.