Soil Testing
The standard penetration test (SPT) is an in-situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. It is done for exploatory bore holes for knwoing the sub soil strata.
The main purpose of the test is to provide an indication of the relative density of granular deposits, such as sands and gravels from which it is virtually impossible to obtain undisturbed samples. The great merit of the test, and the main reason for its widespread use is that it is simple and inexpensive. The soil strength parameters which can be inferred are approximate, but may give a useful guide in ground conditions where it may not be possible to obtain borehole samples of adequate quality like gravels, sands, silts, clay containing sand or gravel and weak rock.
The test uses a thick-walled sample tube, with an outside diameter of 50 mm and an inside diameter of 35 mm, and a length of around 650 mm. This is driven into the ground at the bottom of a borehole by blows from a slide hammer with a weight of 63.5 kg (140 lb) falling through a distance of 760 mm (30 in). The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is termed the "standard penetration resistance" or the "N-value". In cases where 50 blows are insufficient to advance it through a 150 mm (6 in) interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the ground, and it is used in many empirical geotechnical engineering formulae.
Plate loading test
Quick and easy to apply, the plate loading test checks the bearing capacity and settlement of foundation soil and substrate. It is used to ensure safe design and quality control.
The test applies a vertical load to a variety of specialist, steel bearing plates, measuring the penetration to determine the degree of compaction of back-fill, under-foundation or foundation soil, sand or stone.
Because it can be applied to thin soil layers, the test is mainly used in the construction of roads, airstrips and embankments or in the calculation of floor slabs.
The vertical load on the plate is applied using a hydraulic jack and counterweight. The resulting surface deflection or penetration of the plate is read after stabilization at three points spread over 120 degrees from a fixed frame. The average deflection is calculated and this allows the determination of the compression modulus or the modulus of subgrade reaction and spring constant.
Block Vibration test For a single massive foundation block, the majority of the damping would be due to radial or geometric damping provided by the surrounding soil. The effect of material damping within the foundation block itself would be likely much smaller than the effect of geometric damping.
When the soil-structure interaction is modeled by a single link, the damping input for such a link on the "Linear Link/Support Directional Properties" form is the actual damping in units of Force-Sec/Length (i.e. Force/Velocity). The damping assigned to the link should represent the actual radial damping. This approach is described in Wilson 2004.
The modal damping specified on the "Analysis Case Data - Linear Modal History" form would represent the material or structural damping provided by the foundation system itself.
Soil Resistivity Measurement Moisture content changes seasonally, varies according to the nature of the sub layers of earth, and the depth of the permanent water table. Since soil and water are generally more stable at deeper strata, it is recommended that the ground rods be placed as deep as possible into the earth, at the water table if possible. Also, ground rods should be installed where there is a stable temperature, i.e. below the frost line.
As you can see, four earth ground stakes are positioned in the soil in a straight line, equidistant from one another. The distance between earth ground stakes should be at least three times greater than the stake depth. So if the depth of each ground stake is one foot (.30 meters), make sure the distance between stakes is greater than three feet (.91 meters). The Fluke 1625 generates a known current through the two outer ground stakes and the drop in voltage potential is measured between the two inner ground stakes. Using Ohm's Law (V=IR), the Fluke tester automatically calculates the soil resistance.
Because measurement results are often distorted and invalidated by underground pieces of metal, underground aquifers, etc. additional measurements where the stake's axis are turned 90 degrees is always recommended. By changing the depth and distance several times, a profile is produced that can determine a suitable ground resistance system.
Soil resistivity measurements are often corrupted by the existence of ground currents and their harmonics. To prevent this from occurring, the Fluke 1625 uses an Automatic Frequency Control (AFC) System. This automatically selects the testing frequency with the least amount of noise enabling you to get a clear reading.
Field Density TestIn soil testing for civil construction, Field Density testing would be amongst the most common. Its purpose is to determine the Field Dry Density (in t/m3) and Moisture Content (as a %) of the material being tested. The Field Dry Density is usually compared with a laboratory compaction test of the same soil type, to produce a ratio between field and laboratory compaction. (See "Compaction" below)
Compaction testing as carried out in a soil testing laboratory is done to determine the Maximum Dry Density (t/m3) and the moisture content at which that is achieved known as the Optimum Moisture Content (%).
This data is used to compare to the Field Dry Density (see Field Densities above) to determine the Density Ratio and Moisture Variation.
Compactions are either performed as Standard or Modified and sometimes Oversized if the material being tested is of a larger particle size (rock).
Particle Size Distribution test results (or Gradings) are used for many reasons such as determining the compliance of manufactured gravels with required standards and specifications in the earthwork and concrete stages of construction works.
This Soil test is also part of the process used to classify a soil sample in conjunction with Atterburg Limits testing (see below).
Atterburg Limits cover a range of soil tests relating to reactivity to moisture (water), better known as Plasticity. These tests include Liquid Limit, Plastic Limit, Plasticity Index and Linear Shrinkage. Atterburg Limits play an important part when classifying soil types and work in conjunction with Particle Size Distribution tests (above).
Soil cohesion is vital for structures such as road embankments and the like. Civil Engineers often need to know if a soil will hold together satisfactorily on its own or whether it may need to be supported or even replaced. One group of soil tests used to determine cohesion properties of soils is called the Emerson Class.
The main purpose of the test is to provide an indication of the relative density of granular deposits, such as sands and gravels from which it is virtually impossible to obtain undisturbed samples. The great merit of the test, and the main reason for its widespread use is that it is simple and inexpensive. The soil strength parameters which can be inferred are approximate, but may give a useful guide in ground conditions where it may not be possible to obtain borehole samples of adequate quality like gravels, sands, silts, clay containing sand or gravel and weak rock.
The test uses a thick-walled sample tube, with an outside diameter of 50 mm and an inside diameter of 35 mm, and a length of around 650 mm. This is driven into the ground at the bottom of a borehole by blows from a slide hammer with a weight of 63.5 kg (140 lb) falling through a distance of 760 mm (30 in). The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is termed the "standard penetration resistance" or the "N-value". In cases where 50 blows are insufficient to advance it through a 150 mm (6 in) interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the ground, and it is used in many empirical geotechnical engineering formulae.
Plate loading test
Quick and easy to apply, the plate loading test checks the bearing capacity and settlement of foundation soil and substrate. It is used to ensure safe design and quality control.
The test applies a vertical load to a variety of specialist, steel bearing plates, measuring the penetration to determine the degree of compaction of back-fill, under-foundation or foundation soil, sand or stone.
Because it can be applied to thin soil layers, the test is mainly used in the construction of roads, airstrips and embankments or in the calculation of floor slabs.
The vertical load on the plate is applied using a hydraulic jack and counterweight. The resulting surface deflection or penetration of the plate is read after stabilization at three points spread over 120 degrees from a fixed frame. The average deflection is calculated and this allows the determination of the compression modulus or the modulus of subgrade reaction and spring constant.
Block Vibration test For a single massive foundation block, the majority of the damping would be due to radial or geometric damping provided by the surrounding soil. The effect of material damping within the foundation block itself would be likely much smaller than the effect of geometric damping.
When the soil-structure interaction is modeled by a single link, the damping input for such a link on the "Linear Link/Support Directional Properties" form is the actual damping in units of Force-Sec/Length (i.e. Force/Velocity). The damping assigned to the link should represent the actual radial damping. This approach is described in Wilson 2004.
The modal damping specified on the "Analysis Case Data - Linear Modal History" form would represent the material or structural damping provided by the foundation system itself.
Soil Resistivity Measurement Moisture content changes seasonally, varies according to the nature of the sub layers of earth, and the depth of the permanent water table. Since soil and water are generally more stable at deeper strata, it is recommended that the ground rods be placed as deep as possible into the earth, at the water table if possible. Also, ground rods should be installed where there is a stable temperature, i.e. below the frost line.
As you can see, four earth ground stakes are positioned in the soil in a straight line, equidistant from one another. The distance between earth ground stakes should be at least three times greater than the stake depth. So if the depth of each ground stake is one foot (.30 meters), make sure the distance between stakes is greater than three feet (.91 meters). The Fluke 1625 generates a known current through the two outer ground stakes and the drop in voltage potential is measured between the two inner ground stakes. Using Ohm's Law (V=IR), the Fluke tester automatically calculates the soil resistance.
Because measurement results are often distorted and invalidated by underground pieces of metal, underground aquifers, etc. additional measurements where the stake's axis are turned 90 degrees is always recommended. By changing the depth and distance several times, a profile is produced that can determine a suitable ground resistance system.
Soil resistivity measurements are often corrupted by the existence of ground currents and their harmonics. To prevent this from occurring, the Fluke 1625 uses an Automatic Frequency Control (AFC) System. This automatically selects the testing frequency with the least amount of noise enabling you to get a clear reading.
Field Density TestIn soil testing for civil construction, Field Density testing would be amongst the most common. Its purpose is to determine the Field Dry Density (in t/m3) and Moisture Content (as a %) of the material being tested. The Field Dry Density is usually compared with a laboratory compaction test of the same soil type, to produce a ratio between field and laboratory compaction. (See "Compaction" below)
Compaction testing as carried out in a soil testing laboratory is done to determine the Maximum Dry Density (t/m3) and the moisture content at which that is achieved known as the Optimum Moisture Content (%).
This data is used to compare to the Field Dry Density (see Field Densities above) to determine the Density Ratio and Moisture Variation.
Compactions are either performed as Standard or Modified and sometimes Oversized if the material being tested is of a larger particle size (rock).
Particle Size Distribution test results (or Gradings) are used for many reasons such as determining the compliance of manufactured gravels with required standards and specifications in the earthwork and concrete stages of construction works.
This Soil test is also part of the process used to classify a soil sample in conjunction with Atterburg Limits testing (see below).
Atterburg Limits cover a range of soil tests relating to reactivity to moisture (water), better known as Plasticity. These tests include Liquid Limit, Plastic Limit, Plasticity Index and Linear Shrinkage. Atterburg Limits play an important part when classifying soil types and work in conjunction with Particle Size Distribution tests (above).
Soil cohesion is vital for structures such as road embankments and the like. Civil Engineers often need to know if a soil will hold together satisfactorily on its own or whether it may need to be supported or even replaced. One group of soil tests used to determine cohesion properties of soils is called the Emerson Class.
