The state of the art equipment use modern techniques to obtain required parameters of subsurface deposits. STS has been providing following geophysical testing services.
Downhole Seismic Test
The downhole seismic test provides a designer with information pertinent to the seismic wave velocities of the materials in question. The P-wave and S-wave velocities are directly related to the important geotechnical elastic constants of Poisson’s ratio, shear modulus, bulk modulus and Young’s modulus. Accurate in-situ P-wave and S-wave velocity profiles are essential in geotechnical foundation designs. These parameters are used in both analyses of soil behaviour under both static and dynamic loads where the elastic constants are input variables into the models defining the different states of deformations such as elastic, elasto-plastic, and failure. Another important use of estimated shear wave velocities in geotechnical design is in the liquefaction assessment of soils.
Electrical Imaging (Tomography)
Electrical resistivity tomography or electrical resistivity imaging is a geophysical exploration technique used to measure electrical resistivity of subsurface deposits. With the help of this technology images of the static subsurface conditions can be obtained. During environmental remediation, series of images can also be obtained to investigate the rapid changes. Subsurface heating and steam injection are some of the remediation processes which can cause a change in electrical resistivity. The study of differences in resistivity over a certain time period can be a helpful guide in remediation process. Other applications of these tests include investigation of pollutant plums, archaeological surveys, monitoring of waste deposits, mapping and monitoring of groundwater contamination. The images of the subsurface deposits can be two-dimensional or three-dimensional.
Vertical Electric Sounding (VES)
Vertical Electrical sounding is an electrical resistivity method used to measure the resistivity of shallow and deep subsurface deposits. There are a number of test arrangements to perform this tests which include Wenner method, Schlumberger method and Wenner-Schlumberger method. The test is performed by taking readings in a number of spacing intervals starting from short to large spacing. One measurement is termed as sounding which is a function of depth. The readings for resistivity at different depths are then evaluated based on the spacings used during the test.
The test method conforms to the transient line heat source theory. The thermal conductivity and thermal resistivity tests were performed in accordance with the ASTM D-5334.
The test method is based on the theory that the rate of temperature rise of a line heat source depends on the thermal constants of the medium in which it is placed. A long, cylindrical, stainless steel needle sensor is used as a line heat source. The sensor (TR-1) is a 10 cm long thermal needle sensor. The sensor contains a heating element and a thermocouple and is inserted into the material to be tested. After the sensor is inserted, the heating element is turned on and kept on for 1-10 minutes (time is based on the sensor used). Sensor temperature variations are measured and analyzed by the Thermal Properties Analyzer Instrument to calculate the Thermal Resistivity and Thermal Conductivity. These readings are read directly on the LCD panel of the instrument.
Soil Electrical Resistivity Test
Electrical resistivity testing measures the conductivity and corrosivity of soil. It is expressed in ohm-meters. Properties that affect the resistivity of a soil or rock include porosity, water content, composition (clay mineral and metal content), salinity of the pore water, and grain size distribution. This test is helpful for designing of earthing system, and design of protection of buried structures like metallic tanks against corrosion.