Geophysics HM Ltd (GHM) is a professional corporation specializing in "STATE of the ART" geophysical surveys and structure NDT imaging technics including Ground Penetrating Radar, Seismic, MASW, Electric Resistivity Tomography, Induced Polarization, Electromagnetic, Magnetic, Gravity, Borehole Logging and many more. The processed data and interpretation results are provided to the clients according to current industry standards for Geotechnical, Geological and Environmental Investigations, Road and Bridge NDT Investigations, Utility Locates, Archaeology and Mineral Exploration.
The "EPSILON" high speed GPR scanning systemwas built and currently in use by Geophysics HM Ltd for estimating the asphalt thickness for roads and HWY's. The road asphalt pavement layers are designed for interacting with wheel forces of the heavy traffic, temperature variations and and weather conditions. The performance of the pavement will dictate the quality of the road service and the life span of the structure.
The thickness, structure and composition of the asphalt layers will dictate the performance of the road under different load and conditions. If the asphalt layer is thin the deterioration of the road will increase rapidly, alternatively with the increases of the thickness, the bearing capacity of the pavement increases leading to better performance and longer service.
The acquisition system is antenna interchangeable and capable of measuring the asphalt conditions up to four (4) meters below the asphalt surface. The GPR data is collected at posted traffic speed synchronously with a sub-meter precision GPS receiver mounted on the antenna enclosure. The "EPSILON" data acquisition does not require supplemental traffic management or lane closure in order to complete the survey.
The Geophysics HM Ltd "DELTA" Bridge Ground Penetrating Radar imaging system is a high efficiency and low cost NDT alternative options to chain dragging and visual inspections on the bridge decks since they are reliable, precise, high speed and traffic independent.
High resolution GPR scanning can be effectively deployed over the surface of the concrete bridge components to provide information on the deterioration andinternal conditions of the concrete structure and components layout not provided from visual observations. The integration of the GPR, thermal imagery and other nondestructive techniques are necessary to complete a sound and full bridge condition assessment and rehabilitation.
Ground Penetrating Radar carried over concrete structures with embedded corroded steel bars will show very distinctive diffraction responses and high signal attenuation due to cracking, delamination and change of the concrete properties due to the presence of chemical sub-products of the corrosion process. The attenuation of the GPR signal generated from the steel bar is used for estimating the degree of deterioration of the concrete structure and bridge decks.
Geophysics HM Ltd is researching and developing an innovative multi-parameter time series acquisition system. As part of our program we are prototyping a "POISSON" Distributed Acquisition System for acquiring and processing time series of Induced Polarization, Seismics, Borehole, Magnetotellurics, Natural Fields, Thermal Conductivity and Electromagnetics.Our mission is to provide high quality geophysical exploration and geophysical data acquisition using the most advanced datalogging technology, comparable with the processing and interpretation tools currently available in the industry today. Our goal is to acquire multiple geophysical data sets with one spread layout in the field and process them individually with a robust processing platform "XG" developed and coded in house.
"XG" is a graphical user interface designed and coded for acquisition, QA/QC and processing of natural and induced Time Domain Induced Polarization, Refraction Seismic, and Magnetotelluric among other geophysical datasets. The computer program is written in LabVIEW for efficiently controlling the generation and acquisition of multiple sources time series.
The user interface is capable of handling the excitation source, the multi-sensor survey array, the multichannel multiplexer and multiple high precision data loggers. The acquisition and processing of time series contemplates the following geophysical techniques:
Ground Penetrating Radar is a geophysical mapping and imaging NDT technique based on the reflection and diffraction of electromagnetic waves from manmade buried objects, structure, utilities and natural features such as voids, sinkholes, bedrock and stratigraphy. GPR is similar to the reflection seismic method and can provide high accuracy 2D and 3D structural images and conditions of the subsurface objects, features and materials. Measurements are usually done by pushing or pulling antennas of different frequency over the ground along predefine surface profiles and grids. The penetration depth of the GPR method depends on the frequency of the antenna and the electric conductivity of the subsurface materials.
At Geophysics HM Ltd most of our applications are addressed using GSSI State of the Art GPR systems. At GSSI, the antenna is the crucial element of a RADAR system. It determines data quality, range resolution, maximum depth of penetration, etc. The 900, 400, 270, and 200 MHz and 300/800 MHz antennas used in UtilityScan and UtilityScan DF represent the state of the art in high-resolution, ground-based antennas. They possess the best combination of depth and resolution for ground inspection. Bi-static refers to the fact that the transmitter and receiver are two separate antenna elements even though they exist within the same enclosure. This differs from a mono-static antenna in that a mono-static uses the same antenna element to transmit and receive signals (GSSI, 2021).
The refraction seismic method is used to measure the depths and velocities of subsurface layers. It is particularly useful for mapping the depth and topography of the bedrock surface. It can also be used to find the elastic properties of these layers, which are useful for engineering purposes. Using the velocity of the bedrock, the rippability of the bedrock can be determined along with an estimate of the size of machine required.
The Multichannel Analysis of Surface Waves (or MASW) is a seismic survey technique used for evaluating the elastic properties and stiffness of the subsurface soils for geotechnical purposes. The propagation of the surface waves in the sub-surface soils depends on the shear-wave velocity (Vs) distribution and on the elastic constants on the materials such as the Young’s modulus. The shear wave velocity is directly related to the stiffness of the soils. The velocity information and estimated parameters using MASW can be presented in profiles, cross-sections, plan maps and 3D earth models.
The EM61-MK2A is a high sensitivity, high resolution, time domain metal detector suitable for the detection of both ferrous and non-ferrous metal. Typical target response is a single, sharply defined peak, facilitating quick and accurate determination of location. Achievable depth of detection will depend on several target characteristics, with the surface area and orientation of the target of particular importance. A single 200 litre (55 gal.) drum can be detected at depths greater than three metres. In comparison with the previous-standard EM61-MK2, the EM61-MK2A provides the same feature and performance specifications. Differences between the two models are ergonomic: because the A-model does not include a backpack for system components, the electronics console is mounted on the U-handle, and the battery is positioned in the centre of the coils.
Data from multiple time gates -- three or four, user-selectable -- are recorded to provide a description of the response decay rate, supporting both the characterization and limited discrimination of targets. Data collection is supported by the DAS70-AR Data Acquisition System. The system can be pushed or pulled as a trailer, by person or vehicle, as either a single unit or an array of multiple units; for multiple unit configurations, options are available to customize component specifications and layout. As may be required, with the addition of a backpack and associated cable set, the system can be carried by a single person with a belt harness (Geonics, 2020).
The EM31 equipment is a simple "Slingram" method consisting of a magnetic dipole (a current loop) transmitter (Tx) and a coplanar magnetic dipole receiver (Rx) operating at a fixed frequency of 9.8 kHz and with a fixed distance between Tx and Rx of 3.66 m. When a current is injected into the Tx coil a primary magnetic field is generated. When the primary magnetic field interacts with the electrical conductors in the earth secondary currents are induced in them. These secondary currents in turn generate a secondary magnetic field that adds to the primary field at the position of the receiver.
The outputs of an EM-31 survey are the conductivity (quadrature) and In-phase components of the secondary magnetic field. The secondary magnetic field is a complicated function of the intercoil spacing, the operating frequency, and the ground conductivity. The relationship is simplified when certain constraints, technically defined as "operation at low induction number", are met. When the low induction number constraints are not satisfied the measured quadrature and In-phase responses deviate from expected values.
The EM31-MK2 maps geologic variations, groundwater contaminants, or any subsurface feature associated with changes in ground conductivity. Using a patented electromagnetic inductive technique that allows measurements without electrodes or ground contact. With this inductive method, surveys can be carried out under most geologic conditions including those of high surface resistivity such as sand, gravel, and asphalt.
Borehole logging consists of measuring the physical properties of soil, rocks, groundwater and mineral occurrences inside geological and geotechnical boreholes with a variety of geophysical sensors and dedicated ADC data loggers. The sensors are usually deployed inside the bore and run along the drillhole path at equal intervals measuring the variations of the physical properties, with an ADC located at the surface near the borehole collar. The borehole sensors or probes are connected to a multi-wire cable winded in a winch with an encoder for depth measurements. The measured properties are recorded digitally in 2D format with the vertical axis along the bore and the measured magnitude at the horizontal axis.
Borehole electrical logging is usually carried out using an array of electrodes or with special sondes. The mise-à-la-masse method is commonly used for delineating the depth, shape and extend of the mineral occurrence around the borehole. This technique is a borehole to surface method widely used in mineral exploration. In-hole and cross-hole logging are techniques commonly used for supporting surface geophysical exploration and mapping.
Geophysics HM Ltd can assist environmental, mineral exploration and geotechnical professionals with a variety in-hole and cross-hole physical property measurements for contamination monitoring, mineralization characterization, hydrogeological studies, groundwater exploration and landfill site assessment.
The resistivity of soil and rocks depends on the water content, porosity percent, pore interconnection type, moisture, clay content, salinity and mineral content. The degree of compaction of sediments is another factor contributing to the resistivity of soils and engineering fill materials. An empirical formula relating the materials resistivity to porosity, degree of pore saturation, and resistivity of the liquids was developed by Archie in 1942.
The Resistivity and Induced Polarization surveys for geology, environmental and mining exploration can be done measuring potential voltages of the induced and transmitted signal in an array of cables and distributed electrodes on the surface of the ground with a Current Transmitter (Tx) and a Time Series data acquisition instruments or datalogger (Rx). A direct current transmitter is utilized to energize the ground with a half duty current pulse using one or two steel rods planted into the ground. In the time domain applications, after two seconds of uninterrupted current injection, the current pulse is terminated and the decay of the voltage or induced polarization effect is measured with another pair of electrodes..
Subsurface Utility Mapping and Locating tools provides construction and geotechnical professionals the required information of the buried utilities, the location, depth and status for project design, maintenance, renovation, demolition, drilling, coring, trenching and excavation activities usually carried out in the construction site. The use of non-destructive techniques such as Electromagnetic Induction Locates, GPR and Time Domain Electromagnetics for Quality Level B, C and D in Utility Mapping applications guarantees several benefits to the industry including reducing project cost due to utility damages, construction delays and increases the project and public safety in general.
For an efficient identification, mapping and presentation of utility information in Subsurface Utility projects, Geophysics HM Ltd adheres and follows the Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data ( ASCE Standard 38-02) and the CSA Standard S250 released in 2011 by the Canadian Standards Association (CSA).