Geophysical measurements | Topographic engineering | Geotechnical study | Geological reports

Surface Waves Analysis (SWA)

In an infinite homogeneous isotropic medium, only P and S waves exist. However, when the medium does not extend to infinity in all directions, other types of waves can be generated. These waves are called surface waves because they are confined to the vicinity of one of the surfaces that bound the medium. In exploration seismology, the main type of surface wave of importance is the Rayleigh wave, often called ground roll. This wave travels along the surface of the earth and involves a combiread more

Reflection method

This method has developed very much because it is the main method for surveying the oil and gas retaining rock layers. In engineering geophysics this method is used for studding the bedrock proprieties, detecting possible sinkholes and discontinuities in the earth’s consistency, this being very useful in big construction projects. The method is based on tracking the waves that are reflected from the limit between two layers with different elastic properties.read more

Refraction method

This was the first method used in seismic prospecting. It has a major applicability in shallow investigation, being frequently used in geology and hydrogeology investigations. The method is based on tracking and analyzing the seismic waves which are refracted on a surface that separates two different mediums with different proprieties of wave velocity. Generating the signal for the measurements does not pose particular problems for small depths, like in case of engineering projects.read more

Seismic

The seismic method is by far the most important geophysical technique in terms of expenditures and number of geophysicists involved. Its predominance is due to high accuracy high resolution, and great penetration. Seismic methods are important in groundwater searches and in civil engineering, especially to measure the depth to bedrock in connection with the construction of large buildings, dams, highways, and harbor surveys. Seismic techniques have found little application in direct exploration read more

Self Potential (SP)

Self Potential (SP) surveying, one of the oldest geophysical methods, involves passively measuring natural earth voltages. The method is commonly used in hydro geological and geotechnical applications. The SP method involves measuring natural earth voltages using two electrodes at the surface. The natural earth voltages are typically caused by moving water and ions through pore spaces of soil and rock (electro kinetic potential). The potential drop (voltage) is measured between two non-polarizaread more

Microgravimetry

The gravimetry method is useful wherever the formations of interest have densities that are appreciably different from those of surrounding formations. It is an effective means of mapping sedimentary basins where the basement rocks have a consistently higher density than the sediments. It is also suitable for locating and mapping salt bodies because of the generally low density of salt compared with that of surrounding formations. Occasionally it can be used for groundwater studies and for direcread more

Magnetic Field Intensity and Vector

Magnetic prospecting maps variations in the magnetic field of the earth that are attributable to changes of structure, magnetic susceptibility, or remanence in certain near-surface rocks. Sedimentary rocks generally have a very small susceptibility compared with igneous or metamorphic rocks, which tend to have a much higher magnetite content, and most magnetic surveys are designed to map structure on or inside the basement or to detect magnetic minerals directly. The magnetic method was initiallread more

Measurements of the Natural Potential

I. Magnetic Field Intensity and Vector II. Microgravimetry III. Self Potential (SP) read more

Hummel

The Hummel array is actually a more practical variant of the Schlumberger array, easy to adapt to difficult working conditions. In practical terms is a half of the Schlumberger array, one of the power electrodes being placed at infinity perpendicular on direction of the array. The computing of the apparent resistivity is done using the same formula as for the Schlumberger array, but to be accurate the resistivity is doubled. Roa =2* V/I*PI* b^2/a Using this method we can reduce the personal nread more

Dipole - Dipole

The dipole-dipole array is logistically the most convenient in the field, especially for large spacing. All the other arrays require significant lengths of wire to connect the power supply and voltmeter to their respective electrodes and these wires must be moved for every change in spacing as the array is either expanded for a sounding or moved along a line. The convention for the dipole-dipole array shown below is that current and voltage spacing is the same, “a”, and the spacing between tread more

Schlumberger

One of the first arrays used in the 1920 and still popular today is the Schlumberger array shown below with its formula for apparent resistivity. It is another variant of the pole-dipole, again with the second current electrode placed symmetrically opposite the first. The voltage difference is consequently doubled and so the apparent resistivity is the same as that for the general pole-dipole with a factor of 1/2 in the geometric factor. In a Schlumberger sounding the voltage electrodes are usuaread more

Wenner

The Wenner array is now seen to be a simple variant of the pole-dipole in which the distant pole at infinity is brought in and all the electrodes are given the same spacing, “a”, as seen in the following configuration Roa=2*PI*a*V/I The Wenner array is normally used for sounding and the apparent resistivities are plotted vs. “a” such as is shown in figure.read more

Pole - Dipole

If only one of the current electrodes is placed at infinity the configuration and the apparent resistivity are as shown: Roa = 2*PI*[b(a+b)/a]*V/I This array is used frequently in resistivity surveying and the spacing are usually described, and taken, in integer multiples of the voltage electrode spacing b = na. The standard nomenclature is to call the potential electrode spacing “a” so the configuration and apparent resistivity becomes: Roa=2*PI*an(n+1)*V/I Pole-dipole sounding data iread more

Pole - Pole

The simplest array is one in which one of the current electrodes and one of the potential electrodes are placed so far away that they can be considered at infinity. This configuration with its formula for apparent resistivity is shown below. Roa=V/I*2PIa This array can actually be achieved for surveys of small overall dimension when it is possible to put the distant electrodes some practical distance away. For a survey in an area of a few square meters infinity can be on the order of a hunread more

Used configurations

All the arrays of electrodes used to obtain the apparent resistivity are basically superposition of the fundamental equation for the potential from a current source with appropriate sign for the current. The formulas for apparent resistivity are a product of the impedance V/I (Ohms) and a geometric factor with the units of length (meters). To investigate the resistivity distribution with depth, called a sounding, the arrays are expanded about a center point and the apparent resistivities are ploread more

Mise-a-la-Masse

The method is derived from the pole-dipole method and is characterized by a long current line and a short distance between the measuring electrodes. The main characteristic is that one power electrode is put directly in contact with the solid body we are interested in. It is better if the rock body has a lower resistivity. Thus around the body a current field will be created that will be detectable on the surface. Through grid profiling, the main directions of current movement can be establishedread more

Induced Polarization (IP)

When a current is passed through earth materials not containing metallic minerals, the amount of current is related to the driving potential only by the ohmic resistance of the formations involved. When the formations contain metallic minerals, the currents give rise to an exchange of ions at the surface of contact between the minerals and the electrolytes dissolved in the fluid filling the inter-granular pore spaces. This electrochemical exchange creates a voltage which opposes the current flowread more

Geoelectrical tomography

It can be considered the lead technique in geo-electrical measurements. This method combines modern techniques of data acquisition with performing interpretation solutions. The data acquisition is made uniform along the profile with a density established by the distance between the electrodes and the type of array used. With one length of the multielectrode cable we can obtain hundreds of resistivity measurements thus creating a 2D image of the underground resembling a tomography. This dataread more

Geoelectrical profiling

The electric resistivity profiling method uses the same type of arrays as in the vertical electric sounding (VES), just that in this case the interest is concentrated on several levels of depth. There for, there are arrays conceived with fixed distances between the electrodes so the measuring technology becomes simple and fast, the number of operators is smaller, the costs are smaller and the results can be visible immediately. This method is ideal when we need to survey for shallow depth gread more

Vertical Electrical Sounding (VES)

This method is by far the most used method for geoelectric surveying, because it is one of the cheapest geophysical method and it gives very good results in many area of interest. The field measurements technique is adjustable for the different topographic conditions and the interpretation of the data can be done with specialized software, with a primary interpretation immediately after the measurements. The results of the measurements can be interpreted qualitatively as well as quantitatively.read more

Geoelectrical resistivity

The resistivity method is designed to yield information on formations or bodies having anomalous electric conductivity and it has been used for a long time to map boundaries between layers having different conductivities. It is employed in engineering geophysics to map bedrock, for determining the homogeneity of the terrain and possible sinkholes, in groundwater studies to determine salinity and the depth to the water table. Most recently it has been applied in the search for geothermal power beread more

Geoelectric

Electrical prospecting uses a large variety of techniques, each based on some different electrical property or characteristic of materials in the earth. There for this techniques are divided into three major categories; for resistivities, being a method with a large applicability and complex, there are subcategories retaliated. 1. Geoelectrical resistivity 1.1. Vertical Electrical Sounding (VES) 1.2. Geoelectrical profiling 1.3. Geoelectrical tomography 2. Induced Polarization (IP)read more

Ground Penetrating Radar (GPR)

Ground-penetrating radar (GPR) uses a high-frequency (80 to 1,500 MHz) EM pulse transmitted from a radar antenna to probe the earth. The transmitted radar pulses are reflected from various interfaces within the ground, and this return is detected by the radar receiver. Reflecting interfaces may be soil horizons, the groundwater surface, soil/rock interfaces, man-made objects, or any other interface possessing a contrast in dielectric properties. The dielectric properties of materials correlate wread more

Very Low Frequency (VLF)

The VLF method uses powerful remote radio transmitters set up in different parts of the world for military communications (Klein and Lajoie, 1980). In radio communications terminology, VLF means very low frequency, about 15 to 25 kHz. Relative to frequencies generally used in geophysical exploration, these are actually very high frequencies. The radiated field from a remote VLF transmitter, propagating over a uniform or horizontally layered earth and measured on the earth's surface, consists of read more

Radio Frequency (RF)

This method has a relatively restricted applicability, resuming itself to tracking buried metallic bodies or lines. Its principle is based on the response of metallic bodies when radio waves are deployed. The investigation depth is of a few meters, the method being very good in surveying for cables, pipes, drums and other buried metal objects.read more

Metal Detection (MD)

The term "metal detector" (MD) generally refers to some type of electromagnetic induction instrument, although traditional magnetometers are often used to find buried metal. The disadvantage of magnetometers is that they can be used only for locating ferrous metals. MD instruments in geotechnical and hazardous-waste site investigations have several uses. The main advantages of MD instruments are that both ferrous and nonferrous metals may be detected; the surface area of the target is more imporead more

Frequency Domain (FD) and Time Domain (TD)

Electromagnetic methods fall in two categories, frequency domain and time domain. In the frequency domain method, the transmitter emits a sinusoidal varying current at a specific frequency. Because the mutual inductance between the transmitter and conductor is a complex quantity, the electromagnetic force induced in the conductor will be shifted in phase with respect to the primary field. At the receiver, the secondary field generated by the currents in the conductor will also be shifted in pharead more

Electromagnetic

Electromagnetic methods detect anomalies in the inductive proprieties of the earth's subsurface rocks. An alternating voltage is introduced into the earth by induction from transmitting coils either on the surface or in the air, and the amplitude and phase shift of the induced potential generated in the subsurface are measured by detecting coils and recorded. Metal based can often be detected by this technique. Electromagnetic (EM) surveys provide an accurate and cost effective means of charactread more

Remotely Operated Vehicle Video

With the Remotely Vehicle Video method the interpreting of the data requires minimum effort. This application has a restricted area of interest but can give good results in a very short time.read more

Sonar scan

When looking for under water features, either relief or objects, the sonar is the most usual technology to use. The sonar can be compared with radar but it uses sound instead of electromagnetic waves. At high frequencies a sonogram (the result of the sonar scan) can have the detail of a photo. Physic characteristics of the features looked up can be easily determined. The method was successfully used in rivers and lakes after and before dragging for determining the level of alluviums deposited aread more

Other Methods

I. Sonar scan II. Remotely Operated Vehicle Video Other methods used in geophysical investigations: Electromagnetic Geoelectric Measurements of the Natural Potential Seismic read more

Geophysical Methods

In engineering geophysics the main interest is for the first tens of meters from the surface. Therefore, there are methods and techniques developed to deal with the requirements of depth and resolution that are needed in engineering geology. 1. Seismic 1.1. Refraction seismic 1.2. Reflection seismic 1.3. Surface waves analysis 2. Geoelectric 2.1. Electrical resistivity 2.1.1. Vertical Electrical Sounding (VES) 2.1.2. Electrical profiling 2.1.3. Electrical tomograread more

Borehole Investigation

In borehole investigation, geophysics provides a means of evaluating a great variety of physical properties of subsurface rocks, sediments and fluids. Borehole logging offers an economical alternative to continuous sampling or coring, furnishing continuous, objective data sets in a graphical form that can be rapidly interpreted in the field. Additionally, geophysical logging provides information about the subsurface that cannot be obtained through standard drilling and sampling techniques. Whread more

Lake and River Prospecting

Determining the position of flaws in the isolating membrane of lakes constitutes one of the main problems in dealing with the fluid leakage. Through geoelectrical methods viable solutions are available for this kind of problems. For leakage prospecting that may occur in dams, geophysics uses two of the most appreciated geoelectrical methods. One of these methods is a less conventional method, called “Mise-a-la-Masse” and it gives very good results when investigating the flaws in the isolatiread more

Archeological Surveying

In archeological sites it is very important to gather as much information as possible without having destructive consequences and be at the same time cost effective. Geophysical methods of surveying provide just that. Thanks to geophysical methods, it is possible to detect the underground presence of structures such as walls, foundations, floors, roads, kilns, hearths, tombs, graves, pit cavities, mounds and filled ditches. Geophysical methods allow the drawing of an "archaeological map" of the read more

Utility and Buried Objects Detection

Buried utility and objects can pose problems when their precise underground location is unknown. With geophysical methods we can detect and map them very precisely. Most of the locating equipment is operating through the principles of electromagnetism, designed to detect electrically conductive materials. This application has been developed especially to back up engineering projects planning that will be developed in locations where the subsurface may contain different types of objects and acread more

Determining the geological and hydrological conditions

In areas with poorly constrained geology, geophysics can be used to gather valuable information. Underground flaws such as natural voids, fractures and faults or sedimentary structures can cause significant problems if they remain undetected. In infrastructure development projects, a good knowledge of geological and hydro-geological features can help for the correct planning of the project development and for reducing the costs. In the case of quarries and gravel pits, surveys bring valuable read more

Inorganic Contaminants

Geophysical techniques are successfully used and provide good and rapid reconnaissance of contaminated sites. Electromagnetic Mapping, Electrical Tomography, Vertical Electrical Sounding, Self Potential and Ground Penetrating Radar are techniques that can highlight areas of potential contamination, without exposing any personnel to the hazards of contaminated sites. Geophysical surveys can be applied to a site in order to determine the size of the contaminated area and the depth of the contaminaread more

Geophysics

Engineering geophysics, by using dedicated methods and equipment, develop a series of applications designed to support projects and investigations which have an immediately applicative character. Methods used in geophysical investigations: Seismic Geoelectric Electromagnetic Natural Potential Engineering projects of infrastructure development (roads, bridges, railways, pipelines and underground cables, etc.) and evaluation of mineral resources in quarries and gravel pits are oftread more

Anemometry

Anemometry is the set of techniques used to measure the wind speed. Among our services, you can find: Providing lattice masts from 20 m to 145 m Installation and mounting of masts and measurement instruments Data recovery and processing Reports and data banking We can also provide for our clients: Urbanism Certificate Documentation Building Permit Documentation Geotechnical and geophysical studies Topographical assistance by poles assembly Providing tubular poles from 1read more

Topographic Engineering

By their nature, engineering works require a good knowledge of the land’s topographical features in order to design and plan works, as well as specialized topographical assistance during the progress of these works. Drawings and verticalizations Mapping of urban utilities Construction scaled drawings Dimensions monitoring and control High precision leveling Other topographical applications: GIS Applications Construction Measurements GPS Measurements Topographic Sitread more

Topographic Site Surveys

The topographical site surveying is the technique and science used to determine the exact spatial position of points and distances and the angles between them. These points are usually on the Earth's surface and are often used to establish land maps, property boundaries or for governmental purposes. Situation and site plans Precision leveling Control measurements Surface Computing Modeling land Digital Terrain Model (DTM) Contouring Longitudinal and transversal profiles Volread more

Construction Measurements

This type of measurements is performed in order to draw situation plans of some existing buildings, this being necessary in planning future work or updating old plans. Drawings of the elements of a scaled construction Measurements of heights Cross and longitudinal sections Roof plans Reinforcement plans Space planning Other topographical applications: GIS Applications GPS Measurements Topographic Site Surveys Topographic Engineering Maps and Plans Vectorization read more

GIS Applications

GIS applications enable the integration of graphics and text information in a geospatial database that becomes a powerful and effective tool in the management of multiple information involved in a large project. GIS applications enable the user to analyze and simulate various situations that implicitly depend on several factors (climatic, geological, altimetrical, hydrogeological, etc.). Procurement of GIS data by converting the existing data into a digital format Field procurement of thread more

Maps and Plans Vectorization

Plans and maps conversion from digital support into classic support can be done by digitizing the characteristic features bringing thus in a vector format, with multiple possibilities of exploitation. Digitization of cadastral and topographical plans and maps Vectoring civil and industrial projects Touristic and thematic maps Obtaining of maps with isolines Vectoring the communication lines on the raster maps Putting into coordinates of raster format topographical maps and plans read more

GPS Measurements

The GPS measurement technique enables the operator to determine the coordinates of points of interest with high precision, regardless of location, in a shorter time compared to traditional techniques. Possibility of fast and accurate determination of the X,Y coordinate Achievement and thickening of the support topographic networks Determination of the property boundaries Limitations of interest areas Monitoring of the movements in time Other topographical applications: GIread more

Topography

Topography is a branch of geodesy which deals with the measurement technique of a portion of Earth's shell, with determining the position of earth elements on small surfaces (considered flat), as well as graphical or numerical representation technique of the measured surfaces, for drawing up maps and plans; detailed description of a place in terms of placement, configuration, etc.; how elements of an ensemble are arranged in space. Topographical services: GIS Applications Constructionread more

Geology

Geology studies the composition of both surface rocks and those of deep mineral deposits (solid, liquid and gas), the structure of the planet, tectonic plates of the Earth's shell, its fluid successive layers, which are located between the solid shell of the earth surface and its hard core, composed mainly of melted heavy elements, subject to very high pressures. The first stage of geological research of a region starts with mapping the land, paying particular emphasis to the surface rocks. Folread more

Geotechnics

Represents the first stage of the construction or strengthening of a target. This kind of investigation gives information about soil structure or consistence, phreatic level and formulates recommendations for the technical project. The geological structure and the physical-mechanical characteristics of the earth play an important role in designing buildings. Using direct methods (open digging, drilling, sampling for laboratory tests, etc.) and indirect methods (geophysical methods), determinatiread more

Bathymetry

Bathymetry can be considered the equivalent of altimetry applications over water. It is the study of water depth with the help of which maps and profiles of the underwater relief can be created. The method is successfully being used on lakes and rivers (before and after dredging) in order to determine the silt deposit and to estimate the useful material reserves or in order to create maps of flood risk areas, of recreational lakes or beach areas for signaling deep places with drowning danger, uread more

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