GEOPHYSICS TECHNOLOGY SEISMIC AND RESISTIVITY
BNC31803 SITE INVESTIGATION GROUP 2
Group Members
NIK RAHIMAN BIN NIK AZHAR CN190213
MUHAMMAD HAZMAN SHAFIQ BIN ROSZANIHAR CN190060
Group Members
NURUL ALEYA BINTI ROSTAM AFFANDY AN190075
NOR IMAN FATIHAH SOIFUL BAHRI AN190140
1 Technical component
The wave speed relating to the density and bonding characteristics
Geophysical technology is indirect method for site investigations,
of the material. The velocity is determined. The magnitude of the
also known as subsurface explorations, are carried out to learn
velocity is than analysed to identified the material. The travel time
more about the underlying conditions of a building site. Soil
of a seismic wave is a function of soil and rock density and
exploration include defining the profile of the site's natural soil
hardness. Primary application for seismic refraction is for
deposits, collecting soil samples, and assessing the engineering
determination of depth and thickness of geologic strata, structure
qualities of soils using laboratory and in-situ testing procedures.
and anomalous conditions. The critical distance between a place
The method is carrier out quickly, meaning will save more time.
and the distance beyond it is calculated using geophones. The most
The most common method that use in geophysical are seismic,
crucial equipment for registering reflected or refracted waves is a
resistivity, gravity and magnetic. Based on the industrial talk the
geophone, an amplifier, and a galvanometer. Seismic refraction
method that will be focusing this time is seismic and resistivity.
investigations are beneficial for exploring depths more than 100
SEISMIC Seismic is elastic characteristics of different subsurface rock formations layer. There are two type of seismic that is refraction and reflection, for reflection At layer interfaces, the seismic signal is reflected back to the surface and recorded at distances less than the depth of investigation while refraction seismic application measurement of the travel time of a refracted seismic wave as it travels from the surface through one layer to another and is refracted back to the surface where it is picked up by geophones. Shock or impact is made at a point, seismic waves through the surrounding soil & rock.
metres, however they are useless for exploring shallow depths. The technology of refraction is utilised to study depths ranging from a few metres to hundreds of kilometres. Depth can be calculated under each geophone to produce a detailed two-dimensional top of rock profile. If compressional P-wave and shearS-wave velocities are measured,in situ elastic moduli of soil and rock can be determined. To determine the soil type whether it in soil or in rock can be refer to it velocity which is 150 – 3000 m/s is soil and 1500 - 6000 m\s in rock, this measurement is for seismic refracted. The equipment for seismic method is terrameter 5454000, resistivity multicore cable, cable corrector, Electrode selector, data transfer cable, jumper cable, steel electrode, terrameter to switch box cable.
1 Technical component
Profiling is used to discover lateral resistivity changes, while sounding is used to find vertical resistivity variations, which reveals lithology differences at a specific place when depth is increased. This method monitors the potential differences between a pair of potential electrodes, and current is injected into the ground through a pair of current electrodes. Soundings are mostly used to determine the depth and thickness of geologic layers using resistivity measurements. Can be used to assess fracture
This diagram shown how the refraction wave of seismic work through the soil RESISTIVITY
orientation using azimuthal data. The resistivity of dense rocks with few voids and low water content ranges from 100 to 1000 ohm-m. Low resistivity is found in soft saturated clays and organic deposits, ranging from 5 to 150 ohm-m.
Resistivity application is to determine depth and thickness of geologic strata, weathering profile, water boundaries, sinkholes or cavity of limestone and any other mineral. By injecting a DC current into the ground through two electrodes and measuring the resultant voltage at the surface with two additional electrodes, resistivity may be measured. The electrode spacing affects the measurement depth. The concentration of ionised salts in the soil pores determines the electrical conductivity of the soil layer. The bulk electrical resistivity of the soil and rock matrix, as well as the
This diagram shown voltage and current movement through the
water quantity and type of pore fluids, is measured using
soil during resistivity method
resistivity. Profiling and sounding are two types of resistivity studies.
1 Technical component SOIL TYPE
TEMPERATURE
Because rocky soil is so resistant, more caution should be exercised
The effect of temperature on soil resistivity is most obvious at or
when dealing with it. Encircling the anode with bentonite clay,
around 0oC, when the resistivity considerably rises. Compaction of
which may contain water while also providing a high conductivity
the soil influences resistivity as well. Loose soil, as opposed to
layer.
compacted soil, is more resistant.
MINERAL CONTENT
CONTAMINANTS
Rock conductivity is affected by the fluid's conductivity and
To minimise resistivity, conducting salts can be found naturally in
chemical composition, the degree of fluid saturation, porosity and
the soil or added externally. Soil additives such as chlorides,
permeability, and temperature. The resistivity of rocks increases
nitrates, and sulphates of sodium, potassium, magnesium, or
as they lose water, such as when clastic sedimentary rocks are
calcium are often utilised. Furthermore, these added salts must
crushed at deep. For resistivity the point need to be consider is
first dissolve in the moisture present in the soil in order to reduce
pores in rocks that are generally filled with fluids, primarily water.
the resistivity, and provisions should be made for the supply of
Rocks become electrolytic conductors as a result. Electrical current
water to the soil surrounding the electrode to speed up this
is transported through a rock mostly via porewater passage.
process, particularly in dry places.
MOISTURE CONTENT LEVEL
WEATHER
Dampness is essential for high soil conductivity. Because soil
Observing the weather whether it suitable to run the test or not
wetness varies with the seasons, it's best to place the cathodes at a
because if it heavy rain or thunderstorm, the test must be stop
depth where dampness will be present all year, ensuring that dirt
such as resistivity test which use electricity and electrode can be
resistivity doesn't fluctuate too much..
potentially attract the thunder and harm surrounding people
2 Project Management A. Operational Safety and Environmental Wellbeing RESISTIVITY METHOD •
This process should not be carried out inside an area that can i. get affected by noise disturbance. This can be done through the use of indoor facilities.
•
Air traffic is a common issue when a large number of vehicles are at the traffic. It is not recommended to handle this issue in an open area.
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The presence of feet during the process can also affect the efficiency of the operation. This is why it is important that the people involved in the process are reduced or eliminated entirely.
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Safety Measurement
i.
Site safety. There can be assorted risks associated with working on any site and site regulations as laid down by the owner or operator should be observed.
ii. PPE. Wearing the minimum personal protective equipment and any other equipment required by the site operator or deemed necessary by the task.
Electric shock. To avoid the risk, ensure that the test leads are attached to the pins and the pins are firmly inserted in the ground. SEISMIC METHOD •
Poor Electric Current
• The presence of a weak electrical current is also one of the factors that can cause the process to fail. This issue can be solved by ensuring that the environment where the operation occurs has a consistent and large supply of electricity. •
Safety Measurement
i.
Safety ratio. Safety ratio is a ratio between peak particle velocity and acceptable peak particle velocity at particular frequency. A safety ratio of less than 1 means that a building structure is able to tolerate the vibration at a particular frequency.
2 Project Management B. Site coordination, preparation and execution. NECESSARY PREPARATION BEFORE CARRIED OUT THE EXPERIMENT
SAFETY MEASUREMENT
•
Ensure that all relevant site conditions and working practices • Site safety are observed. Working on any site carries a variety of dangers, and the owner's Obtain a work permit as required by the site. operator's restrictions must be followed
•
Do a survey coverage before carried out the seismic methods.
•
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Geotechnical investigation. This should be based on the results of geophysical. The geotechnical investigation may include additional sampling and analyses to identify the vertical and horizontal extent of geohazards and characterise site conditions.
Wearing the bare minimum of personal protection equipment that the site operator or the task deems essential
•
•
PPE
Electric shock
To avoid this danger, make sure the test leads are securely secured to the pins and that the pins are firmly embedded in the ground.
3 Financial Acuity SEISMIC RESISTIVITY EFFICIENT
TECHNOLOGICAL IMPROVEMENT
Seismic resistivity is proven best method to do ground testing rather than any typical geotechnical site investigation. Geotechnical in situ methods are usually hard to get accurate results for the soil testing because of the disturbance caused while conducting the assessment. The process of getting the ground sample into a tube needed special care to avoid any modification to the soil shears and characteristic. Meanwhile seismic resistivity assessment is being conducted right on the site location, without removing any subsoil structure hence not giving any disturbance to the results.
Some improvements that could be done in conducting soil investigation of seismic resistivity would be the integrations of electric resistivity and seismic refraction methods to reduce ambiguity inherent in the ground. Due to lack of recognition of low contrast gap between low resistivity value by electrical resistivity, combining seismic sure helps a lot with dissimilar velocities ability to differentiate it. The interpretation then could be done by using software where it traces ray through models and generating tomography images.
Other than that, seismic resistivity being conducted for a large parameter of ground for subsoil site investigation, ease the testing session to be done quickly thus efficient work time depending on the density of the ground. It is also allowed mapping of many horizon layers using tomography and graph making it easy to be read while do assessment in many surfaces on this earth includes dams and bedrocks. So that, it can detect and seepage or leakage going on at the locations with water.
The calculation yields resistivity and seismic models that are reliable with the test information and have worked on underlying similitude. At any position, the progressions can be described as far as two credits, the force or size and the particular course. A shared characteristic of circulation of these progressions decides if electrical resistivity and seismic speed pictures are seen as being primarily comparable. For another option and more thorough methodology we suggest utilizing the estimated technique for introductory intermingling and afterward changing to a legitimate resistivity limited contrast answer for the last emphases
REFERENCES Aki, K.I. & Richards, P.G. (1980): Quantitative seismology: Theory and methods, vol. 1. Freeman, New York. Ismadiana Izika. (2021). APPLICATION OF GEOPHYSICS TECHNOLOGY IN SITE INVESTIGATION: SEISMIC AND RESISTIVITY METHODS [YouTube Video]. Retrieved from https://www.youtube.com/watch?v=bf2A4k9FiDM Büker, F., Green, A. & Horstmeyer, H. (1998a): Shallow 3-D seismic reflection surveying: Data acquisition and preliminary processing strategies. Geophysics, 63, 1434–1450. Frei, W. (1995): Refined field static corrections in near-surface reflection profiling across rugged terrain. The Leading Edge, 259–262 Aronses, H.A., Osdal, B., Dahl, T., Eiken, O., Goto, R., Khazanehdari, J., Pickering, S. and Smith, P. 2004. Time will tell: New insights from time-lapse seismic data. Oilfield Review 16(2), 6–15 Li, Q., Deckman, H. W., & Ertas, D. (2018, October). Magnetoseismic resistivity mapping: Fundamentals and challenges. In 2018 SEG International Exposition and Annual Meeting. OnePetro.
Cardarelli, E., Cercato, M., & De Donno, G. (2014). Characterization of an earth-filled dam through the combined use of electrical resistivity tomography, P-and SH-wave seismic tomography and surface wave data. Journal of Applied Geophysics, 106, 87-95. Gallardo, L. A. (2004). Joint two-dimensional DC resistivity and seismic travel time inversion with cross-gradients constraints. Journal of Geophysical Research, 109(B3). https://doi.org/10.1029/2003jb002716