Geophysical Survey In Bangladesh

Introduction of Geophysical Survey:

Geophysical survey involve systematically collecting data on Earth's magnetic and gravitational fields to understand seismic activity and internal structure. Analyzing these electric and magnetic fields is crucial for their informative content. This article discusses extending 1-D transformation techniques to analyze multi-dimensional signals like electromagnetic and gravitational waves. Surveys employ diverse sensing instruments, gathering data from Earth's surface, aerial, orbital, or marine platforms, with applications in geology, archaeology, mineral exploration, oceanography, and engineering. Instruments such as gravimeters, gravitational wave sensors, and magnetometers detect field fluctuations. Analysis focuses on spectral density and time-frequency localization to derive meaningful insights, crucial for applications such as oil exploration and seismography.

Market Size and Growth:

Market Size: The global geophysical survey market is substantial, with estimates in the range of several billion dollars. The market includes services related to oil and gas exploration, mining, construction, and environmental assessments.

Growth Rate: The industry has been growing steadily, driven by increasing investments in infrastructure, resource exploration, and environmental sustainability. Technological advancements are also contributing to market growth.

Key Technologies:

Seismic Surveying: Widely used in oil and gas exploration, seismic surveying involves measuring the reflection of seismic waves off subsurface structures. In Bangladesh Petro Bangla, BPC and BPPA are the main user of this survey in oil and gas field.

Magnetic and Gravity Surveys: These surveys detect variations in the Earth's magnetic field and gravitational field, respectively, which can indicate the presence of mineral deposits. Mainly Coal Industry, BBA, LGED, RHD, and the Archaeological Department are the main user of this survey in Bangladesh.

Electrical and Electromagnetic Surveys: These methods measure the electrical conductivity or electromagnetic properties of the ground to locate resources and contaminants.

Ground-Penetrating Radar (GPR): GPR uses radar pulses to image the subsurface, valuable in archaeology and civil engineering. In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB and BPDB Etc.

Regional Insights:

North America: The U.S. and Canada are major players in the geophysical survey market, with strong industries in oil and gas, mining, and environmental consulting.

Europe: European countries, particularly the UK, Germany, and France, have significant geophysical survey activities, with a growing focus on environmental monitoring and renewable energy.

Asia-Pacific: Countries like Australia, China, and India are expanding their geophysical survey activities, driven by mining, infrastructure development, and resource exploration.

South America: Nations such as Brazil and Chile are active in mining and exploration, contributing to the demand for geophysical surveys.

ICONIC ENGINEERING LTD, Role: As Iconic Engineering Ltd. conducting geophysical surveys in Bangladesh, have a unique opportunity to play a significant role in both advancing international technology and contributing to the development of a Digital Bangladesh. Here how we make bridge international techniques and support digital advancement in the country-

Bridging International Techniques:

Adopting and Localizing Advanced Technologies:

• Implement Cutting-Edge Tools: Utilize the latest geophysical survey equipment and methodologies from global leaders in the field. This includes advanced seismic, magnetic, and electrical resistivity
• Customization for Local Conditions: Adapt these international techniques to fit the specific geological and environmental conditions in Bangladesh.

Training and Knowledge Transfer:

• Workshops and Training Programs: Organize training sessions and workshops for local engineers and geoscientists on international best practices and new technologies.
• Knowledge Sharing: Collaborate with global experts to facilitate knowledge exchange and technical upskilling for your team and local stakeholders.

Collaborative Projects:

• International Partnerships: Partner with international firms and research institutions to undertake joint projects, which can help bring global expertise and innovation into local practices.
• Global Standards and Certification: Ensure that your practices meet international standards and seek certifications that recognize your adherence to global quality norms.

Contributing to Digital Bangladesh:

Leveraging Data for Digital Platforms:

• Geospatial Data Integration: Integrate the data collected from geophysical surveys into digital platforms and GIS (Geographic Information Systems) to enhance accessibility and usability.
• Digital Databases: Develop and maintain digital databases of survey results, which can be made accessible to policymakers, researchers, and the public. In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB and BPDB

Developing Digital Solutions:

• Software and Apps: Create or contribute to software solutions and mobile apps that facilitate the visualization and analysis of geophysical data. This can help in making data-driven decisions more accessible and actionable.
• Automation and AI: Explore the use of artificial intelligence and machine learning to analyze geophysical data more efficiently and to predict geological phenomena.

Supporting Infrastructure Development:

• Smart Mapping: Use digital tools to assist in planning and monitoring infrastructure projects. For instance, geophysical surveys can inform the planning of roads, bridges, and urban development by providing detailed subsurface information. In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB and BPDB
• Disaster Management: Develop digital solutions for better disaster preparedness and response, using geophysical data to predict and mitigate the effects of natural disasters.

By integrating international best practices and leveraging digital tools, Iconic Engineering Ltd. can not only enhance the efficiency and accuracy of geophysical surveys in Bangladesh but also play a pivotal role in supporting the country’s broader goals of digital transformation and technological advancement.

Types of Geophysical Survey:

• Seismic Cross hole Test (SCHT);
• Seismic Downhole Test (SDHT);
• Seismic Refraction Test;
• Seismic Reflection Test;
• Multichannel Analysis of Surface Wave (MASW);
• Horizontal to Vertical Spectral Ratio (HVSR);
• Electrical/Earth Resistivity Test (ERT);

1. Seismic Cross hole Test (SCHT):

Seismic cross hole testing is a sophisticated geophysical technique used to investigate the properties and structure of the subsurface with high precision and resolution. By deploying seismic sources and receivers within multiple boreholes, this method allows geophysicists and engineers to analyze how seismic waves propagate through the earth. These waves carry valuable information about the elastic properties, density variations, and structural integrity of the subsurface materials, ranging from soil layers to bedrock formations.

Test Procedure:

Preparation: Seismic Crosshole Test requiredTwo or more boreholes are drilled to specified depths and distances apart, typically ranging from tens to hundreds of meters. Boreholes are cased to maintain stability and prevent collapse during testing.

Instrumentation: Seismic sources (such as small explosive charges or seismic hammers) are placed at known depths in one borehole. Geophones (receivers) are positioned at predetermined depths in another borehole. Both sources and receivers are connected to recording equipment at the surface.

Data Acquisition: Seismic waves are generated by the source and travel through the subsurface. Waves are recorded by the geophones at various depths in the receiving borehole. Travel times and arrival patterns of seismic waves are carefully recorded and analysed.

Data Analysis: Arrival times of seismic waves at different depths are used to calculate seismic velocities. Velocity profiles are generated, providing detailed information about subsurface layers and interfaces. Advanced processing techniques, such as tomographic imaging, may be used to create 2D or 3D velocity models.

Interpretation: Velocity profiles are interpreted to identify geological features like bedrock depths, soil types, and potential water-bearing zones. Results are compared with geological maps and site-specific models to assess ground stability and suitability for construction.

Advantage:

• Provides high-resolution images of subsurface velocity profiles.
• Ideal for site characterization and identifying geological structures.

Applicable Area:

• Geotechnical Engineering: Assessing soil stability and properties for construction projects.
• Civil Engineering: Designing earthquake-resistant structures and evaluating ground conditions.
• Environmental Engineering: Monitoring groundwater and assessing contamination pathways.
• Mining and Exploration: Evaluating geological conditions for mining feasibility.
• Infrastructure Planning: Assessing urban subsurface for infrastructure development.
• Research and Education: Advancing geophysical techniques and educating future engineers.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

 Future Scope:

• Advanced data processing, automation, and machine learning will enhance the speed and accuracy of seismic data interpretation.
• Integration with technologies like electrical resistivity tomography and ground-penetrating radar will enable more comprehensive subsurface imaging.
• Seismic crosshole testing's applications are expanding into environmental monitoring, climate change research, and sustainable resource management.

Standard: ASTM D7400 - Standard Test Methods for Downhole Seismic Testing, Eurocode 8 - Design of Structures for Earthquake Resistance, International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) Technical Committee TC102 - Ground Property Characterization from In-Situ Tests.

1. Seismic Downhole Test (SDHT):

A Seismic Downhole Test is a precise geophysical method used to analyze subsurface geology by transmitting seismic waves through a borehole drilled deep into the Earth. This technique provides detailed data on geological structures such as rock layers and fault lines, offering insights essential for resource exploration, hazard assessment, and construction planning, particularly in complex or challenging environments. Unlike surface seismic surveys, which may be hindered by terrain or shallow depths, downhole tests deliver high-resolution information directly from deeper underground layers. This capability makes them invaluable in modern geophysics and engineering, continually advancing our understanding of the Earth's subsurface and enhancing the accuracy of geological and engineering projects. Specially LGED, DMTCL, RHD, BBA are using these technique presently for their recent project.

Procedure:

Borehole Preparation: A single borehole is drilled to the desired depth, often deeper than for SCHT, depending on the project's objectives.

Instrumentation: Downhole geophones are lowered at regular intervals within the borehole. Seismic sources (similar to SCHT) are deployed at various depths within the same borehole.

Data Acquisition: Seismic waves are generated by the sources and recorded by the downhole geophones. Wave arrival times and amplitudes are measured at each geophone depth.

Data Analysis: Similar to SCHT, travel times and wave characteristics are analyzed to determine subsurface seismic velocities. Velocity-depth profiles are constructed, providing insights into geological layering and structural integrity.

Interpretation: Results are interpreted to assess seismic wave propagation characteristics and subsurface conditions. Engineers use the data to design foundations, evaluate seismic risks, and optimize construction methods.

Advantage:

• Provides detailed information on seismic wave propagation in the subsurface.
• Useful for seismic hazard assessment and structural engineering.

Applicable Area:

Resource Exploration: Assessing underground reserves of oil, gas, and minerals by analyzing subsurface structures and properties.

Geological Research: Studying the composition, structure, and history of the Earth's crust to understand geological processes.

Civil Engineering: Evaluating ground conditions for infrastructure projects like tunnels and bridges to ensure stability and safety.

Seismic Hazard Assessment: Identifying fault lines, subsurface structures, and soil properties to assess earthquake risks.

Environmental Studies: Analyzing groundwater flow, contamination pathways, and geothermal reservoirs for environmental management.

Monitoring and Surveillance: Monitoring changes in subsurface conditions over time, such as in reservoir management or underground storage facilities.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

Future Scope:

• Advancements in sensor technology for higher resolution.
• Integration with AI for improved data analysis and interpretation.
• Expansion into multi-physics approaches for comprehensive subsurface characterization.
• Growing applications in environmental monitoring and urban infrastructure development.
• Potential adaptation for space exploration and extraterrestrial subsurface analysis.
• Continued role in enhancing seismic resilience and disaster mitigation strategies.

Standard: ISO 19565:2017 - Geotechnical investigation and testing - Field testing - Part 7: Downhole seismic testing, ASTM D7400-20 - Standard Test Methods for Downhole Seismic Testing, API Recommended Practice 63-2 - Recommended Practices for Evaluation of Well Perforators, IEEE 1609.3-2016 - IEEE Standard for Wireless Access in Vehicular Environments (WAVE) - Networking Services.

1. Seismic Refraction Test:

Seismic refraction testing is a geophysical method used to explore subsurface structures by measuring seismic wave velocities. It provides critical data for engineering projects, environmental assessments, and geological studies by analyzing how waves travel through different materials at varying speeds.

Procedure:

Field Setup: A seismic line is established on the ground surface, typically several hundred meters long. Geophones are spaced at regular intervals along the line, often ranging from 1 to 5 meters apart. Typically, we use 5m ranging. For special case like, MRTL-5 the range was 2-3m as per client requirement.

Source Deployment: A seismic source is activated at one end of the line, generating seismic waves that travel through the ground. We use hammer and steel plate for source.

Data Acquisition: Seismic waves refract (bend) at interfaces between subsurface layers, reaching the geophones at different times. Arrival times of refracted waves are recorded by the geophones.

Data Analysis: Arrival times are analyzed to determine the first arrival times (refracted waves) and calculate their velocities Velocities are used to construct a velocity-depth model, showing layer boundaries and depths to various subsurface features.

Data Interpretation: Interpretation involves correlating velocity-depth profiles with known geological data to identify geological structures. Engineers use the results to assess foundation suitability, groundwater conditions, and seismic risk.

Advantages:

• Provides depth to bedrock and soil layer thicknesses.
• Effective for identifying groundwater conditions and rock quality.

Applicable Area:

Civil Engineering: Assessing the depth and characteristics of bedrock and soil layers for infrastructure projects such as roads, bridges, and buildings.

Environmental Studies: Locating and characterizing groundwater resources, investigating contamination plumes, and assessing the stability of landfills.

Geological Exploration: Mapping geological structures, identifying fault lines, and studying sedimentary basins for oil and gas exploration.

Mining: Determining the depth and composition of mineral deposits and assessing potential mining sites.

Archaeology: Mapping buried archaeological features and understanding site stratigraphy without excavation.

Disaster Risk Assessment: Identifying subsurface conditions that may affect the stability of slopes and potential for landslides.

Future Scope:

Advancements in Technology: Continued improvement in equipment and data processing for higher resolution and accuracy in subsurface imaging.

Integration with Other Methods: Combining with seismic reflection, electrical resistivity, and ground-penetrating radar (GPR) for more detailed subsurface models.

3D Imaging: Development of three-dimensional imaging techniques for clearer visualization of underground structures.

Automation: Implementation of automated data acquisition systems and robotic platforms to streamline field operations.

Environmental Monitoring: Increasing use in continuous monitoring of groundwater, subsidence, and environmental changes.

Urban Infrastructure: Application in planning and assessing underground utilities and infrastructure in smart cities.

Risk Assessment: Integration into quantitative risk assessment models for infrastructure resilience against natural hazards.

AI and Machine Learning: Utilization of AI and machine learning for automated data analysis and interpretation.   

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

Standard:

• ISO 22282 series: Ensures standardized procedures for seismic exploration, maintaining consistency in data collection and interpretation globally.
• ASTM D5777 - Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation.
• ASTM D6432: Specifies protocols for equipment calibration, data acquisition, and reporting, ensuring accuracy and reliability in seismic refraction
• Eurocode 8: Provides guidelines for using seismic methods in structural design, ensuring safety and reliability based on regional seismic conditions.
• AGS Guide: Offers best practices for managing and reporting geotechnical data, including seismic survey results, enhancing transparency and quality assurance.

1. Seismic Reflection Test:

Seismic reflection testing is a key geophysical method for imaging subsurface structures and geological formations. By generating controlled seismic waves and recording their reflections using sensors like geophones or hydrophones, this technique provides detailed underground images. It is essential for locating oil and gas reservoirs, mapping geological features such as fault lines and stratigraphy, and assessing site suitability for construction. Technological advancements continually improve the precision of seismic surveys, enhancing our ability to interpret subsurface conditions accurately. This method supports resource exploration, environmental management, and hazard mitigation by revealing crucial information about the Earth's subsurface with high resolution and reliability.

Procedure:

Survey Design: Multiple seismic lines are laid out over the survey area, typically covering large distances (up to several kilometres). Geophones are spaced along each seismic line at intervals optimized for the desired resolution. The interval between geophone should be 2m (standard).

Source Deployment: A seismic source, such as a specialized vehicle or explosive charge, generates high-energy seismic waves. Waves propagate through the subsurface and reflect off geological interfaces and boundaries.

Data Acquisition: Reflected waves are detected by geophones along the seismic lines. Data recording is synchronized to capture wave arrival times and amplitudes accurately.

Data Processing: Recorded data undergoes complex processing to enhance signal-to-noise ratios and extract reflection events. Reflection events are stacked and migrated to produce subsurface images (seismic sections) with high spatial resolution.

Interpretation: Interpreters analyze seismic sections to identify and map subsurface structures, such as faults, stratigraphic layers, and potential hydrocarbon reservoirs. Results guide exploration and development decisions in oil and gas industries and inform engineering designs for infrastructure projects.

Advantages:

• Provides high-resolution images of subsurface layers.
• Valuable for oil and gas exploration, as well as archaeological studies.

Applicable Area:

Oil and Gas Exploration: Seismic reflection testing locates potential hydrocarbon reservoirs by mapping subsurface geological structures.

Geological Studies: It maps fault lines, stratigraphy, and rock formations to understand the Earth's history and structure.

Engineering and Construction: It assesses site suitability by determining soil types, bedrock depth, and potential hazards like faults.

Environmental Assessment: Provides data for impact assessments and remediation projects by understanding subsurface geology and groundwater pathways.

Natural Resource Management: Helps in locating groundwater, mineral deposits, and assessing land use potential based on subsurface characteristics.

Seismic Hazard Assessment: Evaluates earthquake risks by mapping fault lines and subsurface geological conditions.

Archaeological Studies: Locates buried structures or artifacts without excavation by imaging subsurface anomalies.

Future Scope:

Urban Development: Essential for planning and constructing infrastructure in urban areas by understanding soil and rock layers.

Disaster Risk Reduction: Helps assess geological hazards such as earthquakes and landslides, aiding in disaster preparedness and mitigation efforts.

Water Resource Management: Assists in locating groundwater reservoirs and managing water resources efficiently.

Industrial and Agricultural Development: Provides valuable information for industrial site selection and optimizing agricultural land use.

Environmental Monitoring: Supports environmental impact assessments and monitoring of groundwater contamination.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

Standard:

• ASTM D6429 - Standard Guide for Selecting Surface Geophysical Methods
• ASTM D6235 - Standard Practice for Expedited Site Characterization of Vadose Zone and Groundwater Contamination.
• ISO 18406 - Geotechnical investigation and testing -- Geophysical testing -- Part 2: Seismic refraction testing
• BS EN 16911-1 - Geotechnical investigation and testing -- Geophysical testing -- Part 1: General rules
• AGS Guide - Association of Geotechnical and Geoenvironmental Specialists (UK) - AGS guide to geophysical testing
• ASCE Manual of Practice No. 110 - Subsurface Investigation for Design and Construction of Foundations of Buildings
• Nordtest NT Build 443 - Ground investigations using seismic methods - principles, equipment, verification and interpretation
• USGS Techniques and Methods 2-D1 - Techniques of Water-Resources Investigations of the United States Geological Survey: Surface Geophysics

1. Multichannel Analysis of Surface Waves (MASW):

Multichannel Analysis of Surface Waves (MASW) is a geophysical method that uses seismic waves traveling along the Earth's surface (Rayleigh waves) to determine the shear wave velocity profile of near-surface layers. By deploying multiple geophones in a linear array and analyzing recorded signals, MASW extracts dispersion curves showing the phase velocity of surface waves across frequencies. Inverting these curves yields a shear wave velocity profile, essential for assessing soil stiffness and layering in geotechnical, environmental, and seismic hazard studies. MASW is valued for its non-invasive approach, high resolution, and cost-effectiveness compared to traditional methods.

Procedure:

Field Setup: Geophones are arranged in a linear array along a seismic line, typically spaced at regular intervals (1 to 5 meters). A seismic source, often a sledgehammer or a small explosive charge, generates surface waves.

Wave Propagation: Surface waves propagate along the ground surface and are recorded by the geophones. Geophones capture ground motion in both horizontal and vertical components.

Data Acquisition: Seismic signals are digitized and recorded for subsequent analysis. Multiple shots are often acquired to ensure data consistency and quality.

Data Processing: Recorded signals undergo spectral analysis and dispersion curve inversion. Dispersion curves reveal the relationship between wave velocity and frequency, providing information on subsurface stiffness.

Interpretation: Engineers interpret dispersion curves to determine shear wave velocity profiles. Results aid in seismic site classification, liquefaction potential assessment, and seismic design considerations.

Advantages:

• Provides detailed information on soil layer stiffness and depth.
• Useful for seismic site classification and liquefaction studies.

Applicable Area:

Geotechnical Engineering: Assessing soil properties for infrastructure projects such as buildings, roads, and bridges. It helps in understanding soil stiffness and layering, which are critical for foundation design.

Environmental Studies: Mapping geological formations, identifying groundwater levels, and assessing contamination risks in near-surface layers.

Natural Hazard Assessment: Evaluating seismic site response and potential for liquefaction in earthquake-prone areas.

Mining and Exploration: Characterizing subsurface geological structures and identifying potential mineral deposits.

Civil Engineering: Evaluating the stability of slopes and embankments, as well as assessing the integrity of dams and levees.

Archaeology: Locating buried structures and archaeological remains without excavation.

Infrastructure Rehabilitation: Assessing the condition of existing structures and foundations.

Future Scope:

Infrastructure Development: MASW can aid in detailed subsurface investigations for urban development projects, ensuring stable construction practices by assessing soil properties and potential hazards like liquefaction.

Environmental Management: It can contribute to environmental studies by mapping geological formations and groundwater levels, assisting in sustainable water resource management and mitigating environmental risks.

Disaster Risk Reduction: Given Bangladesh's susceptibility to natural disasters such as earthquakes, MASW can help assess seismic site response and identify areas prone to ground shaking and soil liquefaction.

Agriculture and Land Use: MASW can assist in optimizing agricultural land use by providing insights into soil characteristics and groundwater levels, supporting efficient irrigation and land management practices.

Industrial and Mining Applications: It can aid in locating and characterizing mineral deposits, supporting sustainable mining practices and industrial development.

Urban Planning and Management: MASW data can inform urban planners about subsurface conditions, supporting infrastructure planning and management to accommodate the country's rapid urbanization.

Research and Development: Ongoing advancements in MASW technology and methodologies can further enhance its capabilities and applications in diverse fields, fostering research collaborations and innovations in geophysical investigations.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

Standard:

• ASTM D7400 - Standard Test Methods for Downhole Seismic Testing
• ASTM D7949 - Standard Guide for Selection of Techniques for Electrical Subsurface Exploration
• BS EN 16948 - Geotechnical investigation and testing -- Geophysical testing -- Part 2: MASW
• AGS Guide - Association of Geotechnical and Geoenvironmental Specialists (UK) - AGS guide to geophysical testing.

1. Horizontal to Vertical Spectral Ratio (HVSR):

Horizontal to Vertical Spectral Ratio (HVSR) is a geophysical method used to analyze seismic data by comparing the spectral amplitudes of horizontal (X and Y axes) and vertical (Z axis) components of ground motion recorded by a seismometer. By calculating the ratio of horizontal to vertical spectral amplitudes across a range of frequencies, HVSR reveals the site's predominant resonant frequencies and amplification characteristics. This information is essential for seismic hazard assessment, site characterization, and engineering design, as it helps in understanding how ground motion varies with frequency and guides decisions on constructing resilient structures in earthquake-prone areas. HVSR plays a crucial role in seismic microzonation studies, aiding in the classification of regions based on their seismic response properties, thereby contributing to safer urban planning and infrastructure development.

Procedure:

Instrumentation: A single geophone or accelerometer is positioned at the measurement location, typically at the ground surface.

Data Acquisition: Microtremors, natural ground vibrations, are recorded over a period of time. Both horizontal (North-South and East-West) and vertical components of ground motion are measured.

Spectral Analysis: Fourier transforms are applied to the recorded time series data to obtain power spectral densities (PSDs) for each component.

Ratio Calculation: The horizontal-to-vertical spectral ratio (HVSR) is computed by dividing the averaged horizontal PSD by the vertical PSD.

Interpretation: Peaks in the HVSR curve correspond to resonance frequencies of the site. Engineers use HVSR results to estimate site amplification factors and assess seismic hazard levels.

Advantage:

• Provides rapid assessment of site amplification potential.
• Useful for seismic microzonation and site-specific hazard assessments.

Applicable Area:

Seismology and Earthquake Engineering: HVSR helps assess the amplification of seismic waves at specific sites, providing essential data for seismic hazard analysis and engineering design of structures. It aids in understanding how different types of soils and geological conditions affect ground motion during earthquakes.

Site Characterization: HVSR is essential for evaluating the dynamic properties of soil and rock layers beneath the ground surface. This information is critical for infrastructure projects, as it determines the site's suitability and potential hazards related to ground shaking.

Microzonation Studies: In urban planning and disaster management, HVSR data contributes to microzonation studies, helping to classify areas within a region based on their seismic response characteristics. This classification assists in developing appropriate building codes and land-use policies to enhance seismic resilience.

Environmental and Geotechnical Investigations: HVSR can also be used in environmental and geotechnical studies to understand the geological and geophysical properties of the subsurface. It aids in groundwater exploration, geological mapping, and assessing potential hazards such as landslides and liquefaction.

Future Scope:

Seismic Risk Assessment: Bangladesh's vulnerability to seismic activity, HVSR can provide critical insights into how ground motion amplifies across different soil types and geological conditions. This data is essential for enhancing seismic hazard maps and improving building codes to mitigate earthquake risks.

Infrastructure Development: HVSR can aid in site-specific characterization of soil dynamics, helping to optimize the design and construction of resilient infrastructure that can withstand seismic events more effectively.

Urban Planning and Disaster Management: HVSR data can contribute to microzonation studies in urban areas, guiding land-use planning and development regulations to enhance seismic resilience and reduce potential losses during earthquakes.

Environmental and Geological Studies: Beyond seismic applications, HVSR can assist in mapping subsurface geological features, assessing groundwater resources, and identifying potential hazards.

Research and Education: Continued research and education initiatives focusing on HVSR can enhance local expertise in earthquake engineering and geophysics, fostering a more informed approach to seismic risk reduction and disaster preparedness.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

1. Electrical/Earth Resistivity Test (ERT):

The Electrical Resistivity Test (ERT), commonly referred to as the Earth Resistivity Test, is a geophysical method used to determine the electrical resistivity of subsurface materials such as soils, rocks, and groundwater. This test plays a critical role in geotechnical and environmental investigations, providing valuable information for a wide range of applications including civil engineering, environmental studies, and groundwater exploration. ERT works on the principle that different materials have varying electrical resistivities. By measuring the resistance of the ground to an electrical current, it is possible to infer the subsurface's resistivity distribution. The test typically involves injecting an electrical current into the ground through electrodes and measuring the resulting potential differences at other electrodes. These measurements are then analyzed to create a resistivity profile of the subsurface.

Dipole Array

Procedure:

Electrode Placement: Arrays of electrodes are placed on the ground surface at specified intervals (1 to 5m range). Electrode arrays may vary depending on the desired depth of investigation and survey objectives.

Current Injection: Direct current (DC) is injected into the ground through selected electrodes. Potential differences (voltages) are measured using other electrodes to capture subsurface resistivity variations.

Data Acquisition: Voltage measurements are recorded for each electrode configuration. Multiple measurements are taken along the survey line or grid to cover the entire survey area.

Data Processing: Inverse modeling techniques are applied to interpret resistivity data and generate 2D or 3D resistivity models. Models depict variations in subsurface resistivity, highlighting geological structures, groundwater tables, and potential contaminants.

Interpretation: Interpreters correlate resistivity models with geological data to delineate subsurface features. Results inform groundwater exploration, mineral prospecting, and environmental remediation strategies.

Advantage:

• Non-destructive and non-invasive method.
• Provides detailed information about subsurface conditions.
• Cost-effective compared to traditional drilling methods.
• Provides information on groundwater salinity, contamination plumes, and lithological boundaries.
• Useful for archaeological surveys and environmental investigations.

Applicable Area:

Geotechnical Engineering: ERT is extensively used in geotechnical investigations to assess soil properties such as porosity, permeability, and moisture content. This information is crucial for designing foundations, evaluating slope stability, and assessing the potential for subsidence.

Environmental Studies: In environmental studies, ERT helps in identifying contaminated areas and monitoring the movement of pollutants underground. It can also delineate geological structures that influence groundwater flow, aiding in the design of remediation strategies.

Groundwater Exploration: ERT is a valuable tool for mapping groundwater aquifers and determining their extent and depth. This information is essential for sustainable groundwater management and locating suitable sites for wells and boreholes.

Civil Engineering: For civil engineering projects, such as the construction of dams, bridges, and tunnels, ERT provides insights into the subsurface conditions that affect construction feasibility and stability.

Archaeology: ERT is increasingly used in archaeology to detect buried structures and artifacts without disturbing the site. It helps archaeologists plan excavations and understand the historical context of an area.

In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, WASA, City Corporation, RAJUK, PWD, Bangladesh Railway Department and other private industry like construction company, electrical industry, oil and gas industry etc.

Future Scope:

Infrastructure Development: Bangladesh is undergoing rapid urbanization and infrastructure development. ERT can play a crucial role in assessing the subsurface conditions for constructing foundations, roads, bridges, and other infrastructure projects. By accurately mapping subsurface layers and identifying soil properties, ERT can help engineers design more resilient and cost-effective structures that withstand local geological conditions, such as soft clayey soils in deltaic regions. Main user in Bangladesh are LGED, PWD, DMTCL, BBA, RAJUK, WASA, CITY CORPORATION, BHRI and other private construction company.

Flood Risk Assessment and Management: Bangladesh is prone to flooding due to its low-lying deltaic geography and monsoonal climate. ERT can be instrumental in mapping groundwater levels, understanding aquifer characteristics, and assessing flood vulnerability. By identifying areas with high groundwater potential and understanding subsurface water flow dynamics, ERT can aid in developing effective flood risk mitigation strategies, such as improved drainage systems and floodplain management.

Environmental Monitoring and Remediation: Environmental degradation and pollution are growing concerns in Bangladesh, particularly in urban and industrial areas. ERT can help in assessing soil and groundwater contamination, identifying sources of pollution, and monitoring the effectiveness of remediation efforts. By mapping contaminant plumes and understanding subsurface transport mechanisms, ERT can support environmental agencies and industries in making informed decisions to protect water resources and public health.

Groundwater Resource Management: Bangladesh heavily relies on groundwater for drinking water and agricultural irrigation. ERT can assist in mapping groundwater aquifers, determining their extent, depth, and recharge rates. This information is crucial for sustainable groundwater management, preventing over-exploitation, and ensuring equitable distribution of water resources among communities and agricultural sectors.

Archaeological and Cultural Heritage Preservation: Bangladesh has a rich cultural heritage with numerous archaeological sites and historical monuments. ERT can be employed to non-invasively explore and map subsurface structures and artifacts without disturbing the archaeological sites. This can aid archaeologists and cultural heritage experts in planning excavations, preserving historical sites, and gaining insights into the region's history and civilization.

Technological Advancements and Capacity Building: As technology advances, there are opportunities to improve the efficiency, accuracy, and applicability of ERT in Bangladesh. This includes developing locally adapted protocols and standards, enhancing data interpretation techniques, and integrating ERT with other geophysical and remote sensing methods for comprehensive subsurface characterization.

Standard: ASTM D6431 - Standard Guide for Using the Direct Current Resistivity Method for Subsurface Investigation.

Contributing to Smart Bangladesh Mission through GEOPHYSICAL SURVEY:

Iconic Engineering Ltd. can play a significant role in creating a "Digital Bangladesh" and contributing to the "Digital Bangladesh Mission 2041" by leveraging your expertise in geophysical surveys. Here’s how:

1. Infrastructure Development:

Geospatial Data for Planning: Provide detailed geospatial data and analysis to support the development of digital infrastructure. This includes mapping for fiber optic networks, data centers, and smart city planning. In Bangladesh main user of this survey are LGED, RHD, BBA, DMTCL, DNCC, DSCC, WASA, City Corporation, RAJUK, DPHE, CAAB, PWD, Bangladesh Railway Department, DESCO, NESCO, EGCB, PGCB, BPDB and other private industry like construction company, electrical industry, oil and gas industry etc.

Site Suitability Assessments: Conduct surveys to determine optimal locations for new infrastructure projects, ensuring they are resilient to natural hazards and environmental conditions.

2. Disaster Management and Resilience:

Hazard Mapping: Create detailed maps identifying areas prone to natural disasters such as flooding, earthquakes, or landslides. This information is critical for digital emergency management systems.

Risk Assessment: Assist in assessing the risk to digital infrastructure from natural and human-made hazards, supporting the creation of robust and resilient systems.

3. Smart City Initiatives:

Subsurface Mapping: Provide information on underground utilities and structures to facilitate the development of smart city infrastructure without disrupting existing systems.

Environmental Monitoring: Use geophysical methods to monitor environmental conditions that affect urban planning, helping to maintain a sustainable and liveable urban environment.

4. Data Integration and Management:

High-Resolution Data: Supply high-resolution geophysical data that can be integrated into Geographic Information Systems (GIS) and other digital platforms, enhancing the accuracy and efficiency of digital services.

Data Quality Assurance: Ensure the reliability and accuracy of geospatial data used in various digital applications and platforms.

5. Support for Remote Sensing Technologies:

Integration with Remote Sensing: Combine geophysical survey data with remote sensing technologies to create comprehensive digital maps and models for various applications.

Enhanced Monitoring: Utilize your data to improve the monitoring of natural resources and urban areas, contributing to smarter resource management and urban planning.

6. Collaborations and Partnerships:

Public and Private Sector Collaboration: Partner with government agencies, technology firms, and academic institutions to contribute to national digital initiatives and research.

Capacity Building: Work with local and national stakeholders to build capacity in digital geospatial technologies and data analysis.

7. Innovation and Research:

Advanced Techniques: Explore and implement cutting-edge geophysical techniques and technologies that can enhance digital infrastructure and services.

Research Contributions: Engage in research and development projects that push the boundaries of how geophysical data can be used in digital applications.

By focusing on these areas, Iconic Engineering Ltd. can significantly contribute to the vision of a Digital Bangladesh, helping to drive forward the goals set out in the Digital Bangladesh Mission 2041. Your expertise in geophysical surveys will be crucial in ensuring that the digital infrastructure and services are well-planned, resilient, and effective.

Conclusion:

In conclusion, geophysical surveys are a vital component in the advancement of modern infrastructure and digital transformation. For Iconic Engineering Ltd., your role in this field extends beyond traditional surveying; it encompasses a broad range of contributions to Bangladesh’s digital future.

Key Points:

Foundation for Digital Infrastructure: Your geophysical surveys provide essential data for the planning and development of digital infrastructure. This data supports the creation of smart cities, reliable data networks, and efficient utility management, all crucial for a Digital Bangladesh.

Enhancing Resilience and Safety: By mapping natural hazards and assessing subsurface conditions, you help enhance the resilience of digital infrastructure against environmental and man-made risks. This contributes to the safety and sustainability of urban and rural environments.

Data Integration and Innovation: The integration of high-resolution geophysical data with digital platforms and GIS enables more precise and effective planning. Your innovative approaches and advanced survey techniques drive forward technological advancements and improve digital services.

Support for National Goals: By partnering with government bodies, technology providers, and research institutions, Iconic Engineering Ltd. supports national initiatives, such as the Digital Bangladesh Mission 2041, through your expertise and collaboration.

Capacity Building and Research: Your involvement in research and capacity building helps to elevate local expertise and fosters the development of new technologies and methodologies in geophysical surveying.

In essence, Iconic Engineering Ltd. plays a crucial role in shaping the digital landscape of Bangladesh. Your work not only supports the development of physical infrastructure but also enhances the overall quality and effectiveness of digital solutions, contributing significantly to the nation's vision of a technologically advanced and digitally integrated future.