Thursday, 18 January 2018

Principles and limitations geophysical method of exploration

Geophysics simply means the application of principles of physics in the study of the earth. The application of geophysics is vast. It can be used to study the entire Earth (Global geophysics), or for localized survey of the crust e.g for Engineering purposes.

Geophysical survey is broadly classified into two based on the source of energy.

         Natural field: This uses the electric, magnetic,  electromagnetic and gravitational fields of the           Earth.

         Artificial source: Involves the generation of artificial electrical or electromagnetic fields into the       earth by a means of a D.C.

Magnetic method is applied when searching for buried magnetite ores because of their high magnetic susceptibility.

Electrical method is used when exploring for ground water because rocks resistances differ according to their water saturation levels.

Seismic method is used for hydrocarbon exploration.

It is worth noting that these methods can be combined in a survey such as in metallic mineral exploration in which electromagnetic and airborne magnetic methods are jointly used. The essence of combining different methods in one survey is to remove ambiguity.

If it were possible to know precisely and certainly the physical properties of the Earth, the magnitude of any particular geophysical measurement taken at the Earth’s surface could be predicted easily.

Friday, 28 July 2017

Grain Size Distribution Analysis

Grain Size Distribution Analysis is usually employed in sedimentology. It is employed to determine the size of the different grains that make up a sedimentary rock or soil unit under consideration.

From the analysis, the following can be deduced:

            The sortability of the grains;

            The environment of deposition (Paleoenvironmental reconstruction);

            The energy of deposition (Paleocurrent current reconstruction);

            Transportation agent.

Please note that this analysis does not in any way show / determine the mineralogical composition of the rock / soil unit.

Grain sizes range from gravel (conglomerates and coarser particles) to clay (fine particles). It is determined by its diameter and measured in millimeters (mm), micrometers (µm) or phi (ø).

Below are the soils ranges (in mm):
            Boulders                                              >200
            Cobbles                                               63-200
(Coarse)                                  20-63
                        (Medium)                                6.3-20
                         (Fine)                                      2 - 6.3
                        (Coarse)                                  0.63-2
                        (Medium)                                0.2-0.63
                        (Fine)                                       0.063-0.02
                        (Coarse)                                  0.02-0.063
                        (Medium)                                0.006-0.02
                        (Fine)                                       0.002-0.006
            Clay                                                     <0.002

It is worth noting that no particular grain size exists naturally. It always exists as mixtures / intercalations e.g silty-clay, silty-sand. However, a particular grain size usually dominates the other.

Whenever Grain size (or Particle size) distribution analysis is mentioned, what usually comes to the mind is sieve analysis. Sieve analysis is the rudimentary part of grain size distribution analysis. Other methods exist. Examples are:

            Laser Diffraction

            Dynamic Light Scattering


Sieve Analysis
Just as the name implies ‘sieve analysis’. It is the passage of a weighted amount of soil (usually dried) through a set of sieves with known diameters. The coarses settle on the sieves while the fines pass through to the next sieve till the finest which settles in the tray. It has its pros and cons. It is cheap and easy to operate manually. But it burns the energy of the operator as a result of the constant and vigorous shaking required.

Laser diffraction:
This measures the angular dependence of laser light scattered by particles. It does not require a sieve analysis first. It is done in situ and always accurate. It has the capacity of detecting particle sizes of <100nm to 3mm.

Dynamic Light Scattering:
This measures the intensity of scattered light variations due to Brownian motion of particles in suspension. It is usually accurate and suitable for very fine particles (<1nm – 1µm).

It measures the rate of sedimentation of soil particles in water. It is used for very fine soil particles.

Laser diffraction and dynamic light scattering techniques are newer methods and are more accurate.

Wednesday, 12 July 2017



Is there really any need for an Environmental assessment at all? By the way, what is an Environmental Impact Assessment (EIA for short)? It is an assessment conducted to ascertain the potential effect of a project that is to be sited in a place. The assessment is to appraise whether it will be harmful to the host community or otherwise and the international best practice to adopt.

Activities like mining, quarrying, oil exploration, dredging, citing of power plants, nuclear plants and factories, etc, all requires an EIA before taking off. In some cases, EIA can also be carried out for an already existing project. It is sometimes called Environmental Study, Environmental Impact Statement or Environmental Effect Study.

History has it that EIA was first introduced in 1969 in the United States of America as an Act. Since then, it has been adopted and fine tuned by increasing number of countries to suit them.

It is a norm in most countries of the world and it is usually required by law especially in industrialized countries. There is no definite modus-operandi for this. But in general, it is aimed to ensure that the air, water, land and wildlife (in fact the ecosystem) will not be affected as a result of the project in that vicinity and the environs. An EIA involves a sequence of steps:

  1. Screening to decide if a project requires assessment and to what level of detail;
  2. Preliminary assessment to identify key impacts, their magnitude, significance and importance;
  3. Scoping to ensure that key issues are focused on;
  4. Implementation of the Assessments.

Health Impact Assessments, Strategic Environmental Assessments, Social Impact Assessments and Cumulative Effects Assessments all sums up EIA. Economic and social consequences of the project may be part of factors to be integrated into the EIA or one may decide not to include them in the EIA.

However, the consent of the host community MUST be sought during the assessment and they MUST be carried along in the course of this exercise and their suggestions and inputs are factored in.

In cases where there will be toxic emissions emanating from the project, it will be factored into the study and also how the level of the emissions will be monitored periodically.

Tuesday, 4 July 2017


There are some facts one may think he knows in Geology but…oops! They are really obfuscating. The look so elementary that they are easily jettisoned.

A Rock is an aggregate of naturally occurring minerals.

A Mineral is an inorganic, crystalline and naturally occurring substance with a definite chemical composition.

Physical Properties of Minerals

  1. Hardness (measured in Mohs Hardness Scale). It increases downwards.

Talc (softest)










  1. Luster: is the manner the mineral reflects light.
  2. Color: each mineral has its basic colour for which it is known. But this is usually deceptive.
  3. Streak: The color of the mineral in powdered form.
  4. Cleavage: How the Mineral breaks along its plane of weakness.
  5. Fracture: How the mineral breaks unevenly.

Your Safety And Your Job

It has always been an issue on how best to stay safe in our environment especially in work places coupled with the fact that jobs are much demanding and hectic.

You can’t talk of safety if there is no likelihood of an accident occurring either before, during / or after.

Accident is an unplanned happenstance that occurred as a result mistake, carelessness, or even negligence of a staff(s) in a company. The accident may give rise to small / minor injuries or may lead to death as the case may be.

By WHO standard, ‘Occupational health (your safety and your job) should aim at the promotion and maintenance of the degree of physical, mental and social well-being of workers in all occupations; the prevention amongst workers departures from good health caused by their working conditions; the protection of workers in their employment from risks resulting from factors adverse to health; the placing and maintenance of the worker in an occupational environment adapted to his physiological and psychological capabilities; and, to summarize, the adaptation of work to man and of each man to his job’.


The type and severity of the accident is dependent on:

  1. Your work type (i.e your job function). Sedentary jobs have minimal accidents attached to them.
  2. The nature of your work environment: Is where you work fitted and up-to-date with the necessary safety gadgets?
  3. How prompt the accident victim gets a  medical attention and treatment
  4. Safety skills you have.
  5. Level of noise pollution in the work place.


These factors can cause serious accidents in work places:

  1. Fire and Explosions (especially in mines and oil companies)
  2. Vehicle accident (especially involving heavy trucks)
  3. Falls (especially walking on slippery surfaces and wet terrains)
  4. Air tight offices
  5. Negligence / carelessness / feeling sleepy or dizzy while working with heavy equipments like crushers, mixers, etc.
  6. Poor knowledge of your equipments.


The way out (Remedies)

  1. Be H.S.E compliant and up-to-date.
  2. When at work place, be well kitted.
  3. Sound the alarm in case of an accident.

Monday, 3 July 2017

The Importance Of Geophysics In Groundwater Investigation

Before we delve into this, we need to first of all define some terms.

What is Geophysics?      It is the use of Physics to solve Geology problems.

What then is Geology?  Simply the study of the Earth. This includes the structure and the rocks.

Geophysics is usually employed when it involves probing the subsurface. In physical Geology, you are dealing with the surface geology, i.e. the structures, forms, and the lithofacies that are visible on the surface.

To solve environmental issues, mining, archeological, engineering (Geotechnical) and geological (hydrogeological) problems, geophysics is employed. It is achieved by passing an electric current via two current electrodes and the potential drop between the two current electrodes is measured by a voltmeter. From this, the resistance is deduced. Here, the current (I) is already known and the potential drop (V) is known as well.
Given the formula:          
V=I×R                                                                           ------- (1)
Making R the Subject:    R=V/I                                    ------- (2) {where R is measured in Ohms}

The essence of carrying out this is to determine the intrinsic properties of the geologic materials present in that environment. What the geophysicist is interested in per see is the Apparent Resistivity. This is usually affected by the presence minerals, groundwater, and porosity.

For groundwater investigation, Electrical Method is used. It involves the introduction of current via wires to the electrodes i.e. Vertical Electrical Sounding (VES). There are two main arrays for this: The Schlumberger array and Wenner array. Although each array has its own limitation, it will help you infer how the subsurface looks like.

There are however some factors that determine the accuracy of your results and are:

  1. The accuracy of the equipment (terrameter) used.
  2. The competency of the geophysicist.

Fig 1: ASSEMBLAGE OF THE EQUIPMENT(Terrameter) for Geophysical Investigation.

From the readings gotten and interpretation made, the rock-bearing-water is ascertained and the depth of penetration is known.


For every super structure, there must be an underlying substructure. This substructure is also known as foundation. The essence of the substructure is to transmit the load of the superstructure to the ground and make it firm.

There are broadly two (2) types of foundations:

  1. Shallow Foundations
  2. Deep Foundations

Shallow foundation is any foundation that is between 1m to 3m. it is very near to the surface.

Deep foundation is any foundation that is beyond 3m.

The type of the foundation to be chosen is dependent on the type of superstructure to be erected and the load bearing capability of the soil in that place. These factors have to be determined by a competent Engineering Geologist.

Shallow foundation includes:

Strap footings. This is also called Cantilever footings. Here, two single footings are connected with a beam.

  1. Mat footings. Are mostly used in cases where the soil is so weak and the building loads extensive. A mat is a flat concrete slab massively reinforced with steel. The load is evenly distributed over the entire area. However, for heavy buildings, supplementary foundations can be erected to complement in the even distribution of loads.

Pad footing. Can either be Isolated footing (if it is only one footing); or Combined footing (if it supports two columns).

Pad footing is usually rectangular or square in shape.

Deep Foundations:
They include (but not limited to):
  1. Pile Foundation
  2. Caisson foundation.
The commonest is Pile Foundation and it what we will be discussing here.
It is used:
  1. When the bedrock is far from the surface and the soil is soft.
  2. When building bridges along rivers and/ or seas.
  3. If pad foundation is expensive.

Piles vary based on their composition and this in turn determines its strength and durability. They range from Timber piles, Pre-cast piles, Concrete piles, and Steel piles. Each has its own pros and cons.

Nevertheless, it is always advisable to consult a competent Engineering Geologist.