More blue water - why is the Nil Diya Pokuna blue?

On my last visit to Sri Lanka, I was keen on exploring some lesser-known attractions and decided to visit Nil Diya Pokuna (නිල් දිය පොකුණ) located close to Ella in the Uva Province. I was impressed and fascinated by the massive underground cave complex and the blue water pond at the end of the 850m hike through the cave. This was the second time I saw clear blue water in Sri Lanka, the first being in a limestone quarry.  

The usual reason for ponded water to appear bright blue or turquoise in colour is the fine particulates that selectively scatter light through water (the same reason why the sky is blue). In the case of the limestone quarry the fine particulates are minute calcite crystals and in the case of glacial lakes they are finely ground rock particles known as glacial flour. 

Nil Diya Pokuna has a very interesting geology, with several different rock types present around and within the caves, and I wanted to understand what gives the water its blue colour. Caves of this scale are usually formed by the action of weathering and erosion of sedimentary rocks such as limestone. However, this region of Sri Lanka consists of primary of metamorphic rocks. This blog post by Dr Jayasingha describes the geological origins of the cave complex containing Nil Diya Pokuna. According to it, the caves have been formed by the initial dissolution of Marble, which leads to weakening of rock joints and bedding planes and subsequent collapses of the other rock masses creating the large underground caverns. 

Marble is formed by the metamorphosis of limestone, and its dissolution would lead to the release of calcite crystals. There are stalactites formed at several places within the cave, as seen in the photos below, that confirm the occurrence of marble or limestone dissolution. Therefore, it is reasonable to conclude that the reason for the blue coloured water in Nil Diya Pokuna is the calcite crystals that are accumulated in the water as it flows through the joints and fissures in rock containing marble or limestone before making its way into the pond. Below are some photos from my visit:

Stalactites in the cave indicating marble or limestone dissolution
 

Evidence of weathering and staining in the rock

Visible bedding planes and smooth joint surface of a possible collapse leading to cave formation

Blue water and more stalactites

High water levels were blocking off some more expansive areas of the cave

The water was a little murky due to recent rains

Estimating surface settlement induced by underbore or tunnel construction

It is often necessary to estimate the potential ground surface settlement caused by underground infrastructure projects involving tunnels and underbores. Such settlement assessments are used to determine if any additional protection works are necessary particularly if underbores are tunnels are to be constructed underneath roads, railways or buildings. Finite element analysis programs such as Plaxis 2D/3D, Optum G2/G3 or FLAC are typically used to model settlements in such instances. Accurate information on ground properties, tunnel parameters and loading conditions is required to provide accurate settlement assessments. 

In situations where a quick estimate with minimum data inputs is required, a common semi-empirical method developed by Peck (1969) is also commonly used. This method is based on field observations made by Peck, and the ground settlement trough profile is approximated by a Gaussian distribution curve. The volume loss in the tunnel (overbreak or annular collapse) is equated to the area under the Gaussian curve from which a settlement profile is generated. The width of the settlement trough varies between soil types and is controlled by a parameter (Kg) that is specified for different soil types and strengths. I developed a web application (https://underbore-settlement.anvil.app/), also embedded below, to estimate settlements based on the Gaussian curve method developed by Peck.

 

It should be noted that since this method does not consider any volume change in soils (consolidation or dilation), it is valid only as an initial estimate under short-term conditions. 

The figure below shows results from the above method compared to the results from a simple Plaxis 2D model. A tunnel with 1m diameter and 2m of cover subject to a volume loss of 10% bored through undrained soft clay and loose sand was modelled separately in Plaxis 2D to compare against the results using Peck's method with recommended numbers for Kg, for clay (0.5) and sand (0.3) respectively.

Comparison between Plaxis output and Gaussian curve method by Peck (1969)

It can be seen that the results from Plaxis and Gaussian curve method are similar for sand, but varies slightly for clay. Using a Kg value of 0.7 for clay leads to a curve very similar to the Plaxis 2D output. The choice of Kg for various soil types with different strengths is a subject of research, and available literature suggests that a Kg value of 0.4-0.7 is appropriate for soft clays. However, with an understanding of the limitations of the Gaussian curve method, it can be used as a rough initial estimate of settlements before embarking on detailed finite element analysis. The web application linked above will be useful for such quick assessments. 

Building a web app with nothing but (a bit of) Python

My knowledge of Python (the programming language) is not extensive. I have used it a few times to streamline some of my research activities that include data handling and processing. I find Python easy to get into without much programming experience and sources like Stack Overflow help very much to do this. So when I came across a web platform called Anvil that claims to let you build fully functional web apps with nothing but Python, I decided to give it a try. I was pleasantly surprised, and happy with the web application that I was able to build with a relatively basic knowledge of Python and nothing else. My code may not be the most efficient, but it gets the job done.

I decided to build an app within my area of research. It is an app to estimate soil hydraulic properties and oxygen diffusion coefficients at different degrees of saturation, based on water retention properties of the soil. I used equations from literature and those developed in my own research to do this. Two water retention curve parameters (van Genuchten α and n) and the soil porosity are used as inputs and the hydraulic conductivity function and oxygen diffusion coefficient characteristic are generated using the equations. I used the Plotly library built into Anvil to generate three plots for the generated functions and the water retention curve. I also built in an option to export the generated data as a text file that can be used for further analysis.

I was able to do this with the free plan that Anvil offers. Anvil also has a paid subscription plan that has more Python libraries and more options for development support and deployment. I believe it is a great product with exciting capabilities.

My first web app can be accessed at :  https://rukshan-azoor-wrc.anvil.app/

Backfill for underground infrastructure: Soil strength or corrosivity? Which do we choose?

This post is inspired by one of my research findings published recently. My PhD research involved the evaluation of underground corrosion from a unique viewpoint combining the two traditionally separate fields of soil mechanics and electrochemistry.

Corrosion requires both water and oxygen to occur, and in the case of underground corrosion, soil supplies these reactants for the reactions to proceed. It follows that the ability of the soil to store and supply water and oxygen will to some extent, govern the rate of corrosion of metal buried in soil. It is known that there is a critical level of moisture at which corrosion is soil is maximized. Too much water will stifle corrosion because the supply of oxygen to metal is severely limited under waterlogged conditions.

As part of my research, we investigated these mechanisms in detail. Buried infrastructure such as pipelines and storage tanks fail due to corrosion, causing large economic losses and environmental damage due to leaks and bursts, exposing contents such as oil and gas to the surrounding environments. An understanding of underground corrosion and its prevention helps increase longevity of such buried assets and is a step towards sustainable development. While corrosion and its prevention are handled by electrochemical practitioners, the installation of buried infrastructure and backfilling is under the purview of geotechnical engineers. Given that the problem of underground corrosion overlaps both these fields, its study should be an interdisciplinary effort.

Our experiments showed that the critical level of moisture for corrosion is related to a relationship known as the soil water retention curve, or the soil water characteristic curve. Combining results from several electrochemical experiments and soil tests we were able to identify the behavior of water in soil that governs corrosion. We saw that in different soil types, the continuity of air and water phases change differently with the degree of water saturation, and that the transition point at which the air phase becomes occluded coincides with the critical degree of saturation for corrosion (where corrosion is maximized) for each soil type. What was more interesting was that this critical water content for corrosion is the same as the optimum water content for soil compaction. It has been shown that the same mechanisms for air entrapment occurs at the optimum water content during soil compaction.

This finding is important because, it is usual practice among geotechnical engineers to compact soil to its optimum water content to maximize its strength. In the installation of buried infrastructure and the subsequent compaction of backfill, if this usual practice is followed, we will be inadvertently creating the most conducive conditions for corrosion of the buried metallic asset. So, the question is whether we increase our soil strength, of the rate of deterioration of the buried metal. One possible solution is to compact soil in the drier side of the optimum water content. But there may be other factors at play that need to be considered. What is more important is to identify that this problem is interdisciplinary in nature and needs to be solved that way. Corrosion engineers need to be aware of this in planning prevention techniques such as cathodic protection, and geotechnical engineers need to know the effect of soil compaction on the corrosion of buried metallic infrastructure.

Like many of our modern problems, underground corrosion needs to be viewed and solved by taking a multidisciplinary approach. Confining our engineering efforts to the traditionally isolated fields is likely to worsen the problem rather than solving it, and our knowledge and forces need to combine to achieve sustainable progress.

The point of maximum corrosion was identified as the degree of saturation at the inflection point of the water retention curve also coincident with the degree of saturation at the optimum moisture  content (OMC) in the compaction curve

Beach Nourishment in Sri Lanka

Beach Erosion is a problem faced by many countries and erosion mitigation has been traditionally done using hard engineering solutions such a seawalls, revetments, groins and breakwaters. However, research in this field has identified that such engineered structures are not suitable as long term solutions for erosion as they interfere with the dynamic coastal processes. It has also been suggested that soft engineering solutions which work along with these coastal processes are the best approach in solving the problem of beach erosion. Beach nourishment is currently the most popular soft engineering solution and is increasingly being used to protect beaches all around the world. Sri Lanka has also joined this trend and completed its first beach nourishment program along a 1.8km stretch in the the Uswetakeiyawa Palliyawatta area in early 2012.

The project involved a large capital investment and a total of volume of 300,000 cubic meters had been used in the nourishment process. The sand used to nourish the beach was offshore sand dredged using a vessel anchored far away from the coastal zone. This is important because, using sand in the coastal zone itself would have been ineffective. The dredged sand had been pumped via pipeline and released as a slurry onshore and the beach reconstructed using earth moving equipment. Several offshore breakwaters had also been constructed with the intention of retaining the nourishing sand. While the project seemed to be an initial success with positive results shown in surveys carried out immediately before and after the project, over a period of time it is evident that the nourishment has not changed the rate of erosion. At present, the beach has once again severely eroded and continues to erode despite the breakwaters.

Severe erosion of the nourished sand

The success of a beach nourishment program depends on many factors. Coastal processes such as waves, near-shore currents, tides and even wind affect the nourishment process. Parameters such as beach profile and gradient and grain size of sand also matters in this regard. For this reason, a beach nourishment effort is site specific and all these site specific data needs to be considered when planning a nourishment program. In addition, it also vital to continuously monitor the performance of the beach after nourishment and to take necessary remedial action to maintain the project.

While most of the above information had been gathered prior to the nourishment project at Uswetakaiyyawa, the effort has fallen short in post project monitoring. The construction of breakwaters to retain the sand being a tried and tested method, has failed to perform properly possibly due to incorrect layout and dimensions of the breakwaters. Our final year research project aims to assess the performance of this nourishment effort and to provide a solution to the problems faced in this project.

To do this, beach profile measurements are taken using a dumpy level and total station along transects perpendicular to the nourished coastal strip. This process is done during several visits to the area covering the main seasonal cycle of the country. This data is used to model the beach profile and to analyse the sand volume changes with respect to time. A particle size analysis is performed on samples collected at each transect and will be used to determine the direction and severity of the sand transport. In addition to this, a temporal analysis of satellite images is also expected to be incorporated in the research in order to further enhance the field data. Using these findings, our research team expects to propose a suitable solution to minimize the rate of erosion and provide a methodology to effectively monitor beach nourishment programs in Sri Lanka. This would be of immense use in future nourishment projects in the country.

Mining for Petroleum

Although Mining Engineering and Petroleum Engineering are two different fields of study, the two fields cross paths when it comes to the Oil Sands Industry. Oil Sands refers to the deposits of petroleum in the form of heavy bitumen being present in a mixture of sand or loosely consolidated sandstone. Because this heavy oil is too thick to flow and because it is thoroughly mixed with sand, the conventional methods of extraction of petroleum by drilling cannot be applied here. For this reason and also if the oil sand deposit lies relatively close to the surface, open pit mining is used to extract the oil sands. Once mined, the sands are processed to produce synthetic oil.

The mining for oil sands begins like in most mines by the overburden removal process. Common machinery such as excavators, bucket scrapers, and bulldozers are used to remove the overburden and the overburden is hauled by trucks and piled separately for refilling purposes. Once the overburden is removed and the oil sand layer exposed, the mining process begins. Since the oil sand deposits are unconsolidated, they can be easily be extracted by shovels or excavators. For this reason and for obvious safety reasons blasting is not performed. In addition to these machines, draglines and sometimes continuous excavators such as bucketwheel excavators are also used for mining the oil sands. The mined sand is hauled to a plant where the petroleum is extracted and refined by a variety of processes including crushing, froth flotation and distillation.

Although previously termed as an unconventional source of petroleum, the depletion of "conventional oil" and the associated rise in oil price has resulted in a shift of attention towards the oil sands industry. The largest oil sands deposits are located in Canada and Venezuela and the total volume of oil contained in the sands exceeds the conventional oil reserves of the world.  Oil sands have been commercially extracted in the Athabasca region in Canada since the 1930s and since have developed along with the advances in extraction technology. The following graph shows the value of sales  of oil sands and conventional crude oil in Canada and it can be seen that the oil sands sales have shown a significant rise during recent years.

value of sales of crude oil and oil sands (data taken from : http://www.capp.ca/library/statistics/Pages/default.aspx)

New methods have been developed to extract oil sands deposits that are too deep to extract using surface mining. These methods involve the reduction of the viscosity of the bitumen and the separation from the sand and enables the oil to be pumped to the surface. These methods are termed "In-situ methods". Cyclic Steam Stimulation (CSS), Steam Assisted Gravity Drainage (SAGD) and Toe to Heal Air Injection (THAI) are some of these methods. With advances in in-situ methods like these, the the recovery percentages of oil sands deposits have increased and now it can be considered as a viable alternative to conventional oil.

Limestone Mining in Pictures

In this post I have attempted to summarize the limestone mining process in pictorial form (and a video). Short descriptions have been included where necessary.

Overburden Removal

once the overburden is removed, the beds are cleaned and are prepared for drilling

Drilling

drilling is performed according to a pre determined pattern to accomodate explosives for blasting

Blasting

Rock Blasting is performed to fragment and loosen the consolidated limestone.

Loading and Hauling

Dispatching 

Tyre Maintenance of Mine Machinery

The performance of machinery and their availability plays a major role in the productivity and output of a mine. For this reason, every aspect of the machines should be properly maintained. The tyres of these machines are what keeps the machine in contact with the ground and bears the weight of the machine. While tyres for mining machinery are designed to withstand a beating, incorrect maintenance can reduce lifetime of the tyres, or ultimately lead to catastrophic accidents. Therefore, the proper maintenance of the tyres is as important as the maintenance of any other component of the machine.

Handling large tyres of the gigantic mine machinery is not an easy task. Even a simple task such as changing the tyre is difficult and results in a considerable amount of downtime. Therefore the best strategy in this case is preventive maintenance. This means checking tyre inflation daily, ensuring that valve caps are on, checking tread depth and removing stones and other debris lodged between the treads.

changing tyres is a difficult task

When it comes to daily maintenance, the first thing that comes to mind is the inflation pressure. Both over-inflation and under-inflation are detrimental to the tyre, and therefore, it must be ensured that the inflation pressure lies within the accepted limits. It should be noted that when running the machine the tyre pressure increases by about 10-20 percent. Therefore, this must be taken in to account when setting inflation pressure bounds. Tyres kept in good condition with the proper inflation will last longer and perform better.

External conditions of the mine also affect the tires. The road condition for example is what determines how fast the tyres will wear out. While it is not practical to maintain spotless roads, roads should be kept clear of scattered rocks and sharp pits as driving over these can cause a crack in the rubber, and subsequent running will cause it to propagate and destroy the tyre. Therefore clearing fallen debris off the roads and maintaining the road surface is also a part of tire maintenance. Wet rubber cuts better. therefore it is best to avoid wet road conditions. While most haul roads in mines are watered regularly to minimize dust, it must be ensured that the roads don't get too wet.

Bad road conditions can cause cracks to develop

The handling of the machines and their usage are two other areas that need to be considered. Driving too fast, especially in the case of dump trucks can cause several types of tire damage. In the case of heavy machinery used in mines, a combined parameter combining both speed and weight is assigned to tyres. This parameter is called the TKPH rating (Ton Kilometer per Hour). The TKPH rating should be considered when selecting and using tyres. When loading dump trucks, they should be loaded symmetrically so that the load is distributed over tyres equally. asymmetric loading can cause uneven wear and later result in more severe damages. It should also be noted that shear forces generated when steering the trucks while stationary at the loading points could cause ruptures in the tyres.

When dealing with damaged tyres, it is always best to attend to it them at the start of the problem. Neglecting small faults like cracks and running with them can cause these small faults to quickly propagate and result in serious and irreversible damage. When a crack appears it can be removed altogether by cutting around it. This however has to be done with proper equipment and knowledge of the tyre. When replacing tyres, it is always best to replace it with a tyre of similar amount of wear.

In summary, daily maintenance goes a long way in increasing the lifetime of the tyre. Inflation pressure must always be within the specified limits. The road surfaces, loading and dumping points should be free of fallen debris and excessive water, because wet rubber gets cut better. payload weight and hauling speed must be controlled. The TKPH rating assigned to the tyre must be adhered to. Proper handling of the machinery such as symmetric loading, avoiding steering while stationary and avoiding excessive tyre spinning will reduce the likelihood of damages. when repairing, the first stages of the problem is always easy to cure.

The Intricacies of Mud Crack Formation

Patterns found in nature are most often astoundingly complex while also being elegant and aesthetically pleasing. Snowflakes for example consist of extremely delicate, symmetric structures of frozen ice and are always different from each other. Yet these infinite patterns are influenced by only two main controlling factors, temperature and humidity. A  more obvious example of patterns in nature are mud cracks. Although they are not as delicate and complex as snowflakes, they also exhibit some patterns that are interesting to observe. What follows are some facts I gathered from a small study about mud cracks and some  photographs taken during my training period at the Aruwakkalu limestone mine.

Mud cracks are formed quite obviously, when  mud dries up. So the main factor controlling mud crack formation is moisture content. Unlike in glass and many other materials, cracks in mud do not originate at single point and then propagate. If the rate of drying is uniform across a surface of a layer of mud, cracks will start appearing simultaneously across the surface. Mud starts to dry from the exposed surface. So when the moisture content of the surface layer starts to drop, the mud particles come close to each other as the space occupied by water is emptied. This results in the contraction of the surface layer. This causes stresses to build up on the surface layer and ultimately results in the formation of cracks. First the main cracks divide the exposed surface into a series of "islands" then, secondary cracks may occur within these islands.

primary and secondary cracks

Since drying starts from the surface, the bottom layers still contain some water and still remain expanded. Therefore the width of the crack is lesser in bottom layers, like a cut made from the surface. As the moisture content further reduces and the bottom layers also dry up, the crack propagates to the bottom layers and the gap widens. 

If the moisture content in a single layer of mud differs at the top of the layer and the bottom, the amount of contraction also differs. The top portion will contract more than the bottom portion. This will result in an upward curving of the layer like in a bimetallic strip. If the wet mud has been standing for a long period, stratification of different layers will take place. Stratified layers can be observed when a portion of the cracked mud is viewed sideways. Stratified layers can have a bigger difference in contraction rates, and if the layers are strongly adhered to each other, a more prominent curving of the layers will be seen.

stratification and upward curving of layers

If the layers are not strongly adhered, instead of curving upwards, the layers will separately contract producing a step like effect of the cracks. 

step like contraction

Although the mechanics of mud crack formation has no immediate practical application, crack formation in other substances is studied extensively. Crack formation on thin surface layers in electronic circuits can lead to peeling off of printed components and cause problems. Therefore a lot of effort is put into preventing the formation of such cracks. A very fine network of small cracks can be seen on the surface of old paintings on close inspection. This fine set of cracks is called "craquelure".  The characteristics of these cracks depend on the type of pigments, oil and also the ambient conditions at the time of painting. For this reason, these cracks are used to authenticate old paintings. 

Creating a 3D Terrain Model using Surfer

A three dimensional model of a particular land feature can be very useful for visualization. A 3D model which can be manipulated in a digital environment is even more useful, especially if volume calculations need to be performed. A good software package for this purpose is, "Surfer". It has a relatively simple user interface and is easy to learn.

Essentially what Surfer requires to create a 3D surface model is a set of spot heights along with their northing and easting coordinates. The data can be imported into Surfer by many ways, of which using a MS Excel file or an ASCII text file are simplest. The software will interpolate the data points and create a surface. The algorithm used for interpolation can be changed according to the requirement.

Obtaining spot heights of the area can be done by performing a level survey. If high accuracy is not required, a quick and easy method of obtaining spot heights is to overlay a grid with known coordinates over a topo sheet with contours. Using the contours, the heights of the vertices of the grid can be determined. Since the northing and easting of the grid are also known, it can be fed into Surfer via MS Excel Another method of creating a 3D model using Surfer is to directly import a DEM (Digital Elevation Model) into the software. DEMs can be downloaded from the USGS website.

A simple volume calculation based on spot heights obtained by the gridding method is illustrated below.

First, the grid was drawn over the contour map in the AutoCAD environment. In this example, the contour interval is 2 m, and the grid spacing has been selected as 3 m.  

The spot heights were found by using the contours closest to the vertices of the grid and the data was entered as x, y and z coordinates into an MS Excel sheet.

Using Surfer, the excel sheet was input and a grid file was created. (Grid>Data). The gridding method used for this example is "Kriging". Other methods can be used depending on the requirement.

A 3D surface was created using the grid file previously created.

This 3D surface can be used for volume calculations as well. For example, Consider that the trough indicated in the above terrain model needs to be filled with water, up to the 8m contour level and it is required to calculate the volume of water required.

This means we need to calculate the volume between the modeled surface and the plane z=8. To do this, the volume calculation dialog box was opened (grid>volume..) and the upper surface was given as z=8 and for the lower surface, the grid file was selected. The calculated positive volume indicates the volume of water required to fill the trough. In this example the calculated volume is, 696.73 cubic meters. 

Optimization of production of a Mine

The main objective of a mine is to extract a mineral deposit in an economical manner and to maintain a continuous output. In order to do this, the operations performed in and out of the mine must complement each other. While intensive planing and monitoring of all unit activities is required to achieve this, the following steps will help to optimize production and reduce cost thereby increasing efficiency.

Calculate and plan production targets and compare with actual production.

In order to determine whether a mine is operating efficiently, first targets should be established. To do this, drilling and blasting cycles and hauling capabilities can be factored in initial calculations. To set more specific production targets, modelling software can be used. The important thing is to compare the actual data with these targets and to take corrective action when the production does not meet the target.

Maintain a buffer stock of material

While in normal conditions, production can be carried out without interruption, due to various reasons the rate of production can decrease or in worst cases, halt altogether. Interruptions due to bad whether in open pit mines is a good example for this. To cope up with these delays it is essential to have a stockpile of material ready to be dispatched. This stockpile will act as a buffer until production resumes and the mine will produce the expected output throughout.

Proactive maintenance of machinery

Several approaches can be taken in the case of maintenance of mine machinery. in order to minimize losses due to downtime and faulty operation it is best to employ a preventive or proactive maintenance strategy. When doing maintenance work, it is vital to get operator feedback as it will help to diagnose problems better. Another very important fact to be considered when acquiring a new fleet of machines to a mine is to obtain all the machines of one particular brand. This ensures inter machine compatibility. It also saves time and resources in ordering, acquiring and using of spare parts.

Streamline work and physical movement

A mine is a place of continuous movement. To increase efficiency, these movements must be streamlined and effective. This means that access paths and haulage ways must be as short as possible with sufficient room for maneuvering. The mine layout itself must be orderly and separate operations should not disturb each other(except in unavoidable circumstances such as blasting). These reduce cycle times of the mine and increase production.

Safety

This is a factor overlooked in most mines. However safety plays a major role in the overall efficiency of the mine. A mine with a lot of accidents suffers a lot of downtime and it will reduce production. Proper safety procedures will enable continuous operation and will also enhance working conditions, both of which will ultimately result in an increase in efficiency.

Global Tidal Variations Explained

Tides are periodic variations of the ocean surface caused by the gravitational attraction of the moon and the sun. On a fundamental level, tides can also be considered as waves. Since these tidal waves have extremely long wavelengths, they are essentially shallow water waves(Shallow water waves are waves which travel over depths lower than 1/20th their wavelength). This means that the speed of the tidal wave is proportional to the depth. The depth of the ocean basin, the time of year and month, latitude and earth's rotation affect the type and magnitude of tides. While the exact relationship between all these variables can be somewhat complex, certain scientific theories and models help simplify and explain the behavior of tides.

Depending on the occurrence of high and low tides, tidal patterns are classified into three types. These are,
1. Diurnal tides
2. Semi-diurnal tides
3. Mixed Tides.
If the tidal wave shows 1 crest and 1 trough within a period of 1 lunar day(24hrs and 50mts), then it is called a diurnal tide. If it shows two crests and two troughs or vice versa in one lunar day, it is called a semi-diurnal tide. Mixed tides are a mixture of these two, often with significantly different amplitudes.

While tidal variations can be attributed to the gravitational attraction of both the sun and moon, the effect of the moon is significantly larger. "The Equilibrium theory of tides" attempts to explain these variations with the following assumptions.
-the ocean is indefinitely deep
-no land masses are present
-no inertial forces
With these assumptions, the key tide generating forces are, gravitation and centripetal force. These two forces act differently on different locations on the earth. While the gravitational force directs to the center of the moon, the centripetal forces at different locations are parallel to each other. This is because, centripetal force is the force that keeps an object in circular orbit, and the different locations have their own circular orbits parallel to each other.

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

The gravitational attraction provides the required centripetal force to keep the earth in orbit. However, the gravitational attraction and the required centripetal force are unequal at different locations on the earth. These two are equal only at the center of the earth. The difference between these two forces creates a resultant force which acts as shown in the diagram. It is this resultant force that is responsible for the generation of tides. This is also why, tidal bulges appear on both sides of the planet, because the resultant forces at the two sides of the earth are oppositely oriented. 

The orbital plane of the moon is inclined by approximately 28.5 degrees to the earth's axis of rotation. This causes the tidal bulges also to orient as shown below. The earth rotates through these tidal bulges. This explains the occurrence of diurnal and semi-diurnal tidal patterns explained above. By inspecting the diagram below it can be seen that high latitude locations receive diurnal tides, equatorial regions receive semi-diurnal tides and mid latitude locations receive mixed tides. 

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

This shows how the equilibrium theory explains the occurrence of the diurnal and semi-diurnal tides. This means that, tidal patterns on earth should be related to latitude. According to the above diagram it is also seen that tidal heights should also vary with latitude, with the highest tidal heights in mid latitude regions. However, the following tide map of the world shows that no such connection between tidal characteristics and latitude can be observed. This is where the equilibrium theory of tides fails.

-world tidal patterns- Source : Invitation to oceanography / Paul R. Pinet. — 5th ed.

The equilibrium theory of tides does not take into account the depth variations of the ocean basins. It also neglects the effect of the earth's rotation. To overcome these issues, another theory, "The Dynamic Theory of Tides" was proposed. Proposed in the 18th century by Pierre Simon Laplace, it attempts to explain tidal variations with the Coriolis Force.

To illustrate this theory, consider a large rectangular ocean basin in the northern hemisphere. when the water level rises in the upper portion of the basin due to the tidal action, the Coriolis force deflects the mass of travelling water towards the right. this causes the water to build up in the upper right corner of the basin. The resulting pressure gradient causes the water to flow downwards, but is again deflected to the right by the Coriolis force. This cycle continues, and it results in a counterclockwise oscillation of the water mass. The nodal point where the water does not oscillate is known as an "Amphidromic Point."

Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

If the ocean basin is situated in the southern hemisphere, the Coriolis force will deflect the water towards the left side, and the resulting oscillation would be clockwise. While ocean basins found on earth are not ideal basins like the above explained, several Amphidromic Points can be identified in the earth's oceans through tidal action. This amphidromic system of tides better explains the tidal variations depicted in the above tidal map. Since the amphidromic system is an oscillatory system, tides can undergo resonance. If the natural period of the ocean basin equals the period of the tides, tidal resonance will occur creating a massive tidal wave. An example of this is the Bay of Fundy where tidal ranges of over 17metres have been observed.

Global Amphidromic Points - Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

The depth of ocean basins also affect tidal heights. As explained above, tides being shallow water waves, have speeds that are proportional to depth. This means that a lower depth would cause the tidal wave to slow down, and due to the conservation of energy, the amplitude of the wave would increase, thus creating a higher tide. Taking all these factors into consideration, tides can be accurately modeled and predicted.

This understanding of tidal action opens up means of using it as an energy source. In places where a high tide variation is present, tidal energy can be tapped into by building dams to trap the incoming tidal flood current, and then channeling them through turbines like in a hydro-power plant. Power plants of this type are already in operation around the world, an exmaple is the La Rance tidal power plant at St. Malo, France. Tidal power plants do not pose a significant threat to the environment and are therefore are a good alternate source of renewable energy.

Geochemical Exploration

Geochemical Exploration is defined as, "The systematic measurement of one or more chemical properties of naturally occurring materials to identify abnormal chemical patterns or geochemical anomalies related to mineralization". In simple words it means, the identification of mineral deposits by the use of chemical methods. Although geochemical exploration alone is insufficient to detect and pinpoint ore reserves, it is used in conjunction with geologic and geophysical exploration methods. However when the effectiveness of geologic or geophysical methods become limited due to certain reasons, geochemical prospecting becomes a useful tool to confirm the presence of mineral deposits.

The term "Mineral deposit" is defined as an abnormal concentration of a naturally occurring material(Note that "economic viablity of extraction" is not included in the definition anymore). Since an abnormal concentration of any naturally occurring material is bound to leave behind traces, the objective of geochemical exploration is to identify these clues left by the mineral deposit and to use them to locate it.

Geochemical exploration usually includes the measurement of concentrations of group elements, trace elements, and single elements in,
- Soil, rock, Sediment
- Water, (sea/river)
- Plant material
- Glacial Debris
to determine geochemical anomalies that might indicate a mineralization. Before carrying out the investigation it is essential to have an idea about the behaviour and characteristics of the chemicals involved, the exploration methods to be used and the analytical techniques to be used. Once these factors are considered, proper planning and preparation will help optimize the exploration.

Depending upon the ways of sampling and analysis several methods of Geochemical exploration or surveys can be defined.

Stream sediment surveys - this is of two types, stream sediment panned concentrate surveys and stream sediment surveys. this method is used when heavy minerals and chemicals that bond with clay are involved.

Soil Geochemical surveys - used when looking for surface mineralizations especially in sedimentary environments.

Hydro Geochemical surveys - in analyses for highly soluble and mobile chemical elements.

Bedrock Geochemical surveys - This is usually done during  the last stages of the exploration in order to confirm the mineralization.

Biogeochemical surveys - Although rarely used, in certain cases of mineralization, plants that grow in the area show certain characteristics that point to the mineralization - in the case of copper the leaves of a certain plant that grows in the vicinity turns to a brownish colour due to the absorption of copper.

Considering the conditions and expected methods of mineralization, a suitable geochemical exploration methods can be adopted if required along with geologic and geophysical methods in order to identify areas of mineralization.

Lens Stereoscopy

3D viewing is widely used in cinemas today. Technologies such as, Active Shutter, Polarization and Interference filter method are used for 3D projection. In all these methods the basic idea is to provide two different images to each eye like we naturally perceive the world. Then the brain does the rest of the work and combines those images to perceive depth. Although 3D vision is most common in movies at present, in the past it was used in Remote Sensing for military purposes. The instrument used for this purpose is the Stereoscope.

the stereoscope with an image

The Stereoscope consists of two lenses resting on a stand that focus on the two separate images of the stereoscopic image sheet. When looking through the two lenses, each eye sees a slightly different image that is meant for that eye and this results in the perception of depth - the image appears 3 dimensional. This is very useful in analyzing aerial photographs because it allows viewing the ground terrain in 3D.

test image for stereoscopic vision

Shown above is a test image that is used to check stereoscopic vision. The relative heights at which the symbols appear to be seen can be checked against the actual order of heights which are provided overleaf.

Stereoscope with a test image

While in modern remote sensing, stereoscopes have been replaced by more advanced computerized equipment that not only provide 3D views but also help manipulate images in 3D, the stereoscope helps understand the basics of stereoscopic vision. Lens Stereoscopy can also be considered as the foundation of all modern stereoscopic equipment.

Stepping into Field Geology

While Geology is a field of study that takes place both outdoors in the field and indoors in laboratories, Field Geology is a primary constituent of Geology. Most of the activities that are involved in Geology like sample collecting, mapping and recording takes place in the field. When moving into field geology for the first time, several important points need to be considered.

The first thing that needs to be considered is, Safety in the field. Mostly this means to be aware and protect one's self against threats from nature and wild animals. For this purpose a thorough knowledge about the surroundings, proper equipment and first aid facilities are essential. In the case of snake bites it is useful to know the closest hospital or medical center equipped with anti-venom serums. In addition to the above, proper usage of tools like the hammer and chisel will reduce the likelihood of an accident.

Once the safety is taken care of, the right tools and equipment related to field work must be made available. The common tools used in field geology are, Geological Compass(Brunton pocket transit or Silva compass), Hand lens(10X), Hammer and chisel, waterproof field book, mineral testing kit and sample bags. In addition to these basic tools, additional tools such as camera, GPS, binoculars  gold pans, metal detectors and Geiger  counters may be used for specific requirements.

The Geological Compass is arguably the most useful tool at the disposal at the Geologist or Engineer. In addition to the obvious purpose of locating the direction of north and calculating the bearing, a geological compass has the following functions.
- Finding the dip and Strike of geological features such  as foliation, joints bedding planes etc.
- Measuring slope angles
- approximating heights of objects
- a level
When using a compass, it is essential to keep away from vehicles, power lines and any other magnetized objects. This means that the Hammer and chisel also needs to be kept aside when using the compass. With the emergence of smartphones with magnetic sensors and accelorometers, applications that perform similar to a geological compass have been developed. One such application that can be used for traversing, calculating Dip and Strike along with a host of other useful functions is, Rocklogger which is available for the Android mobile platform.

Another important aspect of Field Geology is Sample Collection. When collecting rock samples, an approximate sample size of 3"x3"x3" or 4"x4"x4" is preferred. Weathered rock samples are generally avoided unless it is a specific requirement. Once collected, sharp edges should be trimmed off before bagging the sample to avoid tearing the bag. Cloth bags made out of a cotton fabric are usually used for this purpose. Samples should also be numbered systematically. While there is no hard and fast rule for this, a meaningful numbering system incorporating information such as collection year, area, and collectors initials is used to avoid confusion.

Field photography is also a requirement in certain cases. When taking a picture always a scale should be used. For small objects, a pen or another small object with a known size must be in the picture. In the case of photographing macro structures, wetting the surface of the rock helps to bring out the fine details on the surface. Care should be taken to avoid shadows to fall on a part of the rock when  photographing because it could lead to misinterpretation.

Brunton Compass - image from wikipedia

An Introduction to Remote Sensing

Remote Sensing, like the name implies, means observing and gathering information of an object from afar. In this sense we humans perform remote sensing all the time with our eyes and ears, where eyes and ears are our remote sensing equipment. However when moving away from the basics and expanding the scope of observation, many factors become involved and remote sensing becomes a broad and detailed area of study. Incorporating all these ideas, a general definition for remote sensing can be given as,

"The art and science of obtaining information about an object without being in direct contact with the object"

Remote sensing is extensively used in observing the earth and the environment for various purposes. The most common application of remote sensing is done in mine development, disaster mitigation and large scale environmental studies. Depending on the application, the sensors and the type of radiation used, the method of recording and processing and the analysis of the data will differ.

The major components in remote sensing are,
- an energy source for illumination :- usually the sun or an artificial source of radiation.
- medium of travel for energy :- the atmosphere.
- sensor :- orbits in a satellite eg. Landsat, Quickbird
- receiver on earth :- gathers the data transmitted from the satellite.
- equipment for interpretation and analysis of data :- remote sensing software.

All remote sensing systems have four types of resolution. They are,
- Spatial resolution :- refers to the pixel resolution of the image produced.
- Spectral resolution :- refers to the range of EM radiation that can be detected. A broader range increases the scope of analysis.
- Temporal resolution :- refers to the orbital period of the satellite carrying the sensor. Faster the period, higher the resolution.
- Radiometric resolution :- refers to the differences of the intensity of radiation that can be distinguished by the sensor. Given as a bit range. A higher bit range can distinguish smaller variations.

Once all the above details are decided according to the application, remote sensing is performed. Then a "reflectance pattern" is produced from the gathered data. By comparing these patterns with the spectral signatures of known objects, the type and extent of the sensed objects on the earth can be inferred. In addition to various applications on earth, remote sensing is also used in other planets to gather data about surface conditions etc without landing on the planet.

Remote sensing in Mars. image form wikipedia

 

A Diamond is Forever

Gemstones have been objects of desire since ancient times and are commonly seen as symbols of wealth and prosperity. The field of Gemmology aims to identify, classify and add value to gem material. Of all the gemstones identified, the diamond holds a special place due to various reasons. While already being the most sought after gem stone, efforts companies like De Beers have increased the value of diamonds even more. An example is, the De Beers advertising slogan "A Diamond is Forever". This slogan increased diamond sales to such an extent that a diamond was a part of almost every engagement ring. It was coined by Frances Gerety and is regarded as the best advertising slogan of the 20th century.

The value of a gemstone usually depends on its beauty, rarity and hardness. Although these are very vague terms and beauty is not quantifiable, the factors that contribute to beauty are colour and clarity. In gemstones like aquamarine, value generally increases with colour intensity. In blue saphire, the value is highest at a particular colour, termed the "optimum colour". Clear gemstones without any intrusions or impurities are usually cut so that they are faceted. translucent, opaque or sometimes clear stones with intrusions are cut with a convex top and are called "cabochons". Even opaque stones can be valued highly due to properties such as Chatoyancy (cat's eye) eg- Chrysoberyl. and Asterism eg. Star saphire. Among so many varieties of stones the clear, faceted diamond is the most sought after.

The other factor that contributes to the value of a gemstone is its rarity. while gemstones are naturally rare, the demand for it creates an increase in value. However in some cases the rarity can be increased by the producers or traders of gemstones by stockpiling and controlling the release of gemstones to the market, like what De Beers did when they held the monopoly in the diamond business at a certain period of time. These practices however, rarely take place today. Hardness is the other key property of a gem quality material. A high hardness value means high durability and therefore it stands the test of time. Whether it's the case of beauty, rarity or hardness, the diamond clearly stands on top.

image from : wikipedia

The Evolution of Human Resource Management

Human Resource Management is a diverse field that aims to bring out the best in employees in order to accomplish organizational goals while facilitating personal development of the employees as well. Most organizations in various industries have embraced Human Resource Management as a core function of the organization and are reaping its benefits. Although field of HRM is a comparatively recent development, its roots can be traced back to the pre-industrial era.

During the pre-industrial era the closest thing to the employer-employee relationships was the relationship between landowners and slaves. Here the landowner had the slave/s at his disposal and had complete power over him/them. Although it is a violation of human rights according to present standards, slavery was commonplace until it was abolished in many parts of the world.

The industrial revolution resulted in the creation of the factory system. Now the relationship shifted to, owners of factories and workers. It was during this time that The theory of Scientific Management was put forward by Frederick Winslow Taylor. In Scientific management, ways in which efficiency of a factory could be increased were discussed. Although some of these methods included training of employees and selecting the employees with the right skills, even this was a long way from the modern HRM approach because among the basic assumptions in Scientific Management were the notions that, man is an "economic animal" and that money was the primary factor in motivating employees.

An improvement of Scientific Management came in the form of the "the Modern Management Theory" by Henry Fayol. In this theory fair treatment of all employees is argued while giving more consideration to the proper treatment of employees. In this theory Fayol also claims that people can be motivated by more than just money. This was a major milestone in the road towards modern Human Resource Management because employee motivation and fair treatment of employees are key areas in modern HRM.

After the modern management theory and its successors came into place, the Human relations movement began taking shape. With this came the labour movement and the state got involved in the protection of employee rights. This resulted in a tripartite relationship between the state, employer and employee that aims to bring stability to the industry while working for the benefit of all three parties.

Now with the state involved and legal matters involved in the field of employment, organizations felt the need of "Personnel Management". personnel management, as the name implies is meant to manage employees in an organization. It focused mainly on getting the right employees for the organization to perform a job while also fulfilling the legal requirements and ensuring that employee rights are not violated.

While Personnel Management was effective in the short term, it did not produce significant improvements for an organization in the long run. Thus organizations opted for another option that would be fruitful in the long term. This was the beginning of Human Resources Management. Like the name says, HRM considers employees as a "resource" to be developed. Therefore, a key area in HRM is providing development and career advancement opportunities to employees. In other words HRM aims not to provide just a job, but to provide a career to their employees. Human Resource Management aims to attain organizational objectives by simultaneously developing its employees, and this approach has been proven to be successful.

A Brief History of Management

Management is an essential component in any business or organization and it applies at every level in all types of organizations. Management can be defined as "The attainment of organizational goals in an effective and efficient manner through planning, organizing, leading and controlling organizational resources." The terms planning, organizing, leading and controlling are called "management functions". Today management is a broad area of study that has been developed throughout the past century and is still evolving.

The invention of the steam engine by James Watt kick-started the industrial revolution. With the industrial revolution, the concept of a factory emerged. Factories that did mass production with thousands of workers from different backgrounds mushroomed in the industrial world and thus a need for management arose. The idea of management at that time was to bring efficiency and order to an otherwise chaotic workplace.

This was the time when management was perceived and studied as a science. Frederick Winslow Taylor is considered the father of Scientific management. Through his experience and observations, Frederick Taylor came up with scientific management which aimed at increasing efficiency at the production level. In his monograph "The principles of Scientific Management", he highlighted four principles. They are
1. Study the way a job is performed and create a new scientific way to perform it with maximum productivity
2. Codify the new method into rules and train and equip the workers with the new method
3. Select workers whose skills match the rules developed and provide detailed instruction and supervision.
4. Establish fair levels of performance and reward higher performance.
In Scientific Management it it assumed that man is an "economic animal" and that money is the motivating factor. Also this system of management only applies at the operational level of the organization.

While efforts in management were only applied to the operational level of an organization, gradually attention moved to the upper hierarchical levels of the organization. This led to the development of the "Modern Management theory". A french mining engineer Henry Fayol is considered the father of modern management theory. Fayol was the first to define the 4 management functions quoted in the first paragraph of this post. In his book, "Industrial and general Administration", he divided all administrative activities into six categories. They are,
1. Technical
2. Commercial
3. Financial
4. Security
5. Accounting
6. Administrative
He also proposed 14 principles of administration - Division of work, Authority and responsibility, discipline, unity of command, unity of management, subordination of individual interests to the common good. remuneration, centralization, hierarchy, order, equity, stability of the staff, initiative, espirit de corps.
Unlike Taylor's Scientific management which focused in the operational level of an organization, Fayol's theory of management focused in the managerial level. Fayol also claimed that workers can be motivated by more than just money and also argued for equal treatment of all workers.

While the management process that is practiced today is mostly based on Fayol's theories, certain aspects of management are still evolving. The functions of management are interconnected and each function needs to be performed collectively and to various degrees for the management process to be successful. Although based on scientific principles management also requires a certain level of creativity in application. The management process can also depend on factors such as the culture and structure of the organization. By adapting to this dynamic nature and selecting the proper approach to management, organizations will be able to succeed in today's world.

Asteroids as a Resource

Recently, the company planetary resources unveiled their plan to mine asteroids. Their approach to this extremely challenging task by trying to get there in 4 different stages, seems to be a practical. They are planning to mine asteroids for platinum group metals and water. With all this attention to mining from outer space it is worthwhile to consider whether asteroids actually have the potential to be a resource that is economical to exploit.

There is no denying that asteroids contain valuable metals and water in abundance. But these are even found on earth. At the moment there is no shortage of platinum here on earth although it is quite expensive due to the costly extraction process. Unless platinum occurs as pure metal on asteroids, processing will still have to be done, and doing it in outer space is going to be even more difficult.

Looking at this situation it might seem a better option to invest on the existing platinum mining and processing here on earth in order to make it more efficient. However mining from asteroids has the advantage of avoiding the environmental damage created by mining on earth. Also if the platinum demand rises sharply within the next few decades and if it becomes increasingly difficult and costly to mine for platinum on earth, mining it from asteroids will be the best solution.

Although lots of minerals and metals are found in the crust of the earth, most of the heavier metals such as iron and nickel lie inside the core of the earth due to the gradual gravitational sinking of these metals during the formation of the earth. Asteroids however are mostly of small sizes and therefore in most cases the metals are somewhat evenly distributed throughout the volume of the asteroid. This makes mining easier. Even in larger asteroids where metals have settled like on earth, accessing it will be easier.

The other important resource that is planned to mine form asteroids is water. A source of water outside earth is valuable because it would no longer be necessary to carry a heavy load of water in future space missions. It would also pave the way to colonization in space since one of the main challenges faced in such a situation is finding access to an appreciable reserve of water.

If the constituents of water, Hydrogen and Oxygen are separated, they can be used to power rockets. This could also one day lead to fuel stations in space which will not only reduce the cost of space travel but also widen our reach in space. Having both fuel and water readily available in space, our dream to colonize in space will come closer to us.

Mining asteroids seems a far fetched idea and it might not look like it is economical at a first glance. But this situation will change in the future and sometimes asteroid mining might be the only option. We will be able to advance only if we plan for the future and act accordingly. We should remember that before the internal combustion engine was invented, commercial drilling of petroleum seemed unnecessary..

image from : wikipedia