Soil testing for constructing a 55 storey building in Chennai

Soil testing (in  geotechnical investigations) is a broad term used to describe the various tasks involved in gathering the required information for planning foundations and “earth works”.  Structures such as buildings or bridges require a strong and stable foundation to stand on. Geotechnical experts gather
information about the physical properties of rocks and soil from a proposed site to assess the suitability of the particular site. For example, bridges are
meant to support heavy loads such as vehicles or trains. Bridges are built on piles and the foundation should support the load. Swampy areas often have
“loose” soil with high water content and are not ideal for construction. However, soil testing studies would confirm the property of the soil and rocks at a site.

To get adequate information about a site, surface and subsurface investigations must be undertaken. Geologic mapping and direct field studies provide information about the surface. For large projects such as bridges on seas, geophysical methods are used to gather subsurface data. For building constructions and designing foundations for bridges, many methods are available. However, the most common method is the use of boring techniques to get soil or rock samples.

Soil samples provide evidence of what lies beneath the surface. Geology of the area might indicate the age and type of rock one can expect in
the formations. Boring brings up the soil or rock and often the lithology can be established. Rocky sub surfaces act as strong bed rocks. However, soil
testing focuses more on finding out whether the site is suitable for construction or whether there could be potentially dangerous sink holes, mud
slides, or faults. This is done through analysis of the sand grains for grain size, water content, ability to withstand stress and shear, etc.

To test soils or rocks of a site:

  • Conduct field or site investigations in situ
  • Study associated geological maps
  • Gather data from nearby sites
  • Use appropriate method to understand subsurface
  • Get samples and analyze physical property of soil in the laboratory
  • Depending on the results, make a decision

Here are some photographs of the equipment used to gather core samples. The usual tools used include samplers such as augers, Shelby tubes
or pistons. At times, undisturbed samples are required to make a decision. The sampler selected depends on the type of sample required and the rock or soil
property. The photographs show sampler tubes with the core.

Working with groundwater data using Arc Hydro Groundwater and ArcGIS Groundwater Toolset: An overview of the steps to study water levels in wells around an aquifer

Hydrological analysis using GIS requires that several aspects of the water cycle – occurrence, movement, and their relationship with the environment – be understood and addressed. Hydrology includes the study of surface and groundwater. Surface water has been understood well over the years and tools and models are available. However, groundwater has not been so well understood as for this, hydrogeological aspects also need to be incorporated.

ArcGIS from ESRI provides the tools for hydro analysis. ArcHydro is a set of data models and tools that allow you to study surface and groundwater. Surface water can be studied using ArcGIS Hydrology Toolset or ArcHydro. For Groundwater, use ArcHydro Groundwater (that has been developed by AQUAVEO and ESRI) or ArcGIS groundwater toolset (that is part of ArcGIS). Use ArcHydro Groundwater to:

  • Create maps depicting water  levels, water quality, etc
  • Create and visualize both 2D  and 3D geologic models and subsurface analysis

Use ArcGIS Groundwater Toolset for Spatial Analysis (Darcy analysis, particle tracking, etc).

Here we will look at how to use Arc Hydro Groundwater to study wells around an aquifer and understand the water level
changes over time by generating time series plots of water level data for selected wells. For this the overall steps would include the following:

  • Importing a map of the area including aquifers
  • Importing well data
  • Mapping the feature type in ArcGIS Hydro to column names in the data imported
  • Filtering the well data to specific types of wells
  • Symbolizing the filtered wells
  • Assigning Hydro IDs
  • Importing time series data for water level measurements of a particular well at a particular time
  • Create relationship between column in data file and feature type in ArcGIS
  • Join the time series data to well data based on a field
  • Calculate the elevation as well depths are negative values
  • Find wells with transient data using Make Time Series statistics
  • Create graphs and Interpolate data to a raster to create map of water levels for specific period
  • Generate flow direction for the wells

The procedure with a few screen shots is discussed here. For an elaborate discussion and detailed procedures refer to the ESRI and AQUAVEO websites.

Importing a map of the area with aquifers

Map of Area with Aquifer

The tool bars for groundwater analysis

Importing well data

Import Groundwater Data (in this case water wells in the selected area)

Mapping the feature type in ArcGIS Hydro to column names in the data imported

The field data collected must be in text files, spreadsheets, or supported formats. Although, various data can be collected the Arc Hydro data model will have a few features to which the collected data must be mapped. This data is specified by the Arc Hydro Framework and research is underway to improve the models.

Note that these wells have a state well number, associated aquifer code, and names of owners that helps in managing groundwater.

Filtering the well data to specific types of wells

Wells can be classified on different parameters and labeled accordingly. For example, wells can be for monitoring, agricultural, or drinking water purposes or can be classified according to the geology – sandstone aquifer wells, igneous wells, etc.

Assigning Hydro IDs

Hydro features are identifiers of hydrological and hydrogeological components. Hydro ID is unique across the geodatabase that is needed to build a model of the well or aquifer. Hydro Code is also unique and describes the features in an external data source. This is a key step.

Importing time series data for water level measurements of a particular well at a particular time and Creating relationship between column in data file and feature type in ArcGIS

Join the time series data to well data based on a field

We have already imported well data and symbolized it. Next for analysis, a second parameter is required. For this we imported time-based data as the purpose is to study water levels over time. Next we join the time series data collected at the particular well to the well data. This is where the Hydro ID is useful as it is unique.

Calculate the elevation as well depths are negative values

Remember that wells are beneath the surface and is assigned negative values. However, this needs to be “normalized” for calculation and for meaningful inference of the data. This is done using the elevation and time series values.

Find wells with transient data using Make Time Series statistics

Now that you have well data and time series data and assigned unique Hydro IDs, you can do further analysis. One of the important tasks is to separate out the wells without time-bound data. This happens as some wells might have gone dry or simply data might not have been captured or the wells might not be significant for the study.

Wells with transient data

You can use the Make Time Series statistics tool to find features such as wells with transient data for specific periods.

Analysis

Creating graphs: Graphical representations help you study the selected wells and make decisions. You can use the Time Series Grapher to do this.

Interpolating data to raster catalog: you can create raster maps such as water level maps for future use using the Spatial Analyst tools.

Generate flow direction for the wells: you can find out the direction of water flow using the flow direction generator tool. This helps in identifying the downward gradient and where water flows into.

Flow direction of water is downhill

This concludes the overview of the steps to study water levels in wells around an aquifer.

A flock of cranes (of the mechanical kind)

For those who work in onshore and offshore rigs, ports, tall building construction sites, and generally in any structural and construction engineering projects, cranes might be an everyday occurence. In Chennai, there has recently been a lot of construction activities and cranes are being used a lot. These may not be massive projects compared to those in the USA, China, or elsewhere – but this does seem interesting to those who have never seen big machines before.

Here are some photographs of different cranes:

  • A hammer-head tower crane at work on a building construction site
  • A crawler-mounted Latticework Boom Crane with a clamp shell bucket for dredging out the sediment at a desalination plant construction site near Muthukadu on ECR at Chennai
  • A wheel-mounted standard crane with rotating operator’s cabin that is used when construction has to take place within a limited area. These cranes are used for building the “Chennai Metro Rail” and the construction has to take place amid heavy traffic. I did not find enough safety mechanisms but the city is so populous and there is hardly any alternative travel route for people
  • A modified overhead gantry (hoist) on a beam to move each concrete block into place on the overhead road bridge. The roads seem so full what with a large storage of scaffoldings, hooks, sockets, shackles, wire ropes, chains, slings and hitches, rods, concrete and other equipment close to the places of construction

I included this post in this blog as there is some geo-engineering involved in the form of soil-testing, feature mapping, dredging, drilling, etc … and more so because I get excited by cranes 😉

Hope the cranes can lift us to a less-congested future.

Technical English for Geosciences: A text/workbook – Short Review

Technical English for Geosciences is a text plus workbook for students and others who wish to improve their command of English language with regard to geosciences communication.

The author Brigette Markner-Jager is a lecturer for English as a language for special purposes. Since 2001 she has been teaching Technical English and Business English at the TFH Georg Agricola in Bochum, Germany.

Geology and geosciences have plenty of terms and words that are unique to the field. Although, students have some exposure to terminology in subjects such as chemistry, physics, mathematics, business, and even law, there seems to be a bit of difficulty when geological terminology is used. Words such as schist, gneiss, porphyry, bedding, marble, footwall, and so on are either new or mean something else for those unfamiliar with geological sciences. Speakers of other languages other than English find it even tougher to get a good hold of the vocabulary.

This is where the book helps. The book is ideal for students who need to learn and use geosciences terms. Students belonging to any stream of study – from applied geology, mining, hydrology, to environmental science – will find this book useful.

The book is structured based on various branches and disciplines of geosciences. This is very convenient as students from a particular stream can go directly to the lesson. The chapters use text from various sources and have tasks to check reader understanding. The book can be used as a self-study material or in classes.

I have studied a master’s in geology and have worked as a writer and I found this book a bit basic at times. I wish this book had been part of my studies though! Springer published the book in 2008 and has used text extracts from different sources. I found a few errors in punctuation in the extracts and I wonder whether students without adequate English knowledge would be able to understand the errors. Springer might not have changed the text due to copyright issues.

Some of the examples used in the book such as Chapters 18 to 20 (Tara Mines) are interesting and add subject knowledge too.

Overall this is a good book to have especially in the undergraduate degrees. The book is available on www.amazon.com

Geomorphology of Adyar River estuary, Chennai, India

The Adyar river drains into the Bay of Bengal and forms an estuary behind the Theosophical Society near MRC Nagar, Chennai.  Small dunes are visible and thick alluvium covers the Archaen rocks. The river supplies sediment heavily to continually alter the geomorphology of the unique environment. A broken bridge adds a bit of drama to the landscape.  Would be interesting to see how much the 2004 Indian Ocean Tsunami has altered the features. The estuary is small but can probably be classified as a depositional and semi-lagoon spit type.

Niagara falls – river erosion at work

The Niagara Falls -mesmerizing and powerful was formed a million years ago after the Ice age. The huge volume of water empties into Lake Ontario. The rock type of the area is Shale – Rochester Shale. Erosion reveals Dolomite and other sedimentary rock formations. Silurian age fossils are typical of this area.

Hyderabad Rock Formations (Gneiss and Granite)

Hyderabad – situated in India is part of the Deccan plateau. The area is full of spectacular rock formations – toadstools, mushroom rocks, hanging monsters, and turtle back. These rocks were formed probably 2.5 billion years ago.

Earth formed about 4.5  billion years ago. The surface of the Earth solidified about 3.5 billion years ago (when water too appeared as seas). About 2.5 billion years ago, some molten magma oozed on to the surface (Earth crust) in typical “Deccan lava flow” fashion. Much molten magma however probably pushed up the crust but cooled beneath the crust (which could have been thicker then due to lesser time of weathering) unable to push anymore.  The magma formed granitic domes, sheets, and stocks or massive intrusive batholiths.

Later through Precambrian and Cambrian the crust underwent weathering and eroded exposing the Granite beneath. The Granite developed horizontal and vertical cracks and were weathered to their present spectacular forms.

Some photos of the landscape near the airport.

 

Abandoned Gypsum Mine, Seegrotte, Austria

This is an abandoned Gypsum mine close to Vienna, Austria. For details see: http://www.seegrotte.at/index.php?id=6&L=1

You can see textbook images of piles, stacks, trolley, etc. The underground lake is amazing too.

Geology Books Collection

I have a fantastic collection of books on Geology. I am going to review a few and hopefully one day after I retire start a library on Geological books and rock collections.

Vesuvius – lava rivers, caldera, and ash

Volcanoes – fiery or silent – always inspire awe. However many times you may have read about volcanoes, the feeling – when you are near the cone is – great. Here are a few pictures of the Vesuvius in Italy.

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now at blogs.agu.org/tremblingearth