Well Construction Techniques
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Questions and Answers

Manual excavation using a pick and shovel is employed in the construction of driven wells.

False (B)

Bored wells or augered well are suitable for formations with deep water tables.

False (B)

The process of constructing a jetted well involves driving pipes into the ground through repetitive impact.

False (B)

Driven wells are ideal for formations that have large gravel or rocks.

<p>False (B)</p> Signup and view all the answers

The irrigation water requirement should be determined based on PNS/BAFS/PAES 217:2018.

<p>False (B)</p> Signup and view all the answers

A site's slope should not be considered when determining its suitability for a well.

<p>False (B)</p> Signup and view all the answers

A site should have high vulnerability to pollution and a high potential for seawater intrusion.

<p>False (B)</p> Signup and view all the answers

The depth of the water-bearing formation is not important when designing a well.

<p>False (B)</p> Signup and view all the answers

The thickness of the aquifer affects the length of the screened or perforated section of the well.

<p>True (A)</p> Signup and view all the answers

The presence of a hard confining layer doesn't affect well design or drilling methods.

<p>False (B)</p> Signup and view all the answers

Groundwater salinity is irrelevant when determining the suitability of water for irrigation.

<p>False (B)</p> Signup and view all the answers

Hydraulic conductivity or transmissivity are important for determining the economic value of an aquifer as a water source.

<p>True (A)</p> Signup and view all the answers

The specific yield of an aquifer has no relation to well spacing.

<p>False (B)</p> Signup and view all the answers

A pilot borehole should be reamed down to the lower 2 meters if the confining layer is soft.

<p>False (B)</p> Signup and view all the answers

When encountering resistance while lowering the pipe, turning the pipe with pipe wrenches can enhance its downward penetration.

<p>True (A)</p> Signup and view all the answers

Turning the pipe during driving is recommended to ensure an air-tight connection between the pipe and the confining layer.

<p>False (B)</p> Signup and view all the answers

Water jetting should be avoided when the perforated portion of the pipe is within the confining layer.

<p>True (A)</p> Signup and view all the answers

It is permissible to use cast couplings during driving to securely fasten the pipe sections.

<p>False (B)</p> Signup and view all the answers

Well development is done to decrease its discharge capacity and aid in continuous sand pumping.

<p>False (B)</p> Signup and view all the answers

During jetting, the drilling stem may be equipped with a reduced jetting head to cause water surge within the well.

<p>False (B)</p> Signup and view all the answers

Jetting should be started at the top of the well and proceed down to the bottom of the perforated pipe.

<p>False (B)</p> Signup and view all the answers

Schedule 40 GI pipe is recommended for naturally developed wells with a hard confining layer.

<p>True (A)</p> Signup and view all the answers

For artificially developed wells, schedule 80 GI or PVC pipe is recommended.

<p>False (B)</p> Signup and view all the answers

For aquifers thicker than 4.6 m, the extent of aquifer penetration should be 95% of the aquifer thickness.

<p>False (B)</p> Signup and view all the answers

For naturally developed wells with a design discharge of over 15 lps, the aquifer penetration will be between 50 percent and 100 percent.

<p>True (A)</p> Signup and view all the answers

The total pipe length is calculated by adding the depth of the well, the length of the extension and the percentage of penetration.

<p>False (B)</p> Signup and view all the answers

For a single borehole, at least 1.4 meters should be added for the nipples for the installation of the pumping unit

<p>False (B)</p> Signup and view all the answers

Slots in well pipes should be 5 to 8 mm in width and 40 to 70 mm in length.

<p>False (B)</p> Signup and view all the answers

The pipe bottom should be closed.

<p>False (B)</p> Signup and view all the answers

The full load continuous duty horsepower of a prime mover should be less than the pump brake horsepower.

<p>False (B)</p> Signup and view all the answers

An electric motor's body indicated power rating is estimated to be about 1.15 times the brake horsepower.

<p>True (A)</p> Signup and view all the answers

A water-cooled diesel engine has a higher body indicated power rating than an air-cooled diesel engine.

<p>False (B)</p> Signup and view all the answers

A gasoline air-cooled prime mover has a body indicated power rating factor between 1.40 and 1.50.

<p>True (A)</p> Signup and view all the answers

The recommended borehole size for well logging is 4 inches in diameter or smaller.

<p>False (B)</p> Signup and view all the answers

Resistivity logging is a method used to determine the chemical characteristics of an aquifer.

<p>False (B)</p> Signup and view all the answers

Spontaneous potential logging is a common method used for well logging according to the provided text.

<p>True (A)</p> Signup and view all the answers

Todd and Mays published a book called 'Engineering Hydrology'.

<p>False (B)</p> Signup and view all the answers

The effective size and uniformity coefficient of aquifer materials are determined through mechanical analysis like the sieve-hydrometer method.

<p>True (A)</p> Signup and view all the answers

A gravel pack with a thickness of at least 25 cm is recommended for aquifers having a uniformity coefficient less than 2.0 and an effective size less than 0.30 mm.

<p>False (B)</p> Signup and view all the answers

In aquifers with an effective size greater than 0.30 mm, a graded gravel pack is essential for filtration purposes.

<p>False (B)</p> Signup and view all the answers

For uniformly grained sand, the optimal gravel pack gradation should fall outside of two lines plotted using the 50% passing diameter multiplied by 5 and 10.

<p>False (B)</p> Signup and view all the answers

Well screen slot size should be greater than 1/2 of the 85% passing of the gravel pack materials.

<p>False (B)</p> Signup and view all the answers

For graded pack aquifer materials, the 50% passing size should be multiplied by 12 and 58 to determine plotting points for the gravel pack limits.

<p>True (A)</p> Signup and view all the answers

For graded pack materials, no gravel pack material should exceed a size of 20 mm.

<p>False (B)</p> Signup and view all the answers

A uniformly grained gravel envelope is recommended for aquifers with a UC of 2.5 and ES of 0.20 mm.

<p>False (B)</p> Signup and view all the answers

Flashcards

Depth of water-bearing formation

The depth at which water-bearing layers occur in the ground.

Aquifer Thickness

The thickness of the layer containing groundwater.

Confining layer (confined, semi-confined, or unconfined)

A layer that restricts the flow of groundwater.

Annual range of water table fluctuations

The yearly change in the level of groundwater.

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Hydraulic conductivity

The ease with which water flows through the aquifer.

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Specific yield

The amount of water an aquifer releases when the water pressure decreases.

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Spacing of wells

The distance between wells should be calculated based on the aquifer's properties.

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Pumping unit specifications

Pumping units should be designed to match the aquifer's properties.

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Manual Well

Wells constructed by manually digging with a pickaxe and shovel, hauling the excavated material to the surface using containers.

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Bored Well

Wells constructed by drilling into the ground using a powered auger, extracting material with the auger's blades, and repeating the process until desired depth and diameter are reached.

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Driven Well

A well made by driving lengths of pipe into the ground until they reach below the water table, where water enters through a screened end.

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Jetted Well

A well dug by using a high-pressure jet of water to excavate the hole and carry away the excavated earth.

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Irrigation Water Requirement

The amount of water required to properly irrigate a specific area, determined by using a specific standard.

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Reaming a Pilot Borehole

Reaming a pilot borehole ensures a tight seal between the well pipe and the confining layer. It's done to prevent water leaks and maintain well integrity.

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Installing the Well Pipe

The process of installing the well pipe involves carefully lowering it into the reamed borehole, possibly with a bit of turning and hammering to ensure it's securely placed.

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Driving the Well Pipe

Driving the well pipe through the confining layer requires careful hammering and avoiding turning the pipe to preserve the tight seal created by reaming.

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Water Jetting for Installation

Water jetting is a technique used to clear blockages in the well pipe during installation, but it should be used cautiously to avoid damaging the seal or causing leaks.

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Jetting for Well Development

Once the screen portion of the well pipe is placed below the confining layer, jetting with high velocity water can be used for well development.

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Well Development

Well development aims to improve the well's performance by increasing its discharge capacity, preventing sand from being drawn up, and ensuring a steady and long-lasting water supply.

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Jetting as Development

Jetting is a common well development technique to remove drilling mud and fine aquifer materials, increasing the well's water flow rate.

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Jetting Sequence

Proper jetting during well development starts at the bottom and moves upward, ensuring the entire length of the perforated pipe is cleaned.

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What are the recommended pipe materials for different types of wells?

Artificially developed wells use Schedule 20 GI or PVC pipes. Naturally developed wells with design depth of ≤ 9 m use Schedule 20 GI. Wells with relatively soft confining layers use Schedule 20 GI. Hard confining layers require Schedule 40 GI.

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How much of the aquifer should a well penetrate based on well type?

The extent of aquifer penetration depends on the well type. Artificially developed wells penetrate 100%. Naturally developed wells with aquifers thicker than 4.6 m penetrate 85% of the aquifer thickness. Wells with a design discharge less than 15 lps penetrate less than 25%. Wells with a design discharge greater than 15 lps penetrate 50% to 100%.

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How is the total pipe length for a single borehole calculated?

The pipe length for a single borehole is calculated using:

Pipe length = E + D + (B x % penetration)

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How are perforations made in well pipes?

Pipe perforations are created by cutting vertical slots 3 to 6 mm wide and 60 to 90 mm long on the pipe sections that penetrate the water-bearing formations. The total area of the slots should be at least 15% of the pipe's surface area and the bottom of the pipe should be open.

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How are well pipes installed?

A pilot borehole is drilled using a drilling rig down to the design depth. PAES 127:2002 specifies the requirements for drilling rigs used in agricultural applications.

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What factors determine the pipe material chosen for a well?

The pipe material used for a well depends on the type of well construction and the conditions of the surrounding soil and water.

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What factors influence the pipe length for a well?

The pipe length is calculated based on the depth of the well, the thickness of the aquifer, and the desired penetration percentage.

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Why are perforations important in well pipes?

Perforations are essential for allowing water to enter the well pipe. The size and spacing of the perforations impact the flow rate of water.

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Uniformity Coefficient (UC)

A measure of the range of particle sizes in an aquifer material. It is calculated by dividing the diameter of the particles at the 60th percentile by the diameter of the particles at the 10th percentile.

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Effective Size (ES)

The average diameter of particles in an aquifer material. It is calculated by finding the diameter of the particles at the 50th percentile.

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Gravel Pack

A layer of gravel placed around a well screen to prevent fine-grained aquifer material from entering the well and clogging the screen. It helps ensure reliable water flow into the well.

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Uniformly Grained Gravel Pack

Used when the aquifer material has a narrow range of particle sizes and a small effective size (UC < 2.0, ES < 0.30 mm). This type of pack ensures even water flow into the well.

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Graded Gravel Pack

Used when the aquifer material has a wider range of particle sizes and a small effective size (UC > 2.0, ES < 0.30 mm). This type of pack provides optimal water flow with various particle sizes.

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Gravel Envelope

This type of pack supports the borehole and prevents collapse in aquifers with a large effective size (ES > 0.30 mm). Less material is needed due to larger particle sizes.

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Screen Size Rule

The rule that the screen or perforation slot size of a well should be less than or equal to half the size of the 85th percentile material in the gravel pack. This ensures that fine material from the aquifer does not clog the screen.

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Gradation Curve

A visual representation showing the distribution of particle sizes in a sample of aquifer material. It helps determine the optimal gradation of the gravel pack based on the grain size distribution of the aquifer.

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Prime Mover Full Load Continuous Duty Horsepower

The capacity of a prime mover, expressed in horsepower, needed to operate a pump continuously without overheating or damage.

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Pump Brake Horsepower (BHP)

A measure of the power output of a prime mover, used for calculating the required power for a pump.

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Table 5: Estimated Body Indicated Power Rating

A table used to estimate the body indicated power rating of prime movers based on their type and pump brake horsepower.

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Body Indicated Power

The power output of a prime mover, taking into account losses due to friction and other inefficiencies.

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Prime Mover

A prime mover that provides power to drive a pump.

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Electric Motor

A type of prime mover commonly used in irrigation systems.

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Diesel Engine

A type of prime mover commonly used in irrigation systems, known for its efficiency and durability.

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Gasoline Engine

A type of prime mover commonly used in irrigation systems, known for its portability and ease of use.

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Study Notes

Philippine National Standard for Groundwater Irrigation - Shallow Tubewell

  • This standard outlines procedures for shallow tubewell design, installation, and development using suction lift pumps.
  • The standard was initiated by the Agricultural Machinery Testing and Evaluation Center (AMTEC) under a project focusing on nutrient and water use efficiency.
  • The Bureau of Agriculture and Fisheries Standards (BAFS) is responsible for developing and endorsing standard specifications and test procedures for agricultural and fisheries machinery, as mandated by the Agricultural and Fisheries Mechanization Law of 2013.
  • The standard adheres to BPS Directives Part 3:2003 regarding structure and drafting of international standards.

Scope

  • The standard covers procedures for shallow tubewell design, installation, and development.
  • The scope is limited to shallow tubewell capabilities using suction lift pumps.

References

  • Normative documents referenced include PAES 127:2002 (Agricultural Machinery - Drilling Rig Specifications) and PNS/BAFS/PAES 217:2017 (Requirements for Determination of Irrigation Water).

Definitions

  • Aquifer: A geologic formation containing water that transmits it at a sufficient rate for economical pumping.
  • Confined aquifer: An aquifer confined or overlain by a relatively impermeable layer.
  • Effective size: The particle diameter corresponding to a 10% sieve passing.
  • Pumping test: Evaluation of aquifer properties by pumping water from a well and observing drawdown in observation wells.
  • Shallow tubewell: A tube or shaft drilled to a depth typically less than 15 meters for shallow groundwater extraction using suction lift pumps.
  • Unconfined aquifer: An aquifer with a water table as its upper surface.
  • Uniformity coefficient: The ratio of the 60% passing size to the 10% passing size.
  • Well log: A record documenting aquifer stratification, depth, thickness, lithology, and other characteristics.

Site Selection

  • Site selection should ensure adequate yield based on aquifer transmissivity and specific yield, meeting irrigation water requirements.
  • The site should have sufficient aquifer recharge or be located near suitable surface water sources.
  • Water quality should meet national implementing agency standards for irrigation water.
  • Sites should have low vulnerability to pollution and saltwater intrusion.

Well Characteristics

  • Key aquifer properties and their importance in well design, drilling, and development, and in selecting pumping systems are outlined in Table 1.
  • Well design, drilling, and development methods are further detailed.
  • Methods used for well characterization and site investigation are detailed in Table 2, covering surface, remote sensing, and geophysical exploration, as well as electrical resistivity and seismic refraction methods, and test drilling for subsurface investigation.

Well Classification

  • Various well types, including dug wells, bored wells, driven wells, and jetted wells, depending on the geological formation and water table depth are categorized and described.
  • Details on materials and limitations for each type are given.

Discharge

  • Section 7 outlines the procedure for determining the required pump discharge based on irrigation water requirements.
  • Equations and calculations to determine the maximum sustained yield for confined and unconfined aquifers are given.
  • Instructions for comparing and adjusting pump discharge to meet maximum sustained yield are included.

Shallow Tubewell Design, Installation, and Development

  • Details on tubewell design, including pipe selection considerations, aquifer penetration, pipe perforation, drilling techniques, pipe installation, and well development procedures, are described.

Pump Selection

  • Section 10 guides the selection of a pumping unit based on the required brake horsepower, total dynamic head, pump discharge, and efficiency.
  • Tables outlining required power ratings for various prime movers (e.g., electric motors, diesel engines) are provided.

Well Logging Methods

  • Appendix A describes well logging procedures to assess subsurface characteristics and evaluate aquifer properties, including sample collection and analysis.
  • Provides guidance on using different methods and interpreting results.

Detailed Additional Info

  • Specific details, like recommended pipe materials for different well types and aquifer characteristics, are included based on the provided documents.

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Related Documents

Groundwater Irrigation - Shallow Tubewell PDF (PNS/BAFS/PAES 231:2017)

Description

Test your knowledge on various well construction methods such as manual excavation, bored wells, and jetted wells. This quiz covers important factors like site suitability, water table depth, and aquifer thickness that influence well design and irrigation water requirements. Prepare to delve into the nuances of groundwater management and its implications.

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