Drilling Wells Methods – Advantages and Disadvantages

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Drilling Wells Methods – Advantages and Disadvantages

There are several different types of drilling methods. Choosing a method depends on many factors including soil type, underground water level and common practice in every country. Cities using groundwater usually depend upon deep wells. These wells have the advantage of tapping deep and extensive aquifers. All deep wells are drilled wells. The successful digging of drilled wells requires special training, experience, tools and equipment.

The main methods of drilling wells are :

1- Rotary Drilling

The principle of rotary drilling is based upon a rotating drill stem made of lengths of drill pipe about 15 feet long. A bit is attached to a heavy stabilizer or drill collar at the end of the column of drill pipe. The extra weight and larger outside diameter of the stabilizer just above the bit helps to maintain a straight drill hole. The drill stem is hollow and has a drilling fluid of either mud or air circulating down the drill stem out through the nozzles in the bit and up along the outside of the drill stem. The rotating action of the bit breaks up the material and the drilling fluid carries the cuttings to the surface where they settle out in a mud tank.

Advantages:

Speed of Drilling: 5 to 7 times faster than cable tool, capable of several hundred feet per day (dependent on geologic material).

Options of Well Design: Screen can be telescoped or attached, separate screens can be installed, filter packing to enhance formation production, down holle casing hammer method.

Grouting: Oversized borehole requires grouting of annular space surrounding casing, most adaptable to various grout placement methods, practical for grout placement thru casing.

Disadvantages:

Cost of Equipment: 5 times as costly as a cable tool or jetting rig, bit cost and tooling more
Maintenance & Support: Much more extensive and costly than cable tool, higher fuel consumption, water truck needed.

2- Cable Tool Drilling

Cable tool drilling, also known as percussion drilling or spudding, is a widely used well drilling method.

Although it is a slower drilling method, the cable tool is less costly and simpler to operate than a rotary drill rig and is suitable for most geologic conditions.

The cable tool operates by raising and dropping a heavy drill string in the drillhole. The drill string, with bit on the bottom and rope socket (or swivel socket) on top, is suspended in the hole with a cable. The cable is threaded over the crown sheave located at the top of the mast, down to the walking beam, and onto the cable drum where it is stored.

The up-and-down drilling action imparted to the drill stem and cable by the walking beam. The walking beam is pivoted at one end, has a cable sheave at the other end and is connected to the crank gear with a pitman. Rotation of the crank gear causes the walking beam to move up and down. Additional cables called sand lines or casing lines are used to raise and lower casing, bailers, plungers, or other tools.

Advantages:

Inexpensive Equipment: 1/5 cost of rotary rig, less grouting equipment needed, large water truck unnecessary, lower fuel consumption, lower operating cost.

Limited Tooling Required: Bits can be resurfaced, less expensive tooling, used items readily available.

Less Material Removed During Drilling: Generally, no oversized borehole, material removed from casing inside diameter, lighter soils can be bailed from casing.

Repair Work: Cable tool rigs ideal for casing reaming, screen replacement, and

Disadvantages:

Slow Drilling Speed: Bedrock drilling – 1/7 as fast as rotary drilling, Glacial drift drilling – 1/5 as fast as rotary drilling
Depth Limitations with Single Casing String: Driving generally difficult in caving formations, ability to drive casing is limited by tool weight and ground

Outer Casing Needed for Gravel Packing or Full Length Grouting: 3 to 4 inch larger casing needed to maintain annulus and must be extracated during grouting.

Steel Casing Material Only: PVC casing can not be used unlesss installed in an oversized borehole without driving.

3- Auger Drilling

The auger method utilizes spiral augers, usually in 5 foot lengths. The auger stem is turned by a hydraulically-controlled rotary drive head. After drilling the length of an auger, the auger joint is broken and another 5 foot section is added.

Cuttings spiral their way up to the surface where they appear around the borehole, making formation identification relatively simple. If enough clay is present in the formation, the drillhole will remain open when augers are removed.

Dry sands and other caving formations may be a problem for the auger driller and will occasionally result in the loss of long flights of augers. When the auger encounters saturated sand (the water bearing formation to be screened), drilling generally can be continued for a short distance but the hole will not remain open in the saturated formation when the augers are removed.

The auger flight is then broken down and removed from the drillhole after drilling the depth of the well or when changing to another type of drilling operation.

Advantages:

Speed of Drilling: Fast for shallow holes without cobbles or gravel and with low water table, auger/cable tool or jetting combination rigs are common
Limited Equipment: Less expensive than rotary, minimal amount of equipment

Disadvantages:

Limited Depth: Poor results in caving formations, gravel, or high water table, less than 100 feet.

4- Hand Driving

Driven wells are common in many areas, especially around lakes where groundwater may be close to the surface.

Simple installation methods and the low cost of materials make them attractive to homeowners or cottage owners who wish to install their own water supplies.

However, since the well point and casing are driven into the ground, soil conditions are a major factor in suitability of the site. The site must be generally sandy and free of boulders or bedrock to be suitable for a driven well. Hard clay, silt, and very fine sand are generally difficult to drive through.

The installation of a driven well often begins by augering a hole with a hand auger or posthole digger as far as possible. A drive point, consisting of a reinforced well screen with a steel point on the end, is coupled to a 5 foot length of galvanized casing. The most common casing size for driven wells is 1-1/4 inch inside diameter.

A drive cap is placed an the top of the casing and a heavy weight is used to strike the top of the drive cap, driving the point into the ground, When the drive cap is driven close to the ground and driving cannot be continued, another length of casing is added and driving is resumed.

Special drive couplings are used to join sections of casing, Hand driving is usually accomplished by using a weighted driver consisting of a 3 or 4 foot piece of 3 inch diameter pipe capped on the top end. Extra weight is placed in the top portion of the driver. The driver fits over the casing and is guided by it. Another type of driver has a steel rod on the bottom that slides into the casing through a hole in the drive cap.

Raising and dropping the driver is done with the use of handles welded on the sides of the driver. The weighted driver may also be suspended from a tripod and tackle arrangement. The use of a sledge hammer for driving is not recommended since it may result in bent or broken casing from glancing blows.

5- Jetting

Jetting is a drilling method suited for the sandy areas. Jetting remains a popular method for drilling small diameter wells due to its simplicity and inexpensive cost of equipment. Many of the portable, do-it-yourself drilling machines advertised in magazines utilize the jetting method.

Jetting and hollow-rod equipment are quite similar except that drilling water is pumped with the jetting method and the direction of water flow is opposite.

The jetting method involves using a high velocity stream of water to break up the formation material and wash the cuttings away. A chisel-shaped bit with holes to serve as nozzles is attached to the end of a string of hollow drill pipe. Water pressure is provided to the nozzles by using a high-pressure pump.

Water exits from the nozzles and loosens the material being drilled while keeping the bit clean. The bit is raised and lowered and rotated slightly to maintain a round hole. The cuttings are washed to the surface on the outside of the drill pipe and flow into a settling pit or tank.

Cutting samples are easily obtained at this point. A 55 gallon drum is often used for this purpose. After cuttings are allowed to settle, the water is recirculated through the pump, swivel, drill pipe and down to the bit. Jetting can also be done without recirculation of the drilling water; however, a continuous supply of water must be available at the site.

6- Hollow-Rod

Drilling Hollow-rod is referred to as the hydraulic-percussion drilling method.

The hollow-rod is an old drilling method that can be time consuming in some situations, but remains popular due to its simplicity and relatively low cost of equipment.

Most hollow-rod wells are 2 inch diameter, but 4 inch casings are installed occasionally. This method is well suited for sand and soft clay formations with relatively few boulders. It can also be used for drilling rock wells, but progress is slowed considerably. Wells several hundred feet in depth have been completed by the hollow-rod method.

The drill string used in hollow-rod drilling is similar to that used in jetting, except that the chisel bit has a ball check valve in it. Water or a clay-water mixture is kept in the annular space between the drill rods and well casing to help prevent the uncased portion of the hole from collapsing.

The water is supplied to the annulus by gravity intake from a small mud tank. A 55 gallon drum is often used as a settling tank. Drilling is done by lifting and dropping the drill stem and bit. The drill pipe used has triple wall thickness to add weight to the drill string.

The drill string is also rotated slightly by hand during each stroke to maintain a round drill hole. As the bit drops, the ball check opens and mud and cuttings enter the hollow drill rods. On the upstroke, the check valve closes and keeps the cuttings in the drill rods.

Advantages:

Inexpensive Equipment: 1/5 cost of rotary rig, less grouting equipment needed, large water truck unnecessary, lower fuel consumption, lower operating cost.
Limited Tooling Required: Bits can be resurfaced, less expensive tooling, used items readily available, many tools
Less Material Removed During Drilling: Generally no oversized borehole, material removed from casing inside diameter.
Repair Work: Jetting rigs ideal screen replacement and development.

Disadvantages:

Slow Drilling Speed: Bedrock drilling – uncommon, requires heavy drill bar, 1/7 as fast as rotary drilling, Glacial drift drilling – 1/5 as fast as rotary drilling, limited use in gravel formations.
Depth Limitations with Single Casing String: Driving generally difficult in caving formations, ability to drive casing is limited by tool weight and ground
Outer Casing Needed for Gravel Packing or Full Length Grouting: 3 to 4 inch larger casing needed to maintain annulus and must be extracated during grouting.
Steel Casing Material Only: PVC casing can not be used unlesss installed in an oversized borehole without driving.

Fundamentals Of Hydrology Free PDF

It is the presence or absence of water that by and large determines how and where humans are able to live.
This in itself makes water an important compound, but when you add in that the availability of water varies enormously in time and space, and that water is an odd substance in terms of its physical and chemical properties, it is possible to see that water is a truly extraordinary substance worthy of study at great length.

To study hydrology is to try and understand the distribution and movement of fresh water around the globe. It is of fundamental importance to a rapidly growing world population that we understand the controls on availability of fresh water.

To achieve this we need to know the fundamentals of hydrology s a science. From this position it is possible to move forward towards the management of water resources to beneﬁt people in the many areas of the world where water availability is stressed.

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Fountain Design Guide Free PDF

Water – The ultimate medium for the creation of an architectural masterpiece. Water appeals to all of our senses by adding life to an environment with the added dimensions of sound and movement. When used effectively an architectural fountain can enhance and add focus to a project, distinguishing it from the ordinary.

The Fountain People, believe that the creation of an architectural water feature should have no limitations other than the designer’s imagination. Our many years of experience and in-house design testing facilities provide us with a unique insight into the design of successful water creations.

This Fountain Design Guide has been designed for the sharing of that insight. Our intent is to assist you better understanding the design elements that result in a successful fountain design.

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All Plumping Calculations Spreadsheet

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The most important Drainage Calculation Spreadsheets

14 day Residence : This sheet calculates the required minimum pond size at SHW for a 14 day residence permanent wet pool
Boring Calculations : This sheet calculates the required number of borings and hydraulic conductivity tests for a pond
Buoyancy Calculations: This sheet verifies the required soil depth over a pond liner
Channel Sections : This sheet calculates geometric elements of various cross sections and segments of a circle
Conversions – DRI and Metric : This sheet converts metric to English and vice versa and DRI to conductivity conversions
Curve Number Calculations : This sheet converts Curve Numbers to coefficient of runoff numbers
Effluent Filtration : This sheet verifies the recovery time for an effluent filtration system
Head Loss: This sheet calculates head losses in pipes
Intensity (Rainfall) : This sheet calculates rainfall intensity and allowable discharge in FDOT’s Zones 1 through 11 for the 2 to 50 years events
Kinematic Wave : This sheet calculates the time of concentration using the kinematic wave formula
Littoral Shelf: This sheet calculates the required shelf size if the pond is larger than required
Modified Rational : This sheet calculates the required storage volume for a 2 to 50 year storm event in all 11 FDOT zones
NRCS Runoff Calculator: This sheet calculates runoff by the NRCS method
NRTS Tc Calculator: This sheet calculates the NRCS time of concentration
Orifice Bleeddown Calculator: This sheet calculates the required orifice size to discharge ½ the treatment volume in 60 hours or more
Pipe Calculations: This sheet calculates slopes, volumes, velocities and capacities of pipes flowing full
Pond Volume: This sheet calculates pond volumes based on surface area and elevation
Rainfall Hydrograph Calculator: This sheet generates rainfall hydrographs for input into other programs
Rating Curve Calculator: This sheet calculates rating curves for compound weirs for input other programs
Retention Basin Recovery: This sheet calculates retention basin recovery timeframes
Sediment Sump Sizing: This sheet calculates the required sediment sump size.
Simplified Analytical Method: This sheet provides a simplified pond (surface water management system) volume recovery analysis
Tc Lag Method: This sheet calculated lag time
V-Notch Calculations: This sheet verifies the 24 hours bleeddown requirement for a V-notch weir
Vegetative Upland Buffer: This sheet calculates vegetative upland buffers for a residential stormwater quality treatment alternative practice
Weir Calculations: This sheet calculates weir dimensions based on height, width or discharge rate
Weir Notch Flow: This sheet calculates the bleed down time for a weir notch

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Hydraulic Ram Design Spreadsheet

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Development and Splice Of Reinforcement In Masonry Spreadsheet

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Types and Applications of Fly Ash in Construction

Since wide scale coal firing for power generation began in the1920s, many millions of tons of ash and related by-products have been generated. The current annual production of coal ash world-wide is estimated around 600 million tones, with fly ash constituting about 500 million tones at 75–80% of the total ash produced.

Thus, the amount of coal waste (fly ash), released by factories and thermal power plants has been increasing throughout the world, and the disposal of the large amount of fly ash has become a serious environmental problem. The present day utilization of ash on worldwide basis varied widely from a minimum of 3% to a maximum of 57%, yet the world average only amounts to 16% of the total ash.

Fly ash is generally grey in color, abrasive, mostly alkaline, and refractory in nature. Pozzolans, which are siliceous or siliceous and aluminous materials that together with water and calcium hydroxide form cementitious products at ambient temperatures,are also admixtures.

Fly ash from pulverized coal combustion is categorized as such a pozzolan. Fly ash also contains different essential elements, including both macro nutrients P, K, Ca, Mg and micro nutrients Zn, Fe, Cu, Mn, B, and Mo for plant growth. The geotechnical properties of fly ash (e.g., specific gravity, permeability,internal angular friction, and consolidation characteristics) make it suitable for use in construction of roads and embankments, structural fill etc.

The pozzolanic properties of the ash, including its lime binding capacity makes it useful for the manufacture of cement, building materials concrete and concrete-admixed products.

Fly Ash Types :

There are two common types of fly ash: Class F and Class C.

Class F fly ash contain particles covered in a kind of melted glass. This greatly reduces the risk of expansion due to sulfate attack, which may occur in fertilized soils or near coastal areas. Class F is generally low-calcium and has a carbon content less than 5 percent but sometimes as high as 10 percent.

Class C fly ash is also resistant to expansion from chemical attack. It has a higher percentage of calcium oxide than Class F and is more commonly used for structural concrete. Class C fly ash is typically composed of high-calcium fly ashes with a carbon content of less than 2 percent.

Currently, more than 50 percent of the concrete placed in the U.S. contains fly ash.2 Dosage rates vary depending on the type of fly ash and its reactivity level. Typically, Class F fly ash is used at dosages of 15 to 25 percent by mass of cementitious material, while Class C fly ash is used at dosages of 15 to 40 percent.3

Fly Ash Applications :

Utilization of fly ash appears to be technically feasible in the cement industry. There are essentially three applications for fly ash in cement

(1) replacement of cement in Portland cement concrete

(2) pozzolanic material in the production of pozzolanic cements

(3) set retardant ingredient with cement as a replacement of gypsum

Cement is the most cost and energy intensive component of concrete. The unit cost of concrete is reduced by partial replacement of cement with fly ash.

The utilization of fly ash is partly based on economic grounds as pozzolana for partial replacement of cement, and partly because of its beneficial effects, such as, lower water demand for similar workability, reduced bleeding, and lower evolution of heat.

It has been used particularly in mass concrete applications and large volume placement to control expansion due to heat of hydration and also helps in reducing cracking at early ages.

The major drawback of fibre reinforced concrete is its low workability. To overcome this shortcoming, a material is needed, which can improve the workability without comprising strength.

The use of fly ash in concrete enhances the workability of concrete and being widely recommended as partial replacement of cement. This also reduces the cost of construction. Fly ash concrete provides much strong and stable protective cover to the steel against natural weathering action.

Stone Column Method For Ground Improvement

Stone column method for ground improvement

Stone column method for ground improvement is a vibro-replacement technique, where the weak soil is displaced using a cylindrical vibrating probe (i.e. vibroflot), thus creating a column that is then filled and compacted with good-quality stone aggregates.

With the inclusion of stone aggregates to the in situ soil, its stiffness and load-carrying capacity increases. It also helps to reduce the static as well as differential settlement of the soils.

Bulging action of the stone columns imparts lateral confinement to the surrounding soils and it also acts as a drainage path accelerating the consolidation of cohesive soils.

These stone columns are generally used for soils that are much more compressible but not weak enough to necessitate a pile foundation. Moreover, for the construction of low-to-medium rise buildings on soft soils, pile foundation sometimes becomes expensive. In such cases, stone columns are preferred.

Stone columns are very useful for the improvement of cohesive soils, marine/alluvialclays, and liquefiable soils. Stone columns have been used successfully for a widerange of applications from the construction of high-rise buildings to oil tank foundation, and for embankment and slope stabilization.

Stone column installation methods

For the installation of stone columns a vibrating poker device is used that can penetrate to the required treatment depth under the action of its own weight, vibrations, and actuated air, assisted by the pull-down winch facility of the rig.

This process displaces the soil particles and the voids created are compensated with backfilling of stone aggregates. The vibroflot penetrates the filled stone aggregates to compact it and thus forces it radially into the surrounding soils.

This process is repeated till the full depth of the stone column is completed. The lift height is generally taken as 0.6–1.2 m for the filling and compaction of the stone aggregates.

Depending upon the feeding of stone aggregates into the columns there are basically two methods for the installation of stone columns:

1- Top-feed method

In the top-feed method, the stone aggregates are fed into the top of the hole. The probe is inserted into the ground and is penetrated to the target depth under its own weight and compressed air jetting. However, jetting of water is also done especially when the soil is unstable. This also helps to increase the diameter of the stone columns and to washout the fine materials fromthe holes.

The top-feed method is suitable when water is readily available and there is enough working space to allow for water drainage. Moreover, the soil types should be such that it would not create messy surface conditions due to mud in water.

The top-feed method is preferable when a deeper groundwater level is encountered.

Stone Columns installation Top-feed Method

2- Bottom-feed method

The bottom-feed method involves the feeding of stone aggregates via a tremie pipe along the vibroflot and with the aid of pressurized air. The bottom-feed method is preferable when the soil is highly collapsible and unstable. However, the stability of holes will also depend upon the depth, boundary conditions, and the groundwater conditions. In areas, where the availability of water and space and the handling of mudin process water are limiting factors, the bottom-feed method can be implemented.

Due to limited space in the feeding system, a smaller size of aggregates is used inthe bottom-feed method compared with that used in the top-feed method. On the otherhand, the flow of stones to the column is mechanically controlled and automatically recorded in the bottom-feed method.

Stone Columns installation Bottom Feed Method

Read More about Stone Columns: What are Stone Columns?

The Main Materials Of Ties Used in Railways

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The Main Materials Of Ties Used in Railways

The purpose of the tie is to cushion and transmit the load of the train to the ballast section as well as to maintain gage.

Wood and even steel ties provide resiliency and absorption of some impact through the tie itself. Concrete ties require pads between the rail base and tie to provide a cushioning effect.

Ties are typically made of one of four materials:

Timber
Concrete
Steel
Alternative materials

1. Timber Ties

It is recommended that all timber ties be pressure-treated with preservatives to protect from insect and fungal attack. Hardwood ties are the predominate favorites for track and switch ties.

Bridge ties are often sawn from the softwood species. Hardwood ties are designated as either track or switch ties.

Factors of first importance in the design and use of ties include durability and resistance to crushing and abrasion. These depend, in turn, upon the type of wood, adequate seasoning, treatment with chemical preservatives, and protection against mechanical damage. Hardwood ties provide longer life and are less susceptible to mechanical damage.

Hardwood Track Ties

2. Concrete Ties

Concrete ties are rapidly gaining acceptance for heavy haul mainline use, (both track and turnouts), as well as for curvature greater than 2°. They can be supplied as crossties (i.e. track ties) or as switch ties. They are made of pre-stressed concrete containing reinforcing steel wires. The concrete crosstie weighs about 600 lbs. vs. the 200 lb. timber track tie.

The concrete tie utilizes a specialized pad between the base of the rail and the plate to cushion and absorb the load, as well as to better fasten the rail to the tie. Failure to use this pad will cause the impact load to be transmitted directly to
the ballast section, which may cause rail and track surface defects to develop quickly.

An insulator is installed between the edge of the rail base and the shoulder of the plate to isolate the tie (electrically). An insulator clip is also placed between the contact point of the elastic fastener used to secure the rail to the tie and the contact point on the base of the rail.

Concrete Track Ties

3. Steel Ties

Steel ties are often relegated to specialized plant locations or areas not favorable to the use of either timber or concrete, such as tunnels with limited headway clearance. They have also been utilized in heavy curvature prone to gage widening. However, they have not gained wide acceptance due to problems associated with shunting of signal current flow to ground.

Some lighter models have also experienced problems with fatigue cracking.

Steel Track Ties

4. Alternative Material Ties

Significant research has been done on a number of alternative materials used for ties. These include ties with constituent components including ground up rubber tires, glued reconstituted ties and plastic milk cartons.

Appropriate polymers are added to these materials to produce a tie meeting the required criteria. To date, there have been only test demonstrations of these materials or installations in light tonnage transit properties. It remains to be seen whether any of these materials will provide a viable alternative to the present forms of ties that have gained popularity in use.