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There are number of dewatering options available for excavations to facilitate construction activities. The choice of best and suitable dewatering system brings economy in construction activities. For this, it is essential to have knowledge on different dewatering systems and each of their features in detail.

The best system is selected from different systems gathered. The choice of dewatering system for a site condition mainly depends on the:

The cost invested for a dewatering system or a dewatering method is dependent on four main factors. They are:

The method of slurry cut off walls have helped in controlling the ground water, that have in turn reduced the amount of pumping. Those projects that require high pumping can make use of barrier walls like slurry cut off walls.

If a project involves the construction of foundation in the ground level that is below water table of that site, it is necessary to undergo dewatering through methods like well point system or deep well system. This problem cannot be solved by methods like trenching or sump pumping.

The equipment operations, or the sliding or the sloughing of the side slopes can result in damage to the foundation. These effects on foundation can be reduced by dewatering systems.

The deep well and well point system does not require any detailed analysis or design before implementing in a site that does not bring huge pressure fluctuation underground. Here conventional dewatering system can be used.

But wherever there is unusual pressure relief, it is advised to have a detailed design prepared by the engineer to perform the dewatering. These details must be specified in detail by the engineer in the contract documents also. The use of unusual dewatering equipment must be specified by the engineer prior to the construction activities.

A conventional well point system is found economical and safe when dewatering has to be conducted in a ground area where the water table level is at a lower depth. A lowering of the water table level to a depth of 20 or 30 feet require deep well system or jet-educators to conduct the dewatering.

For excavations that are surrounded by cofferdams, either well point system or a deep well system or both in combination can be employed for dewatering.

A deep well system or a jet-eductor well point system is a best choice for dewatering that requires penetration into a field pervious soil or rock. These are mostly implemented for the construction of deep shafts or tunnels or caissons. The choice between the two is based on the soil formation in the area and the rate of pumping that is desired.

The type of dewatering system and drainage system for an area is best dictated based on the soil and the geological conditions of the area. A conventional well system or well point system can be used if the soil below the water table of the area is deep, free draining sand and more or less homogeneous in nature.

If the soil is highly stratified and there exist an impervious layer of rock, shale or clay then well point systems that are installed closely in space can be employed. Wherever the soil is in need for the relief of artesian pressure, deep wells or jet educators well points in few numbers can be installed.

The magnitude of depth to which the drawdown has to be conducted is one of the primary factor based on which the type of dewatering system is chosen. If the drawdown to be made is very deep, the deep well dewatering system or the jet eductor well points are used. The conventional well points system requires many stages of drawdown for a single depth of excavation.

A wide variety of flows can be met by using the deep well system given that appropriate pumps depending on the flow must be chosen. This type of flexibility is not available for jet eductor well point system. The jet eductor pumps are more employed where the flow is small as in the case of silty to find sand cases.

The design of dewatering pumps chosen, the standby power, equipment and the power supply is influenced significantly by the reliability of ground water control for a particular project.

For example, if the problem that is faced during dewatering is the relief of the artesian pressure so that blow up during the bottom excavation is prevented. This situation affects the choice of pressure relief system that is selected and the need for a standby equipment with the provision of automatic power transfer.

The pumping rate that is required to undergo dewatering of an excavation ranges between 5 to 50,000 gallons per minute or higher. The selection of walls, piping system, and the pumps are affected by the flow to the drainage system.

For deep well dewatering system, the pumps are available from sizes of 3 ro14 inches that have capacities ranging from 500 to 5000 gallons per minute. These have head value up to 500 feet.

The pumps used in well point system have sizes ranging 6 to 12 in inches with capacities ranging from 500 to 5000 gallons per minutes. This is dependent on the vacuum and the discharge heads.

The jet eductor pumps have pumping ability from 3 to 20 gallons per minute that lift upto 100 feet.

The rate of pumping is largely affected by the:

Having single or double shifts for dewatering per day brings the labor cost down. This principle cannot be followed wherever the depth of dewatering is very large, the subsoil is pervious and homogeneous. Under these situations, the pumping system can be operated such that large drawdowns are taken during single or double shifts.

The foundation soils that is below the ground water table is loaded additionally when the groundwater table of that area is lowered through dewatering system. Application of additional load results in the consolidation of the soil. This consolidation results in settlement of structures that are already constructed within the radius of influence.

Before the application of any dewatering system on a site, it is recommended to check for before mentioned possibility of settlement of active structures around. The water table level of nearby wells has to observed before and after dewatering. If any claims raised due to the dewatering procedure is raised, these observations are the basis on which the evaluation is made.

The control of water during excavation can be best done economically by the process of dewatering. But for certain applications like for the wet side of a cofferdam or a caisson, a tremie sealing is done on the bottom side of the excavation. Any other method like slurry cut off walls or other dewatering procedures are employed.

Other techniques are chosen based on suitability like the use of freezing techniques and rotary drilling machines that is conducted without the lowering of the water table can be employed. The use of concrete cut off walls in a slurry supported trench are other examples.

Surface drainage system is most important in Highway engineering. A pavement without proper drainage facilities will not serve for long time. The water or rainfall on road should be collected by side drains which carries the drain water to nearest stream or any water course.

So, prior to the construction of road, the designer should leave required space for providing proper drainage facilities as well as the pavement should also be constructed with minimum camber.

Fig 1: Surface drainage system on a highway

Design of Surface Drainage System for Highway

 

The design of surface drainage system carried by two types of analysis:

• Hydrologic analysis
• Hydraulic analysis

Hydrologic Analysis of Drainage for Highway

 

Whenever there is a rainfall, some of the rain water infiltrated into the ground and stored as ground water and some of the portion may evaporate into the atmosphere. Other than these losses, the water left on the surface is called as run off.
The method of estimating the run off is called hydrologic analysis. To estimate the maximum quantity of water expected to reach the drainage system is the main objective of hydrologic analysis. For this, one need to know the factors affecting run off and they are:

• Rate of rain fall
• Moisture condition
• Soil type
• Ground cover presence
• Topography

Other than the above factors, rain fall intensity, occurrence of storms in that area are to be studied from the old records. Hence, maximum run off can be estimated to build safe surface drainage system. The run off can be calculated by below formula:
Where;
Q = run off (m³/sec)
C = run off coefficient
i = intensity of rain fall (mm/sec)
A_d = area of drainage (m²)

Fig 2: Pavement Drainage Design

Run off coefficient “C” is the ratio of run off to the rate of rainfall. So, it is not same for all types of surfaces. It varies for different types of surfaces and its values for different surfaces are as follows:

Fig 3: Types of Surfaces & their Coefficients  

C = (A₁C₁+A₂C₂+A₃C₃) / (A₁+A₂+A₃ )

Q = A.V

Fig 7: Soil Types & their Velocities

V=1∕n R⅔S½

Fig 9: Rough Coefficients

By linking the Pacific and Atlantic oceans, the Panama Canal revolutionized global shipping when it opened nearly a century ago. However, the canal's capabilities are quickly being outpaced by the ever-growing ships that pass through it. In order to accommodate the next generation of over-sized vessels, the Panama Canal is receiving its most ambitious upgrade in 93 years - a third channel hemmed in by these gargantuan flood gates.

A major milestone was reached on the Panama Canal expansion project on April 28, as the eighth and fi nal lock gate was installed on the Pacifi c side of the route. Th ere are another eight lock gates already installed on the Atlantic side, for a total of 16. The final gate is one of the heaviest. It weighs 4,232 tonnes and measures 57.6 m wide by 10 m long by 33 m high. Manufactured in Italy, the new gates arrived in Panama in four staggered shipments starting in August 2013.

Panama Canal administrator Jorge L Quijano said, “Today’s installation is a key milestone in the expansion programme and another important step forward for the Canal,” The Panama Canal Authority (ACP) reports that expansion work is now 88% complete. It added that several major project components, including all excavation and dredging work have been completed.

In other news, ACP is to appeal against the December adjudication board ruling that it has to pay US$ 234 million to consortium Grupo Unidos por el Canal, (GUPC) and extend its contract by six months. The appeal will go before an arbitration hearing in Miami, US.

The dispute relates to poor quality basalt, which was to be used for aggregates on the project as well as a delay on ACP’s part in approving the concrete mix to be used on the project. GUPC said the rock was not of the same quality as indicated in the bidding documents issued by ACP.

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This manual describes the development and use of response spectra for the seismic analysis of concrete hydraulic structures. The manual provides guidance regarding how earthquake ground motions are characterized as design response spectra and how they are then used in the process of seismic structural analysis and design. The manual is intended to be an introduction to the seismic analysis of concrete hydraulic structures. More detailed seismic guidance on specific types of hydraulic structures will be covered in engineer manuals and technical letters on those structures.

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The end of the 19th century was a time of visionaries who conceived of projects that would change the history of humankind. Since the time Vasco N unez de Balboa crossed Panama and discovered a great ocean, planners had conceived of the idea of a water link between the Atlantic and the Pacific Oceans. Having successfully connected the Mediterranean with the Red Sea at Suez, in 1882 the French began work on a canal across the narrow Isthmus of Panama, which at that time was part of Colombia. After struggling for 9 years, the French were ultimately defeated by the formidable technical difficulties as well as the hostile climate and the scourge of yellow fever.

Theodore Roosevelt became president during this period and his administration decided to take up the canal project and carry it to completion. Using what would he referred to as ‘‘gun-boat’’ diplomacy, Roosevelt precipitated a revolution that led to the formation of the Republic of Panama. Having clarified the political situation with this stratagem, the famous ‘‘Teddy’’ then looked for the right man to actually construct the canal. That right man turned out to be John F. Stevens, a railroad engineer who had made his reputation building the Great Northern Railroad. Stevens proved to be the right man at the right time.

Stevens understood the organizational aspects of large projects. He immediately realized that the working conditions of the laborers had to be improved. He also understood that measures had to be taken to eradicate the fear of yellow fever. To address the first problem, he constructed large and functional camps for the workers in which good food was available. To deal with the problem of yellow fever he enlisted the help of an army doctor named William C. Gorgas. Prior to being assigned to Panama, Gorgas had worked with Dr. Walter Reed in wiping out yellow fever in Havana, Cuba. He had come to understand that the key to controlling and eliminating this disease was, as Reed had shown, the control of the mosquitoes that carried the dreaded infection and the elimination of their breeding places (see The Microbe Hunters by Paul DeKruif). Gorgas was successful in effectively controlling the threat of yellow fever, but his success would not have been possible without the total commitment and support of Stevens.

The construction of this system of locks presented a formidable challenge. Particularly on the Atlantic side of the canal, the situation was complicated by the presence of the wild Chagres River, which flowed in torrents during the rainy season and dropped to a much lower elevation during the dry season. The decision was made to control the Chagres by constructing a great dam that would impound its water and allow for control of its flow. The dam would create a large lake that would become one of the levels in the set of steps used to move ships through the canal. The damming of the Chagres and the creation of Lake Gatun itself was a project of immense proportions, which required concrete and earthwork structures of unprecedented size.

The other major problem had to do with the excavation of a great cut through the highest area of the canal. The Culebra Cut, as this part of the canal was called, required the excavation of earthwork quantities that even by today’s standards stretch the imagination. Stevens viewed this part of the project as the construction of a gigantic railroad system that would operate continuously (24 hours a day) moving earth from the area of the cut to the Chagres dam construction site. The material removed from the cut would provide the fill for the dam. It was an ingenious idea.

To realize this system, Stevens built one of the greatest rail systems of the world at that time. Steam-driven excavators (shovel fronts) worked continuously loading railcars. The excavators worked on flexible rail spurs that could be repositioned by labor crews to maintain contact with the work face. In effect, the shovels worked on sidings that could be moved many times each day to facilitate access to the work face. The railcars passed continuously under these shovels on parallel rail lines.

Stevens’ qualities as a great engineer and leader were on a level with those of the Roebling’s. As an engineer, he understood that planning must be done to provide a climate and environment for success. Based on his railroading experience, he knew that a project of this magnitude could not be accomplished by committing resources in a piecemeal fashion.

He took the required time to organize and mass his forces. He also intuitively understood that the problem of disease had to be confronted and conquered. Some credit for Stevens’ success must go to President Roosevelt and his secretary of war,William Howard Taft. Taft gave Stevens a free hand to make decisions on the spot and, in effect, gave him total control of the project. Stevens was able to be decisive and was not held in check by a committee of bureaucrats located in Washington (i.e., the situation present before he took charge of the job).

Figure 5: How Panama Canal Works?

Having set the course that would ultimately lead to successful completion of the canal. Stevens abruptly resigned. It is not clear why he decided not to carry the project through to completion. President Roosevelt reacted to his resignation by appointing a man who, as Roosevelt would say, ‘‘could not resign.’’ Roosevelt selected an army colonel and West Point graduate named George Washington Goethals to succeed Stevens. Goethals had the managerial and organizational skills needed to push the job to successful completion. Rightfully so, General Goethals received a great deal of credit for the construction of the Panama Canal. However, primary credit for pulling the job ‘‘out of the mud,’’ getting it on track, and developing the technical concept of the canal that ultimately led to success must be given to Stevens—a great engineer and a great construction manager.

The large prefabricated box or cylindrical type structures that can be sunk through soft ground or water and then filled with concrete thus forming a foundation are called as Caissons.

The caisson is generally a box like structure with an open bottom and open top some times. The structure keeps water out of the construction area while its open bottom allows workers to place foundations and piers in the sea bed or riverbed. An open caisson can be used in shallow water; its open top allows light and air to enter from above the water line.

For deep-water construction, a pneumatic caisson has a closed top; pressurized air is pumped in, and personnel enter and leave through an airlock. Both types have sharp inclined lower edge, which allows the caisson to be deeply embedded in the ground.

Before putting the caisson in its place, engineers look for stable seabed like rock. But if they don’t find this layer they make artificial layer to provide safety to the caisson. In pneumatic caissons, an airlock allows access to the chamber and the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson.

• Caissons are similar to pile foundations but installed using different ways.
• These are actually deep foundations constructed above ground level & sunk into earth to the required level by excavating material within the caisson. 
• Caissons also provide dry space to carry out other construction works. 

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The time was the early 1930s, the president was Herbert Hoover, and the situation in the United States looked bleak. The stock market had crashed in 1929, and most Americans were hurt by the Great Depression, which left a majority of them jobless, homeless, and penniless. But in the West, a beacon of hope was in the works— a major structure that would symbolize the nation’s technological prowess. That structure, built as graceful as it was strong, would come to be known as the Hoover Dam.
In the dry western United States, water resources and water rights had almost always been an issue. For this growing area of the country, water for drinking and irrigating land was an everincreasing necessity. The United States Reclamation Service was formed to help deal with these concerns. This government entity and its engineers would come to play a great part in the construction of the Hoover Dam.
When early settlers arrived in the West, they could hardly have been able to imagine that any structure could control the Colorado River and its strong- minded fl ow. Yet a man named Arthur Powell Davis dreamed an amazing dream for the area of the Colorado Basin. Davis’s dream certainly did not become a reality overnight. For a project of this magnitude to succeed, field investigations would have to be conducted, politicians would have to organize, seven western states that had been arguing for years would have to make a final and lasting negotiation on water rights, and a company that could actually bring to life such an enormous entity would have to be found. It took years, but eventually all obstacles were overcome.
Created from a whopping 4.5 million cubic yards (3.4 million cubic meters) of concrete, the majestic dam was built in the middle of nowhere, stretching across the mighty Colorado River in the desolate Black Canyon. To provide for the dam’s construction, the government would have to lay down rail line, electricity would have to be connected, and living quarters for thousands of workers would have to be built. In short, the dam was an immense undertaking.
The organization in charge of building this one of a kind dam from the canyon floor up was Six Companies-a conglomeration of several businesses and individuals with construction and engineering experience who could not possibly have done the job alone. The ones responsible for its actual rise, block by block, 726 feet (221.3 meters) into the air were 5,000 men who came from all across the country. Most of these men were desperate to feed themselves and their families in the hungry times of the Depression. Living and working in extreme conditions, these workers— some with no previous construction experience jackhammered, blasted, dug, and swung hundreds of feet in the air from the canyon walls, all in the name of progress.
Over the course of several years— from 1931 to 1936—the dam took shape, a reservoir was created, and a hydroelectric power plant was built. During this time, the construction claimed 96 lives. In the end, however, this fascinating superstructure— and the world’s tallest dam at the time— would prove to be a lasting memorial to the thousands of men who saw it to completion.

Although the Hoover Dam has since been surpassed in height, it remains one of the most widely recognized structures in the world and a crowning achievement in American engineering.

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Water is the greatest resource of humanity. It not only helps in survival but also helps in making life comfortable and luxurious. Besides various other uses of water, the largest use of water in the world is made for irrigating lands. Irrigation, infact, is nothing but "a continuous and a reliable water supply to the different crops in accordance with their different needs". When sufficient and timely water does not become available to the crops, the crops fade away, resulting in lesser crop yield, consequently creating famines and disasters. Irrigation can, thus, save us from such disasters.

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This text is loosely based on a course on ‘Hydraulic Structures’ which evolved over the years in the Department of Civil Engineering at the University of Newcastle upon Tyne. The final-year undergraduate and
Diploma/MSc postgraduate courses in hydraulic structures assume a good foundation in hydraulics, soil mechanics, and engineering materials, and are given in parallel with the more advanced treatment of these subjects, and of hydrology, in separate courses.
It soon became apparent that, although a number of good books may be available on specific parts of the course, no text covered the required breadth and depth of the subject, and thus the idea of a hydraulic structures textbook based on the course lecture notes came about. The hydraulic structures course has always been treated as the product of team-work.
Although Professor Novak coordinated the course for many years, he and his colleagues each covered those parts where they could make a personal input based on their own professional experience. Mr Moffat, in particular, in his substantial part of the course, covered all geotechnical engineering aspects. In the actual teaching some parts of the presented text may, of course, have been omitted, while others, particularly case studies (including the discussion of their environmental, social, and economic impact), may have been enlarged, with the subject matter being continuously updated.
We are fully aware that a project of this kind creates the danger of presenting the subject matter in too broad and shallow a fashion; we hope that we have avoided this trap and got it ‘about right’, with worked examples supplementing the main text and extensive lists of references concluding each chapter of the book.

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In pipe lines when the valves are operated then the flow parameters changes with respect to time and its state becomes unsteady.

 

 

 

 

f = pipe friction factor

K = Separation Losses