well point system of dewatering

WELL POINT SYSTEM OF DEWATERING

Manasa S1, Dr.P.Shivananda2

1student of first year MTech (T.E & M), Reva University, Bangalore, India

2 professor, Department of Civil Engineering Reva University, Bangalore-560064, India [email protected] [email protected]

Abstract: Dewatering techniques mainly control the common and complicated problems like groundwater or water logging. Construction dewatering can become a costly issue if overlooked during project planning. The aim of dewatering techniques is to permit the structure to be constructed “in the dry”.

This leads to concepts like pre-drainage of soil, control of ground water, and even the improvement of physical properties of soil. If ground water issues are addressed appropriately at the investigation and design stage, construction dewatering, which involves temporarily lowering the ground water table to permit excavation and construction within a relatively dry environment, is rarely a problem. The most common methods for dewatering include sumps, wells and well-points. Resulting from this, verify feasibility of several options and technology for water removal from the dewatering processes and should be useful and important part of construction.

Keywords: Dewatering, Ground Water, Well Point.

1. INTRODUCTION

Many civil engineering or smaller projects involve excavation below groundwater level. Dewatering is a term to describe the removal of groundwater within a soil material and is carried out to ensure excavations are undertaken in dry and stable conditions. Normally, builders tend to use water pumps to dewater these areas but are not paying attention to the place where water is discharged, causing erosion and other problems. Construction dewatering is used on most construction sites due to accumulated water in trenches and excavations, places with inadequate slope or due to high water table.

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In construction projects, this water should be removed to keep working as scheduled or to provide a safe workplace. Ground conditions and objectives command dewatering requirements and appropriate method can be determined by pumping testing.

2. REVIEW OF LITERATURE

M.U. Ergun and M.S. Nalcakan (1993) “Dewatering of a large excavation pit by wellpoints”, An excavation, rectangular in dimensions of 55 m ? 95 m at the base and approximately 120 m ? 160 m at the ground surface was made possible by the use of multi-staged wellpoint dewatering system. Ground water table was lowered more than 20 meters using four stage wellpoint system to construct the main wastewater pump station for the city of izamir. They concluded that the most important factor in the design of wellpoint dewatering system is the coefficient of field permeability. Therefore, for large and important projects field pumping test must be performed to estimate the coefficient of field permeability, as accurate as possible.

Jigar Patel, Prof. Jayeshkumar Pitroda, Prof. J. J. Bhavsar (2014) “well point system and freezing techniques for dewatering”, They concluded that, today is improved well equipment and well construction techniques make possible the dewatering of many projects with wells and wellpoints. Though construction dewatering has not been reduced to an exact science yet, the selection of the dewatering system should hinge on the experience and professional judgment of the engineer based on the soil materials, the source of water, and the demands of the project.

M. L. Angel, S. Johnston, K. O’Steen, C. Brown and T. Sando (2015) “Groundwater Control Issues in Transportation Engineering: A Short Review of Dewatering Methods and Lessons Learned”, More building and transportation structures are being constructed today in areas where high ground water tables precluded construction years before. To control groundwater during the construction process, various dewatering techniques are designed depending heavily on the amount of water to be removed, the subsurface profile at the site, and the underlying hydrological chacteristics. A review of common dewatering systems and methods used in the construction of transportation facilities found that similar techniques are used in other industries. A common thread among all construction initiatives is the need for thorough subsurface site investigation.

3. DEWATERING:

Definition: Dewatering means “the separation of water from the soil,” or perhaps “taking the water out of a particular construction problem completely”. Many excavations are carried below groundwater level. Techniques for dealing with the problems that result depend on the excavation dimensions, the soil type, and the groundwater control requirements, among other factors.

3.1 TYPES OF DEWATERING:

1. Sumps, trenches, and pumps

2. Well point system

3. Electro osmosis process

4. Vacuum dewatering system

3.2 WELL POINT SYSTEM

Definition: A series of well points connected to a header and used to drain an area or to control ground water seepage into an excavation. The well-point consists of a slotted or perforated pipe which is covered with a screen mesh. At the foot of this pipe is an orifice which permits jetting of the pipe into the ground during installation. A well-point dewatering system consists of a series of closely placed small diameter wells installed to shallow depths. These wells are connected to a pipe or header that surrounds the excavation and is attached to a vacuum pump. The construction steps in the well-point system are:

1. The well-points are jetted into the ground;

2. The annular void is filled with filter media;

3. The well-points are connected to a header pipe by means of a riser;

4. The header pipe is connected to suction pumps for pumping.

3.3 TYPES OF WELL-POINT SYSTEM

1. Single stage well point system: Adopted up to 6m excavation depth below the water table

2. Multiple stage well point system: Adopted when excavation depth exceeds 6m below the water table

Fig.1 Single stage well point system fig.2 multiple stage well point system

3.4 Advantages

• Installation – very rapid

• Equipment – simple & cheap

• Carries little or no soil particles with filtered water

• Subsidence of the surrounding ground – less

3.5 Disadvantages

• Limited suction lift

• In deeper excavation – Well point installation in two or more stages

• Well points placed in bore holes when ground consisting – large gravel or sand containing cobble or boulders which increase the installation costs

3.6 Applications

• Land Use: Transportation (highway construction), urban (utility construction, and commercial development), and construction sites.

• Soil/Topography/Climate: Dewatering is important in areas that have high ground water tables, or which do not have adequate drainage.

• When to Apply: Apply at the beginning of and during construction when it is necessary to lower the ground water table. Pumping needs to be maintained to keep utility ditches and cofferdams dry until all underground work is completed.

• Where to Apply: Apply on construction sites, where appropriate, or anywhere else dewatering is done.

4. CONCLUSION

More building and transportation structures are being constructed today in areas where high ground water tables precluded construction years before. To control groundwater during the construction process, various dewatering techniques are designed depending heavily on the amount of water to be removed, the subsurface profile at the site, and the underlying hydrological chacteristics. Today is improved well equipment and well construction techniques make possible the dewatering of many projects with wells and well-point. Though construction dewatering has not been reduced to an exact science yet, the selection of the dewatering system should hinge on the experience and professional judgment of the engineer based on the soil materials, the source of water, and the demands of the project. A common thread among all construction initiatives is the need for thorough subsurface site investigation.