METHOD STATEMENT FOR DEWATERING
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Table of Contents 1
PURPOSE................................................................................................................................................... 5
2
SCOPE........................................................................................................................................................ 5
3
ABBREVIATIONS & DEFINITIONS............................................................................................................. 5
4
REFERENCE DOCUMENTS...................................................................................................................... 6
5
RESPONSIBILITIES.................................................................................................................................... 6
6
Plant, Equipment and Devices:................................................................................................................... 7
7
SUBMITTALS.............................................................................................................................................. 8
8
METHODOLOGY........................................................................................................................................ 8
8.1
Deep Well Sump:......................................................................................................................................... 8
8.2
Open cut submersible pump system:........................................................................................................ 10
9
INSPECTION AND ACCEPTANCE......................................................................................................... 100
10
HEALTH & SAFETY CONSIDERATIONS............................................................................................... 100
10.1 General Safety Issues............................................................................................................................. 100 10.2 Emergency Arrangement......................................................................................................................... 100 10.3 Consent and Permits............................................................................................................................... 100 10.4 Environmental Considerations................................................................................................................. 100 10.5 Housekeeping............................................................................................................................................ 11 11
ATTACHMENTS...................................................................................................................................... 111
Figures Figure 1: Deep Sump Well..................................................................................................................................... 8 Figure 3: Open cut Dewatering System................................................................................................................. 9
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1 PURPOSE The purpose of this document is to establish the procedure for the dewatering system in the ground where the groundwater table/ water seepage area is above the excavation level, and to remove/ divert the same water until a dry working environment is obtained for completing the works.
2 SCOPE The scope involves de-watering of the proposed area to enable the construction to be carried out in dry, safe conditions within the area using suitable dewatering system.
3 ABBREVIATIONS & DEFINITIONS The words like Contract, Contractor, Engineer, Drawing, Employer, Works, Work site used in this methodology shall be considered to have the meaning as understood from the definitions of these terms given in the General Conditions of the contract. The following abbreviations shall have the meaning as set forth below: QCS:
Qatar Construction Specification
BS:
British Standards
ASTM:
American Society for Testing and Materials
ITP:
Inspection and Test Plan
PQP:
Project Quality Plan
SC:
Supervision Consultant
4 REFERENCE DOCUMENTS 1. QCS 2010- Section 8; Part- 2.
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2. QCS 2010- Section 12; Part- 2.
5 RESPONSIBILITIES The responsibilities and authorities of Project personnel shall be assigned as per the project requirements. Project in Charge: 1. Ensure that the project works are carried out with the requirement of this Method Statement and project document/specification as well as QCS 2010. 2. Ensure full compliance of the subcontractors with the company quality policies and the Method Statement. 3. To ensure that all the required equipment to execute the works according to the construction program are available, in good condition and provide any additional equipment that might be required. 4. To co-ordinate with the Construction manager, Project Engineer, Safety Engineer, Foreman and Surveyor for safe and proper execution of the works as per the Method Statement. 5. To guide specific attention to all safety measures in co-ordination with the safety officer/engineer. Construction Manager: 1. Ensure area is ready and sage to start the works. 2. Ensure all the required approvals/NOC is obtained from the relevant authorities prior to the commencement of works. 3. Set up required equipment and plant through discussion with the Project In Charge and Project Engineer. 4. Ensure the works are carried out according to the specification, quality plan, approved shop drawings and construction program. 5. Provide sufficient and safe access for operatives, trucks and pumps. Project Engineer: 1. Set up the required equipment and allocate required manpower through discussion with the Project In Charge and Construction Manager. 2. Ensure works are carried out according to the specification, quality plan, approved shop drawings and the construction program. 3. Provide sufficient and safe access for operatives, trucks and pumps. QA/QC Engineer: 1. Ensure that Consultant/Client inspection requests are implemented. 2. Compilation of all necessary quality control check lists. 3. The control of work performed at site by means of checking the work before consultant’s inspection. 4. Issuing RFI’s and assisting consultant during the inspections. HSE Engineer: 1. To ensure implementation of all safety measures related to the nature of works being carried out, and in accordance with the Project CEMP.
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2. To ensure that all the persons involved in the works are aware of their responsibilities, and that they have enough understanding of the safety procedures. 3. To provide and distribute risk assessment of the various activities 4. The safety officer in co-ordination with the Project In Charge shall ensure that all the implemented safety measures are effective enough to maintain safe working on the site. 5. To maintain continuous inspections of the site activities and advise and train persons on a daily basis to prevent accidents and personnel injury. 6. To give special concern to housekeeping and ensure that the site is maintained clean and tidy. 7. To ensure all the relevant safety sign boards for different works are in place. Surveyor: 1. To establish benchmarks from agreed reference points, provide required setting out and level markings and follow up with regular checks. 2. Co-ordinate with the project engineer and ensure the approved shop drawing shall be implemented properly. 3. Maintain survey details and reports, periodically check the progressing works and advise the project manager of any deviation from the drawings.
6 Plant, Equipment and Devices: The equipment used for dewatering system are: Dewatering Pumps:
To lower the groundwater table.
Suction Hoses:
To discharge water in settling tank.
Dewatering lay flat hoses:
To discharge water in settling tank.
Survey Equipment:
To mark and monitor the dewatering work.
Settling Tank:
To separate solid particles. (Tanks of size 4mX3mX1.5m)
Piezometers:
To check the level of the groundwater table.
Mobile Generators:
To provide uninterrupted power supply.
7 SUBMITTALS The Contractor will submit to the Consultant prior to start of work at site the following: a) All necessary permits from the stakeholders. b) Working drawings, Quality assurance and control documents. c) Methods statements to supplement the working drawings d) safety procedures and protective equipment
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8 METHODOLOGY Well point piezometers/standpipes to be placed at location to determine the drawdown of the water
table
level. The dewatering pump will be placed at location as shown in approved drawing. The dewatering will be done by two or any of the following method suitable to the situation.
1.1 Deep Well Sump:
Figure 1: Deep Sump Well 1. The area for installing deep sump well will be marked by surveyor and the area will be checked for existing underground utilities. 2. The sump well will be installed into the ground using water jet. If the strata are hard to penetrate, then suitable bore holes will be made for installing the deep well sump. 3. After the hole is drilled, an Ø300mm UPVC perforated pipe is installed into the drilled hole surrounded with 3/8 3/16 aggregate filter materials to prevent the fines entering the system. 4. The submersible pump will be installed into the perforated pipe. The pump is connected to the electrical power generator. 5. The outlet of these well pumps is connected to the vertical pipes, which is connected to the suction hose. 6. The suction hose transfers the water to the sand settling tank. The silts settled in the tanks will be removed and dumped in an approved location. Page 6 of 11
7. The pumps will be operated until the work is completed. On completion of all dewatering activities the bore holes will be filled with suitable approved material. 8. Water levels will be checked and recorded regularly to derive the drawdown.
Figure 2: Open cut Dewatering System
1.2 Open cut submersible pump system: 1. At areas affected by low water seepage, an open cut submersible pumping system will be installed to pump out the seeping water instead of the deep well system. 2. The size of the pump will depend on the amount of seepage occurring. 3. The pump will be placed at a low level area. 4. The water is pumped to the settling tank using a flat suction hose. 5. The water will be removed periodically from the settling tank to avoid spilling of water. 6. The silt will be removed and dumped at an approved location.
2 INSPECTION AND ACCEPTANCE
Drawdown at piezometer up to the required level will be recorded.
During dewatering, leaching of materials such as fines and silts should be prevented.
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Settlement of surrounding area should be monitored regularly.
3 HEALTH & SAFETY CONSIDERATIONS 3.1 General Safety Issues a. Staff should wear correctly PPE and enter the site b. Operators must have valid certificate for proper equipment operation c.
Operators must maintain daily equipment complying with operation requirement
d. Barriers to prevent unauthorized entry e. Regular safety checks will be performed to eliminate all potential hazards and to conform to safety regulations
3.2 Emergency Arrangement a. Emergency contact number should be informed to all staff before the work
3.3 Consent and Permits a. Before starting the work, all permits should be made available and the Engineer should be notified before commencing the work.
3.4 Environmental Considerations a. The leakage of equipment might occur. Leakage prevention should be provided for leakage incidents
3.5 Housekeeping a. The site shall always be kept in clean and dry condition, rubbish and waste materials shall be frequently and regularly removed off the site b. Adequate number of rubbish collectors or designated areas shall be provided for waste disposal c.
Materials shall be stacked safely and securely
d. Plant, equipment and material shall be positioned in order not to cause obstruction to the site accesses
4 ATTACHMENTS a. b.
ITP – Inspection Test Plan Risk Assessment. NOTE: Location Drawing will be submitted before the execution of work for approval.
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