Method Statement for Crosshole Sonic Logging for Bored Piles

What is Method Statement for Crosshole Sonic Logging for Bored Piles?

The Method Statement for Crosshole Sonic Logging (CSL) for Bored Piles is a document that outlines the process of using the CSL technique to assess the integrity of concrete in bored piles. The statement details the necessary equipment, procedures, and safety precautions required for the CSL testing.

What is Crosshole Sonic Logging?

Cross-Hole Sonic Logging (CSL) is a non-destructive testing technique that utilizes ultrasonic waves to evaluate the integrity of concrete in deep foundations, such as drilled shafts and cast-in-place piles. This method involves placing multiple probes in pre-drilled holes within the concrete structure and transmitting ultrasonic pulses between them. The received signal is analyzed to determine the time taken for the signal to travel between the probes.

By examining the collected data, CSL can detect any abnormalities or defects, including cracks, voids, and delamination, within the concrete. CSL is widely employed in the construction industry for quality assurance and control, as well as for evaluating the structural soundness of existing concrete foundations.

Crosshole Sonic Logging (CSL) is carried out on drilled shafts/bored piles to inspect the structural integrity, and extent and location of defects, if any, by sending ultrasonic pulses through the concrete from one probe to another (probes located in parallel tubes). The CSL is carried out as per ASTM 6760.

Both the time between pulse generation and signal reception (“First Arrival Time” or “FAT”) and the strength of the received signal give a relative measure of the quality of concrete between transmitter and receiver.

Dividing the distance between the transmitter and receiver by the FAT value yields the approximate concrete wave speed which also is a relative indicator of concrete quality. For equidistant tubes, uniform concrete between the test tubes yields consistent arrival times with reasonable pulse wave speed and good signal strengths.

No uniformities such as contaminated or soft concrete, honeycombing, voids, and inclusions exhibit delayed arrival times with reduced signal strength.

TABLE OF CONTENTS

I. Description of Works

1. Introduction
2. Definitions
3. Reference
4. Responsibilities
5. Interfacing with Other Operations
6. Duration, Phasing with the Subcontractors
7. List of Subcontractors

II. Resources

1. Plant and Equipment
2. Workforce
3. Light Tools

III. Materials

IV. Site Planning

1. Preparation
2. Site Clearance
3. Traffic Management
4. Pre-construction Safety Meetings
5. Methodology

V.1 Mobilization

V.2 Equipment

V.2.1 Access Tubes

V.3 Timing of the CSL Test

V.4 Methodology

V.5 Analysis and Report

VI. Risk Assessment

VII. Permit and Licensing Requirements

VIII. Drawings, Diagrams, Maps, and Survey Data

IX. Pre-Start Safety Briefing Arrangements

1. Protective and Safety Equipment
2. Information to Personnel
3. Special Safety Requirements
4. Emergency Contact Numbers

X. Supervision and Monitoring Arrangements

XI. Environment and Quality Issues

1. Precautionary Measure
2. Disposal Requirements
3. Inspection, Test, and Sampling
4. Quality Assurance Requirements Table

XII. Attachments

APPENDIX A: CSL Logs
APPENDIX B: Risk Assessment
APPENDIX C: Calibration Certificate

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Method Statement of Bored Piles

1. Introduction

The purpose of this method statement is to describe the mobilization plan and execution of the Crosshole Sonic Logging on selected piles.

This method statement can be grouped into Civil Disciplines.

Crosshole Sonic Logging (CSL) is carried out on drilled shafts to inspect the structural integrity, and extent and location of defects, if any, by sending ultrasonic pulses through the concrete from one probe to another (probes located in parallel tubes). The CSL is carried out as per ASTM 6760.

2. Definitions

• Name of Client
• Project Management Team
• Supervising Consultant
• Third-Party Testing Laboratory
• SE Site Engineer
• QC Quality Control Engineer
• SF Site Foreman
• PM Project Manager
• SA Site Agent representative from the Lab
• HSE Manager Health, Safety & Environmental Manager
• HSE Officer Health, Safety & Environmental Officer
• Main Contractor
• Project Specifications
• MMUD Ministry of Municipality and Urban Planning
• GIS Geographical Information System
• Project Specifications
• CEMP Construction Environmental Management Plan
• QCP Quality Control Plan
• HSE Plan Health, Safety, and Environment Plan
• GWL Ground Water Level (meter)
• NGL Natural Ground Level (meter)

Note: All dimensions are in mm unless specified.

3. Reference

• ASTM D6760– Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing
• Health and Safety Plan
• Overall Construction and Environment Management Plan
• CEMP (Construction and Environment Management Plan)
• Construction of Bored Piles

4. Responsibilities

Project Manager

Responsible for accomplishing the stated project objectives which include creating clear and attainable project objectives, building the project requirements, and managing the constraints of the project management triangle, which are cost, time, scope, and quality.

Construction Manager

Responsible for overall construction activities ensuring that all quality and safety procedures are implemented and required approved permits are obtained.

QA/QC Engineer

Ensure the proper implementation of the Quality system and monitor the overall quality of the work is maintained. Conduct inspection and monitor tests. Determine and report any non-conformance and recommended corrective actions. Ensure that all personnel is aware of the quality requirement. Training of relevant personnel. Conduct surveillance and inspection duties at various stages to ensure compliance with QA/QC Plan.

HSE Manager

Health, safety, and environmental (HSE) managers generally plan, coordinate and implement issues and directives within the organization. They ensure safe environmental working conditions for all employees.

HSE Engineer

Ensure enforcement of safety procedures in accordance with the approved HSE Plan. Will be closely monitoring the site engineer’s strict implementation of the Method Statement for Crosshole Sonic Logging for Bored Piles and Risk Assessment, the use of proper tools and equipment to maintain safety, certifications of equipment and their adherence to safety regulations, reporting of any unsafe work, or stopping work that does not comply with ES&H procedures. Will advise for Health & Safety requirements and monitor the Hazard controls implemented on-site as per the Method Statement/Risk assessment.

Instrumentation Engineer

Manage, update, and supply collected data. Analyze and ensure to standardize equipment on return. Supervise current equipment service contracts. Maintain and update instrumentation systems and electronic control.

Geotechnical Engineer

The head of the Geotechnical Division will have direct responsibility for the work. The Head of the Geotechnical Division and his team will ensure that all equipment conforms to the specifications and that the work and documentations are according to the required standards.

Surveyor

Carry out a pre-construction survey to fix the locations and corresponding elevations as per the approved shop drawings. Ensure quality and compliance during phases of surveying works and the regular checking of the surveying equipment or periodic calibration from the third party. 

Ensure the validity and the serial number of calibration certificates are available and posted on the survey equipment. Ensure proper safety guarding of surveying equipment. To maintain the records of all surveying equipment handled.

Data Encoder
Enters various pieces of information or data in the mainframes. Maintain accurate records and even complete data that is necessary for the project. Provide assistance to one’s superior by encoding the right information or data needed.

5. Interfacing with Other Operations

• Excavation Works
• Dewatering Works
• Shoring Works

6. Duration, Phasing with the Subcontractors

• The duration of work is indeterminate but will not critically affect the progress of the project.

7. List of Subcontractors

• Main Contractor:

Name of Main Contractor here

• Sub-Contractor:

(Third-Party Approved Testing Agency)

II. Resources

1. Plant and Equipment

Note:
The regular maintenance schedule will be followed and conducted by the company’s mechanic and technicians to ensure that the equipment is always in proper condition. Attention will be given to ensuring the safety of all devices being used for the job.

2. Workforce

3. Light Tools

III. Materials

• Clean Water
• Schedule 40 Steel Tubes or Schedule 40 or 80 PVC Pipes
• Tie Wires or Fixing Clips
• Mechanical Coupling

1. Site Planning

• The duration of work shall be indeterminate but will not critically affect the progress of the project.

2. Preparation

• Permits from the concerned authority shall be obtained prior to starting work at the site.
• The Contractor shall ensure that all gate passes, permits, tools, materials for safety precautions, manpower, and equipment are available before the commencement of work.
• The Site Team shall make sure that access roads are always clear from any obstruction and site is always accessible.
• Proper coordination with the Shoring Subcontractor in relation to the proper sequence of works prior to proceeding with the installation of testing accessories.

3. Site Clearance

• Before commencing the work, the area shall be cleared of all debris, materials, or other obstructions.
• The location of installation has been properly bored and steel cages are ready to accommodate the tubes.

4. Traffic Management

• The Site Team with the assistance of the Safety Officers shall coordinate logistics and materials movement through the site following the direction and road signs displayed on site. The required diversion routes shall be marked on drawings including the required traffic signs.
• The Work Permits and Technicians shall be compiled and filed for reference by authorized personnel.

5. Pre-construction Safety Meetings

A meeting shall be scheduled prior to the beginning of the work and before any Subcontractor starts on the project.

• General contractual safety, health, and environmental requirements.
• Traffic safety will be discussed to emphasize these meetings.
• Roles of the contractor, subcontractors, authorized representatives, and all project workers.
• Accident reporting requirements.
• Specific details of the work to be performed along with the use of personal protective equipment.
• Emergency procedure.

V. Methodology

The purpose of this method statement is to describe the mobilization plan and execution of the Crosshole Sonic Logging on selected piles.

V.1 Mobilization

In order to conduct the Crosshole Sonic Logging works on-site in a well-timed manner, the equipment and manpower will be made ready upon receiving a job notification at least 24 hours prior to the targeted time for the job.

The manpower and equipment will be on-site to make the necessary preparations at least 30 min prior to the actual cross-hole sonic logging.

V.2 Equipment

Cross Hole Analyzer™ (CHAMP) manufactured by PDI, USA with the following:

A computer-based CSL data acquisition system for the display of signals during data acquisition and recording of all pulse signals for full analysis and individual inspection.

• Ultrasonic transmitter and receiver probes capable of producing records at a minimum frequency of 40,000 Hz with good signal amplitude and energy through good quality concrete.
• Two depth sensors to independently determine transmitter and receiver probe depths.
• Triggering of the recording system time base with the transmitted ultrasonic pulse.
• The Contractor shall provide cooperative assistance, suitable access to the site and drilled shafts to be tested, and labor as required to assist Engineer / Technician in performing the required tests. Prior to testing, the contractor should also provide the drilled shaft lengths, tube lengths, positions, and drilled shaft construction dates to additional specifications that are provided in the Cross Hole Analyzer (CHAMP).

V.2.1 Access Tubes

The number of Access Tubes in each Drilled Shaft:
The actual number of tubes is often selected as one tube for every 0.25m to 0.35m of drilled shaft diameter (a minimum of four access tubes is recommended). Drilled shafts with different diameters at the same site may require a different number of access tubes.

Properties of Access Tubes:
Nominal 50 mm inside diameter standard weight schedule 40 steel tubes or schedule 40 or 80 PVC pipes shall be provided by the contractor for probe access in each drilled shaft (Schedule 80 PVC is preferred for longer tubes). Round tubes with a regular internal diameter free of defects and obstructions, including any tube joints, shall be used to permit the free, unobstructed passage of the probes.

Tubes shall be watertight and free from corrosion with clean external faces to ensure a good bond between the concrete and the tubes. Tubes may be extended with mechanical couplings. Duct tape or other wrapping material to seal the joints and butt welding of joints is prohibited. When couplings are used, record their location.

Installation of Access Tubes:

• Tubes shall be installed by the Contractor in a manner such that the CSL probes pass through the entire length of the tube without bending.
• The contractor should ensure that the access tubes are plumb and verify that the unobstructed passage of the probes is achievable before the Engineer/Technician arrives.
• The tubes shall be fitted with a watertight shoe on the bottom and a removable cap on the top.
• Tubes shall be secured to the interior of the reinforcement cage at regular intervals not to exceed 1.0 m.
• Tubes shall be installed uniformly and equidistantly around the circumference such that each tube is spaced parallel for the full length and at the maximum distance possible from each adjacent tube.
• Tubes shall be extended to within 150 mm of the bottom of the drilled shaft, to at least 0.2‐0.5 m above the top of the concrete.
• After placement of the reinforcement cage, the access tubes shall be filled with clean fresh water as soon as possible but within at the latest one hour after concrete placement (Note that the tubes should preferably be filled with water prior to concrete placement, but must be filled with water within at most 4 hours after placing concrete to prevent debonding of the access tubes due to differential temperatures. This is particularly important for PVC tubes.)
•  Tube tops shall be capped to prevent debris from entering the access tubes. Do not apply excessive torque, hammering, or other stresses which could break the bond between the tube and concrete when removing caps from the tubes.
• After all CSL testing has been completed, and after acceptance of the drilled shaft by the Engineer, the Contractor shall remove the water from the access tubes, place grout tubes extending to the bottom of the access tube, and fill all-access tubes of the drilled shafts with grout.

V.3 Timing of the CSL Test

CSL testing can be performed any time after concrete installation when concrete has obtained sufficient strength (e.g. 66% of design f’c), although 2‐3 days are usually the minimum acceptable wait, but within 10 days after placement and prior to loading for test drilled shafts. Because the concrete strength and quality generally increase as the concrete cures, longer wait times are usually desirable, particularly if minimum pulse wave speeds are specified or to reduce result variability between drilled shafts or even as a function of depth in a single drilled shaft. However, if PVC tubes are used for wet cast shafts (e.g. cast under slurry), long wait times increase the tube debonding which is detrimental to the test.

V.4 Methodology

• Prior to CSL testing, the Contractor shall provide the Engineer and Technician with a record of all drilled shaft lengths with elevations of the top and bottom, and installation dates of all drilled shafts. The access tubes shall be clearly labeled for identification by Technician. For example, for a test pile having 4 access tubes, the tubes should be labeled T1, T2, T 3 & T4.
• The CSL testing shall be performed with the transmitter and receiver probes in the same horizontal plane in parallel tubes unless test results indicate potential defects, in which case the questionable zone may be further evaluated with angled tests (source and receiver vertically offset in the tubes).
• Using the labeling established for the tubes, CSL testing shall be performed between all adjacent perimeter access tube pairs and across at least all major diagonals within the drilled shaft. In the event that defects are detected in drilled shafts with more than four tubes, additional logs in other diagonal tube pairs may be required to estimate the extent of the defect.
• Probes shall be lowered from the top, effectively measuring the access tube lengths.
• Probes shall be pulled simultaneously, with CSL measurements taken at intervals of 50 mm or less from the bottom to the top of the drilled shaft.

V.5 Analysis and Report

The report includes the presentation of CSL logs for all tested tube pairs. The rating of the shaft integrity considers the increases in “first arrival time” (FAT) and the energy reduction relative to the arrival time or energy in a nearby zone of good concrete.

Flaw or Defect zones, if any, shall be indicated and addressed as per the following criteria:

• Flaws must be addressed if they affect more than 50% of the profiles.
• Defects must be addressed if they affect more than one profile at the same cross-section.
• Flaws or Defects covering the entire cross-section define a full layer concern requiring repair.
• The log for each tube pair shall be clearly identified and oriented relative to the structure.

The Contractor shall not perform any load testing or other construction associated with these drilled shafts until after acceptance by the Engineer. If the drilled shaft is accepted by the Engineer, the Contractor may then proceed with construction.

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The report will include the following:

 GENERAL:

• Project Identification
• Project Location
• Owner Name

TEST PILES:

• Identification of Test Pile(s)
• Type of Pile(s)
• Dimension of Pile(s)

CSL RECORDS:

• Description of the test apparatus
• Graphical presentation of CSL logs for all tested tube pairs
• Signal peak diagram as a function of time versus depth
• Computed initial pulse arrival time vs. depth
• Computed relative pulse energy vs. depth
• Each pair tube log identification and orientation
• The statement whether the tested piles contain any integrity problems and the location of the damage (if any)

VI. Risk Assessment

Please refer to the attached document in Appendix B.

VII. Permit and Licensing Requirements

The Contractor shall issue a “Permit to Work” prior to the start of the activity.

VIII. Drawings, Diagrams, Maps, and Survey Data

The data logging format is attached in Appendix A.

IX. Pre-Start Safety Briefing Arrangements

Refer to Risk Assessment in Appendix C.

1. Protective and Safety Equipment

All workers involved shall be equipped with adequate PPE as stated below:

1. Safety Helmet with Company Logo
2. Safety Boots
3. High Visibility Vest
4. Safety Goggles
5. Hand Gloves
6. Coveralls
7. Information to Personnel
8. Safety Induction
9. Job training
10. Superintendents Notices/Memos
11. Toolbox talks
12. START Card

Special Safety Requirements

1. All necessary personal/protective equipment (PPE), as well as a harness, be provided.
2. Banksman, wearing distinctive vests, shall be assigned to help operators maneuver their equipment.
3. The equipment operators shall possess the required licenses and certificates.
4. Generated dust shall be controlled by periodic water spraying.
5. The project safety officer is responsible along with the project zone site engineer for ensuring that all operations are carried out with due regard to the safety of all project personnel & property.
6. All working activity shall comply with Client Safety Procedure.
7. First Aid Material.
8. General management of protection/operation hazards is to be observed.
9. Emergency Procedures

The Flow Chart below shows the Emergency Contact No. during work:

1. Emergency Contact Numbers

X. Supervision and Monitoring Arrangements

Construction Manager

Overall in charge of Construction activities. Schedule the project in logical steps and budget the time required to meet deadlines. Inspect and review projects to monitor compliance with building and safety codes and other regulations.

Site Engineer

The Site Engineer shall evaluate the number of materials consumed by each trade to be compared against the planned quantity.

QA/QC Engineer

The QA/QC Engineer shall monitor whether the installation works are conforming to the required quality otherwise he shall notify the Site Engineer should he find nonconformance to the ongoing activities. The Site Engineer shall immediately rectify the work to avoid receipt of NCR from the QA/QC Engineer.

HSE Engineer

The Safety Engineer shall be full-time at the site and shall frequently visit all the ongoing works at the site. All safety violations and on-conformance of the HSE Plan shall be registered and immediate action shall be done in coordination with the Site Engineer.

Instrumentation Engineer

Manage, update, and supply collected data. Analyze and ensure to standardize equipment on return. Supervise current equipment service contracts. Maintain and update instrumentation systems and electronic control.

Geotechnical Engineer

Will have direct responsibility for the Crosshole Sonic Logging work. Ensure that all equipment conforms to the specifications and that the work and documentations are according to the required standards.

Surveyor

• Carry out a pre-construction survey to fix the locations and corresponding elevations as per the approved shop drawings.
• Ensure quality and compliance during phases of surveying works and the regular checking of the surveying equipment or periodic calibration from the third party.
• Ensure the validity and the serial number of calibration certificates are available and posted in the survey equipment.
• Ensure proper safety guarding of surveying equipment. To maintain the records of all surveying equipment handled.

Data Encoder

Enters various pieces of information or data in the mainframes. Maintain accurate records and even complete data that is necessary for the project. Provide assistance to one’s superior by encoding the right information or data needed.

Note: Site Engineers / HSE Staff shall have access on-site to each MS/RA.

XI. Environment and Quality Issues

1. Precautionary Measure

All precautionary measures shall be briefed to all workers prior to commencing the activity

2. Disposal Requirements

All waste shall be disposed of as per the Construction Environmental Management Plan and as per Government approved disposal areas.

3. Inspection, Test, and Sampling

Request for Inspection and Testing will be submitted prior to and after the execution of works.

4. Quality Assurance Requirements Table

Refer to Project Quality Plan

1. Project Specifications

XII. Attachments

1. Reference Documentation

Project Specifications

2. Appendices

Appendix A: CSL Logs

Appendix B: Risk Assessment

Appendix C: Calibration Certificate

tag: Method Statement for Crosshole Sonic Logging for Bored Piles

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