Last Updated on July 12, 2020 by Jose Villegas Jr.
II. Resources
1. Plant and Equipment
| Description | No. of Units |
Application |
| Cross Hole Analyzer™ (CHAMP) (Including Computer-based CSL
Data Acquisition System, Ultrasonic Transmitter & Receiver Probes and Two Depth Sensors) |
1 set |
Crosshole Sonic Logging |
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 ensure the safety of all devices being used for the job.
2. Workforce
| Designation | No. of Persons |
| Site Engineer | 1 |
| Geotechnical Engineer | 1 |
| Instrumentation Engineer | 1 |
| QC Engineer | 1 |
| Data Encoder | 1 |
| Helper | 1 |
| Safety Officer | 1 |
3. Light Tools
| Description | No. of Units | Application |
| Hand Tools | As per site requirement | For Construction |
| Power Tools | As per site requirement | For Construction |
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 start work at the site.
- The Contractor shall ensure that all gate passes, permits, tools, materials for safety precautions, manpower and equipment are available before 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 Shoring Subcontractor in relation to the proper sequence of works prior to proceeding 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 have 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 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 files 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 Sub-contractor 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 crosshole sonic logging.
V.2 Equipment
Cross Hole Analyzer™ (CHAMP) manufactured by PDI, USA with the following:
A computer-based CSL data acquisition system for 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 and 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 is 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.
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)