crosshole sonic logging
TRANSCRIPT
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CROSSHOLE SONIC LOGGING (ASTM 6760
02)
USAMA KHALID (2011-MS-CEG-24)
ZIA-UR-REHMAN (2011-MS-CEG-18)
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ContentsO INTRODUCTION O CROSS-HOLE SONIC LOGGINGO TUBE INSTALLATIONO WAVE REQUIRMENTSO TUBE SPECIFICATIONSO LIMITATIONSO CASE STUDYO References
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INTRODUCTION
O Deep foundations integrity testing mostly applies to foundations constructed on-site from concrete or grout, such as drilled shafts, drilled mini piles and pre-cast concrete piles.
O The integrity testing is required for quality control during construction to detect flaws in the pile.
O CSL is used for non-destructive testing (NDT) and involve generating a sonic pulse with one transducer (transmitter) and picking the signal up with another transducer (receiver).
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Cross-Hole Sonic Logging
O Cross-Hole Sonic Logging (CSL) is the most common integrity testing method for drilled or cast-in-place foundations.
O A transducer is used to generate a signal that propagates as a sound (compression) wave within the concrete, while another transducer is used to detect the signal.
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CSL APPARATUS
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TUBE INSTALLATION
O Each transducer is placed into a vertical PVC or steel tube that has been attached to the reinforcement cage and filled with water prior to the concrete placement.
O The water acts as a coupling medium between the transducer and the tube.
O For any reason the condition of the concrete is compromised, the wave speed will be reduced relative to that of the sound concrete value.
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O The tubes must have with watertight cap on bottom and removable cap on top.
O Tubes tie with wire to interior of cage at regular intervals of every 3 ft to maintain tube alignment during cage lifting, lowering and concrete placement.
O The generally accepted practice is to place tubes 0.5 ft above shaft bottoms and extend the tubes 2-3 ft above the concrete.
O After completion of test, remove the water from tubes and fill with grout material.
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WAVE REQUIRMENTS
O Speed is related to the modulus, E, and bulk density (unit weight, γ, and gravitational acceleration, g).
O The emitter generates a sonic pulse (on the order of 10 pulses per second)
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O The source and receiver transducers are lowered to the bottom of their respective tubes and placed such that they are in the same horizontal plane.
O The emitter transducer generates a sonic pulse (on the order of 10 pulses per second), which is detected by the receiver in the adjacent tube.
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TUBE SPECIFICATIONS
CSL tests can be performed after minimum of 24 hours for concrete curing.In case of steel pipe, de-bonding between pipe and concrete can occur after 45 days. In case of PVC pipe, de-bonding between pipe and concrete can occur after 10 days.
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Number And Spacing Angles Of Tubes
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Limitations
O The testing can be performed only on drilled shafts for which access tubes were installed.
O De-bonding between the tubes and concrete is common if testing occurs long after the concrete placement.
O Testing in fresh concrete is also difficult as certain zones may cure at a lower rate, creating difficulties in the interpretation of the threshold time and energy. These zones may therefore be interpreted as poor quality concrete.
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CASE STUDY
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LYMAN STREET BRIDGE HOLYOKE, USA
INTRODUCTIONO A CSL test was performed on the Lyman Street
Bridge to identify any flaws in the construction. The tests were performed on two shafts, C-1and C-5.
O Each shaft was 42” in diameter. C-1 was 45 m and C-5 was 48 m in depth.
O The 4 steel tubes in each shaft were used for this test.
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Site Location Map
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Test results
O The tests on shafts C-1 and C-5 showed less than 10% increase in FAT.
O Shaft C-1 showed a defected zone at approximately 13.5 m to 14.5 m below the top of the tubes.
O 20 to 45% FAT was increased from surrounding good concrete with decrease in relative energy.
O More than 10% reduction in velocity from surrounding good concrete indicate POOR concrete.
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O In order to confirm the test data, cores were taken within the defected zone. The concrete within zone was segregated concrete.
O The compromised concrete was flushed using high pressure water and the void was then grouted.
O There are no standards or universal criteria to evaluate CSL results.
O The Federal Highway Administration’ USA did develop a CSL criteria guideline called the Concrete Condition Rating Criteria (CCRC)
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• One more CSL test was performed on the repaired shaft to check the solidity of the repair. •After the flushing procedure. A video camera was also used to visually inspect the defected zone to ensure the debris had been cleaned out. • After the grouting of the shaft a CSL test was performed. • Than only 15 to 20% average reduction in velocity from the surrounding “good” concrete was observed.
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CSL FIELD DATA OF FIRST TEST
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CSL TEST DATA AFTER REPAIRING
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REFERANCES
O Using Crosshole Sonic Logging (CSL) To Test Drilled-Shaft Foundations by Branagan & Associates, Inc.
O Examination of a New Cross-Hole Sonic Logging System for Integrity Testing of Drilled Shafts by Samuel G. Paikowsky
O Graff, Karl F. Wave motion in elastic solids. [Columbus]: Ohio State UP, 1975.
O Malhotra, V. M. Handbook on nondestructive testing of concrete Boca Raton, Fla: CRC, 2004.
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THANKS