CROSSHOLE SONIC LOGGING (ASTM 6760

02)

USAMA KHALID (2011-MS-CEG-24)

ZIA-UR-REHMAN (2011-MS-CEG-18)

ContentsO INTRODUCTION O CROSS-HOLE SONIC LOGGINGO TUBE INSTALLATIONO WAVE REQUIRMENTSO TUBE SPECIFICATIONSO LIMITATIONSO CASE STUDYO References

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).

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.

CSL APPARATUS

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.

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.

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)

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.

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.

Number And Spacing Angles Of Tubes

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.

CASE STUDY

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.

Site Location Map

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.

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)

• 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.

CSL FIELD DATA OF FIRST TEST

CSL TEST DATA AFTER REPAIRING

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. 

THANKS