GGL is viewed to be the most accurate non destructive testing method to analyze Cast In Drilled Hole (CIDH) piles by the California Department of Transportation. GGL consists of the lowering of a steel probe that contains a sealed radioactive source into a inspection tube and raising it out at the rate of 10 to 12 ft per minute, during which gamma photons are emitted from the radioactive source. The rate at which these particles arrive at the detector is recorded and later converted to units for density measurements. The denser the material tested is the more gamma particles will be shielded corresponding to a lower count read by the detector.
CSL testing is another nondestructive test for CIDH piles that consists of lowering probes to the bottom of the shafts through access tubes. Sonic pulses are then generated from one probe and received by the other probe at depth Increments of 2 centimeters. Sonic logs from the CSL testing show the ultrasonic wave arrival pattern as a function of time, in microseconds, versus depth.
PIT testing, aka sonic echo (SE) testing, consists of striking the pile head with a hammer to generate a compression wave. Pile head velocity is recorded and interpreted to help evaluate the structural continuity of the pile. The testing equipment includes a hammer and an accelerometer located near the pile head. These instruments are then connected to a digital dynamic signal analyzer with digital storage, which includes a filter and amplification functions to facilitate field data validation.
PDA testing records the strains and accelerations experienced by a pile during the driving operations. This dynamic monitoring system provides an efficient medium in identifying pile capacity, driving stresses, pile integrity and pile driving hammer performance. Dynamic monitoring is performed by placing instruments 4 feet from the pile head and recording signals with a PDA. The instruments consist of two sets of accelerometers and strain transducers, located on opposite sides of the pile shaft. The PDA acquires and processes the signals during driving, and provides real-time evaluations of the maximum hammer transferred energy, maximum compressive and tensile force, and mobilized static bearing capacity.
WEAP studies are performed to investigate driveability and driven pile acceptance criteria preceding the field operations in order to prevent pile damage during installation. WEAP also helps appraise the relationship between pile capacity and perceived fieldconditions. The main advantage of the wave equation based field consent criteria is its site and hammer specific applicability with the treatment of time dependent capacity relationship.
CAPWAP is performed proceeding the pile driving operations using the data obtained at the end of the initial drive or at the beginning of restrike from PDA (Pile Driving Analyzer) to evaluate the bearing capacity behavior of the pile, and in particular the skin friction capacity and distribution, the toe resistance, and the downward displacement necessary to mobilize them.
SPT energy measurements are performed similarly to PDA monitoring, a 2 ft instrumented section of drill rod with two sets of accelerometers and strain transducers is placed in between sections of existing sampling rods and the hammer.It triggers to record at the first strike of the SPT hammer at which time the PDA acquires and processes the signals, providing real-time evaluations of the maximum SPT hammer transferred energy.
Vibration monitoring is performed at sites where above ambient vibration conditions can create concerns for surrounding structures, business' and residences. Most common situations are those where neighboring structures contain vibration sensitive equipment, large concentrations of people, or residences where louder than ambient sound levels are not acceptable. The testing consists of placing seismographs with geophones and/or microphones at the different locations of concern and recording vibration/sound levels. The data is later analyzed to provide attenuation studies that correlates vibration levels and distance.