A. High Strain Dynamic Pile Testing (HSDT) (ASTM D 4945)Offshore Pile Monitoring/ Dynamic Pile Testing (Over Water and Under Water Monitoring of Offshore piles)
Instrumenting offshore piles to monitor for driving performance and pile/ soil response to measure the mobilized compressive capacity has been one of SGES’s core competences. A pre-installation drivability study for various driving conditions (i.e. SRD’s- soil resistance to driving) will be performed (using GRLWEAP software) to choose the optimal hammer size necessary to drive the pile, safely to the intended target penetrations.
The pile driving monitoring is carried out by instrumenting a pair of strain gage and accelerometer at a pre-determined depth below the pile top. A high strain compressive stress wave is generated upon an impact on pile top by the hammer. The stress wave travels down to the pile toe and reflects back to gage location where the force and velocity signals as a function of time are measured by strain gage and accelerometer connected to the Pile Driving Analyzer (by PDI Inc. USA) for every blow. This process is continued until the pile reached the required penetration.
The force and velocity signatures thus captured by the PDA are further analyzed using a signal matching software viz., "CAPWAP" to confirm the mobilized compressive capacity (together with resistance distribution along shaft and toe) and to arrive at dynamic soil constants.
SGES has accumulated rich experience by monitoring driven piles of over 100 off-shore platforms in geographies of offshore India, South East Asia and Middle East. These projects include monitoring of over-water driving as well as under-water driving of skirt piles using specially fabricated water proof sensors.
A team of qualified and experienced geotechnical engineer/technician will be mobilized on every project. The experience gained over several offshore pile monitoring projects of various oil companies, enables us in making good field measurements and engineering judgment/ interpretations required for piles acceptance.
The same test method can also be used to monitor pre-cast driven piles for hammer/driving system performance, driving stresses and soil resistance to driving for the construction of on-land projects.
High Strain Dynamic Pile Testing (HSDT) on Bored Cast In-situ Piles
It is a quick non-destructive test to measure the mobilized compressive capacity and to evaluate structural integrity of bored pile. A high strain compressive stress wave is generated upon an impact on pile top by a free fall guided drop-weight. The stress wave travels down to the pile toe and reflects back to gage location where the force and velocity signals as a function of time are measured by strain gage and accelerometer.
A pre-test desk top analysis is carried out to arrive at the weight, height of fall and driving assembly, i.e. pile cap and cushion thickness based on the information provided such as the ultimate load to be proved, pile geometry and sub surface condition. Usually, a dead weight equal to 1-2% of the ultimate capacity to be proved is used as drop weight for testing the piles.
The test pile is instrumented with two pairs of strain gage and accelerometer at about 1.5 times the pile diameter from pile top. The pile top shall be neatly prepared with levelled surface using concrete. The stick up length for mounting the sensors shall be made available either by excavating around the pile or growing the pile above the ground level. The impacts are given on the center of the pile top by dropping the pre-determined dead weight from several heights so long as the stresses are within the limits and the required compressive capacity is measured by Pile Driving Analyzer (by PDI Inc. USA).
An experienced geotechnical engineer having extensive knowledge of operating PDA and wave theory can make decision on when to stop the testing and raise concern for defects/damage if any.
The force and velocity signatures thus captured by the PDA are further analyzed using a signal matching software viz., "CAPWAP" to confirm the mobilized compressive capacity (together with resistance distribution along shaft and toe) and to arrive at dynamic soil constants. CAPWAP will also provide an equivalent static load deformation curve.
This test method is advantageous over the conventional static load test method by reduced time for testing and provide additional information such as pile integrity. SGES since inception has involved in quality control of deep foundations on various projects by testing the piles (of sizes varying from 3 inches to 1.5m diameter) with dynamic methods and providing solutions to anomalies if detected.
B. Low Strain Dynamic Pile Testing/ Pile Integrity Testing (PIT) –ASTM D5882
It is a quick non-destructive test to check the integrity of pile shaft. A low strain compressive stress wave is generated by an impact using hand-held hammer (either normal or instrumented) of weights ranging from 0.5 to 4.0 kg depending on the geometry and length of pile.
The stress wave thus generated is recorded as force and velocity as a function of time using Pile Integrity Tester (by PDI Inc. USA). The recorded force and velocity curves are interpreted for pile shaft integrity and length.
An experienced geotechnical engineer with extensive knowledge on wave theory can interpret the data and raise the concern for pile defect/damage if any. SGES will mobilize experienced team of engineer/technician on every project.
The data recorded can be further analyzed using PIT-W software (by PDI Inc. USA) by performing necessary filter and data adjustments for better toe interpretation. Profile analysis shall be performed to arrive at the pile profile.
Usually, 100% of the piles will be tested for integrity which provides a means of quality control for the installed pile.