Pile are required for buildings, bridges, towers,dams and other massive structures. A variety of piletypes can be installed by different drivingequipment in all types and even in layered soilsmakes establishing a safe but economicalinstallation difficult.
More Economical Less Time Consuming More Efficient Alternative for Static Pile Load Test for Offshore piles Less logistics involved Provide more information regarding a pile when compared to a static load test
Low Strain Dynamic Testing High Strain Dynamic Testing
Low Strain Pile Integrity Testing is a quick and cost effective method to evaluate the shaft integrity of concrete piles. The testing is able to provide information on: pile continuity consistency of material location of defect degree of defectThe test method is performed with a hand held hammer, a sensitive accelerometer and the Pile Integrity Tester.
High strain dynamic testing consists of estimating soil resistance and its distribution from force and velocity measurements obtained near the top of a foundation impacted by a hammer or drop weight. The impact produces a compressive wave that travels down the shaft of the foundation. A pair of strain transducers obtains the signals necessary to compute force, while measurements from a pair of accelerometers are integrated to yield velocity. These sensors are connected to a PDA that records, processes and displays data and results.
Specifications For High Strain PileLoad Testing:PART ONE: GENERAL It involves attaching strain gauges and accelerometers to the pile near the pile head during driving It shall be performed on required number of indicator piles Dynamic Testing shall be performed on production piles as chosen by the engineer to monitor hammer and driving system performance
PART TWO - Material Impact Force Application Force or Strain Transducer Acceleration or Displacement Transducer Signal Transmission Cables PDA (Model Pak, PAX or PAL) to record, display and analysis data
PART THREE – EXECUTION: Its mandatory that both the accelerometer and strain gage are fixed parallel to the pile axis at a predetermined distance from the pile top. When two sets of gages are used, they shall be diametrically opposite
High Strain Pile Load Testing Preparation: The transducers’ strain gauges and accelerometers are fixed on the pile after performing the initial calibrations checks on them. These are fixed either by bolting or welding. Setup the apparatus required for data recording, reducing and displaying data. Calibrations of the Strain gauges and Accelerometers & Fixing of gauges.
Preconstruction Wave Equation Analyses › Dynamic Testing Consultant shall propose driving system to install the pile to the required capacity and desired penetration depth within the allowable driving stresses, with prior information got by Contractor. › In case of Bored piles, design weight, drop height and cushion of the hammer apparatus shall be proposed. › Proposed Driving System by the engineer shall be based upon the wave equation analysis. › A new pile driving system shall be proposed by the contractor if the pile installation stresses calculated exceed the maximum values specified by the engineer. Indicator Pile Program: › Indicator piles shall be driven based upon the preliminary driving resistance indicated by wave equation results. › Based on the results, the engineer shall select number of indicator piles to be statically load tested.
Production Pile Testing › Dynamic Pile Testing shall be performed on piles during initial driving, restrike driving , initial and restrike driving. › Engineer may request additional piles to be dynamically tested if hammer is modified or replaced or any other piling behaviour different from the normal installation procedure.PART THREE – Reports: › CAPWAP analyses of the dynamic pile testing data shall be performed on data obtained from the end of initial driving and beginning of restrike indicator piles › Upon completion of various testing phases, the Dynamic Testing Consultant shall prepare a formal report summarizing the dynamic testing results.
Advantages: For caissons and drilled shafts, it provides a less expensive alternative to static load testing. For driven piles, testing can be done during installation and/or re-strike very economically. Dynamic pile monitoring has the advantage of providing immediate results that the engineer can use, including estimates of capacity, driving stresses, and pile integrity. Low strain dynamic testing method is a quick, convenient way to check deep foundations for defects. Low strain dynamic testing can be used on concrete piles, drilled caissons, augered cast-in-place piles, concrete filled pipe piles, and timber piles of moderate slenderness. It is possible to check numerous piles on site during a single day.
Transducers PDA system: › Compact, reliable, water resistant, combined acceleration/strain transducers, cables and connectors. › Mounting jig to increase transducer life and for protection › Junction box for easy mounting and storage of transducer cables Signal Conditioning PDA › Maximum reliability › Full digital signal processing › Battery and AC powered › No. of files digital signals only limited by hard disk capacity › Test Box to test system functions. Software Environment PDA › Windows based environment › Easy Installation › Higher quality signal processing
Proven worldwide application now Uses available or easy-to-make drop hammers and minimal pile preparation Confirms capacity, even at large loads Reduced testing time and large cost savings (cost 10 to 30 times less than static cost) PDA with CAPWAP evaluates capacity at low cost for driven piles, drilled shafts,& augercast piles PDA gives extra valuable information (integrity, stresses, hammer energy) PDA potentially saves time or pile length in favorable site conditions Improves quality control by more pile tests
Site specific input factors, such as damping, rapid pore pressure cant be obtained by PDA testing. An experienced Geotechnical engineer or PDA operator is needed to go through the PDA analysis to avoid misinterpretation of the results obtained.
Normal Force Velocity v/s Double Impact CurveSometimes hammer components, cushions, helmet and pile may produce a“Double Impact” effect in the measured test records. This may be due todevelopment of the hammer system impacting event and/or frequencies in themulti-degrees of freedom driving system. Though this feature has no effect onthe quality of the data and doesn’t require special attention in data analysis.
Dynamic Pile driving stresses, especiallyin tension, produce micro-cracks inconcrete piles. Fig A shows test recordswith normal characteristics. While Fig Bcontain the features indicating thedevelopment of tension cracks along thepile length. This is shown by an elongatedwave reflection from pile toe at 2L/c time.The records can be evaluated in real-timedriving to monitor pile structural integrity.
MSRDC 55 Flyover Scheme : Dynamic Pile Testing was extensively used for the above flyovers in Mumbai after conducting many co-relation studies between static & dynamic tests to prove the reliability of High Strain Dynamic Testing. This resulted in significant savings in time and early completion of many flyover projects thus helping the contractors and clients. Further the problem of space availability, which for flyovers in middle of the road was solved resulting in greater working space and more work efficiency for the contractors. Testing was conducted on piles ranging from 600mm to 1200mm piles and capacity ranging from 180 tons to 1375 tons. Delhi Metro Project : Dynamic Pile Testing is being extensively used for Delhi Metro Project where it was used to ascertain capacity of many suspect piles. Numerous co-relation studies were conducted to evaluate the test method & acceptability of the test agency. The results were successful and more than 30 tests have been conducted till date. Testing was conducted on 1500mm piles with test loads upto 675 tons.
Baroda Ahmedabad Expressway Project : NHAI located 128 piles of 500mm that were abandoned by the previous contractor more than 10 years back. No technical data like pile depth or capacity was available. A combination of dynamic and pile integrity tests was used on the project site. Initially PIT conducted on the piles reported pile lengths about 20m. Borehole taken adjacent to two such typical piles confirmed the findings. Dynamic testing on the pile helped establish its design load. Static test was also conducted by the client on the pile dynamically tested for further confirmation. The static and dynamic test results matched well helping the client save lot of time and money, since most of the piles could be used in further construction at no additional cost. GCPTCL Jetty at Dahej : Dynamic Pile Testing was adopted at one of the longest jetty in Gujarat after co-relation with static testing on a land pile. Conventional testing on this jetty would have been extremely difficult, time consuming and expensive. Replacement of static testing by dynamic testing significantly helped in early completion of the project.