Driven Concrete Pile Foundation Monitoring with Embedded Data Collector System
Florida Department of Transportation (FDOT) sponsored research performed at the University of Florida resulted in developing a wireless monitoring and real time static capacity estimate technology for driven piles. This new technology, Embedded Data Collector (EDC), uses two levels of instrumentation, embedded in the body of precast prestressed concrete piles near the head and tip. Strain and acceleration measurements obtained at these instrumentation levels during driving are sent wirelessly to a receiver in the field, and analyzed in real time to provide the operator with estimates of static capacity, stresses in the pile, transfer energy, damping factor, stroke height, and other relevant parameters used to evaluate the pile driving process and the driving system. The EDC system is currently undergoing phase one of a two phase field evaluation program planned by the FDOT to determine the level of reliability that can be anticipated by its use. The first phase consists of monitoring piles with EDC instrumentation and concurrently monitoring them with the Pile Driving Analyzer (PDA), given that there is ample data supporting the reliability of PDA. Measurements of strain and particle acceleration converted to force and velocity traces can then be compared between the two systems, along with the corresponding calculated magnitude of downward and upward traveling stress waves as they move along the pile at any point in time. Selected hammer blows recorded by PDA equipment are analyzed by means of signal matching software (CAPWAP) and the estimated static skin, end bearing, and total resistance obtained are compared against EDC static resistance predictions. The second phase of the evaluation will compare EDC estimates of static capacity against instrumented static load test results. The purpose of this paper, is only to present a summary of results obtained thus far in phase one, and compares EDC estimates of static capacity results with those from PDA and CAPWAP.
Embedded data collector (EDC) evaluation, phase II - comparison with instrumented static load tests.
A total of 139 piles and 213,000 hammer blows were compared between the Embedded Data Collector (EDC), the Pile Driving Analyzer (PDA), and the CAse Pile Wave Analysis Program (CAPWAP) along with SmartPile Review versions (3.6, 3.72, 3.73, 3.76 and 3.76.1). Fixed EDC/PDA ratio was consistent (0.89 to 0.97) for all version numbers, with little variability (max coefficient of variation (CV) = 0.17); UF EDC/PDA ratio was slightly unconservative (1.12) for earlier versions (3.6), but conservative (0.89 to 0.93) for later releases, with little variability (max CV = 0.18); Top pile compressive stresses, CSX (EDC/PDA), were consistent (0.91 to 0.93) for all versions, with little variability (max CV = 0.09); Bottom pile compressive stresses, CSB (EDC/PDA), ranged from 0.77 for earlier version (3.6), but quickly stabilized at 0.74 for all subsequent versions (3.72-3.761), with maximum variability (CV = 0.25); Pile tension stress, TSX (EDC/PDA), was slightly unconservative (1.2) for earlier versions (3.6), but was conservative (0.87 to 0.90) for all later releases, with max variability (CV = 0.29); UF EDC/CAPWAP total capacity ratio varied from 1.0 (ver 3.6) to 0.89 (ver 3.761), with R2 = 0.89; UF EDC/CAPWAP skin friction ratio varied from 0.78 to 1.04, with R2 = 0.57; UF EDC/CAPWAP tip resistance ratio varied from 0.85 to 0.93, with R2 = 0.76. A total of 12 static pile test were collected in Florida and Louisiana. From the 12 piles, a total of 17 independent measurements (i.e., total, skin, and tip capacities) were recorded. EDC and SmartPile had a bias or ʎ (ratio of measured/predicted) of 0.96, CVR, of 0.258 for combined (total, tip and skin) resistances. Using ASHTO, 2012, the Load and Resistance Factor Design (LRFD) Φ was determined to be 0.65, for a reliability, β, of 2.33. CAPWAP had a bias, ʎ, of 0.91, CVR = 0.311, and LRFD Φ = 0.54 for β=2.33 with inclusion of side friction and tip resistance.
A PERFORMANCE INVESTIGATION OF PILE DRIVING HAMMERS AND PILES
THE PRIMARY OBJECTIVE OF THIS STUDY WAS TO DETERMINE THE PERFORMANCE OF DIESEL PILE DRIVING HAMMERS IN RELATION TO STEAM AND AIR TYPE HAMMERS AND TO IMPROVE THE METHODS FOR ESTIMATION OF PILE BEARING CAPACITY. THE STUDY CONSISTS OF AN EXTENSIVE FIELD INVESTIGATION IN WHICH A TOTAL OF EIGHTY- EIGHT PILES WERE DRIVEN AT THREE SITES. AT ALL THREE SITES, THE PILES WERE DRIVEN TO PRACTICAL REFUSAL IN UNDERLYING HIGHLY CONSOLIDATED SAND AND GRAVEL OR HARDPAN, BUT THE OVERLYING LAYERS REPRESENTED A VARIETY OF SOFT CLAYS, TILL CLAYS AND GRANULAR MATERIALS. A SELECTION OF PILE DRIVING HAMMERS WAS USED, INCLUDING SEVERAL LIGHT AND HEAVY DIESEL HAMMERS, AIR AND STEAM HAMMERS, AND A SPECIAL INTERNAL MANDREL HAMMER. PILES WERE MOSTLY OF THE STEEL H OR STEEL PIPE TYPE, ALTHOUGH A FEW PATENTED TYPE STEEL TUBES WERE ALSO INCLUDED. EXTENSIVE SOIL PROFILE DATA WAS COLLECTED PRIOR TO DRIVING OPERATIONS AT EACH SITE AND LABORATORY SHEAR TESTS ON UNDISTURBED SAMPLES WERE PERFORMED. DYNAMIC MEASUREMENTS OF THE DRIVING OPERATIONS WERE MADE, INCLUDING DRIVING FORCE AS INDICATED BY A SPECIAL LOAD CELL, ACCELERATIONS AND DISPLACEMENTS OF THE TOP OF THE PILE. STATIC LOAD TESTS WERE CONDUCTED ON NINETEEN OF THE PILES. ANALYSIS OF THE DATA INCLUDED A CAREFUL COMPARISON OF THE DRIVING EFFECTIVENESS OF THE VARIOUS TYPES OF HAMMERS AS REFLECTED BY BLOW COUNT FOR EQUAL PENETRATION, PENETRATION RATE, AND EFFICIENCY OF ENERGY TRANSMISSION TO THE PILE. THE COMMON PILE DRIVING FORMULAS WERE REEXAMINED TO DETERMINE THEIR RELIABILITY, WITH THE CONCLUSION THAT THEY DO NOT PERMIT ESTIMATION OF PILE CAPACITY WITH ANY DEGREE OF CERTAINTY. IT WAS ALSO CONCLUDED ON THE OTHER HAND THAT SOIL TEST DATA, CONSISTING OF STANDARD PENETRATION MEASUREMENTS AND LABORATORY SHEAR TESTS, PROVIDE A RELIABLE AND ACCURATE BASIS FOR ESTIMATING STATIC LOAD CAPACITY. /BPR/