SLP is Pile Dynamics, Inc  Representative and  user of all PDI equipment and software

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Pile testing

Dynamic (DLT)

Dynamic load testing has as its primary goal the assessment of pile bearing capacity. It is applicable to both cast in situ piles or drilled shafts and impact driven piles.
The Case Method of pile testing, named after the Case Institute of Technology where it was developed between 1964 and 1975, requires that a substantial ram mass (such as that of a pile driving hammer) impacts the pile top such that the pile undergoes at least a small permanent set. The method is therefore also referred to as a "High Strain Method". The Case Method requires dynamic measurements on the pile or shaft under the ram impact and then an evaluation based on closed form solutions of the wave equation. Conveniently, measurements and analyses are done by a single piece of equipment: the Pile Driving Analyzer® (PDA).

Results of field testing with PDA-PAK (Pile Driving Analyzer®):
· Estimates pile/soil bearing capacity
· Measure and evaluates stresses in pile during testing or driving
· Evaluates the pile integrity
· Evaluates hammer performance
· Investigates pile stiffness and soil dynamic characteristics
· Determines stresses on pile during driving
· Determines actual stroke for diesel hammers
· Determines soil strength gain versus time

Little history and theory:
In 1960 E.A. Smith developed the concept of applying one dimensional wave propagation theory to explain the process of driving a pile into the ground.
Wave Equation Analysis of Pile Driving is a technique for predicting the dynamic resistance to pile penetration. In this mathematical model, the hammer and all its accessories (ram, cap, cap block) and the pile are modelled as a lumped mass and spring system. The soil response is modelled as viscoelastic-plastic. The driving energy input to model is the initial velocity or acceleration of the ram on impact. The model predicts the total dynamic and approximate static resistance and the driving stresses *in the pile. The GRLWEAP computer program employs this technique.
Although it is an excellent tool for analysis of impact pile driving, the wave equation approach has some limitations. These are mainly due to uncertainties in quantifying some of the required inputs, such as actual hammer performance and soil parameters. Dynamic Pile Monitoring yields information regarding the hammer, driving system, and pile and soil behaviour that can be used to confirm the assumptions of wave equation analysis. Dynamic Pile Monitoring is performed with the Pile Driving Analyser.
The Pile Driving Analyser uses wave propagation theory to compute numerous variables that fully describe the condition of the hammer-pile-soil system in real time, following each hammer impact. This approach allows immediate field verification of hammer performance, driving efficiency, and an estimate of pile capacity.
When a hammer or drop weight strikes the pile head, a compressive stress wave travels down the pile shaft at a speed c, which is a function of the pile elastic modulus E and mass density. The impact induces at the pile head a force F and a particle velocity v. As long as the wave travels in one direction, force and velocity are proportional:
F = Zv, where Z is the pile impedance, Z = EA/c, where A is the cross sectional area of the pile. Soil resistance forces cause wave reflections that travel to the pile top where force and velocity are measured. It is possible, therefore, to estimate soil resistance if force and velocity on the pile are measured.

The force is computed by multiplying the measured signals from a pair of strain transducers attached near the top of the pile by the pile area and modules. The velocity measurement is obtained by integrating signals from a pair of accelerometers also attached near the top of the pile. Strain transducers and accelerometers are connected to the Pile Driving Analyser that internally performs all the necessary signal conditioning and processing to obtain output results.
Soil resistance computed by the PDA includes both static and viscous components. The static component is a function of a soil parameter called the Damping Factor, which is related to soil grain size. The damping factor is an input to the PDA.
Another technique that evolved from Smith's approach of modelling the wave propagation theory of pile driving is the Case Pile Wave Analysis Program (CAPWAP). CAPWAP combines field measurements (obtained with the PDA) and wave-equation type analytical procedures to predict soil behaviour including static-load capacity,soil resistance distribution, soil damping and quake values, pile load versus movement plots, and pile soil load transfer characteristics. The employment of PDA field measurements in conjunction with CAPWAP analysis defines what is known as Dynamic Load Testing and estimates.
Dynamic Pile Monitoring with the PDA and Dynamic Load Testing with the PDA and CAPWAP are both High Strain Dynamic Testing procedures. The pile driving hammers or drop weights used to perform these tests cause high strains in the piles.

Static (SLT)

Classic static load test is performed with direct load or with tension piles. Normal procedure used is Maintenand load test.

Pile integrity tests
Low Strain Integrity Testing of Piles(PIT)

The application of the wave equation theory to waves caused by small impacts resulted in the practice of Low Strain Dynamic Integrity Testing. This procedure is performed with a Pile Integrity Tester, an accelerometer placed on top of the pile to be tested, and a hand held hammer. Given a known stress wave speed, records of velocity (integrated from the accelerometer signals) at the pile head can be interpreted for pile non-uniformities (changes in impedance).
The PIT can detect the presence of potentially dangerous defects such as cracks, necking, soil inclusions or voids. Pile length may also be determined.

PIT collector is used for testing driven piles and primary bored piles with a hand held hammer utilising both sonic pulse echo and the frequency based sonic mobility methods. PIT economically provides an assessment of structural integrity of deep foundations at a low cost. PS calculates the pile profile based on low strain data from the Pile Integrity Tester (PIT).

PIT collector is used to:
· Controle pile integrity (non-destructive test)
· Investigates possible necking, void, inclusions, separation of concrete in deep foundations
· Detects mayor defects
· Detect location of defect
· Determines approximate degree of defect
· Can test a large number of installed piles on a single day

Sonic Logging Integrity Test

The system consists of an Ultrasonic Pulse Transmitter Probe and a Receiver Probe, which are connected to an Ultrasonic Pulse Generator. The propagation and time of "sonic" waves across tubes are measured to determine the presence of any defects.

Sonic Logging is one of the most advanced and economical tools for testing the integrity of the deep foundation, including bored piles, barrettes and concrete structures. Specific defects detected by Sonic Logging include honeycombing, segregation, necking, arching, soil inclusion and cracks.

CHA is used for:
Pile integrity control
Quality assurance testing for a variety of concrete foundations and slurry/diaphragm walls
Verifying concrete integrity
Locating defects
Identifies several defects and their location and extent in the same shaft
Images critical anomalies

Single hole sonic logging
Diagonal sonic logging

SPT calibration

The Standard Penetration Test (SPT) is a widely used soil exploration tool which involves using a SPT hammer to drive a split barrel sampler or cone diameter 50 mm at the bottom of a drive rod to recover soil samples. The number of blows required to drive the last 300 mm is the "N value", and indicates soil strength or in very hard material "penetrability", which is penetration in cm per 60 blows.

Several different types of SPT hammers are used to conduct SPT tests, and this influence the N value. The American Society for Testing and Materials (ASTM), EUROCODE and others recommend that a measured N value be standardised by multiplying it by the ratio between the measured energy transferred to the rod and 60% of the theoretical potential energy. This compensates for widely variable efficiencies from different SPT hammer types and therefore improves the reliability of soil strength estimates used in geo-technical designs.

Driving Analyzer® (PDA) I used to measure the energy transferred into an instrumented SPT rod. This permits the adjustment of the measured N-value to the normalised N60 for standard 60% energy transfer into the rods.
The SPT rod is instrumented with strain transducers or resistance strain gages that obtain the force and velocity signals necessary for the calculation of transferred energy. These sensors are easily attached to a SPT Analyser or to a PDA.