Pile Driving Analyzer Research Articles

Low Strain Integrity Testing of Piles: Three-Dimensional Effects

Results of low strain integrity testing of piles are normally interpreted using one-dimensional (1D) stress wave theory. While 1D stress wave theory is acceptable for pile-driving analysis, it may not adequately simulate the response of piles in sonic integrity tests where the hammer is small in relation to the size of the pile. Extensive parametric studies were performed using 1D and 3D (axisymmetric) wave equation models to study this problem. The main 3D effect in intact piles lies in the initial velocity response that becomes negative after the first positive peak. This response resembles that of a pile with an anomaly near the pile head. If this is not recognized, it will lead to a wrong assessment of the pile condition with attendant cost implications. This potential source of error can be removed by maintaining a distance between hammer and receiver that is greater than 50% of the pile radius.

A study of the effect of driving on pre‐bored piles

AbstractA finite element model for pile‐driving analysis is developed and used to investigate the behaviour of pre‐bored piles, which are then driven the last 1.25 or 2.25 m to their final design depth. The study was conducted for the case of saturated clays. The model traces the penetration of the pile into the soil and accommodates for large deformations. The non‐linear behaviour of the clay in this study is predicted using the bounding‐surface‐plasticity model, as applied to isotropic cohesive soils. The details of the 3‐D numerical modelling and computational schemes are presented. A significant difference was observed in the pile displacement during driving, and in the computed soil resistance at the pile tip, particularly at the earliest driving stages. No difference in soil resistance at the soil pile interface along the pile shaft was detected between the pre‐bored piles whether driven 1.25 or 2.25 m. Copyright © 2002 John Wiley & Sons, Ltd.

Load and Resistance Factor Design (LRFD) for Driven Piles Using Dynamic Methods—A Florida Perspective

Abstract The parameters for load and resistance factor design (LRFD) of driven piles using dynamic methods are presented based on a database of 218 pile cases in Florida. Eight dynamic methods were studied: ENR, modified ENR, FDOT, and Gates driving formulas, Case Analysis with Wave Analysis Program (CAPWAP), Case Method for Pile Driving Analyzer (PDA), Paikowsky's energy method, and Sakai's energy method. It was demonstrated that the modern methods based on wave mechanics, such as CAPWAP, PDA, and Paikowsky's energy methods, are roughly twice as cost effective to reach the target reliability indices of 2.0 to 2.5 (failure probability = 0.62 to 2.5%) as the ENR and modified ENR driving formulas. The Gates formula, when used separately on piles with Davisson capacities smaller or larger than 1779 kN, has an accuracy comparable to the modern methods. The utilizable measured Davisson capacity, defined as φ/λ (ratio of resistance/mean capacity) obtained from testing at beginning of redrive (BOR), is only slightly larger than the end of drive (EOD) values. Furthermore, past practice with driving formulas reveals the existence of a large redundancy in pile groups against failure. The latter suggests the use of a lower relatively reliability target index, βT = 2.0 (pf = 2.5%) for single pile design. Also, the utilizable measured Davisson capacity, φ/λ, for all the dynamic methods studied, is quite similar to published values (Lai et al. 1995; Sidi 1985) for static estimates from in situ tests.

Value of Methods for Predicting Axial Pile Capacity

The purpose of this paper is to compare the value of predicting capacity using dynamic formulas, wave equation analysis, and dynamic monitoring without load tests. A database of pile load test results is used to quantify the precision associated with predictive methods. These methods are quantified and ranked using a “wasted capacity index” (WCI) to quantify the effect of precision. The WCI is a measure of how inefficiently a method predicts capacity. A precise method will be very efficient and accordingly have a low WCI. On the other hand, a less precise method requires a more conservative design and thus a greater WCI. The value of the wasted capacity index is calculated from the precision of the method and the reliability required for the pile foundation. The WCI is presented for the following methods: Engineering News (EN) formula, Gates formula, wave equation analysis program (WEAP), measured energy (ME) approach, pile driving analyzer (PDA), and CASE Pile Wave Analysis Program (CAPWAP).

A new approach to the analysis of high-strain dynamic pile test data

High-strain dynamic pile tests using the pile driving analyzer (PDA) and the Case method have been available in Canada for over 15 years. During that period of time, the hardware has evolved considerably but the way the data is interpreted has basically remained the same. The evaluation of the bearing capacity of the tested pile still uses the Case method, with the Case J factor being calculated either from the results of a static load test or, more often, from the results of one or more CAPWAP (Case pile wave analysis program) analyses. A computer program has been developed to estimate the bearing capacity of piles using the dynamic test results produced by the PDA. This program uses direct correlations between PDA data and CAPWAP results. It also includes an artificial intelligence module trained to predict CAPWAP pile capacity. It is not designed to replace the CAPWAP program, but rather to indicate when an additional CAPWAP analysis might be required. Key words : dynamic load test, computer program, artificial intelligence, CAPWAP, Case method.

Validity of Smith Model in Pile Driving Analysis

Smith developed a wave equation method by idealizing a pile‐soil system as a series of masses and springs for the analyses of complicated pile driving problems. The soil parameters used in this method were proposed on the basis of his experience in piling practice and hence, were recognized to be relatively crude from soil mechanics aspects. This paper presents results of an analytical procedure for determining the shaft damping parameter and relating it to the soil properties: (1) Shear modulus; and (2) shear strength. A dynamic finite element computer program is developed to analyze the pile shaft resistance by using an elasto‐plastic approach; the relationship between the shaft damping parameter and the other parameters such as pile penetration velocity, radius of yielding zone, and force pulse duration time are also examined. It is found that the Smith damping parameter cannot be back‐calculated to be some simple constant.

Rational wave equation model for pile-driving analysis: Lee, S L; Chow, Y K; Karunarante, G P; Wong, K Y J Geotech Engng Div ASCEV114, N3, March 1988, P306–325

Rational wave equation model for pile-driving analysis: Lee, S L; Chow, Y K; Karunarante, G P; Wong, K Y J Geotech Engng Div ASCEV114, N3, March 1988, P306–325

Rational Wave Equation Model for Pile‐Driving Analysis

A one-dimensional wave equation model for pile-driving analysis is presented. In this model, the pile is represented by discrete elements, while the soil is represented by a series of springs and dashpots, the coefficients of which are derived using elasto-dynamic theory. The soil model incorporates the loss of wave energy to the soil through radiation or geometric damping. In addition, the effect of the increase in soil resistance to failure when subjected to rapid loading is taken into account. The capability of the proposed model is demonstrated by comparison with field data of two instrumented piles. The analyses include predictions of set, and driving stresses at various levels of the piles. Comparisons are made with the sets and driving stresses predicted by the Smith (1960) model. From the analyses by the proposed model and load test results, estimations of soil setup for the two piles are also presented.

Stress Wave Monitoring for a Friction Pile During Driving: A New Analysis Procedure

A pile-driving analysis procedure coupled with stress-wave monitoring, is developed for friction piles in clay or argillaceous rock. Emphasis of the analysis procedure is placed on treating an elastic-perfectly plastic constitutive law of the shaft interface, within the framework of one-dimensional wave propagation along with the method of characteristics. The analysis procedure thus developed is applicable to two types of pile-driving analysis: one is the inverse analysis for identifying the constitutive parameters of the shaft interface from a recorded stress waveform; and the other is the drivability analysis, in terms of the already identified material parameters, for predicting the displacements or stresses in the pile caused by any single hammer blow. Both aspects of the proposed analysis procedure are examined against laboratory pile-driving tests on a “perfect” friction pile with no point resistance. In those tests, a steel pipe pile of 2. 5 cm in outer diameter is quasi-statically jacked into a remarkably homogeneous mudstone, along a slightly undersized guide-hole, and then subjected to striking by a free-falling steel bar. It is then confirmed that there is good agreement between the calculated and measured pile-driving performances.

BATLAB computer program for pile-driving analysis (In French)

BATLAB computer program for pile-driving analysis (In French)

Numerical approximations in pile-driving analysis. Technical note : Davis, R O; Phelan, P J Int J Num Anal Meth Geomech, V2, N3, July–Sept 1978, P303–310

Numerical approximations in pile-driving analysis. Technical note : Davis, R O; Phelan, P J Int J Num Anal Meth Geomech, V2, N3, July–Sept 1978, P303–310

Experimental Studies on Concrete Pile Driving

Recently, concrete piles are driven almost always by blow. This method of driving simplifies the process of construction but sometimes it will have destructive effect on the piles. It is necessary to investigate the process to find out the factors for the destruction of the piles and improve that method.In this study, RC piles (φ350mm×13m) and PC piles (φ350mm×13m+φ350mm×7m), both centrifugally spun, were used as test piles, and drop hummers (1t, 2t and 3t) and diesel hummers (Delmag-12 and Delmag-22) used.The ground into which the piles were driven has layers of sand (N-value=15∼20) at the depth of 6∼7m, gravel (N-value=30∼50) at the depth of 12∼13m and silt and sand (N-value=20∼35) deeper below.The impact strains at the head, center and foot of the piles were measured by means of wire strain gauges, and the effects of cussion materials, eccentric blow and the characteristics of ground on the pile stress have also been investigated. Comparative studies were made of some of the theoretical equations for the impact stresses with their experimental results.Principal conclusions obtained are as follows.(1) Rebound of a pile increases as the ground becomes harder.(2) Set per blow decreases as the ground becomes harder and the depth of the set is greater by drop hummers than by diesel hummers.(3) Delmag-12 cannot drive a pile into the ground which is more than N-value=50.(4) The impact stresses caused by pile-driving ordinarily reach their maximum at the head of the pile and their minimum at the foot of the pile.(5) The impact stress at the foot of the pile increases as N-value of the ground increases. But the impact stress at the head of the pile is not so related with N-value.(6) The impact stress at the head of the piles by drop hummers is greater than that by diesel hummers. The former sometimes exceeds the impact strength of RC pile concrete.(7) The maximum impact stress caused by eccentric blows of both drop hummers and Delmag-22 sometimes exceeds the impact strength of the pile concrete. The tensile stress and bending moment due to the eccentric blows sometimes cause cracks in the pile. In these respects, the PC pile is superior to the RC pile, and the diesel hummer is superior to the drop hummer. It is very important to drive a pile as normally as possible and it is necessary to set a proper cussion at the head of the pile.(8) The impact stress caused by pile-driving should be analyzed by the wave equation rather than by the energy equation.Further studies are needed of the following problems.(1) The impact strength of concrete.(2) The correlation of the compressive strength by the normal test piece and that by the test piece made by the centrifugal force.(3) Estimation of the impact stress in a pile caused by driving.(4) Fundamental studies on pile-driving analysis by means of the electric computer.

Pile-Driving Analysis by the Wave Equation

There are a great many different pile-driving formulas in use, and engineers have never been able to agree as to which one is best. This situation has arisen primarily because, until recently, the mathematics of pile-driving action could not be solved in any practical manner. As a result all pile-driving formulas are partly empirical and, consequently, apply only to certain types or lengths of pile. This paper is presented with the purpose of giving engineers a mathematical method of wider application, depending on the use of electronic computers and numerical integration. The method is also applicable to other impact problems.

Discussion of “Pile-Driving Analysis by the Wave Equation”

Discussion of “Pile-Driving Analysis by the Wave Equation”

Closure to “Pile-Driving Analysis by the Wave Equation”

Closure to “Pile-Driving Analysis by the Wave Equation”

Closure to “Pile-Driving Analysis by the Wave Equation”

Closure to “Pile-Driving Analysis by the Wave Equation”

Discussion of “Pile-Driving Analysis by the Wave Equation”

Discussion of “Pile-Driving Analysis by the Wave Equation”

Discussion of “Pile-Driving Analysis by the Wave Equation”

Discussion of “Pile-Driving Analysis by the Wave Equation”

Pile-Driving Analysis by the Wave Equation

All pile-driving formulas, used at present time, are partly empirical and apply only to certain types or lengths of pile; mathematical method of wider application, depending on use of electronic computers and numerical integration is presented; pile must be divided for calculation into unit lengths considerably shorter than wavelength of stress or impact wave produced by hammer; application to other impact problems.