Cover Image

Not for Sale

View/Hide Left Panel
Click for next page ( 21

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 20
20 TABLE 7a Correlations of soil properties from SPT WEAP Properties From SPT Reference (Kulhawy & Mayne, 1990) Based on Smith (1960), the use of the WEAP (Goble and Peck, Hanson and Rausche, 1976) during design is of great importance for Thornburn: Figure 4.12 54 - 27.6034 exp(-0.014N') achieving compatibility between the driving system, the pile, Schmertmann Figure 4.13 and the soil conditions. Drivability studies and pile stress tan-1[ N / (12.2 + 20.3 '/pa') ] 0.34 and Equation 4.11 analyses often determine the pile type and geometry and the Su (bar) Terzaghi and Peck (1967): 0.06 N Equation 4.59 adequacy of the proposed equipment. Typically, two analyses Hara 1974: 0.29 N0.72 Equation 4.60 are carried out: one by the designer during the design stage OCR Mayne and Kemper for clay 0.5 N / 'o ('o in bar) Figures 3.9 and 3.18 (prebid), in which a range of equipment to be specified in the Dr Gibbs and Holtz's F igures Figures 2.13 and 2.14 bidding documents is examined, and the other by the contrac- tor, demonstrating the adequacy of the proposed construction equipment. The evaluation of WEAP effectiveness for capac- ity predictions is difficult, as a large range of input parameters type of the dynamic methods to be evaluated and (2) the con- is possible and the results are greatly affected by the actual ditions under which these methods need to be examined. Sec- field conditions. Examination of the method through analyses tions 2.5.2 and 2.5.3 address these issues, respectively, based making use of default values is probably the best avenue. on a detailed study by Paikowsky and Stenerson provided in Other evaluations, including WEAP analysis adjustments fol- Appendix B. lowing dynamic measurements (e.g., matching energy), seem to be impractical in light of the other methods available and lead to questionable results regarding their quality and mean- 2.5.2 Methods of Analysis ing (Rausche et al., 1997; Rausche, 2000). The WEAP analy- sis is evaluated in this study as a dynamic method for pile General capacity prediction, using WEAP default input values and the pile's driving resistance at EOD compared to the static Table 9 presents a summary of the major available dynamic load test results. The evaluation of WEAP as a pile design methods for evaluating pile capacity. The methods are sub- method examining the analyzed stresses at the design stage divided according to the project stage (i.e., design vs. con- to the measured stresses during construction leads to a struction) and the need for data obtained through dynamic strength factor (related to the allowed structural stresses in measurements. The incorporation of dynamic equations and the pile) that is beyond the scope of the presented research. WEAP reflects the need to address the state of practice as described in section 2.1. The methods that require dynamic measurements can be Dynamic Equations broadly categorized as those that utilize a simplified analysis of an instantaneous pile capacity evaluation for each hammer The chosen dynamic equations address the state of practice blow and those that require elaborate calculations (i.e., sig- and reflect a range in equation type and performance. While nal matching) traditionally carried out in the office. the Engineering News-Record Equation (Wellington, 1892) TABLE 7b Notations for combinations of correlations between soil parameters and standard penetration test results and their manner of application Notations (1) (2) (3) (4) (5) (6) (7) (8) limit below tip 40 36 contributed zone 2B 11.5B 2B 11.5B 2B 11.5B 2B 11.5B for tip resistance , if from SPT, is Peck, Hanson and Peck, Hanson and Schmertmann Schmertmann correlated by Thornburn Thornburn Su, if from SPT, is Terzaghi and Peck correlated by Notations (1h) (2h) (3h) (4h) (5h) (6h) (7h) (8h) limit below tip 40 36 contributed zone 2B 11.5B 2B 11.5B 2B 11.5B 2B 11.5B for tip resistance , if from SPT, is Peck, Hanson and Peck, Hanson and Schmertmann Schmertmann correlated by Thornburn Thornburn Su, if from SPT, is Hara correlated by

OCR for page 20
21 TABLE 8 Correlations of soil properties from CPT Ru = 1.75 E log 10 N - 100 (27) Reference Properties From CPT (Kulhawy & Mayne, 1990) Robertson and Campanella: Figure 4.14 where: atan(0.1+0.38*log(qc/')) and Eq. 4.12 Theoretical: ( qc - o ) / Nk Eq. 4.61 Ru = Ultimate capacity (tons) Su (bar) qc and o in bars. E = Gross energy of pile hammer, ft-lb OCR Mayne: 0.29 qc / 'o Figure 3.10 Note: The equation includes an 80% efficiency factor for clay qc and o in bars. on the rated energy, which is a value between 75% Jamiolkowski: 68 log(qcn) 68 Figure 2.24 and Eq. 2.20 and 85% recommended by Gates (1957) for drop qcn = q'c (dimensionless) hammers and all other hammers, respectively. Dr Pa '0 N = Number of blows per inch q'c = qc / Kq Kq = 0.9 + Dr/300 Dynamic Measurement: The Case Method qc and 'o in bars. The Case method (Goble et al., 1970 and Rausche et al., has proven to be unreliable through the years--as shown, for 1975) is often used in field evaluations, as it is built into Pile example, by Olsen and Flaate (1967)--it was founded on a Dynamics Inc.'s Pile Driving Analyzer (PDA), the most solid theoretical basis and is still used in construction in about commonly used system for obtaining dynamic measurements half of the states in the country. The equation's traditional for- during pile driving in the United States. The method is based mulation--as used, for example, in the Massachusetts State on simplified pile and soil behavior assumptions (free end Building Code (Massachusetts, 1997)--includes an FS of 6, and plastic soil), resulting in a closed form solution related to which needs to be recognized. The Gates equation (Gates, the impact and its reflection from the tip. With the years, at 1957), while empirical, was found to provide reasonable least five different variations of the method have evolved results (e.g., Olsen and Flaate, 1967; Long et al., 1998). The (GRL, 1999). The Case method utilizes a damping coeffi- equation was further enhanced by Richard Cheney of the cient (Jc) that is assumed to be associated with soil type. The FHWA (FHWA, 1988) (see also Fragaszy et al. 1985), based influence of this factor on predicted static capacity depends on statistical correlations with static load tests and has the fol- on the stress wave reflected from the pile's tip, hence on the lowing format: driving resistance. The Case-damping coefficient was inves- TABLE 9 Dynamic methods for evaluating pile capacity: advantages, disadvantages, and comments Category Method Advantages Disadvantages Comment WEAP - Equipment Match - Non unique Analysis - Required for Construction (Smith, 1960, Design Stage - Drivability Study - Performance sensitive to - Required Evaluation for Goble et al., - Structural Stresses field conditions capacity predictions 1976) ENR - Sound Principles - Needs to be examined (Wellington, - Unreliable - Common use without a built in FS. 1892) Dynamic Gates - Empirical - Depends on original - Found to be more reliable Equations (Gates, 1957) - Common use database than other equations FHWA version - Correction based on of Gates Eqn. - Depends on database - Was found to be reliable additional data (FHWA, 1988) Signal Matching - Solid principle of - Stationary soil forces (e.g. CAPWAP) matching calculations - Office Method - Expensive (Goble et al., to measurements by - Found reliable at BOR - Requires time 1970) imposing msd. B.C. Case Method - Requires local calibration - Was found reliable with (Goble et al., - Simplified Analysis - Presumed dependency of local calibration Dynamic 1970, Rausche et - Field Method soil conditions found - How to obtain national or Measurements al., 1975) baseless international calibration? Energy Approach - Shows long-term capacity - Simplified Analysis (Paikowsky, which may not be present - Ideal for construction - Field Method 1982, Paikowsky at EOD et al., 1994) NOTES: ENR = Engineering News Record; FS = Factor of Safety; BOR = Beginning of Restrike; EOD = End of Driving.