GRLWEAP and DRF-correlated Hiley equivalence

I have written recently about Energy-Movement-Capacity (EMC) relationships for inferring the capacity of untested driven piles.  As I mentioned, pile driving formulas generally, and bearing graphs are all forms of EMC relationships.  When accepting any pile which is not specifically (PDA) tested, we are assuming that there is an underlying relationship between these three parameters which represents the ‘ground truth’.  To be reliable, the chosen pile driving formula or the bearing graph must be correlated back to PDA test results, which provide site-hammer-pile-specific EMC reference values.

I have done a small parametric study to demonstrate the equivalence of GRLWEAP bearing graphs and the Hiley formula corrected by what I call the Dynamic Reduction Function (DRF) – a variable correction/correlation factor about which I have previously posted.  PDA testing provides the basis for evaluating ground truth at a site.  GRLWEAP can be considered to be an assessment based on a preliminary estimate of ground truth (in which things like damping factors, quakes, resistance distributions etc are assumed).

I have attached a spreadsheet which summarizes the results of a single GRLWEAP run.  The spreadsheet lists the assumptions relating to hammer, pile and ground so that you can reproduce this analysis if you wish.  The GRLWEAP output summary for each capacity assumption is tabulated.  These include capacity, transferred energy, maximum movement and pile set – ie these important EMC values.  For each GRLWEAP capacity assumption, the Hiley formula can be calculated : H = EMX / (SET + DMX/2).  The ratio between the capacity and the Hiley estimate is calculated, and a line of best fit for this ratio versus set is established (see spreadsheet).  This line of best fit is the DRF correction.  Finally, the corrected Hiley formula is computed by applying the DRF correction function according to the predicted set.

The graph below compares the GRLWEAP bearing graph with the raw and correlated Hiley Formula estimates.  The agreement between the bearing graph and the correlated Hiley Formula is clear.  But just a word of caution – this is for a single stroke/energy/efficiency.  I will discuss how to deal with variations in transferred energy in a future post.  There is another topic for discussion in the GRLWEAP table – ultimate vs activated capacity.  Again, for another time.

In actual practice, the DRF correction can be developed either directly from the CAPWAP results or indirectly from correlating GRLWEAP analysis to CAPWAP results.

Conclusion : pile driving formulas are themselves unreliable, but once correlated to CAPWAP results they provide a valuable and reliable alternative for construction control and pile acceptance.

#pile #piles #piledriving #pileacceptance #piledrivingmonitoring #geotechnical #geotechnicalengineering #PDA #GRLWEAP #CAPWAP #PDM #PDM3 #FoundationQA #ConstructionQA