TechBeMe
Specifier/Regulator
- Aug 2, 2005
- 1
Further to the question posted by keither21 awhile back at
thread256-110213
respecting the accuracy of embedment testing of timber piles.
Accuracy to within +/- 1” is impossible, but it’s assumed you meant 1’ when posing your question. Even 1 foot accuracy would be elusive.
Testing firms employing propagation wave methods do not claim any greater accuracy than +/- 10% and that percentage is measured against the total length of the pile. There are significant disclaimers relating to knots, bends and the like.
I know of a situation where a piling log could not be rationally explained by an engineer who’d issued a foundation certification which relied upon it. His firm had a monitoring contract with the homeowners but it had neglected to dispatch a representative. They let the contractor FAX in results from pile driving. (It seems to be a troubling problem with certain engineers from the coastal area in question that they don’t show up, rendering themselves stampers and little more.)
The piling contractor initially claimed the numbers represented embedments. The Log set forth numbers ranging from 24’ to 31’ but these could not be made to square with the timber preservative records of what had been delivered to the site.
Dilemma: which documentation was true and which was false? Had undocumented (but long-enough) piles been used for constructing the home, making the timber treatment certificate the “false document” in the certification filed with the building inspector? Or were the embedments falsely stated?
Below is a presentation of side-by-side numbers for the 20 piles which were removed after embedment testing. The comparison lays out embedment numbers of what now appears to have been a falsified Log(L), the predicted values from Test(T), and actual embedments as later Measured(M)
Two different errors are also presented. LE is the error of the Log in overstating embedment (L-M = Log Error). TE is the error of the testing (T – M = Test Error or TE). On average, test error underestimated embedment by 15% with three notable outliers to the test results. However, the original Log had overstated embedments by 40%. Extraction of the piles also disclosed that there could not have been any rational benchmark marked on land, guiding the contractors. Numbers were all "feel good" and "invented".
Log=L Test=T Measured=M Log Error=LE Test Error=TE
26L ... 14T ... 21M.........+5LE -7TE
25L ... 15T ... 18M.........+7LE -3TE
25L ... 21T ... 17M.........+4LE -4TE
25L ... 21T ... 19M.........+4LE -3TE
25L ... 18T ... 20M.........+5LE -2TE
26L ... 17T ... 20M.........+6LE -3TE
25L ... 17T ... 19M.........+6LE -2TE
25L ... 22T ... 20M.........+5LE +2TE
26L ... 16T ... 18M.........+8LE -2TE
26L ... 24T ... 17M.........+9LE +8TE
31L ... 13T ... 19M.........+12LE -6TE
26L ... 9T ... 20M......... +6LE -11TE
27L ... 14T ... 21M......... +6LE -7TE
25L ... 9T ... 21M......... +4LE -12TE
25L ... 12T ... 16M......... +9LE -4TE
26L ... 11T ... 17M.........+9LE -6TE
27L ... 16T ... 17M.........+10LE -1TE
26L ... 12T ... 17M......... +9LE -5TE
26L ... 25T ... 19M........ +7LE +6TE
25L ... 18T ... 18M.........+7LE 0 TE
The structure in question was somewhat unusual, being built partly over water of the IntraCoastal Waterway and 1,600 feet from the shoreline. Graphics linked below help depict the site, and set out in color-coded soil layers the Geotechnical Engineer’s recommendation that the Structural Engineer handle this site as one having three distinct strata of soil using three different soil parameters.
Soil tests taken in the water area at rear of the house and from locations on piers about 4 feet to 7 feet distant from footprint had disclosed 6’ and 8’ of unconsolidated muck at two boring locations, followed at both bore holes by 5’ of SPT-N 1-1-1-1.
Further layers below that were silty sand of progressively greater densities at one location (4-5-10-12 for five feet, then 8-10-13-20) and sand at another (12-13-14-17 then 12-16-17-19).
Links:
Below is a before and after graphic showing two profiles: to the left, the foundation which was removed; to the right, the foundation which replaced it.
The 20 piles located in the water area have exposed lengths ranging from 13’ to 18’ in height.
Any comments from the structural engineers in this forum about a point of fixity?
Any guesses about the bracing design (X-bracing? Batter piles? Other?) chosen by the project engineer who handled the most challenging assignment to move this house and install a new foundation while the house sat in the middle of a street?
thread256-110213
respecting the accuracy of embedment testing of timber piles.
Accuracy to within +/- 1” is impossible, but it’s assumed you meant 1’ when posing your question. Even 1 foot accuracy would be elusive.
Testing firms employing propagation wave methods do not claim any greater accuracy than +/- 10% and that percentage is measured against the total length of the pile. There are significant disclaimers relating to knots, bends and the like.
I know of a situation where a piling log could not be rationally explained by an engineer who’d issued a foundation certification which relied upon it. His firm had a monitoring contract with the homeowners but it had neglected to dispatch a representative. They let the contractor FAX in results from pile driving. (It seems to be a troubling problem with certain engineers from the coastal area in question that they don’t show up, rendering themselves stampers and little more.)
The piling contractor initially claimed the numbers represented embedments. The Log set forth numbers ranging from 24’ to 31’ but these could not be made to square with the timber preservative records of what had been delivered to the site.
Dilemma: which documentation was true and which was false? Had undocumented (but long-enough) piles been used for constructing the home, making the timber treatment certificate the “false document” in the certification filed with the building inspector? Or were the embedments falsely stated?
Below is a presentation of side-by-side numbers for the 20 piles which were removed after embedment testing. The comparison lays out embedment numbers of what now appears to have been a falsified Log(L), the predicted values from Test(T), and actual embedments as later Measured(M)
Two different errors are also presented. LE is the error of the Log in overstating embedment (L-M = Log Error). TE is the error of the testing (T – M = Test Error or TE). On average, test error underestimated embedment by 15% with three notable outliers to the test results. However, the original Log had overstated embedments by 40%. Extraction of the piles also disclosed that there could not have been any rational benchmark marked on land, guiding the contractors. Numbers were all "feel good" and "invented".
Log=L Test=T Measured=M Log Error=LE Test Error=TE
26L ... 14T ... 21M.........+5LE -7TE
25L ... 15T ... 18M.........+7LE -3TE
25L ... 21T ... 17M.........+4LE -4TE
25L ... 21T ... 19M.........+4LE -3TE
25L ... 18T ... 20M.........+5LE -2TE
26L ... 17T ... 20M.........+6LE -3TE
25L ... 17T ... 19M.........+6LE -2TE
25L ... 22T ... 20M.........+5LE +2TE
26L ... 16T ... 18M.........+8LE -2TE
26L ... 24T ... 17M.........+9LE +8TE
31L ... 13T ... 19M.........+12LE -6TE
26L ... 9T ... 20M......... +6LE -11TE
27L ... 14T ... 21M......... +6LE -7TE
25L ... 9T ... 21M......... +4LE -12TE
25L ... 12T ... 16M......... +9LE -4TE
26L ... 11T ... 17M.........+9LE -6TE
27L ... 16T ... 17M.........+10LE -1TE
26L ... 12T ... 17M......... +9LE -5TE
26L ... 25T ... 19M........ +7LE +6TE
25L ... 18T ... 18M.........+7LE 0 TE
The structure in question was somewhat unusual, being built partly over water of the IntraCoastal Waterway and 1,600 feet from the shoreline. Graphics linked below help depict the site, and set out in color-coded soil layers the Geotechnical Engineer’s recommendation that the Structural Engineer handle this site as one having three distinct strata of soil using three different soil parameters.
Soil tests taken in the water area at rear of the house and from locations on piers about 4 feet to 7 feet distant from footprint had disclosed 6’ and 8’ of unconsolidated muck at two boring locations, followed at both bore holes by 5’ of SPT-N 1-1-1-1.
Further layers below that were silty sand of progressively greater densities at one location (4-5-10-12 for five feet, then 8-10-13-20) and sand at another (12-13-14-17 then 12-16-17-19).
Links:
Below is a before and after graphic showing two profiles: to the left, the foundation which was removed; to the right, the foundation which replaced it.
The 20 piles located in the water area have exposed lengths ranging from 13’ to 18’ in height.
Any comments from the structural engineers in this forum about a point of fixity?
Any guesses about the bracing design (X-bracing? Batter piles? Other?) chosen by the project engineer who handled the most challenging assignment to move this house and install a new foundation while the house sat in the middle of a street?
