Pile Driving Issues. Mark McClelland, P.E. Geotechnical Branch Manager Texas DOT

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1 Pile Driving Issues Mark McClelland, P.E. Geotechnical Branch Manager Texas DOT

2 Goldilocks?? This soil it too hard This soil is too soft This soil is just right!

3 This soil is too hard Prestressed concrete piling will refuse to advance into soils with Texas Cone Penetrometer (TCP) values harder than 100 blows per foot (+/-).

4 Texas Cone Penetrometer Developed in Diameter hardened steel cone 170 Pound hammer, 24 drop 6 Penetration or 50 blows, and repeat

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8 Texas Cone Penetrometer Typical Values 2(6 ) - 3(6 ), Total 5 bpf (soft soil) 18(6 ) - 22(6 ), Total 40 bpf (stiff soil) 50(6 ) - 50(5 ), Total 100 blows/11 (Hard Soil, Soft Rock) 50(1 ) - 50(.5 ), Total 100 blows/1.5 (Hard Rock)

9 Why not just use a drilled shaft? Trestle pile interior bents are very cost effective. Some district like to offer both drilled shaft and pile alternates. But, it is generally better to use drilled shafts where significant amounts of 100+ bpf material are present.

10 If you decide to go ahead with piling Minimize the amount of penetration into the 100 bpf material. Add note to plans directing the contractor s s attention to the hard material. Be aware of Item 404, Driving Piling penetration requirements.

11 Item 404 Driving Piling B Penetration Drive piling to within 5 ft. of plan length unless other penetration requirements govern. For unusually hard driving conditions provide either pilot holes or jetting or a combination of both if plan penetration is not obtained.

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15 Item 404 Driving Piling The contractor/inspector can cut off 5 feet of pile if resistance, or more likely refusal, is met. If you need all of the length for stability or scour, you must add a minimum penetration note!

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19 Minimum Penetration Notes Interior bent piling shall be driven to a minimum tip elevation of xxx.x. or Interior bent piling shall be driven to the depth shown. No cut-offs will be allowed.

20 Cutoffs vs. Buildups Cutting off a concrete pile is not a complicated task. Building up a concrete pile is difficult, time consuming, expensive, and likely results in a lower quality finished product. When in doubt, too long is (much) better than too short!!

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22 This soil is too soft Prestressed concrete piling are the foundation of choice in soft soils. Some soils are sensitive to the disturbance associated with pile driving. These soils will lose strength during driving, but will recover in a relatively short period of time. This will result in low apparent dynamic driving resistance.

23 What to do? Be aware of the issue, particularly in silty materials, but also many clays. Some fine sands may show this as well. Consider test piling to establish K factor with 7-day 7 redrive. Even 1 or 2-day 2 redrives will often recover enough strength to accept the piling. Load tests in extreme cases.

24 K-Factor K Factor is a correction factor used to correlate Actual pile capacity to observed dynamic driving resistance. Actual pile capacity can be determined from static design method, pile redrive, load test, or combination of above. Most often the K factor is taken as the ratio of the redrive resistance to the initial driving resistance.

25 Recent Case History Soft Soils IH-10 Bridge over Trinity River

26 Bridge Foundation Facts 18 square prestressed concrete piling Loads (working) range from 75 tons/pile to 175 tons/pile Pile lengths range from 39 to 65 Main span piers on single, 88-pile footings Approach spans bents on two, 10-pile footings

27 Soil Conditions Alluvial deposits Highly variable soils across bridge site Surface soils soft clays and silts, loose sand, muck Deeper soils soft to medium clays and silty clays, medium sand, some packsand

28 Bent 2 History Turned out to be typical of many of the piling on this side of the river.

29 Pile Tip

30 Pile Driving commences Bent 2 Original stated design load was 90 tons per pile Initial driving resistances (Engineering News formula) range from 16 to 33 tons per pile One-day re-drives ranged from 55 to 100 ton per pile. Most tons

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32 Pile A Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /29/ /29/ Pile D Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /29/ /29/ Pile M Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /29/ /29/ Pile R Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /29/ /29/

33 Bent 2 Now what? Recheck original pile design calculations Capacity should be 100 tons +/- Look at Gates formula Approximately the same resistance. Look at Wave Equation analysis 10 15% better resistance. Stroke is very close for a given set, so model seems reasonable

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35 Bent 2 Now what? 7-day re-drive on two piling Pile tons for first inch, dropping to 93 tons at 6 inches and stabilizing at 93 tons per pile Pile tons for first inch, dropping to 65 tons at 6 inches and stabilizing at 60 tons per pile

36 Pile B Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ K factor 1st-3" 5.88 Pile L Date Hop Blows Distance in Bearing 12/28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /28/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ /5/ K factor 1st-3" 4.18

37 Bent 2 Initial driving gave poor results. 1-day re-drives on 18 piling showed significant increases in capacity, but none of the piling attained design load. 1-day re-drives measure driving data for the entire first foot of driving, not recording data for each inch. 7-day re-drives both gave good capacity initially, falling off dramatically as driving progressed. Data captured inch-by by-inch.

38 Bent 2 Conclusions Initial pile driving data is worthless. Soil is losing strength due to disturbance. 1-day re-drive is useful, but too soon to show full strength recovery. 7-day re-drive indicates pile capacities are good.

39 The rest of the story All footings on this side of bridge showed the same tendencies. All piling were left up for at least a 1-day 1 re-drive, with 2 per footing left for 7-day 7 re-drive where necessary. Worst footings had two piling added, turning 10-pile footings into 12-pile footings, thereby reducing load per pile.

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41 The rest of the rest of the story Decided to do some Statnamic Load Testing on selected piling. BOOOM!!!!

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43 Why Statnamic? They were in Texas, having just completed some drilled shaft testing in the Corpus Christi area. Minimal setup. No reaction piling, beam, jack, etc. Minimal delay to contractor.

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48 377 kip ultimate = 94 ton allowable (FOS = 2)

49 Pile Driving Issues Hard Driving: Don t t plan to penetrate far into 100+ bpf material. Include plan notes when necessary. Consider drilled shafts as option. Soft Driving Be aware of strength loss during driving. Understand how to develop and apply K-factor. K Consider test pile and load tests.

50 Bridge Division Geotechnical Branch Mark McClelland Marcus Galvan John Delphia Dina Dewane Scott Walton Fidencio Gonzalez