Schnabel Foundation Company

Transcription

1 Micropiles for Roadway Support, Bridge Abutments and Metal Signal Poles on US-158 from US-17B to East of Pasquotank River, in Elizabeth City, NC Schnabel Foundation Company Presenter: Stephen Dimino, P.E.

2 Owner -NCDOT Team Prime Contractor-Archer Western Construction Micropile Subcontractor-Schnabel Foundation Company

3

4

5 Project Overview Install micropiles to support the roadway, metal signal poles (MSP), bridge abutment and pump station The roadway and approach micropiles were installed through the concrete roadway deck Bridge micropiles were installed in the river MSP micropiles and the pump station piles were installed in foundation excavation.

6 Project Overview Install 258 Roadway Micropiles Install 16 Bridge Approach Micropiles Install 10 ea. Bridge Abutment Micropiles Install 4 Micropiles at 8 separate MSP foundations for a total of 32 piles. Install 8 Pump Station Support Micropiles Install 4 Generator Slab Support Micropiles Install 4 Electrical Building Micropiles

7 Roadway/Approach Piles Install 258 Roadway Micropiles 8-5/8 x 60 ft. casing with casing tip elevation of -52 ft. Bond length of 28 ft. Full length of corrosion protected Center bar Three sacrificial demonstration piles Fifteen proof tests on production piles

8

9

10 Bridge Piles Install 10 Bridge Abutment Micropiles 10-3/4 x 60 ft. casing with casing tip elevation of -58 ft. Bond length of 40 ft. Full length of corrosion protected center bar tied into pile cap One sacrificial demonstration piles Two proof tests on production piles

11

12 MSP Piles Install 32 Bridge Abutment Micropiles (4 each at 8 separate pile caps) 10-3/4 casing with casing tip elevation varies from -40 ft. to -58 ft. Bond length of 22 ft. Full length of corrosion protected center bar tied into pile cap One proof tests at each of the 8 pile caps

13

14 Pump Station Piles Install 16 Pump Station Micropiles 7 casing with casing tip elevation of -40 ft. Bond length of 20 ft. Full length of corrosion protected center bar tied into pile cap One proof tests at each of the 8 pile caps One demonstration test for the 7 piles

15

16 Design The permanent micropile design is in accordance with FHWA Implementation Manual for Micropile Design and Construction Guidelines (FHWA-SA ), dated June 2000 using the Load Factor Design (LFD) Method; AASHTO LRFD Bridge Design Specifications 2010; and The Recommendations of Prestressed Rock and Soil Anchors, PTI, In this design the micropiles are Type A micropiles

17 Design Design loads and test loads given in Contract Documents Roadway/Approach DL=25T (comp) TL=36T Bridge DL=50T (comp) TL=72T MSP DL=24T (comp) ;14T (tension) Specified casing diameter and thickness based on method of installation

18 Design The overburden soils were very soft/weak. The grout to ground bond strengths are per Table 6.3 in The Recommendations of Prestressed Rock and Soil Anchors, PTI, 2004, and AASHTO Table C The bond strengths of the soils of the pile above the minimum tip elevation shown the plans were neglected. Roadway and Approach Piles 3.8klf Bridge Piles 4.5klf MSP Piles 4.5klf

19

20 Issues

21

22 Design Grout mix design Use either of the two grouts: A neat mix of Portland Cement (Type I/II) and potable water at an approximate mix ratio of 5 to 6 gallons of water per cubic foot of grout. Minimum compressive strength at 28 days, fc=3,500 psi. An approved ready mix grout with a minimum compressive strength at 28 days, fc=3,500 psi

23 Testing Tested per ASTM D Quick Test Roadway Piles-The contract called for 3 Demonstration Tests and 15 Proof Tests. Roadway micropiles test load is 36T (72 kips) Bridge Piles-The contract called for 1 Demonstration Test and 2 Proof Tests. Bridge micropiles test load is 72T (144 kips) MSP Piles-The contract called for 1 Proof Test at each pile cap. MSP micropiles test load is 24T (48 kips)

24 Testing

25 Testing

26

27

28

29 Issues We had to stabilize the hole and the environmental requirements affected our planning Original method was not productive Constraints of working on road deck limited our work process Tight schedule due to MOT Changing methods is time consuming Working near the water

30 Overall view of jobsite

31 Construction Method lf x 11 dia. Continuous Flight Auger Drill down to depth and pump grout through auger Push casing and center bar down through plastic grout Main issue was that the auger walked and we could not put the casing in to depth Cleaning the fat clay off the auger took a long time.

32 Method 1 CFA installation

33 Method 1 CFA Installation

34 Method 1 CFA Installation

35 Construction Method 2 Drill down to pile tip elevation using the casing as the drill string Pump grout through the casing as the casing is pulled up to so that the bottom of casing matches pile tip elevation. The casing and grout stabilize the hole. Push bar through plastic grout. Hooking the casing up at the rotary head took a long time.

36 Method 2 Drilling with Casing

37 Method 2 Drilling with Casing

38 Method 2 Drilling with Casing

39 Construction Method 3 Vibrate casing down to casing tip elevation Drill through casing and down to pile tip elevation. Pump grout through drill string as we retracted the inner rod. Very successful in the soil type. We were able to use smaller equipment.

40 Drilling through the Vibrated Casing

41 Drilling through Vibrated Casing

42 Drilling through Vibrated Casing

43 Vibrated Piles at MSP Pile Cap

44 Completed MSP Micropiles

45