FHWA Hollow Bar Soil Nail (HBSN) Test Program Dr. Jesús Gómez, P.E. 36th Annual Conference on Deep Foundations, Boston, MA Outline Introduction and motivation Installation methods for testing Testing and results Conclusions 1
Hollow Core Bars Drill Bit Hollow Titan Bar Centralizer Coupling Bearing Plate Hex Nut Pipe Sleeve Hollow Core Bars Hollow Bar FLUSHING HEAD HOLLOW CORE BARS Cement grout The flushing grout cools the drill bit and increases the durability and efficiency. The flushing grout opens the bore hole and transports the soil out of the hole which is loosened by the drill bit. The grout suspension supports and prevents collapsing of the bore hole. 2
Grout Body 3. 1. Grout body of cement w/c = 0.4 red coloured, 2. Filter cake from flushing cement w/c = 0.8 green/grey coloured 3. Consolidated ground ground improvement Grout Body Consolidated ground Steel tendon Filter Cake from flushing grout w/c ~ 0.8 Final grout w/c ~ 0.4 3
Hollow Core Bars Great for granular formations Formations where casing is needed Faster installation in open areas Larger grout pressures Higher bond strength Can be installed in relatively hard formations Boulders Cost Corrosion protection Research Motivation HBSNs used very frequently How to debond for Proof and Verification Load Tests? What are typical bond strength values for HBSNs? Are they really higher than traditional, pre-drilled soil nails? Why? 4
Research Objectives Develop suitable installation procedure for Verification and Proof Load Test HBSNs. Develop suitable Verification and Proof Load Test testing protocol Increase database of grout-to-ground bond strength of HBSNs Correlation to published nominal values in FHWA-SA-96-069 Research Test HBSNs and pre-drilled soil nails in various sites across the US Try different procedures for debonding HBSNs Exhume nails after testing Compare results and develop recommendations 5
HBSN Installation Protocol: Method A Method A 6
Method A HBSN Installation Protocol: Method B 7
Installation of Casing (Method B) Unbonded Length (Method B) 8
Installation of HCB (Method B) Flushing and Extraction of Casing (Method B) 9
HBSN Installation Protocol: Method C Method D Only applied at one site Predrilled with hollow bar to depth of unbonded length Removed bar, let set Re-drilled to full length Flushed unbonded length 10
Installation of HBSN (Method C) Measurement of G S 11
Test Sites Site 1: City Creek Center, Block 76 (Block 76 Site), located in Salt Lake City, Utah Site 2: Posillico Storage Yard (Posillico Site), located in Bohemia, New York Site 3: Sunset Mesa Gravel Pit (Sunset Mesa Site), located in Montrose County, Colorado Site 4: DIS Wheeler Property (Olympia Site), located in Olympia, Washington Salt Lake City (Site 1) 12
Load Test Setup Typical test results Method A VERIFICATION SOIL NAIL LOAD TEST Hollow Core Bar Research - Salt Lake City, Utah Load (kips) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 0.0 0.2 0.4 0.6 0.8 Displacement (inches) 1.0 1.2 1.4 1.6 1.8 20 2.0 2.2 2.4 2.6 2.8 3.0 Load Test 0.8Lu 13
Typical Test Results Method B VERIFICATION SOIL NAIL LOAD TEST Hollow Core Bar Research - Salt Lake City, Utah Load (kips) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 0.0 0.2 0.4 0.6 0.8 Displacement (inches) 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 Load Test 0.8Lu Typical Test Results Method C VERIFICATION SOIL NAIL LOAD TEST Hollow Core Bar Research - Salt Lake City, Utah Load (kips) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 0.0 0.2 0.4 0.6 0.8 Displacement (inches) 1.0 1.2 1.4 1.6 1.8 20 2.0 2.2 2.4 2.6 2.8 3.0 Load Test 0.8Lu 14
Summary Grout-to-Ground Nominal Strengths Soil Type FHWA (2005) Rotary Drilled Grout-to-Ground Nominal Strengths / Jet Grouted psi (kpa) Installation Installation Installation Installation Method A Method B Method C Method D psi psi psi psi (kpa) (kpa) (kpa) (kpa) Silty Sand (SM) 14.5-21.8/55.1 (100-150)/(380) 12.8-17.1 (88-118) 18.7-24.4 (129-168) Not performed 17.8-23.7 (123-163) Poorly Graded 14.5-26.1/55.1 13.2 71.2-79.6 63.7-131.7 Sand (SP) (100-180)/ (380) (91) (491-549) (439-908) - SP with Gravel 14.5-26.1/101.5 (100-180)/ (700) 50.5-82.2 (348-567) - - - GP with Sand 14.5-26.1/101.5 (100-180)/ (700) 53.2-64.5 (367-445) 62.4-156.3 (430-1059) 116.9-155.7 (806-1074) - Exhumed nails in Montrose, CO 15
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Exhumed nails in Long Island Diameter = 7¾ At 1.5 from bottom of nail Diameter = 6¼ At 4 from bottom of nail. 2 jump in grout height at 6-9 from bottom of nail. Diameter = 9 At 7 from bottom of nail. 0-0 to 4-6 Grout appears to be smooth. No visible signs of cracking. Some rocks from soil adhered to the grout. 4-6 to 6-9 Grout has a rough texture. Project Title Hollow Core Bar Research Excavation of Soil Nails Project Number 07150064 17
Diameter = 10¼ At 10 from bottom of nail 3 horizontal bulge at 10 from bottom of nail. 2 drop in grout height at 11-8 from bottom of nail. Hairline crack from 12-2 to 13-5. Larger cracks and breaks from 13-5 to 16-4. Diameter = 8 At 13.5 from bottom of nail 6-9 to 9-5 Grout body diameter increased. 9-5 to 11-10 Bulge in grout. Rocks from soil adhered to the grout. 12-2 to 16-4 Grout cracked and broken. Project Title Hollow Core Bar Research Excavation of Soil Nails Project Number 07150064 Debonding Ax xial load from gauge (ki ip) 35.0 30.0 25.0 20.0 15.0 10.0 50 5.0 Test Nail B1 Test Nail C2 Test Nail D2 0.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Jack load (kip) 18
Conclusions Ultimate bond strength of hollow core bars in granular soils may be significantly ifi larger than in pre-drilled nails About same values in fine-grained soils Debonding can be achieved efficiently Methods d B and D debonding di preferred Method A 19
Installation of 7 in casing and No 14 Bar (Method A) Tremie Grouting and Verification of grout level (Method A) 20
Extraction of Casing (Method A) Montrose- Summary 21
Other sites Montrose, Colorado. Hogback County Gravel Pit. Contractor: t Mountain Highwall Concrete, TEI Rock Drills Bohemia, Long Island. Posillico Group Yard. Contractor: Peterson Geotechnical Construction, LLC, Posillico Group Salt Lake City- Summary 22
Long Island- Summary HBSN Characteristics 23
Installation of HBSN (Method C) PVC PV appears to C be cut. 12 gap in PVC from 16 to 17 from bottom of nail. Nail bent 12½ from designed location. Grout exists in the annular space between the hollow core bar and the PVC. After observations were recorded, grout was chipped away from the nail. The end of the PVC was discovered at 15-3.5 from top of nail (6-10.5 from bottom of nail). 12-2 to 16-4 Grout cracked and broken. 16-4 to 18-0 PVC visible. 18-0 to 22-2 Hollow core bar visible. Some surface corrosion observed. Project Title Hollow Core Bar Research Excavation of Soil Nails Project Number 07150064 24
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