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OCR for page 99
B-1
APPENDIX B
Proposed LRFD Construction Specifications
for Soil Nail Walls
TABLE OF CONTENTS
1.1 DESCRIPTION .............................................................................................................................................. B-3
1.2 MATERIALS.................................................................................................................................................. B-3
1.2.1 Facing ............................................................................................................................................... B-3
1.2.1.1 Cast-in-place Concrete ................................................................................................... B-3
1.2.1.2 Reinforcing Steel ............................................................................................................ B-3
1.2.1.3 Permanent Shotcrete ....................................................................................................... B-3
1.2.1.4 Architectural Surface Finishes ....................................................................................... B-3
1.2.2 Soil Nails .......................................................................................................................................... B-3
1.2.2.1 Solid Soil Nail Bar .......................................................................................................... B-3
1.2.2.2 Bar Coupler..................................................................................................................... B-4
1.2.2.3 Fusion-Bonded Epoxy Coating ...................................................................................... B-4
1.2.2.4 Encapsulation.................................................................................................................. B-4
1.2.3 Soil Nail Appurtenances ................................................................................................................... B-4
1.2.3.1 Centralizer ...................................................................................................................... B-4
1.2.3.2 Grout ............................................................................................................................... B-4
1.2.3.3 Fine Aggregate................................................................................................................ B-4
1.2.3.4 Portland Cement ............................................................................................................. B-4
1.2.3.5 Admixtures ..................................................................................................................... B-5
1.2.3.6 Film Protection ............................................................................................................... B-5
1.2.4 Bearing Plates, Nuts, and Head-Stud Shear Connectors .................................................................. B-5
1.2.4.1 Bearing Plates ................................................................................................................. B-5
1.2.4.2 Nuts................................................................................................................................. B-5
1.2.4.3 Shear Connectors ............................................................................................................ B-5
1.2.5 Welded-Wire Mesh........................................................................................................................... B-5
1.2.6 Reinforcing Steel .............................................................................................................................. B-5
1.2.7 Geocomposite Sheet Drain ..............................................................................................................B-5
1.2.8 Underdrain and Perforated Pipe........................................................................................................ B-6
1.2.8.1 Pipe ................................................................................................................................. B-6
1.2.8.2 Fittings ............................................................................................................................ B-6
1.2.9 Temporary Shotcrete ........................................................................................................................ B-6
1.3 CONTRACTOR QUALIFICATIONS ........................................................................................................... B-6
1.4 SUBMITTALS ............................................................................................................................................... B-6
1.4.1 Personnel .......................................................................................................................................... B-6
1.4.2 Surveys ............................................................................................................................................. B-7
1.4.3 Construction Plan ............................................................................................................................. B-7
1.5 STORAGE AND HANDLING ...................................................................................................................... B-8
EXCAVATION .............................................................................................................................................. B-8
1.6
1.7 SOIL NAIL INSTALLATION ....................................................................................................................... B-9
1.8 GROUTING.................................................................................................................................................... B-9
1.9 SOIL NAIL TESTING ................................................................................................................................... B-9
1.9.1 Tests.................................................................................................................................................. B-9
1.9.2 Equipment......................................................................................................................................... B-9
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B-2
Section xx – Soil Nail Walls
1.10 VERIFICATION TESTING .........................................................................................................................B-10
1.10.1 Methods ..........................................................................................................................................B-10
1.10.2 Schedule .........................................................................................................................................B-10
1.11 PROOF TESTING ........................................................................................................................................B-11
1.11.1 Methods ..........................................................................................................................................B-11
1.11.2 Schedule .........................................................................................................................................B-12
1.12 ACCEPTANCE CRITERIA OF TEST SOIL NAILS .................................................................................B-13
1.13 REJECTION OF TEST SOIL NAILS ..........................................................................................................B-13
1.13.1 Verification Test Soil Nails ............................................................................................................ B-13
1.13.2 Proof Test Soil Nails....................................................................................................................... B-13
1.14 WALL DRAINAGE NETWORK ................................................................................................................ B-14
1.14.1 Geocomposite Drain Strips............................................................................................................. B-14
1.14.2 Footing Drains ................................................................................................................................ B-14
1.15 SHOTCRETE FACING................................................................................................................................ B-14
1.15.1 Final Face Finish ............................................................................................................................ B-14
1.15.2 Attachment of Nail Head Bearing Plate and Nut ............................................................................B-15
1.15.3 Shotcrete Facing Tolerances........................................................................................................... B-15
1.16 REINFORCING STEEL............................................................................................................................... B-15
1.17 STRUCTURAL CONCRETE ...................................................................................................................... B-15
1.18 ARCHITECTURAL SURFACE FINISHES................................................................................................ B-15
1.19 BACKFILLING BEHIND WALL FACING UPPER CANTILEVER ........................................................B-16
1.20 ACCEPTANCE ............................................................................................................................................B-16
2.0 MEASUREMENT AND PAYMENT ..........................................................................................................B-16
2.1 SOIL NAILS.................................................................................................................................................B-16
2.2 STRUCTURE EXCAVATION .................................................................................................................... B-17
2.3 WALL FACE................................................................................................................................................B-17
2.4 PAYMENT ...................................................................................................................................................B-17
2.4.1 Pay Items ........................................................................................................................................B-17
3.0 CORROSION PROTECTION......................................................................................................................B-18
REFERENCES ........................................................................................................................................................B-18
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.1 DESCRIPTION C1.1
This work consists of constructing a permanent soil nail wall The Owner may choose to have the Contractor design and
as specified herein and as shown on the Plans. The Contractor construct the work at the location shown on the drawings. The
shall furnish all labor, materials, and equipment required to Contractor shall furnish all labor, plans, drawings, design
complete the work. The Contractor shall select the excavation, calculations, and all other material and equipment required to
drilling, and grouting methods and the diameter of the drill-holes design and construct the soil nail wall(s) in accordance with
to meet the performance requirements specified herein or shown this Specification.
on the Plans. Project-specific needs may require a different type of facing
including reinforced shotcrete, cast-in-place concrete, and
The work shall include excavating in staged lifts in accordance
precast concrete panels.
with the approved Contractor’s plan; detailing the drilling of the
soil nail drill-holes to the diameter and length required to
develop the specified resistance; grouting the soil nails;
providing and installing the specified drainage features;
providing and installing bearing plates, washers, nuts, and other
required miscellaneous materials; and constructing the required
temporary shotcrete face and constructing the final structural
facing.
1.2 MATERIALS
1.2.1 Facing
Facing material shall conform to the following sections and
subsections.
1.2.1.1 Cast-in-place Concrete
Cast-in-place (CIP) concrete shall meet the requirements of
Section 5 of the AASHTO LRFD Bridge Construction
Specifications.
1.2.1.2 Reinforcing Steel
Reinforcing steel shall meet the requirements of Section 6
of the AASHTO LRFD Bridge Construction Specifications.
1.2.1.3 Permanent Shotcrete
Permanent shotcrete shall meet the requirements of Section
24, “Pneumatically Applied Mortar,” of the AASHTO LRFD
Bridge Construction Specifications.
1.2.1.4 Architectural Surface Finishes
Architectural surface finishes may include textured surfaces or
a surface finish with color/stain application.
1.2.2 Soil Nails
1.2.2.1 Solid Soil Nail Bar C1.2.2.1
Solid nail bars shall meet the requirements of AASHTO M Bars of A 722, Grade 1035, should not be used in
31/ASTM A 615, Grade 420 or 520, or ASTM A 722 for Grade conventional soil-nailing applications because the material
1035. Soil nail bars shall be continuous without splices or welds, tends to be more brittle and more susceptible to stress corrosion
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
new, straight, undamaged, bare or epoxy coated, or encapsulated than the more commonly used lower-grade steels.
as shown on the Plans. Bars shall be threaded a minimum of Threading may be a continuous spiral, deformed ribbing
150 mm on the wall anchorage end, to allow proper attachment provided by the bar deformations (continuous thread bars), or
of the bearing plate and nut. If threads are cut into a soil nail may be cut into a reinforcing bar.
bar, provide the next larger bar number designation than what is
shown on the Plans, at no additional cost.
1.2.2.2 Bar Coupler
Bar couplers shall develop the full nominal tensile capacity of
the soil nail bars as certified by the manufacturer.
1.2.2.3 Fusion-Bonded Epoxy Coating C1.2.2.3
Fusion-bonded epoxy coating shall meet the requirements of The coating at the wall anchorage end of epoxy-coated soil
ASTM A 775 and have a minimum thickness of 0.4 mm (0.016 nail bars may be omitted over this length provided for threading
in.) as applied electrostatically. Bend test requirements are the nut against the bearing plate.
waived.
1.2.2.4 Encapsulation
Bar encapsulation shall be a minimum 1-mm (0.04-in.) thick,
corrugated, HDPE tube conforming to AASHTO M 252, or
corrugated PVC tube conforming to ASTM D 1784, Class
13464-B.
1.2.3 Soil Nail Appurtenances
1.2.3.1 Centralizer
Centralizers shall be manufactured from Schedule 40 PVC
pipe or tube, steel, or other material not detrimental to the soil
nail steel bar. Wood shall not be used. Centralizers shall be
securely attached to the soil nail bar and shall be sized to allow:
(a) position the soil nail bar within 25 mm (1 in.) of the center of
the drill-hole; (b) tremie pipe insertion to the bottom of the drill-
hole; and (c) grout to freely flow up the drill-hole.
1.2.3.2 Grout
Grout shall be a neat cement or sand/cement mixture with a
minimum 3-day compressive strength of 10.5 MPa (1,500 psi)
and a minimum 28-day compressive strength of 21 MPa (3,000
psi), meeting the requirements of AASHTO T 106/ASTM C
109.
1.2.3.3 Fine Aggregate
Fine aggregate for grout and/or shotcrete shall meet the
requirements of AASHTO M 6/ASTM C 33.
1.2.3.4 Portland Cement
Portland cement for grout and/or shotcrete shall meet the
requirements of AASHTO M 85/ASTM C 150, Type I, II, III, or
V.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.2.3.5 Admixtures C1.2.3.5
Admixtures shall meet the requirements of AASHTO M Admixtures that control bleed, improve flowability, reduce
194/ASTM C 494. Admixtures shall be compatible with the water content, and retard set may be used in the grout subject to
grout and mixed in accordance with the manufacturer’s review and acceptance by the Engineer. Accelerators are not
recommendations. permitted. Expansive admixtures may only be used in grout
used for filling sealed encapsulations.
1.2.3.6 Film Protection
Polyethylene film for moisture loss control shall meet the
requirements of AASHTO M 171.
1.2.4 Bearing Plates, Nuts, and Head-Stud Shear
Connectors
1.2.4.1 Bearing Plates C1.2.4.1
Bearing plates shall meet the requirements of AASHTO M For nominal resistance of bearing plates refer to Article
183/ASTM A 36. 5.10.9.7.2 of the AASHTO LRFD Bridge Design
Specifications.
1.2.4.2 Nuts
Nuts shall meet the requirements of AASHTO M 291, Grade
B, hexagonal, and fitted with beveled washer or spherical seat to
provide uniform bearing.
1.2.4.3 Shear Connectors C1.2.4.3
Shear connectors of the soil nail head may consist of headed- See Article 11.3.3.1 of the AASHTO LRFD Bridge
studs, threaded bolts, etc. Construction Specifications.
1.2.5 Welded-Wire Mesh
Welded wire mesh shall meet the requirements of AASHTO
M 55/ASTM A 185 or A 497.
1.2.6 Reinforcing Steel
Reinforcing steel shall meet the requirements of AASHTO M
31/ASTM A 615, Grade 420, deformed.
1.2.7 Geocomposite Sheet Drain
Geocomposite sheet drain shall be manufactured with a
drainage core (e.g., geonet) and a drainage geotextile attached to
or encapsulating the core. Drainage core shall be manufactured
from long-chain synthetic polymers composed of at least 85
percent by mass of polypropylenes, polyester, polyamine,
polyvinyl chloride, polyoleofin, or polystyrene and have a
minimum compressive strength of 275 kPa (40 psi) when tested
in accordance with ASTM D 1621 Procedure A. The drainage
core with the geotextile fully encapsulating the core shall have a
minimum flow rate of 1 liter per second per meter of width
tested in accordance with ASTM D 4716. The test conditions
shall be under an applied load of 69 kPa (10 psi) at a gradient of
1.0 after a 100-hour seating period.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.2.8 Underdrain and Perforated Pipe
1.2.8.1 Pipe
Underdrain and perforated pipe shall meet the requirements of
ASTM 1785 Schedule 40 PVC solid and perforated wall; cell
classification 12454-B or 12354-C, wall thickness SDR 35, with
solvent weld or elastomeric joints.
1.2.8.2 Fittings
Fittings for underdrain and perforated pipe shall meet the
requirements of ASTM D 3034, Cell classification 12454-B or
C, wall thickness SDR 35, with solvent or elastomeric joints.
1.2.9 Temporary Shotcrete
All materials, methods, and control procedures for temporary
shotcrete shall be submitted to the Owner’s Engineer for review
and approval.
1.3 CONTRACTOR QUALIFICATIONS
The soil-nailing contractor shall meet the following
qualification require ments:
1. Completed at least three permanent soil nail wall projects
during the past three years totaling at least 1,000 m2
(10,000 ft2) of soil nail wall face area and at least 500
permanent soil nails.
2. Provide a Registered Professional Engineer with
experience in the construction of permanent soil nail
walls on at least three completed projects over the past
three years.
3. Provide on-site supervisors and drill operators with
experience installing permanent soil nail walls on at least
three projects over the past three years.
4. Submit a brief description of at least three projects,
including the owning agency’s name, address, and current
phone number; location of project; project contract value;
and scheduled completion date and completion date for
the project.
1.4 SUBMITTALS
1.4.1 Personnel
At least 60 calendar days before starting soil nail work, submit
names of the Engineer, on-site supervisors, and drill operators
assigned to the project, and a summary of each individual’s
experience. Only those individuals designated as meeting the
qualification requirements shall be used for the project. The
Contractor cannot substitute any of these individuals without
written approval of the Owner or the Owner’s Engineer. The
Owner’s Engineer shall approve or reject the Contractor
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B-7
Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
qualifications and staff within 15 working days after receipt of
the submission. Work shall not be started nor materials ordered
until the Contractor’s qualifications have been approved by the
Owner’s Engineer. The Owner’s Engineer may suspend the
work if the Contractor substitutes unqualified personnel for
approved personnel during construction. If work is suspended
due to the substitution of unqualified personnel, the Contractor
shall be fully liable for all additional costs resulting from the
suspension of work, and no adjustment in contract time resulting
from the suspension of the work shall be allowed.
1.4.2 Surveys
The Contractor shall be responsible for providing the
necessary survey and alignment control during the excavation
for each lift, locating drill-holes and verifying limits of the soil
nail wall installation.
1.4.3 Construction Plan C1.4.3
At least 30 days before starting soil nail work, the Contractor In a performance type contract, the Contractor must select
shall submit a Construction Plan to the Owner’s Engineer that one of the specialty contractors listed in the documents and
includes the following. shall identify the specialty contractor on his proposal at the bid
opening. No substitution will be permitted without written
1. Project start date and proposed detailed wall construction approval of the Owner’s Engineer. Substitution after the bid
sequence. opening will not be grounds for changes in bid prices.
2. Drilling and grouting methods and equipment, including Under a performance type contract, the design of soil nail
the drill-hole diameter proposed to achieve the specified walls shall be based on geotechnical data and project
requirements provided by the Owner including but not limited
nominal pullout resistance values shown on the Plans and
to soil/rock nominal shear strength parameters, slope and
any variation of these along the wall align ment.
external surcharge loads, seismic design coefficient, type of
3. Nail grout mix design, including compressive strength
wall facing, architectural treatment, corrosion protection
test results (per AASHTO T 106/ASTM C 109) supplied
requirements, easements, and rights-of-way.
by a qualified independent testing lab verifying the
specified minimum 3-day and 28-day grout compressive
strengths.
4. Nail grout placement procedures and equipment.
5. Temporary shotcrete materials and methods.
6. Soil nail testing methods and equip ment setup.
7. Identification number and certified calibration records for
each test jack, pressure gauge, dial gauge and load cell to
be used. Jack and pressure gauge shall be calibrated as a
unit. Calibration records shall include the date tested, the
device identification number, and the calibration test
results and shall be certified for an accuracy of at least 2
percent of the applied certification loads by a qualified
independent testing laboratory within 90 days prior to
submittal.
8. Manufacturer Certificates of Compliance for the soil nail
ultimate strength, nail bar steel, Portland cement,
centralizers, bearing plates, epoxy coating, and
encapsulation
9. The Owner’s Engineer shall approve or reject the
Contractor’s Construction Plan within 30 working days
after the submission. Approval of the Construction Plan
does not relieve the Contractor of his responsibility for
the successful completion of the work.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
At least 45 days before the planned start of the wall
excavation, the Contractor shall submit complete design
calculations and working drawings to the Owner’s Engineer for
review and approval. Include all details, dimensions, quantities,
ground profiles and cross-sections necessary to construct the
wall. The Contractor shall verify the limits of the wall and
ground survey data before preparing the drawings. The working
drawings shall be prepared to the (Agency) standards. The
Owner’s Engineer will approve or reject the Contractor’s
submittals within 30 calendar days after the receipt of the
complete submission. The Contractor shall not begin
construction or incorporate materials into the work until the
submittal requirements are satisfied and found acceptable to the
Owner’s Engineer.
1.5 STORAGE AND HANDLING
Soil nail bars shall be stored and handled in a manner to avoid
damage or corrosion. Soil nail bars exhibiting abrasions, cuts,
welds, weld splatter, corrosion, or pitting shall be replaced. Bars
exhibiting damage to encapsulation or epoxy coating shall be
repaired or replaced at no additional cost. Repaired epoxy
coating areas shall have a minimum 0.3-mm (0.012-in.) thick
coating.
C1.6
1.6 EXCAVATION
For construction on side hills, a minimum 5-m (15-ft) wide
The height of exposed unsupported final excavation face cut
working bench is required for adequate drill rig access.
shall not exceed the vertical nail spacing plus the required
Shotcrete application may be delayed up to 24 hours if the
reinforcing lap or the short-term stand-up height of the ground,
contractor can demonstrate that the delay will not adversely
whichever is less. Excavation to the final wall excavation line
affect the excavation face stability.
and shotcrete application shall be completed in the same work
shift, unless otherwise approved by the Owner’s Engineer.
Excavation of the next-lower lift shall not proceed until soil
nail installation, reinforced shotcrete placement, attachment of
bearing plates and nuts, and nail testing have been completed
and accepted in the current lift. Nail grout and shotcrete shall
have cured for at least 72 hours or attained at least their specified
3-day compressive strength before excavating the next
underlying lift.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.7 SOIL NAIL INSTALLATION C1.7
The soil nail length and drill-hole diameter necessary to The use of self-drilling soil nail bars (also known as hollow,
develop the load capacity and to satisfy the acceptance criteria self-grouting or pressure-grouted nail bars) are not allowed for
for the design load required shall be provided, but they shall be permanent construction, unless approved by the Owner.
not less than the lengths or diameters shown in the Plans.
Drill-holes for the soil nails shall be drilled at the locations,
elevations, orientations, and lengths shown on the Plans. The
drilling equipment and methods shall be selected to be suitable
for the ground conditions and in accordance with the accepted
installation methods submitted by the Contractor. The use of
drilling mud or other fluids to remove cuttings will not be
allowed. If caving ground is encountered, cased drilling
methods shall be used to support the sides of the drill-holes. Soil
nail bars shall be provided as shown in the Plans.
Centralizers shall be provided and sized to position the soil
nail bars to within 25 mm (1 in.) of the center of the drill-hole.
Centralizers shall be positioned as shown on the Plans so that
their maximu m center-to-center spacing does not exceed 2.5 m
(8.2 ft) and shall be located to within 0.5 m (1.5 ft) from the top
and bottom of the drill-hole.
1.8 GROUTING
The drill-hole shall be grouted after installation of the soil nail
bar and within 2 hours of completion of drilling. The grout shall
be injected at the lowest point of each drill-hole through a grout
tube, casing, hollow-stem auger, or drill rods. The outlet end of
the conduit shall deliver grout below the surface of the grout as
the conduit is withdrawn to prevent the creation of voids. The
drill-hole shall be filled in one continuous operation. Cold joints
in the grout column shall not be allowed except at the top of the
test bond length of proof tested production nails.
Grout shall be tested in accordance with AASHTO T
106/ASTM C 109 at a frequency of one test per mix design and
a minimu m of one test for every 40 m3 (52 cy) of grout placed.
Grout cube test results shall be provided to the Owner’s
Engineer within 24 hours of testing.
1.9 SOIL NAIL TESTING
1.9.1 Tests
The Contractor shall perform both verification and proof
testing of designated test soil nails. Verification tests on
sacrificial test nails shall be conducted at locations shown on the
Plans. Proof tests on production nails shall be conducted at
locations selected by the Owner’s Engineer. Testing of any nail
shall not be performed until the nail grout and shotcrete facing
have cured for at least 72 hours or attained at least their specified
3-day compressive strength.
1.9.2 Equipment
Testing equipment shall include 2 dial gauges, dial gauge
support, jack and pressure gauge, electronic load cell, and a
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
reaction frame. The pressure gauge shall be graduated in 500
kPa (75 psi) increments or less. Nail head movement shall be
measured with a minimum of 2 dial gauges capable of measuring
to 0.025 mm (0.001 in.).
1.10 VERIFICATION TESTING
Verification testing shall be conducted prior to installation of
production soil nails on sacrificial soil nails to confirm the
appropriateness of the Contractor’s drilling and installation
methods, and verify the required nail pullout resistance.
C1.10.1
1.10.1 Methods
At least two verification tests should be conducted in each
The verification tests must be conducted on nails of the same
soil strata in which it is anticipated that nail bond zone will be
design and constructed with the same construction methods to be
grouted.
used on production nails for meaningful results.
Where possible, verification tests should be conducted to
Verification test nails shall have both bonded and unbonded
failure to establish a maximum resistance with respect to
lengths. The nail bar shall not be grouted along the unbonded
pullout.
length. The unbonded length of the test nails shall be at least 1
m (3 ft). The bonded length of the soil nail during verification
tests, LB VT, shall be the smaller value of the following range:
The maximum length for verification tests, LB VT max, is
3 m (10 ft)
LB VT = greater of selected so that the nail load does not exceed 90 percent of
LB VT max
factored nominal tensile resistance of the soil nail bar during
the verification test.
The maxi mum length, LB VT max, is defined as:
C RT × At × f Y × φT −VT
LB VT max =
rPO × φPO
where:
CRT = reduction coefficient;
At = cross-sectional area of soil nail bar;
Use CRT = 0.9 for 420 and 520 MPa (Grade 60 and 75) bars.
fY = nominal yield resistance of soil nail bar;
If 1,035 MPa (Grade 150) soil nail bars are allowed in the job,
rPO = nominal pullout resistance (per unit length) of
use CRT = 0.8.
soil nail, as specified herein or in Plans;
φT-VT = resistance factor for soil nail in tension in
In verifications tests, select φT-VT = 0.4 or, preferably, 0.33.
verification tests; and
Select φPO based on Table 11.5.6-1, “Resistance Factors,” of
φPO = resistance factor for soil nail pullout.
AAHTO LRFD Bridge Design Specifications. For preliminary
values, use φPO = 0.5.
The maximum bonded length shall be preferably based on
The selection of φT-VT during verification tests should be
production nail maximum bar grade. Larger bar sizes shall be
provided at no additional cost, if required, to meet the 3-m (10- consistent with the maximu m test load that has been selected
ft) minimum test bonded length require ment. for the verification test. The maximu m load depends on the
selected φPO and must be selected such that the test bars are not
The Design Load during the verification test, DL, shall be overstressed during the test.
calculated based on as-built bonded lengths, as follows:
DL = LB VT × rPO ×φPO
1.10.2 Schedule C1.10.2
Verification tests shall be conducted by incrementally loading
the verification test nails to failure or a maximum test load of
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
200 percent of the DL in accordance with the following loading
schedule. The Contractor shall record soil nail movements at
each load increment.
In soils that are susceptible to creep, extended creep tests
beyond the tests required by these specifications should be
Verification Test Loading Schedule
conducted based on PTI (2005) methods. The alignment load,
Load Hold Time
AL, should be the minimum load required to align the testing
0.05 DL max. apparatus and should not exceed 5 percent of the DL.
1 minute
(= alignment load, AL)
0.25 DL 10 minutes In projects, for which there is no local experience in soil
nailing or the degree of uncertainty in the pre-selected nominal
0.50 DL 10 minutes
pullout resistance (per unit length) values is significant, the
0.75 DL 10 minutes
Owner or the Owner’s Engineer may require the Contractor to
1.00 DL 10 minutes
perform verification tests up to a maximum test load of 300
1.25 DL 10 minutes
percent of the DL in the tests. For these situations, the loading
1.50 DL (Creep Test) 60 minutes shall be performed according to the schedule below:
1.75 DL 10 minutes
2.00 DL 10 minutes Additional Verification Test Loading Schedule
1 minute (record
0.05 DL max. (AL) Load Hold Time
permanent set)
From AL to 2.00 DL (or as shown
Load levels beyond 200 percent of DL are optional. Failure) previously
Dial gauges shall be set to “zero” after the alignment load has 2.50 DL (optional) 10 minutes
been applied. Following application of the maximum load (3.0 ×
3.0 DL (optional) 10 minutes
DL), the load shall be reduced to the alignment load (0.05 × DL
1 minute (record
maximum) and the permanent set shall be recorded. 0.05 DL max. (AL)
permanent set)
Each load increment shall be held for at least 10 minutes. The
verification test nail shall be monitored for creep at the 1.50 ×
DL load increment. Nail movements shall be measured and
recorded during the creep portion of the test in increments of 1,
2, 3, 5, 6, 10, 20, 30, 50, and 60 minute(s). The load shall be
maintained during the creep test to within 2 percent of the
intended load by use of a load cell.
1.11 PROOF TESTING C1.11
Successful proof testing shall be demonstrated on at least 5
percent of production soil nails in each nail row or a minimum of
one per row. The Owner’s Engineer shall determine the
locations and number of proof tests prior to nail installation in
each row.
C1.11.1
1.11.1 Methods
The unbonded length is temporary because this length is
Production proof test nails shall have both bonded and
grouted after the proof test is completed.
temporary unbonded lengths. The unbonded length of the test
nail shall be at least 1 m (3 ft). The bonded length of the soil
nail during proof production tests, LB PT, shall be at least 3 m
(10 ft) but not longer than a maximum length, LB PT max. The maximum length for proof tests, LB PT max, is selected so
Therefore, the following requirements shall be met: that the nail load does not exceed 90 percent of factored
nominal tensile resistance of the soil nail bar during the proof
test.
3 m (10 ft)
LB PT = greater of
LB PT max
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
The maxi mum length LB PT max is defined as:
C RT × At × f Y × φT − PT
LB PT max =
rPO × φPO
where: Use CRT = 0.9 for 420 and 520 MPa (Grade 60 and 75) bars.
If 1,035 MPa (Grade 150) soil nail bars are allowed in the job,
CRT = reduction coefficient; use CRT = 0.8.
At = cross-sectional area of soil nail bar;
In proof tests, select φT-PT = 0.67. Select φPO based on Table
fY = nominal yield resistance of soil nail bar;
rPO = nominal pullout resistance (per unit length) of 11.5.6-1, “Resistance Factors,” of AAHTO LRFD Bridge
soil nail, as specified herein or in Plans; Design Specifications. For preliminary values, use φPO = 0.5.
φT-PT = resistance factor for soil nail in tension in
proof tests; and The selection of φT-PT during proof tests should be consistent
φPO = resistance factor for soil nail pullout. with the maximum test load that has been selected for these
tests. The maximum load depends on the selected φPO and must
be selected such that the test bars are not overstressed during
The Design Load during the verification test, DL, shall be
the test. This is usually 1.5 DTL. Avoiding bar overstressing
calculated based on as-built bonded lengths, as follows:
during the test allows using the test bars as production bars
after the test.
LB PT × rPO ×φPO
DL =
Production proof test nails shorter than 4 m (12 ft) may be
constructed with less than the minimum 3-m (10-ft) bond
length.
1.11.2 Schedule C1.11.2
Proof tests shall be conducted by incrementally loading the The alignment load, AL, should be the minimum load
proof test nail to 150 percent of DL in accordance with the required to align the testing apparatus and should not exceed 5
following loading schedule. Soil nail movements shall be percent of the DL.
recorded at each load increment.
Proof Test Loading Schedule
Load Hold Time
0.05 DL max. (AL) Until Movement Stabilizes
0.25 DL Until Movement Stabilizes
0.50 DL Until Movement Stabilizes
0.75 DL Until Movement Stabilizes
1.00 DL Until Movement Stabilizes
1.25 DL Until Movement Stabilizes
1.50 DL (Max. Test Load) Creep Test (see below)
Dial gauges shall be set to “zero” after the alignment load has
been applied.
The creep period shall start as soon as the maximum test load
(1.50 × DL) is applied and the nail movement shall be measured
and recorded at 1, 2, 3, 5, 6, and 10 minute(s). Where the nail
movement between 1 minute and 10 minutes exceeds 1 mm
(0.04 in.), the maximum test load shall be maintained for an
additional 50 minutes and nail movements shall be recorded at
20, 30, 50, and 60 minutes. All load increments shall be
maintained to within 5 percent of the intended load.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.12 ACCEPTANCE CRITERIA OF TEST SOIL
NAILS
A test nail shall be considered acceptable when all of the
following criteria are met:
1. For verification tests, the total creep movement is less
than 2 mm (0.08 in.) between the 6- and 60-minute
readings, and the creep rate is linear or decreasing
throughout the creep test load hold period.
2. For proof tests, the total creep movement is less than 1
mm (0.04 in.) during the 10-minute readings or the total
creep movement is less than 2 mm (0.08 in.) during the
60-minute readings, and the creep rate is linear or
decreasing throughout the creep test load hold period.
3. For verification and proof tests, the total measured
movement at the maximu m test load exceeds 80 percent
of the theoretical elastic elongation of the unbonded
length of the test nail.
A pullout limit state does not occur at 2.0 × DL under
4.
verification testing and 1.5 × DL test load under proof
testing. Pullout limit state is defined at a load level at
which the test load cannot be further increased while
there is continued pullout movement of the test nail. The
load at the pullout limit state shall be recorded as part of
the test data.
5. Maintaining stability of the temporary unbonded test
length for subsequent grouting is the Contractor’s
responsibility. If the unbonded test length of production
proof test nails cannot be satisfactorily grouted after
testing; the proof test nail shall become sacrificial and
shall be replaced with an additional production nail
installed at no additional cost to the Owner.
1.13 REJECTION OF TEST SOIL NAILS
1.13.1 Verification Test Soil Nails
The Owner’s Engineer will evaluate the results of each
verification test. Installation methods that do not satisfy the nail
testing requirements shall be rejected. The Contractor shall
propose alternative methods for review by the Owner’s Engineer
and shall install replacement verification test nails. Replacement
test nails shall be installed and tested at no additional cost.
1.13.2 Proof Test Soil Nails
For proof test nails, the Owner’s Engineer may require the
Contractor to replace some or all of the installed production nails
between a failed proof test soil nail and the adjacent passing
proof test nail. Alternatively, the Owner’s Engineer may require
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
the installation and testing of additional proof test nails to verify
that adjacent previously installed production nails have sufficient
nominal pullout resistance. Installation and testing of additional
proof test nails or installation of additional or modified nails as a
result of proof test nail failure(s) shall be at no additional cost.
1.14 WALL DRAINAGE NETWORK
All elements of the soil nail wall drainage network shall be
installed and secured as shown on the Plans. The drainage
network shall consist of geocomposite drain strips, PVC
connection pipes, soil nail wall footing drains, and weepholes, as
shown on the Plans. Exclusive of the wall footing drains, all
elements of the drainage network shall be installed prior to
shotcreting.
1.14.1 Geocomposite Drain Strips
Geocomposite drain strips shall be centered between the
columns of soil nails, as shown on the Plans. Drain strips shall
be at least 300 mm (12 in.) wide and placed with the geotextile
side against the ground. Strips shall be secured to the excavation
face. Contamination of the geotextile with shotcrete shall be
prevented. Drain strips shall be vertically continuous. Splices
shall be made with a 300 mm (12 in.) minimum overlap such
that the flow of water is not impeded. Drain plate and connector
pipe shall be installed at the base of each strip. Damage to the
geocomposite drain strip shall be repaired so that water flow is
not interrupted.
1.14.2 Footing Drains
Footing drains shall be installed at the bottom of the wall, as
shown on the Plans. The drainage geotextile shall envelope the
footing drain aggregate and pipe and shall conform to the
dimensions of the trench. The drainage geotextile shall overlap
on top of the drainage aggregate as shown on the Plans.
Damaged or defective drainage geotextile shall be repaired or
replaced.
1.15 SHOTCRETE FACING
Shotcrete facing and permanent shotcrete facing shall be
provided as required. Where shotcrete is used to complete the
top ungrouted zone of the soil nail drill-hole near the face, the
nozzle shall be positioned into the mouth of the drill-hole to
completely fill the void.
1.15.1 Final Face Finish
Shotcrete finish shall be either an undisturbed gun finish as
applied from the nozzle or a rod, broom, wood float, rubber
float, steel trowel, or rough screeded finish as shown on the
Plans.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
1.15.2 Attachment of Nail Head Bearing Plate and Nut
A bearing plate, washers, and nut shall be attached to each nail
head as shown on the Plans. While the shotcrete construction
facing is still plastic and before its initial set, the plate shall be
uniformly seated on the shotcrete by hand-wrench tightening the
nut. Where uniform contact between the plate and the shotcrete
cannot be provided, the plate shall be set in a bed of grout. After
grout has set for 24 hours, hand-wrench tighten the nut. The
bearing plates with headed studs shall be located within the
tolerances shown on the Plans.
1.15.3 Shotcrete Facing Tolerances
Construction tolerances for the shotcrete facing from plan
location and plan dimensions shall be as follows:
Horizontal location of welded wire mesh; reinforcing bars,
and headed studs: 10 mm (0.4 in.)
Location of headed-studs on bearing plate: 6 mm (1/4 in.)
Spacing between reinforcing bars: 25 mm (1 in.)
Reinforcing lap: 25mm (1 in.)
Complete thickness of shotcrete:
• If troweled or screeded: 15 mm (0.6 in.)
• If left as shot: 30 mm (1.2 in.)
Planeness of finish face surface-gap under 3-m (10-ft)
straightedge:
• If troweled or screeded: 15 mm (0.6 in.)
• If left as shot: 30 mm (1.2 in.)
Nail head bearing plate deviation from parallel to wall
face: 10 degrees
1.16 REINFORCING STEEL
The Contractor shall su bmit all order lists and reinforcement
bending diagrams to the Owner’s Engineer and shall fabricate
reinforcing steel; ship and protect material; and place, fasten,
and splice reinforcing steel as required by the Plans.
1.17 STRUCTURAL CONCRETE
The Contractor shall design the concrete mix; store, handle,
batch, and mix material and deliver concrete; provide quality
control; and construct concrete facing.
1.18 ARCHITECTURAL SURFACE FINISHES
Textured form liners shall be furnished, form liners installed,
and a surface finish (color/stain application) applied that will
duplicate the architectural surface finish shown on the Plans.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
The Contractor shall submit detailed drawings of the form liner
for approval by the Owner’s Engineer at least 7 days before form
liner work begins. Before production work begins, a 1-m (3-ft)
high by 0.5-m (1.5-ft) wide by 3-m (10-ft) long test panel shall
be constructed on site using the same forming methods,
procedures, form liner, texture configuration, expansion joint,
concrete mixture and color/stain application proposed for the
production work.
1.19 BACKFILLING BEHIND WALL FACING
UPPER CANTILEVER
If backfilling is required behind an extension of the wall
facing at the top of a soil nail wall, compaction of the soil
backfill within 1 m (3 ft) shall be limited to light mechanical
tampers.
Backfill shall be relatively free-draining granular soil meeting
the requirement of Article 7.3.5 (of the AASHTO LRFD Bridge
Construction Specifications).
1.20 ACCEPTANCE
Material for soil nail retaining walls will be accepted based on
the manufacturer production certification or from production
records. Construction of soil nail retaining walls will be
accepted based on visual inspection and the examination of
relevant production testing records by the Owner’s Engineer.
2.0 MEASUREMENT AND PAYMENT
2.1 SOIL NAILS
Production soil nails shall be measured by the linear meter (or
foot). The length to be paid will be the length measured along
the soil nail bar centerline from the back face of shotcrete to the
bottom tip end of the nail bar as shown on the Plans. No
separate measurement will be made for proof test nails, which
shall be considered incidental to production nail installation.
Verification test nails shall be measured by each test meeting
the acceptance criteria of Article 1.10. Failed verification test
nails or additional verification test nails installed to verify
alternative nail installation methods proposed by the Contractor
will not be measured.
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
2.2 STRUCTURE EXCAVATION
Structure excavation for the soil nail wall shall be measured as
the theoretical plan volume in cubic meters (cubic feet) within
the structure excavation limits shown on the Plans. This will be
the excavation volume within the zone measured from top to
bottom of shotcrete wall facing and extending out 2 m (6 ft)
horizontally in front of the plan wall final excavation line.
Additional excavation beyond the Plan wall final excavation line
resulting from irregularities in the cut face, excavation overbreak
or inadvertent excavation will not be measured. No
measurement will be made for using temporary stabilizing
berms. General roadway excavation, including hauling, will not
be a separate wall pay item but will be measured and paid as part
of the general roadway excavation.
2.3 WALL FACE
The wall face of soil nail walls shall be measured by the
square meter (square foot) of wall face. Measurement will be
made on the vertical plane of front face accepted in the final
work. No measurement or payment will be made for additional
shotcrete or CIP concrete needed to fill voids created by
irregularities in the cut face, excavation overbreak or inadvertent
excavation beyond the Plan final wall face excavation line, or
failure to construct the facing to the specified line and grade and
tolerances. The final pay quantity shall include all structural
shotcrete, admixtures, reinforcement, welded wire mesh, wire
holding devices, wall drainage materials, bearing plates and nuts,
test panels and all sampling, testing and reporting required by
the Plans and this Specification. The final pay quantity shall be
the design quantity increased or decreased by any changes
authorized by the Owner’s Engineer.
2.4 PAYMENT C2.4
The accepted quantities, measured as provided in Articles 2.1, Under a performance type contract, payment may be made on
2.2 and 2.3, will be paid for at the contract unit price per unit of a lump-sum basis to include all materials, labor and design
measurement for the pay items listed below that are shown on costs.
the bid schedule. Payment will be full compensation for the
work prescribed in this section. Payment will be made under:
2.4.1 Pay Items
Pay Unit
Pay Item
Permanent Soil Nails. No. _ Bar (Grade _) Linear meter
(or linear foot)
Verification Test Nails Each
Structure Excavation-Soil Nail Wall Cubic meter
(or cubic foot)
Soil Nail Wall Square meter
(or square foot)
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Section xx – Soil Nail Walls
PROPOSED SPECIFICATIONS PROPOSED COMMENTARY
3 CORROSION PROTECTION C3
Soil nails and soil nail head components shall be protected Corrosion protection shall be applied in accordance with the
against corrosion consistent with the ground and groundwater provisions of AASHTO LRFD Bridge Construction
conditions at the site. The level and extent of corrosion Specifications, Section 6, “Ground Anchors.”
protection shall be a function of the ground environment and the
potential consequences of a soil nail failure. A full discussion on corrosion of metallic components and a
methodology that assists in selecting the appropriate level of
corrosion protection of soil nail walls is presented in Lazarte et
al. (2003).
REFERENCES
Lazarte, C.A., V. Elias, R.D. Espinoza, and P.J. Sabatini (2003). “Soil Nail Walls,” Geothechnical Engineering Circular No. 7,
FHWAO-IF-03-017, Federal Highway Administration, Washington, D.C., 305p.
PTI (2005). “Recommendations for Prestressed Rock and Soil Anchors,” 4th ed. Post-Tensioning Institute, Phoenix, Arizona.
