VTrans Section 219: Slope Stabilization System

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2-82SECTION 219 – SLOPE STABILIZATION SYSTEM

219.01DESCRIPTION . This work shall consist of furnishing all materials, equipment, labor, and

services necessary to install and test a slope stabilization system (SSS), including, but not limited to , slope stabilization nails and a stabilizing facing, in accordance with the se specifications, the Plans , and as directed by the Engineer.

219.02MATERIALS . Materials shall meet the requirements of the following subsections:

Mortar, Type I II ................................ ................................ ................................ ......... 707.0 1(d) Bar Reinforcement ................................ ................................ ................................ .....713.01 Welded Wire Reinforcement ................................ ................................ ..................... 713.0 3 Slope Stabilization Nails ................................ ................................ ............................ 760.01 Shotcrete ................................ ................................ ................................ .................... 760.02 Slope Drainage ................................ ................................ ................................ ........... 760.03 Wire Mesh Facing ................................ ................................ ................................ ......760.04 In addition to the requirements of Subsection 713.0 3, the welded wire reinforcement shall be galvanized in accordance with ASTM A767 .

(a)Centralizers . Centralizers for solid bars shall be made from plastic, such as schedule 40 PVC.

Centralizers for hollow bars shall be mobile metal type centralizers that have an inside diameter larger than the outside diameter of the slope stabilization nail but smaller than the outside diameter of the couplers .

(b)Grout . Grout shall be Type III mortar in accordance with Subsection 707.0 1(d).

(c)Slope Drainage . Slope drainage shall be strip drain, sheet drain, or PVC drain as shown on the

Plans.

219.03GENERAL WORK REQUIREMENTS . Work required for the SSS includes but is not limited to

slope clearing and scaling as needed, installation and testing of s lope stabilization nails of length and orientation as indicated in the Contract, installation or placement of facing material and related materials, and attachment to slope stabilization nails at specified pre -tensioned levels when applicable. The Contract or shall be responsible for construction means and methods and control of the work associated with SSS construction, including slope stabilization nail and stabilizing facing. This includes, but is not limited to, the construction sequence, the safety of t he workers, temporary handrails, work area access, barriers, and lifting of materials and construction equipment into and out of the work area. The construction sequence shall be in accordance with the approved SSS manufacturer’s instructions, unless appro ved otherwise by the Engineer.

219 2-83 219.04 SUBSURFACE INFORMATION . Available information concerning subsurface soil, rock, and groundwater conditions at designated SSS areas is presented in the Contract. If the Contractor requires additional subsurface information, the Contractor may obtain such information at no additional cost to the Agency.

219.05EXISTING SITE CONDITIONS . The Contractor shall verify all existing dimensions and site

slope conditions where SSS and slope stabilization nails are required and shall be responsible for determining actual locations of all existing utilities shown on the Plans, as well as those utilities or underground obstructions not shown on the Plans that may impact or conflict with the SSS and slope stabilization nail installation.

219.06PRE-INSTALLATION MEETING . A pre -installation meeting shall be held prior to the start of

work on the SSS and shall be attended by the Engineer, Contractor , and subcontractors . The pre - installation meeting shall be conducted t o clarify the construction requirements for the work, to coordinate construction activities, and to identify contractual relationships and responsibilities.

219.07SUBMITTALS

(a)Pre-Construction Submittals . The Contractor shall submit the following information not less than

14 calendar days prior to the beginning of the work. Work shall not begin on the SSS until the submittals have been approved in writing by the Engineer.

(1)Qualifications . The Contractor shall submit p roof and details of the following

qualifications:

a.Three projects in the past 3 years where the Contractor or subcontractor performing

the work has successfully installed slope stabilization nails and the specified slope facing system on slopes of simila r height and steepness as shown on the Plans. A reference list shall be provided for the company and the on -site superintendent. A brief description of each project with the owner’s name and current phone number shall be included.

b.The on -site superinten dent shall have a minimum of 2 years supervising

construction of slope stabilization nails and slope stabilization facing systems of similar nail diameter and slope height and similar geotechnical conditions to those shown in the Contract. The work experie nce shall be direct supervisory responsibility for the on -site operation.

219 2-84 c. The shotcrete nozzleman shall be certified as an ACI Shotcrete Nozzleman in accordance with ACI CP -60. The shotcrete nozzleman shall have a minimum of 5 years of demonstrated e xperience in the installation of shotcrete. The shotcrete finishers and delivery equipment operators shall have a minimum of 2 years of demonstrated experience.

(2)Work Plan . The Contractor shall submit a detailed work plan for the slope stabilization na il

and facing system installation. The work plan shall include, if applicable, but not be limited to:

a.The proposed construction sequence and schedule.

b.The proposed rope access methods and safety plan.

c.The proposed nail type and installation metho ds.

d.The proposed drilling and grouting methods and equipment, including drill rig type

and drillhole diameter; and the method of cuttings removal.

e.Grout mix design, including brand and type of Portland cement; source, gradation,

and quality of all ag gregates; proportions of mix by weight and water -cement ratio; and manufacturer and brand name of all admixtures.

f.Nail grout placement procedures and equipment.

(3)Testing . The following information concerning testing of slope stabilization nails shall be

submitted to the Engineer:

a.The number and locations of nails to be subjected to performance and proof testing,

and the test load to be used in testing.

b.Details of the testing equipment and arrangement, including details o f the jacking

frame and the method of distributing test load pressures to the excavation surface or reaction frame, test nail bar size, and reaction plate dimensioning.

c.Methods of installing test nails, bonded and unbonded test lengths and methods for

maintaining the unbonded length. Identification numbers and certified calibration records for each test jack and pressure gauge pair to be used shall be provided. Calibration records shall include the date tested, device identification number, and the calibration test results and shall be certified for an accuracy of at least 2% of the applied certification loads by a qualified independent testing laboratory within 90 calendar days prior to submittal.

219 2-85 (b) Record Drawings . Accurate records docu menting the SSS as -built construction shall be maintained by the Contractor and submitted to the Engineer. The Contractor shall obtain as -built nail locations and all other information as required by the Agency.

219.08CLEARING AND CLEANING OF SLOPE . The limits of clearing shall extend a minimum of ten

feet outside the limits of the slope protection system or as approved by the Engineer. Vegetation shall be cut flush with the ground surface in a manner that promotes complete contact of the facing system wi th the protected surface. Should removal of face protrusions result in voids beneath the facing system, the Contractor shall determine the appropriate method of backfilling based on field conditions. The proposed method shall be approved by the Engineer.

219.09SLOPE STABILIZATION NAILS

(a)Material Handling and Storage .

(1)Cement shall be adequately stored to prevent moisture degradation and partial hydration.

Cement that has become caked or lumpy shall not be used.

(2)All nail bars shall be carefull y handled and shall be stored on supports to keep the steel

from contacting the ground. Steel bars shall be picked up in such a way as to prevent overstressing. Damage to the steel or galvanized coating as a result of overstressing, abrasion, cuts, nicks, welds, and weld spatter shall be cause for rejection by the Engineer. Grounding of welding leads to the dowel steel will not be allowed. Nail steel shall be protected from and sufficiently free of dirt, rust, and other deleterious substances prior to i nstallation. Heavy corrosion or pitting of bars shall be cause for rejection by the Engineer. For damaged galvanized bars, the coating shall be repaired in accordance with the manufacturer ’s recommendations.

(b)Nail Testing .

(1)For each different metho d of nail installation, two successful performance tests shall be

performed to verify the Contractor’s installation methods, nail pullout capacity, and design assumptions. The tests shall be performed prior to installation of production nails at locations within the limits of work specified by the Engineer.

(2)Proof testing shall be performed on 5% of production slope stabilization nails. Nail testing

shall not be performed until the nail grout has attained the 3 -day compressive strength requirement. Proo f test locations shall be selected by the Engineer. All test data shall be recorded and submitted to the Engineer in writing.

219 2-86 (3) Testing equipment shall include two dial gauges, a dial gauge support, jack with pressure gauge, a load cell, and a reactio n frame. A minimum of two dial gauges capable of measuring to 0.001 inch shall be available at the site to measure the nail movement. The dial gauges shall have a minimum travel sufficient to allow the test to be performed without re-setting the dial gauge . The dial gauges shall be aligned within 5 ° of the axis of the nail and shall be supported independent of the jacking set -up and the rock surface. A hydraulic jack, pressure gauge, and pump shall be used to apply and measure the test load. Test set - up sha ll be as approved by the Engineer.

(4)The jack and pressure gauge shall be calibrated by an independent test laboratory as a unit.

The pressure gauge shall be graduated in 100 psi increments or less. The jack shall be capable of tensioning nail bars to 80 % of the guaranteed ultimate tensile strength of the bars within the rated pressure capacity of the pumping units, unless approved otherwise by the Engineer.

(5)The jack shall be independently supported and centered over the nail so that the nail does

not carry the weight of the jack. The stressing equipment shall be placed over the nail in such a manner that the jack, bearing plates, and stressing anchorage are in alignment. The jack shall be positioned at the beginning of the test such that unloading and repositioning of the jack will not be required during the test. The Contractor will be required to provide a reaction bearing pad for each test. The bearing pad shall be constructed to a size and thickness that will prevent failure of the pad or movement of the test jack or bearing plate.

(6)The test nails shall be constructed using the same equipment, methods, and hole diameter

as planned for the production nails. Changes in the drilling or installation method may

require additional nail testing as determined by the Engineer and such testing shall be

provided at no additional cost to the Agency.

(7)Performance test nails shall have both bonded and unbonded lengths. Prior to testing, only

the bonded length of the test nail shall be grouted. The unbonded length of the test nail

shall be at least 3 feet unless approved otherwise by the Engineer. The bond length shall

be determined by the Engineer based on the design pullout load for the nails and the design

bond strength indicated in the Plans. The design test load (DTL) shall not exceed 1.5 times

the design load (DL) and shall not exceed 80% of the guaranteed ultimate tensile strength

for the bar.

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(8)Performance test nails shall be cyclically and incrementally loaded and unloaded in

accordance with the schedule shown in Table 219.09A. The load shall be decreased to the

alignment load (AL, defined as 0.05 DL) after each cycle maximum, and the movement of

each successive alignment load step shall be recorded. At each load increment, the total

movement of the pulling head shall be recorded to the nearest 0.001 inch with respect to

an independent fixed reference point. The load shall be held at each increment just long

enough to obtain the movement reading but no longer than 1 minute. Movement readings

at the test load of 1.125 DL shall be taken at 1, 2, 4, 5, 6 and 10 minutes to measure creep

rate. If the total creep movement between 1 minute and 10 minutes exceeds 0.040 inches

the test load shall be maintained for an additional 50 minutes. Total movements shall then

be recorded at 20, 30, 40, 50, and 60 minutes from the start of the test load hold time.

TABLE 219.09A – PERFORMANCE TEST NAIL LOADING SCHEDULE

Cycle Load Increment

Alignment 1 2 3 4 5 6 7

1 AL 0.25 DL -- -- -- -- -- --

2 AL 0.25 DL 0.50 DL -- -- -- -- --

3 AL 0.25 DL 0.50 DL 0.75 DL -- -- -- --

4 AL 0.25 DL 0.50 DL 0.75 DL 1.00 DL -- -- --

5 AL 0.25 DL 0.50 DL 0.75 DL 1.00 DL 1.125 DL -- --

6 AL 0.25 DL 0.50 DL 0.75 DL 1.00 DL 1.125 DL 1.25 DL --

7 AL 0.25 DL 0.50 DL 0.75 DL 1.00 DL 1.125 DL 1.25 DL 1.50 DL

(9)Proof test nails shall be incrementally loaded in accordance with the schedule shown in

Table 219.09B. At each load increment the total movement of the pulling head shall be

recorded to the nearest 0.001 inch with respect to an independent fixed reference point.

Movement readings at the maximum test load (1.125 DL) shall be taken at 1, 2, 4, 5, 6, and

10 minutes to measure creep rate. If the total creep movement between 1 minute and 10

minutes exceeds 0.040 inches, the test load shall be maintained for an additional 50

minutes. Total movements shall then be recorded at 20, 30, 40, 50, and 60 minutes from

the start of the test hold time.

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TABLE 219.09B – PROOF TEST NAIL LOADING SCHEDULE

Increment Load Movement

Measurement? Notes

1 AL No --

2 0.25 DL Yes --

3 0.50 DL Yes --

4 0.75 DL Yes --

5 1.00 DL Yes --

6 1.125 DL Yes Test load start

7 Hold Yes Test load at final hold

(c)Nail Testing Acceptance. A test nail shall be considered acceptable when all of the following are

true:

(1)The creep rate is observed to be less than 0.040 inches per log cycle of time between the 1

minute and 10 minute readings or, if exceeded, less than 0.080 inches per log cycle of time

between the 6 minute and 60 minute readings and the rate is linear or decreasing at the end

of the creep test load hold period.

(2)The total movement at the test load exceeds 80% of the theoretical elongation of the

unbonded length (plus jack length).

(3)A pullout failure does not occur during testing. Pullout failure is defined as the load at

which attempts to increase the test load simply result in continued pullout movement of the

test nail.

The Contractor shall evaluate the results of each performance test and submit a test results

summary to the Engineer. Nail installation methods that do not satisfy the nail testing requirements

shall be considered inadequate. The Contractor shall propose alternative methods and install

replacement performance test nails at no additional cost to the Agency.

(e)Nail Installation. Nail installation of the slope stabilization nail type specified in the Plans shall

proceed as detailed in the approved work plan. In addition, the following requirements shall be

met:

(1)Successful nail performance tests shall be performed as described in Subsection 219.09(b)

prior to starting installation of production nails.

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(2)Nails shall be installed at the locations and to the lengths indicated on the Plans or as

directed by the Engineer during construction. The Engineer may add, eliminate, or relocate

nails to accommodate actual field conditions.

(3)The Contractor shall select the drilling equipment and methods suitable for the ground

conditions. The drillhole diameter shall be selected to provide the minimum specified grout

cover over the bar and to develop the specified pullout resistance. If solid bar is specified

and caving conditions are encountered in the drillhole, the Contractor shall use cased or

augercast drilling methods to support the sides of the drillhole. The use of hollow bars (also

known as self-drilling, self-grouting, or pressure-grouted nail bars) will only be allowed if

specified on the Plans. Water, drilling mud, or other fluids used to assist in cuttings removal

shall not be allowed. Uncased and open drillholes shall be observed for cleanliness prior to

insertion of the nail.

(4)For open or cased holes, nail bars shall be inserted into the drillhole to the required length

without difficulty and in such a manner as to prevent damage to the drillhole. Nail bars that

cannot be fully inserted to the design depth shall be removed from the drillhole and the

drillhole shall be cleaned sufficiently to allow unobstructed installation of the bar.

(5)The nail shall be installed in a local depression with an approximate relative depth shown

on the Plans.

(6)Nail bar couplers may be used in accordance with the manufacturer’s recommendation as

required.

(7)Centralizers shall be securely attached to the slope stabilization nail, sized to position the

bar within 1 inch of the center of the drillhole, sized to allow the tremie tube insertion to

the bottom of the drillhole, and sized to allow grout to flow freely up the drillhole.

(f)Grouting. Grouting procedures may differ based on allowable bar types specified in the Plans.

(1)Grout equipment shall produce a uniformly mixed grout free of lumpy and undispersed

cement. A positive displacement grout pump shall be used. The pump shall be equipped

with a pressure gauge that can measure at least twice but no more than three times the

intended grout pressure. The grouting equipment shall be sized to enable the entire nail bar

to be grouted in one continuous operation. The mixer shall be capable of continuously

agitating the grout during usage.

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(2)No portion of the nail hole shall be left open for more than 1 hour prior to grouting unless

approved otherwise by the Engineer. The grout shall be injected at the lowest point of each

drillhole through a tremie tube with the drillhole filled in one continuous operation. Grout

pressures shall be controlled to prevent excessive ground heave or fracturing.

(3)Nail bars shall be inserted prior to grouting and cement grout shall be placed using a 0.75

inch diameter polyethylene (or similar) permanent grout tube attached to the nail bar. The

grout tube shall have three openings cut into the lower 4.0 feet of the bond zone to allow

free flow of grout. If the grout tube bottom opening becomes clogged, grout shall be placed

by pumping grout into the grout tube.

(4)Hollow bar nails using self-drilling techniques shall be drilled with continuous grout

injection unless otherwise approved by the Engineer.

(5)A grout sock may be used to reduce grout loss as determined by the Contractor based on

drilling conditions encountered.

(6)During casing removal for drill holes advanced by either cased or augercast methods, the

grout surface within the casing shall be continually monitored for maintenance of head

sufficient to offset the external groundwater and soil pressure.

(7)Nail grout will be tested by the Agency in accordance with AASHTO T 106 or ASTM C109.

The compressive strength shall be the average of the 3 cubes tested. Grout consistency as

measured by grout density shall be determined by the Contractor in accordance with

AASHTO T 133, ASTM C188, or API RP 13B-1 at a frequency of at least one test per day,

conducted just prior to start of nail grouting. The Baroid mud balance used in accordance

with API RP 13B-1 is an approved device for determining the grout density of neat cement

grout. The measured grout shall have a specific gravity of between 1.9 and 2.0, or as

approved in the mix design submittal.

(8)The Engineer shall verify that the Contractor is using the approved grout mix on a daily

basis. Any deviations from the approved mix will require additional testing.

(g)Tolerances. The nails shall not extend beyond the limits shown in the Plans unless approved

otherwise by the Engineer. Nail bars shall be centered within 1 inch of the center of the drillhole.

Individual nails shall be positioned no more than one foot from the design spacing shown on the

Plans. Nail inclination shall be within ± 3° of that shown on the Plans. Nails that encounter

unanticipated obstructions during drilling shall be relocated by the Contractor with the approval

of the Engineer. Nails that do not satisfy the specified tolerances due to the Contractor’s installation

methods shall be replaced to the Engineer’s satisfaction at no additional cost to the Agency.

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219.10WIRE MESH FACING. If wire mesh facing is specified on the Plans, installation procedures shall

be as follows:

(a)The wire mesh shall be installed after placement of nails following the manufacturer’s guidelines.

The top and sides of the mesh shall be secured as recommended by the manufacturer. Horizontal

and vertical connectors shall be as recommended by the manufacturer.

(b)The specified erosion control product shall be placed prior to the mesh placement. Matting shall

be overlapped as recommended by the manufacturer.

(c)The wire mesh shall be pulled tightly across the slope over the nail tips to ensure contact between

the ground and the mesh.

(d)The mesh shall be extended a distance beyond the boundary rope as shown on the Plans.

(e)Ground around the nails shall be recessed as shown on the Plans.

(f)Spike plates shall fit within the recessed area around the nail and be pressed firmly in the ground.

(g)Following installation of the spike plates, the nuts on the nail bars shall be tightened to the pre-

stress level or tightening torque levels shown on the Plans using methods recommended by the

manufacturer.

219.11SHOTCRETE FACING. If shotcrete facing is specified on the Plans, installation procedures shall

be as follows:

(a)Material Handling and Storage. Materials shall be delivered, stored, and handled to prevent

contamination, segregation, corrosion, or damage. Liquid admixtures shall be stored to prevent

evaporation and freezing

(b)Surface Preparation.

(1)The shotcrete facing shall be installed after placement of nails and installation of the

permanent wall drainage as specified on the Plans.

(2)The geocomposite drain strips shall be 12 inches wide and shall be secured to the

excavation face with the geotextile side against the ground as specified per the Plans. Drain

strips shall be made continuous by using the shingle method of splicing with a 12 inch

minimum overlap such that the flow of water is not impeded, or through use of splices

supplied by the manufacturer.

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(3)The joint between the weep pipe and the geocomposite drain strip, and the discharge end

of the weep pipe shall both be sealed to prevent shotcrete intrusion. Damage to the

geocomposite drain strip which, in the opinion of the Engineer, may cause interruption in

flow shall require installation of additional weep pipes above the damaged section.

(4)The Contractor shall remove all loose material from the surface of the ungrouted zone

above the nail grout at the excavation cut face (bird’s beak) prior to shotcreting.

(5)The Contractor shall remove all loose materials and loose dried shotcrete from previous

placement operations and from all receiving surfaces by methods acceptable to the

Engineer. The removal shall be accomplished in such a manner as not to loosen, crack, or

shatter the surfaces to receive the shotcrete. Any surface material that, in the opinion of the

Engineer, is so loosened or damaged shall be removed to sufficient depth to provide a base

that is suitable to receive the shotcrete. Material that loosens as the shotcrete is applied

shall be removed. Shotcrete shall not be placed on frozen surfaces.

(6)Surfaces receiving shotcrete shall be damp but free of standing water.

(c)Delivery and Application.

(1)A clean, dry, oil-free supply of compressed air sufficient for maintaining adequate nozzle

velocity for all parts of the work and simultaneous operations of the blow pipe for cleaning

away rebound shall be maintained at all times. The equipment shall be capable of delivering

the premixed material accurately, uniformly, and continuously through the delivery hose.

(2)The shotcrete shall be applied from the lower part of the work area upwards to prevent

accumulation of rebound on uncovered surfaces. Thickness, methods of support, air

pressure, and rate of placement of shotcrete shall be controlled to prevent sagging or

sloughing of freshly applied shotcrete. Where shotcrete is used to fill the bird’s beak, the

nozzle shall be positioned into the mouth of the drill hole to completely fill the void.

Rebound shall not be worked back into the placement nor shall the rebound be salvaged.

Rebound that does not fall clear of the working area shall be removed. The nozzle shall be

held at a distance and at an angle approximately perpendicular to the working face so that

the rebound will be minimal and compaction will be maximized. The nozzle shall be

rotated steadily in a small circular pattern.

(3)Shotcrete placement shall be by the bench gunning method when the thickness of the

shotcrete layer is 6 inches or greater. The gunning method shall consist of building up a

thick layer of shotcrete from the bottom of the lift and maintaining the top surface at

approximately a 45° slope.

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(d)Visual Observations.

(1)A clearly defined pattern of continuous horizontal or vertical ridges or depressions at the

reinforcing elements after they are covered will be considered indication of insufficient

cover of reinforcement or poor application and probable void. In this case, the work shall

be immediately suspended and the work carefully inspected by the Engineer. The

Contractor shall implement and complete corrective measures prior to resuming the

shotcrete operations.

(2)The shotcreting procedure may be corrected by adjusting the nozzle distance and

orientation perpendicular to the surface, adjusting the water content of the shotcrete mix,

or other means acceptable to the Engineer. All overspray and rebound shall be removed

from the surface.

(3)Surface defects shall be repaired as soon as possible after initial placement of shotcrete.

All shotcrete that lacks uniformity, exhibits segregation, sagging, honeycombing, or

lamination, or contains any voids or sand pockets shall be removed and replaced with fresh

shotcrete by the Contractor to the satisfaction of the Engineer.

(4)If field inspection or testing, by the Engineer, indicates that any shotcrete produced fails to

meet the requirements, the Contractor shall immediately modify procedures, equipment, or

systems, as necessary, and as approved by the Engineer, to produce shotcrete meeting

specifications. All substandard shotcrete already placed shall be repaired by the Contractor,

to the satisfaction of the Engineer, at no additional cost to the Agency. Such repairs may

include removal and replacement of all affected materials.

(e)Nail Head Connection Hardware.

(1)For bearing plate connections, the plate shall be wet-set while the shotcrete is plastic to

ensure full shotcrete bearing behind the plate. However, the retention nut shall only be hand

tightened such that full bearing is achieved without excessively squeezing fresh shotcrete

out from under the plate.

(2)For embedded plate connections, the embedments shall be located within the wall such that

the proper shotcrete cover is provided as shown on the Plans. In addition, the plate, washer,

and nut shall be pulled up flush together by wiring to the reinforcement or other means

necessary to ensure adequate contact between these parts.

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(f)Finishing and Curing Requirements. The shotcrete shall be protected from loss of moisture for at

least 7 days after placement. When shotcrete is being protected from low temperatures, curing

shall be terminated no sooner than 24 hours after the removal of low temperature protection.

Curing of shotcrete shall commence within one hour of shotcrete application. When the ambient

temperature exceeds 80°F, the Contractor shall plan the work such that curing can commence

immediately after finishing. The curing shall be completed using water, membrane, or film curing

methods in accordance with the following requirements.

(1)If water curing is used, the rate of water application shall be regulated to provide complete

surface coverage with minimum runoff.

(2)Curing compounds shall not be used on any surfaces against which additional shotcrete or

other finishing materials are to be bonded unless the surface is sandblasted in a manner

acceptable to the Engineer. Membrane curing compounds shall be spray applied as quickly

as practical after initial shotcrete set, at a coverage of not less than 40 square feet per gallon.

(3)Polyethylene sheeting may be used to supplement water curing on shotcrete that will be

covered later with additional shotcrete. The sheeting shall completely cover all surfaces,

and have edges overlapped for proper sealing and anchorages.

(g)Weather Limitations.

(1)Shotcrete shall not be applied when ambient, substrate, and material temperatures are

below 40°F or above 95°F, or during rainfall events. Shotcrete shall not be placed in cold

weather unless adequately protected when the ambient temperature is below 40°F or when

the shotcrete is likely to be subjected to freezing temperatures before reaching a minimum

strength of 750 psi. Cold weather protection shall be maintained until the strength of the

shotcrete is greater than 750 psi. Cold weather protection shall include heating under tents,

blankets, or other means acceptable to the Engineer. The temperature of the shotcrete, when

deposited, shall not be less than 50°F nor more than 80°F. The air in contact with shotcrete

surfaces shall be maintained at temperatures above 32°F for a minimum of 7 days.

(2)Shotcrete application shall also be suspended during high winds and heavy rains when in

the opinion of the Engineer the quality of the application is not acceptable. Newly placed

shotcrete exposed to rain that washes out cement or otherwise makes the shotcrete

unacceptable to the Engineer shall be removed and replaced. The Contractor shall provide

adequately secured polyethylene sheeting or equivalent when adverse exposure to weather

is anticipated.

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(h)Test Panels.

(1)Two shotcrete test panels shall be required for pre-production. One shotcrete test panel

shall be required per specified test frequency. Once per job, the Engineer may require a

second test panel during the specified testing frequency to test for encapsulation. Panels

shall be in the same shooting orientation as the production work. Panels shall not be

disturbed or moved within the first 24 hours after shooting. Panels shall be field-cured

under conditions similar to those anticipated for the work. Shotcreting of test panels shall

be performed by qualified personnel in the presence of the Engineer.

Test panels and pre-production test panels shall be cored by the Contractor in the presence

of the Engineer. Cores shall be delivered to the lab for testing no more than 24 hours after

being taken. Cores for encasement scoring may be taken when the shotcrete has attained

sufficient strength to not be damaged by coring. The testing frequency, if not specified

elsewhere, shall be once per working day if the daily lot is less than 50 cubic yards, or

every 50 cubic yard sublot, whichever is greater. If a daily sublot is anticipated to be 35

cubic yards or greater, another test set shall be performed.

(2)Pre-production and acceptance test panels shall be 30 inches by 30 inches (minimum) along

with the following:

a.One pre-production test panel, or one test panel during acceptance testing frequency

if specified by the Engineer, shall be the maximum shotcrete thickness shown on

the Plans and shall include the maximum anticipated reinforcing congestion. Cores

extracted from the reinforced test panel shall demonstrate encapsulation of the

reinforcement in accordance with ACI 506.2 equal to core grade 2 or better. At least

two reinforcing intersections shall be cored.

b.One pre-production test panel and one test panel shall be unreinforced, at least 6

inches thick, and used for absorption and compressive strength testing. Pre-

production test panel shotcrete shall be approved based on the same criteria as the

shotcrete in the test panel.

c.The sides of the test panels shall be chamfered outward at 45° over the full thickness

of the panel.

d.Panels shall be shot at approximately the same pressure as anticipated for the work.

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(3)Shotcrete will be accepted based on the 7-day or 28-day strength of cores taken from the

panels. The shotcrete strengths may be accepted if the average 7 day compressive strength

of each set of three cores extracted from test panels or wall face is equal to or exceeds 85%,

with no individual core less than 75%, of the specified 28 day compressive strength in

accordance with ACI 506.2. The frequency specified for the test panels is approximate. A

greater number of panels may be required by the Engineer.

(4)At least nine cores will be cut from each pre-production test panel and test panel for

compressive strength and absorption testing. Cores shall be taken at a minimum distance

from the edge of core to the edge of test panel in accordance with ASTM C1140 and with

a minimum of 1 inch between cores. Cores shall be conditioned accordance with AASHTO

T 24. Cores shall be at least 4 inches in diameter and shall have a minimum length to

diameter ratio of one. An alternate core size may be requested but shall be no less than 3

inches in diameter. When the length of the core is less than twice the diameter, the

correction factors given in ASTM C42 shall be applied to obtain the compressive strength

of individual cores. Three cores shall be tested at 7-days, and three cores shall be tested at

28-days for compressive strength. Three cores shall be tested at 7-days for absorption in

accordance with ASTM C642.

(i)Tolerances. The tolerances for shotcrete facings shall be as follows:

(1)The shotcrete wall thickness shall be no less than that shown on the Plans minus 0.5 inches.

(2)The horizontal and vertical locations of reinforcing bars shall be within 1 inch of the

locations shown on the Plans.

(3)Reinforcing lap lengths shall be no less than that shown on the Plans minus 1 inch.

(4)Spacing of reinforcing bars shall not exceed that shown on the Plans plus 1 inch.

219.12METHOD OF MEASUREMENT. The quantity of Slope Stabilization Nail to be measured for

payment will be the number of linear feet of nail installed in the complete and accepted work, as

determined by the Engineer.

The quantity of Slope Stabilization Nail Testing to be measured for payment will be the number of tests

completed and accepted, as determined by the Engineer.

219

The quantity of Slope Stabilization System, Shotcrete Facing to be measured for payment will be the

square feet of surface area of the completed facing measured to the neat lines of the facing shown on the

Plans at the thickness specified on the Plans. Test panels will not be measured for payment.

The quantity of Slope Stabilization System, Wire Mesh Facing to be measured for payment will be the

number of square feet of wire mesh installed in the complete and accepted work.

219.13BASIS OF PAYMENT. The accepted quantity of Slope Stabilization Nail will be paid for at the

Contract unit price per linear foot. Payment will be full compensation for furnishing, drilling, installing,

and grouting the slope stabilization nail, including all required submittals and for furnishing all labor,

tools, equipment, and incidentals to complete the work.

The accepted quantity of Slope Stabilization Nail Testing will be paid for at the Contract unit price for

each. Payment will be full compensation for performance testing the slope stabilization nails, proof testing

slope stabilization nails, including all required submittals, and for furnishing all labor, tools, equipment,

and incidentals necessary to complete the work.

The accepted quantity of Slope Stabilization System, Shotcrete Facing will be paid for at the Contract unit

price per square foot. Payment will be full compensation for furnishing and installing the specified

materials for a complete in place shotcrete and welded wire mesh slope stabilization system in accordance

with the Contract, including all required submittals, providing samples for acceptance testing, and for

furnishing all labor, tools, equipment, and incidentals necessary to complete the work. Test panels will be

considered incidental to Slope Stabilization System, Shotcrete Facing.

The accepted quantity of Slope Stabilization System, Wire Mesh Facing will be paid for at the Contract

unit price per square foot. Payment will be full compensation for furnishing and installing the specified

materials for a complete in place wire mesh slope stabilization system in accordance with the Contract,

including all required submittals, and for furnishing all labor, tools, equipment, and incidentals necessary

to complete the work.

Payment will be made under:

Pay Item Pay Unit

00 Slope Stabilization Nail ............................................................................Linear Foot

219.1500 Slope Stabilization Nail Testing ...............................................................Each

219.2000 Slope Stabilization System, Shotcrete Facing ..........................................Square Foot

219.3000 Slope Stabilization System, Wire Mesh Facing ........................................Square Foot

221

2-98SECTION 221 – ROCK SLOPE STABILIZATION

221.01DESCRIPTION . This work shall consist of installing and testing various rock slope stabilization

(RSS)items, including, but not limited to, rock dowels, shear keys, rock anchors, rock drains, rock nails,

and shotcrete, in accordance with these specifications, the Plans, and as directed by the Engineer. This work may require using industrial rope access methods.

221.02MATERIALS . Materials shall meet the r equirements of the following subsections:

Mortar, Type III ................................ ................................ ................................ ......... 707.0 1(d) Welded Wire Reinforcement ................................ ................................ ..................... 713.03 Slope Stabilization Nails ................................ ................................ ............................ 760.01 Shotcrete ................................ ................................ ................................ .................... 760.02 Slope Drainage ................................ ................................ ................................ ........... 760.03 In addition to the requirements of Subsection 713.03 , the welded wire reinforcement shall be galvanized in accordance with ASTM A767 .

(a)Centralizers . Centralizers for solid bars shall be schedule 40 PVC or as stated on the Plans.

(b)Grout . Grout shall be Type III mortar in accordance with Subsection 707 .01(d).

(c)Slope Drainage . Slope drainage shall be strip drain, sheet drain, PVC drain, or unlined drilled holes

in rock as shown on the Plans.

221.03SUBMITTALS . The Contractor shall submit to the Engineer, in accordance with Subsection

105.0 6, the foll owing information for completing the work.

(a)Pre-Construction Submittals . The Contractor shall submit the following information not less than

14 calendar days prior to the beginning of the work. RSS work shall not begin until the submittals have been approved in writing by the Engineer.

(1)Qualifications . The Contractor shall submit proof and details of the following

qualifications:

Referenced in this section

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Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 222–237 of 1,380. View official source ↗

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217 REINFORCED SOIL SLOPE

221 ROCK SLOPE STABILIZATION

219SLOPE STABILIZATION SYSTEM

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