2-98 SECTION 221 – ROCK SLOPE STABILIZATION
221.01 DESCRIPTION . 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.
221.02 MATERIALS . 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.
221.03 SUBMITTALS . 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: 2-99 a. Three projects in the past 3 years where the Contractor or subcontractor performing the work has successfully i nstalled the specified RSS items on rock slopes of similar height and similar geotechnical conditions to those 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 q uantities of relevant rock slope work performed and the owner’s name, and current phone number and email shall be included.
b.The on -site superintendent shall have a minimum of 2 years of experience supervising construction of the specified RSS items on r ock slopes of similar height and similar geotechnical conditions to those shown on the Plans. The work experience shall be direct supervisory responsibility for the on -site operation.
c.The shotcrete nozzleman shall be certified as an ACI Shotcrete Nozzle man in accordance with ACI CP -60. The shotcrete nozzleman shall have a minimum of 5 years of demonstrated experience in the installation and application of shotcrete. Nozzlemen shall be certified in either dry -mix or wet -mix shotcrete based on the process to be used for the work. 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 RSS installation. The work plan shall inc lude, 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 specifications for RSS material and associated hardware including manufacturer’s certifica tes and data sheets.
d.The proposed drilling and grouting methods and equipment, including drill rig type, 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 aggregates; proportions of mix by weight and water -cement ratio; and manufacturer and brand name of all admixtures.
f.Grout installation method and related equipment. 2-100 g. The proposed corrosion protection for RSS materials .
h.The proposed shotcrete product specifications mix design with material testing and data sheets.
i.The proposed steel reinforcement, including rock nails for shotcrete used to support the buttresses during curing, and steel fiber reinforcement.
j.The proposed shotcrete application procedure, anticipated time durations and curing methods, when curing will be applied (including alignment control), surface preparation, delivery and application, rock nails for shotcrete, and finishing methods.
k.The proposed color admixture manufacturer’s product technical data sheets, design mixes, manufacturer’s color charts showing the full range of colors available, and list of completed colored shotcrete projects if colored shotcrete is required per the Contract .
l.The proposed geotextile drainage material, including manufacturer’s product data sheets, manufacturer’s certifications, and the Contractor’s installation methods.
3.Testing . The Contractor shall submit the following information concerning testing o f RSS items:
a.The number and locations of rock dowels and rock anchors 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 of the jacking frame and the method of distributing test load pressures to the excavation surface or reaction frame, test bar size, and reaction plate dimensioning.
c.Methods of installi ng test dowels and anchors, bonded and unbonded test lengths, and methods for maintaining the unbonded length.
d.Identification numbers and certified calibration records for each test jack and pressure gauge pair to be used. Calibration records shall inc lude 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 sub mittal. 2-101 (b) Field Reports . The following information shall be submitted to the Engineer daily.
1.Borehole location, diameter, direction, and angle measured from horizontal.
2.Date and time of drilling, drilling equipment used, and name of driller.
3.Details of encountered subsurface conditions.
4.Location and length of RSS items installed, if applicable.
5.Number of cement bags used, and water cement ratio used.
6.Performance and proof tests performed.
7.Location and volume of shotcrete applied including reinforcement details.
c.Record Drawings . Accurate records documenting the RSS items as -built construction shall be maintained by the Contractor and submitted to the Engineer. The Contractor shall obtain as -built RSS materials locations, identification labels for RSS items and any other information as required by the Agency.
221.04 Rock Dowels .
a.Material Handling and Storage .
1.All RSS rock dowels shall be c arefully handled and shall be stored on supports to keep the steel from contact with 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 steel will not be allowed. Steel shall be protected from and sufficiently free of dirt, rust, and other deleterious substances prior to install ation. Heavy corrosion or pitting of bars shall be cause for rejection by the Engineer. All exposed parts of the RSS rock dowels, bearing plate, and hemispherical nuts on the surface shall be galvanized. Steel ends, where cut, shall be painted with a cold galvanizing compound following installation. For damaged galvanized bars, the coating shall be repaired in accordance with the manufacturer ’s recommendations. 2-102 (b) Testing .
1.For each different method of installation, two successful pre -production proof tests shall be performed to verify the Contractor’s installation methods, pullout capacity, and design assumptions. The tests shall be performed prior to installation of production dowels at locations within the limits of work specified by the Engine er.
2.Unless otherwise stated in the Plans or directed by the Engineer, 5% of production RSS rock dowels will be proof tested.
3.Drilling boreholes for production rock dowels prior to successful pre -production proof tests will be prohibited unless ap proved by the Engineer. The bars used for the pre -production proof tests shall be sacrificial and shall not be incorporated as production.
4.Testing shall not be performed until the grout has attained at least 50% of its specified compressive strength as shown in the Contact Documents. All test data shall be recorded by the Contractor and submitted to the Engineer.
5.Testing equipment shall include two dial gauges, a dial gauge support, jack with pressure gauge, a load cell, and a reaction frame. A min imum of two dial gauges capable of measuring to 0.001 inch shall be available at the site to measure the 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 s hall be aligned within 5° of the axes of the bars 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 shall be as approved b y the Engineer.
6.The jack and pressure gauge shall be calibrated by an independent test laboratory as a unit. The Contractor shall submit calibration reports for the jack and pressure gauge indicating calibration within 90 calendar days prior to use. Te sting will not be allowed until approval of the calibration report by the Engineer.
7.The pressure gauge shall be graduated in 100 psi increments or less. The jack shall be capable of tensioning dowel bars to 80% of the guaranteed ultimate tensile stren gth of the bars within the rated pressure capacity of the pumping units, unless approved otherwise by the Engineer. 2-103 (8) The jack shall be independently supported and centered over the bar so that the bar does not carry the weight of the jack. The stressing equipment shall be placed over the bar 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.
9.Details of the testing arrangement, including the method of distributing test load pressures to the rock surface or reaction frame, test bar size, grouted hole diameter and reaction plate dimensioning shall be developed by the Contractor and submitted t o the Engineer for approval. The test bars shall be constructed using the same equipment, methods, and hole diameter as planned for the production. Changes in the drilling or installation method may require additional testing as determined by the Engineer. Additional testing shall be provided at no additional cost to the Agency.
10.Rock dowels for pre -production proof testing shall have both bonded and unbonded lengths. Prior to testing, only the bonded length of the test bar shall be grouted. The unbonde d length of the test bar 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 and the design bond strength indicated in the Plans. The design test load (DTL ) shall not exceed 1.33 times the design load (DL) and shall not exceed 80% of the guaranteed ultimate tensile strength for the bar.
11.Proof tests shall be performed by incrementally loading the test dowel in accordance with the schedule shown in Table 221.0 4A. 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 (1.33 DL) shall be taken at 1, 2, 4, 5, 6, and 10 minutes to measure the 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 min utes from the start of the test hold time. The alignment load (AL) shall be the minimum load required to align the testing apparatus and shall not exceed 0.25 DL. During load hold periods, the rock dowel load shall not be allowed to deviate from the test p ressure by more than 50 psi. The load shall be returned to the cycle maximum load prior to taking the movement reading at the cycle interval. 2-104 TABLE 221.0 4A – PROOF TEST DOWEL 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 1.25 DL Yes -- 7 1.33 DL Yes Test load start 8 Hold Yes Test load at final hold
c.Proof Testing Acceptance . A test 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 reading or, if exceeded, less than 0.080 inches per log cycle of time between the 6 minute and 60 minute readings and t he rate is linear or decreasing at the end of the creep test load hold period.
2.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 moveme nt of the test. The Contractor shall evaluate the results of each proof test and submit a test results summary to the Engineer. Installation methods that do not satisfy the testing requirements shall be considered inadequate. The Contractor shall propose a lternative methods and install replacement proof test dowels at no additional cost to the Agency.
d.Dowel Installation and Grouting . Dowels shall be installed as specified on the Plans and shall proceed as detailed in the approved work plan. In addition, the following requirements shall be met:
1.Successful pre -production rock dowel proof tests shall be performed as described in Subsection 221.04(b) prior to starting installation of production dowels. 2-105 (2) Dowels 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 dowels to accommodate actual field conditions.
3.The Contractor shall flush the drill hole of all drill c uttings and debris with compressed air prior to the installation of rock dowel. Holes drilled for which installation is considered by the Engineer to be unacceptable or impractical shall be re -drilled at the Contractor’s expense.
4.The cement grout shall be mixed for a minimum of five minutes in a paddle -type grout mixer and passed through a No. 4 (4.75 mm) sieve before being used. Grout may be pumped or fed by gravity into the tremie pipe or grout tube. Grout containing lumps or that has been in the grou t mixer for more than 30 minutes shall not be used. The Contractor shall flush the drill hole of all drill cuttings and debris with compressed air prior to grout installation.
5.For installed bar lengths of 7 feet or less, the Contractor shall tremie nea t cement grout into hole with tremie pipe at the toe of the hole. The hole shall be filled with grout while the tremie pipe is withdrawn at a rate such that the bottom of the tremie pipe remains at or below the rising grout surface. For installed bar lengt hs of greater than 7 feet, the Contractor shall leave hole full of fluid grout for five minutes. If the grout level drops by less than 1 inch, the Contractor shall insert the bar with centralizers into the hole. If the grout level drops by more than 1 inch in five minutes, the Contractor shall re -fill the hole with grout. If the grout level continues to drop for more than 15 minutes, the grout mix shall be thickened as directed by the Engineer. The bar with centralizers shall be inserted once the level stab ilizes.
6.The annular space between the rock dowel and the drill hole perimeter in the completed installation shall be completely filled with cement grout over the full depth of the hole. Sufficient grout shall be used such that, at a minimum, a small am ount of grout extrudes from the collar of the hole when the dowel is inserted to ensure that no voids are left around the bar. The quantity of grout that is required to fill each dowel hole will vary and is highly dependent on geological conditions.
7.For rock dowels, the bird’s beak annulus between the dowel and the hole shall be filled with hand -packed grout as shown on the Plans, and the face plates and nuts shall be attached and tightened with a wrench as directed by the Engineer. 2-106 (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.
e.Grout Testing .
1.The strength of the grout shall be tested for at least every 10 rock dowels ins talled. Grout will be tested by the Agency. Any grout cubes tested by the Contractor will be considered quality control. Acceptable grout shall have a minimum compressive strength as detailed in the Contact .
2.Grout will be tested by the Agency in accor dance 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 the start of dowel 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.
f.Tolerances . The RSS items shall not extend beyond the limits shown in the Plans unless approved otherwise by the Engineer. Bars shall be centered within 1 inch of the center of the drillhole. Individual dowels shall be positioned no more than one foot from the design spacing shown on the Plans. Inclination shall be within ± 5° of that shown on the Plans. RSS items that encounter unanticipated obstructions during drilling shall be relocated by the Contractor with the approval of the Engineer. RSS items 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.
221.05 Rock Anchors .
a.Material Handling and Storage . Materials shall be handled and stored as specified in Subsection 221.04(a) .
b.Testing . Testing shall be performed as specified in Subsection 221.04(b) with the following additional requirement : 2-107 (1) Performance tests shall be performed by cyclically and incrementally loading and unloading the test anchor in accordance with the schedule shown in Table 221.05A . The load shall be decreased to the align ment 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 1.33 DL shall be taken at 1, 2, 4, 5, 6 and 10 minutes to m easure 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 221.05A – PERFORMANCE TEST ANCHOR 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. 25 DL -- -- 6 AL 0.25 DL 0.50 DL 0.75 DL 1.00 DL 1.25 DL 1.33 DL --
c.Testing Acceptance . A test 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 reading 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 decreas ing 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) and is less than 100% of the theoretical elongation of the unbonded length (inclu ding the jack length) plus 50% of the bonded length. 2-108 (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. The Con tractor shall evaluate the results of each anchor test and submit a test results summary to the Engineer. Installation methods that do not satisfy the testing requirements shall be considered inadequate. The Contractor shall propose alternative methods and install replacement test anchors at no additional cost to the Agency.
d.Anchor Installation and Grouting . Anchor installation specified on the Plans shall proceed as detailed in the approved work plan. In addition, the following requirements shall be m et:
1.Anchors 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 anchors to accommodate actual field conditions.
2.The Contracto r shall flush the drill hole of all drill cuttings and debris with compressed air prior to the installation of rock anchor. Holes drilled for which installation is considered by the Engineer to be unacceptable or impractical shall be re -drilled at the Cont ractor’s expense.
3.The cement grout shall be mixed for a minimum of five minutes in a paddle -type grout mixer and passed through a No. 4 (4.75 mm) sieve before being used. Grout may be pumped or fed by gravity into the tremie pipe or grout tube. Grout c ontaining lumps or that has been in the grout mixer for more than 30 minutes shall not be used. The Contractor shall flush the drill hole of all drill cuttings and debris with compressed air prior to grout installation.
4.Anchor installation shall be com pleted with a single stage of grouting that utilizes a fabricated anchor inserted into a prepared borehole. Once in place the anchor will be checked to ensure that there is a level bearing plate surface, and where necessary hand placed grout will be trowel ed around the borehole. With a level anchor head surface the anchor will be tremie grouted to the surface. If an encapsulated anchor is not used, then two stage grouting will be required.
5.Grouting of holes shall be performed by placing grout through a tremie tube installed at the bottom of the open hole. The tremie tube may be withdrawn as grouting proceeds, however, grout shall be maintained over the end of the tremie tube at all times. 2-109 (6) Grouting, to establish the anchorage, will be completed to establish a bond length sufficient to resist the 1.33 DL or as directed by the Engineer. For grouting, the anchor bar shall be inserted in the hole and the grout placed through a tremie tube to fill the borehole. The Contractor shall observe the grout lev el for five minutes. If the grout level drops by more than 1 inch in five minutes, the Contractor shall re -fill the hole with grout to the original level. The use of a grout sock will be permitted to limit grout loss.
7.Following the placement of the gr out through a tremie tube and filling the bird’s beak annulus between the anchor and the hole with hand -packed grout, the washer and nut will be installed and the anchor loaded to 1.10 DL. The nut shall be tightened with a wrench to lock off the anchor at the 1.10 DL load and the jack shall be removed.
8.After acceptance of the anchor by the Engineer, the end of the bar shall be cut to its final length as directed by the Engineer. Cutting of the bars with torches will not be permitted. Anchor ends, where cut, shall be painted with a cold galvanizing compound following installation.
9.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.
e.Grout Testing . Grout testing shall be performed as specified in Subsection 221.04(e) .
f.Tolerances . Tolerances shall be as specified in Subsection 221.04(f) .
221.06 Shear Keys .
a.Material Handling and Storage . Materials shall be handled and stored as specified in Subsection 221.04(a) .
b.Shear Key Installation and Grouting . Shear key installation specified on the Plans shall proceed as detailed in the approved work plan and meet the requirements of Subsection 221.04(d)(2) through Subsection 221.04(d)(6) . In addition, the following requirements shall be met:
1.A minimum of 6 inches of the bar shall stick out from the drill hole. The steel sticking out shall be completely covered by Type III mortar, forming a buttress according to the dimensions shown on the Plans.
2.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. 2-110 (c) Grout Testing . Grout t esting shall be performed as specified in Subsection 221.04(e) .
d.Tolerances . The shear key bars shall not extend beyond the limits shown in the Plans unless approved otherwise by the Engineer. The bars shall be centered within 1 inch of the center of th e drillhole. Individual shear keys shall be positioned no more than one foot from the design spacing shown on the Plans. Bar inclination shall be within ± 3° of that shown on the Plans. Bars that encounter unanticipated obstructions during drilling shall b e relocated by the Contractor with the approval of the Engineer. Bars 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.
221.07 ROCK DRAINS . Rock drains shall be installed as specified in the Plans and shall proceed as
detailed in the approved work plan. In addition, the following requirements shall be met:
a.Drain inclination shall be within ± 3° of that shown on the Plans.
b.Drains that encounter obstructions during drilling shall be relocated by the Contractor with the approval of the Engineer.
c.Drains that do not satisfy the specified tolerances due to the Contractor ’s installation methods shall be replaced to the Enginee r’s satisfaction at no additional cost to the Agency.
221.08 Rock Nails .
a.Material Handling and Storage . Materials shall be handled and stored as specified in Subsection 221.04(a) .
b.Rock Nail Installation and Grouting . Nail installation of the slope stabilization nail type specified on the Plans shall proceed as detailed in the approved work plan and meet the requirements of Subsection 221.04(d)(2) through Subsection 221.04(d)(6) .
c.Grout Testing . Grout testing shall be performed as specified in Subsection 221.04(e) .
d.Tolerances . Tolerances shall be as specified in Subsection 221.06(d) . 2-111 221.09 SHOTCRETE . If a shotcrete is specified on the Plans, the 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.
b.Surface Preparation .
1.The shotcrete shall be installed after placement of rock na ils and installation of the permanent wall drainage as specified on the Plans.
2.When geocomposite drain strips are required per the Plans, then the drain strips shall be 12 inches wide and shall be secured to the excavation face with the geotextile side against the ground as specified in 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.
3.The weep drains shall be installed at the locations and to the lengths indicated on the Plans or as directed by the Engineer during construction. Unless specified in the Plans, drill holes shall be no larger than 3 inches in diameter, and the pipe shal l extend 1 inch to 3 inches beyond the final slope face. The PVC pipe shall be installed before applying the shotcrete.
4.The joint between the weep pipe and the geocomposite drain strip, and the discharge end of the weep pipe shall both be sealed to pr event shotcrete intrusion. Damage of 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.
5.The Contractor shall remove all loose material from the surface of the ungrouted zone if any rock anchors, rock dowels, or rock nails for shotcrete are installed within the limits of the shotcrete, prior to shotcreting.
6.The Contractor shall remove all loose materials and loose dried shotc rete 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 materia l 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 p laced on frozen surfaces.
7.Surfaces receiving shotcrete shall be damp but free of standing water. 2-112 (c) Delivery and Application .
1.Wet-mix shotcrete shall be placed within 90 minutes of mixing the cementitious material with the aggregate, unless a pproved otherwise by the Engineer. Dry -mix shotcrete shall be placed within 45 minutes of mixing.
2.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.
3.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 i n a small circular pattern.
4.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 li ft and maintaining the top surface at approximately a 45° slope.
5.Successful pre-production test panels are required prior to starting installation of production shotcrete.
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 suspende d, and the work carefully inspected by the Engineer. The Contractor shall implement and complete corrective measures prior to resuming the shotcrete operations. 2-113 (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 remove d 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 shal l 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 immediate ly 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 n o 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 shot crete 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 embedment shall be lo cated 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 betwe en these parts.
f.Finishing and Curing Requirements .
1.The shotcrete shall be protected from loss of moisture for at least 7 days after placement.
2.When shotcrete is being protected from low temperatures, curing shall be terminated no sooner than 24 hours after the removal of low temperature protection. 2-114 (3) 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 im mediately after finishing. The curing shall be completed using water, membrane, or film curing methods in accordance with the following requirements:
a.If water curing is used, the rate of water application shall be regulated to provide complete surface c overage with minimum runoff.
b.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 co mpounds shall be spray applied as quickly as practical after initial shotcrete set, at a coverage of not less than 40 square feet per gallon.
c.Polyethylene sheeting may be used to supplement water curing on shotcrete that will be covered later with addit ional 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.
2.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 sh all include heating under tents, blankets, or other means acceptable to the Engineer.
3.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 t emperatures above 32°F for a minimum of 7 days.
4.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. 2-115 (h) Testing .
1.Test Panels . Shotcrete test panels include pre-production test panels and production test panels. Test panels shall meet the following requirements:
a.Panels shall be a minimum size of 30 inches × 30 inches.
b.Panels shall be in the same shooting orientation as the production work.
c.Panels shall be shot at approximately the same pressure as anticipated for the work.
d.Panels shall not be disturbed or moved within the first 24 hours after shooting.
e.Panels shall be field -cured under conditions similar to those anticipated for the work.
f.Shotcreting of test panels shall be performed by qualified personnel in the presence of the Engineer.
2.Pre-Production Test Panels . Two shotcrete test panels shal l be required for pre-production. One pre-production test panel shall be unreinforced, at least 6 inches thick, and used for absorption and compressive strength testing. One pre-production test panel shall be the maximum shotcrete thickness shown on the Pl ans and shall include the anticipated reinforcing congestion.
3.Production Test Panels . Unless specified in the Plans, a minimum of one production test panel shall be required for each 50 cubic yards placed, but no fewer than one production test panel daily for each nozzle operator. One production test panel shall be required whenever the nozzle equipment is changed. At least one production test panel shall be unreinforced, at least 6 inches thick, and used for absorption and compressive strength testin g. Once per job, the Engineer may require an additional production test panel to test for encapsulation.
4.Sampling .
a.Pre-production and production test panels shall be cored by the Contractor in the presence of the Engineer. 2-116 b. At least nine co res shall be cut from each pre-production test panel and production test panel for compressive strength and absorption testing.
c.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 .
d.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.
e.Cores shall be delivered to the Agency’s Materials Testing and Certification Section Central Laboratory for testing no more than 24 hours after being taken.
f.Cores for enca sement scoring may be taken when the shotcrete has attained strength enough to not be damaged by coring.
g.Cores of at least two reinforcing intersections shall be extracted from the reinforced pre-production test panel .
i.Testing Acceptance . Pre-produ ction test panels and production test panels shall be approved based on the same criteria.
1.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 . Shotcrete will be accepted based on the 7 -day or 28 -days 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 .
2.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. 2-117 If a shotcrete section represented by any test panel core is deficient in any of the criteria specified, the Contractor shall propose an alternative repair at no additional cost to the Agency. Repairs may include, but are not limited to, the application of additional shotcrete to the deficient area or removal and replacement of the deficient section.
221.10 METHOD OF MEASUREMENT . The quantity of Rock Slope Stabili zation Dowel to be
measured for payment will be the number of linear feet of rock dowels installed in the complete and accepted work, as determined by the Engineer , and as shown as the pay limits on the Plans. The quantity of Rock Slope Stabilization Dowel Testing to be measured for payment will be the number of tests completed and accepted, as determined by the Engineer. The quantity of Rock Slope Stabilization Anchor to be measured for payment will be the number of linear feet of rock anchors installed in the complete and accepted work, as determined by the Engineer. The quantity of Rock Slope Stabilization Anchor Testing to be measured for payment will be the number of tests completed and accepted, as determined by the Engineer. The quantity of Rock Slope Stabilization Shear Keys to be measured for payment will be the number of linear feet of shear keys installed in the complete and accepted work, as determined by the Engineer. The quantity of Rock Slope Stabilization Drain to be measured for payment will be the number of linear feet of rock drains installed in the complete and accepted work, as determined by the Engineer. The quantity of Rock Slope Stabilization Nail for Shotcrete to be measured for payment will be the number of linear feet of rock nail in stalled in the complete and accepted work, as determined by the Engineer. The quantity of Rock Slope Stabilization Shotcrete to be measured for payment will be the number of cubic yards installed in the complete and accepted work, as determined by the Eng ineer. Test Panels will not be measured for payment.
219.11 BASIS OF PAYMENT . The accepted quantity of Rock Slope Stabilization Dowel will be paid
for at the Contract unit price per linear foot. Payment will be full compensation for furnishing, drilling, installing, and grouting the rock dowels and for furnishing all labor, tools, equipment, and incidentals to complete the work. 2-118 The accepted quantity of Rock Slope Stabilization Dowel Testing will be paid for at the Contract unit price per ea ch price. Payment will be full compensation for performance testing, obtaining acceptable results for all tests, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. The accepted quantity of Rock Slope Stabilizat ion Anchor will be paid for at the Contract unit price per linear foot. Payment will be full compensation for furnishing, drilling, installing, and grouting the rock anchors and for furnishing all labor, tools, equipment, and incidentals to complete the wo rk. The accepted quantity of Rock Slope Stabilization Anchor Testing will be paid for at the Contract unit price per each price. Payment will be full compensation for performance testing, obtaining acceptable results for all tests, and for furnishing all l abor, tools, equipment, and incidentals necessary to complete the work. The accepted quantity of Rock Slope Stabilization Shear Keys will be paid for at the Contract unit price per linear foot. Payment will be full compensation for furnishing, drilling, i nstalling, formwork, and grouting the shear keys and for furnishing all labor, tools, equipment, and incidentals to complete the work. The accepted quantity of Rock Slope Stabilization Drain will be paid for at the Contract unit price per linear foot. Paym ent will be full compensation for furnishing, drilling and installing the rock anchors and for furnishing all labor, tools, equipment, and incidentals to complete the work. The accepted quantity of Rock Slope Stabilization Nail for Shotcrete will be paid f or at the Contract unit price per linear foot. Payment will be full compensation for furnishing, drilling, installing, and grouting the rock nail, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. The accepted quantity of Rock Slope Stabilization Shotcrete will be paid for at the Contract unit price per cubic yard. Payment will be full compensation for furnishing and installing the specified materials for a complete in place shotcrete in accordance with the Con tract, including all required submittal and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. Test panels will be considered incidental to Rock Slope Stabilization Shotcrete. Payment for preparing and making requir ed submittals will not be made separately, but will be considered incidental to the work under this section. 2-119 Payment will be made under: Pay Item Pay Unit 221.1000 Rock Slope Stabilization Dowel ................................ ............................... Linear Foot 221.1500 Rock Slope Stabilizatio n Dowel Testing ................................ .................. Each 221.2000 Rock Slope Stabilization Anchor ................................ .............................. Linear Foot 221.2500 Rock Slope Stabilization Anchor Testing ................................ ................. Each 221.3000 Rock Slope Stabilization Shear Key ................................ ......................... Linear Foot 221.4000 Rock Slope Stabilization Drain ................................ ................................ .Linear Foot 221.5000 Rock Slope Stabilization Nail ................................ ................................ ...Linear Foot 221.6000 Rock Slope Stabilization Shotcrete ................................ ........................... Cubic Yard 2-120 SECTION 225 – CONCRETE RETAINING WALL
225.01 DESCRIPTION . This work shall consist of designing, detailing, fabricating, furnishing, and
erecting a precast or cast -in-place concrete retaining wall at the locations specified and in conformance with the lines and grades shown on the Plans or as directed by the Eng ineer.
225.02 MATERIALS . Materials shall meet the requirements of the following subsections:
Granular Backfill for Structures ................................ ................................ ................. 704.08 Drainage Aggregate ................................ ................................ ................................ ...704.16 Bar Reinforcement ................................ ................................ ................................ .....713.01 Mechanical Splices for Bar Reinforcement ................................ ............................... 713.02 Welded Wire Reinforcement ................................ ................................ ..................... 713.0 3 Precast Concrete Retaining Wall Systems ................................ ................................ .760.0 5 Concrete shall meet the requirements of Section 501 for Performance -Based Concrete, Class PCS, unless otherwise specified in the Contract. Reinforcing steel shall meet the requirements for Level I I corrosion resistance unless otherwise specified in the Plans.
225.03 DESIGN REQUIREMENTS . The wall shall be designed and constructed in accordance with the
AASHTO LRFD Bridge Design Specifications , the Plans, the design criteria, and the geotec hnical information specified in the Contract. Precast and cast -in-place concrete retaining walls shall employ concrete facing. All wall components shall have a minimum design life of 100 years.
225.04 GENERAL REQUIREMENTS . Unless noted otherwise herein, cast-in-place concrete retaining
walls shall meet the requirements of Section 501 and Section 507 as applicable. Precast concrete retaining walls shall meet the requirements of Section 540 and Section 649 as applicable. When the pay item Retaining Wall , Concrete is included in the Contract, the Contractor may choose to use either a precast or cast -in-place concrete retaining wall at their discretion. The wall shall meet the requirements for the applicable type as noted above.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 238–259 of 1,380.