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6.1 Equipment

a) Only wet mix process equipment shall be used for Shotcrete Types, S1, S2, S3, S4, P1, P2 and P3. Equipment for the wet mix process shall be set up according to the

recommendations of the manufacturer. Pumping equipment shall ensure the continuous conveyance of shotcrete at a steady and quantifiable rate with minimal pulsation. The equipment shall allow for air and water in any combination to be available for

preparation of surfaces and/or cleaning of finished work in accordance with this Specification.

b) All equipment used for batching and mixing of materials, and the transport and application of all types of shotcrete shall be of suitable design and shall be maintained in proper working order for the duration of excavation and lining works. The shotcrete gun and ancillary equipment shall be of an adequate capacity for the volumes to be applied, and shall be manufactured from suitable materials compatible with the

proposed accelerators and additives. A stand-by shotcrete system of plant and ancillary equipment shall be available for the duration of excavation operations to ensure

shotcrete is available at all times to stabilise all exposed excavation faces. Air for the equipment is to be clean, dry and oil free and to be provided at the equipment at not less than the operating pressure and volume rates specified by the manufacturer.

c) Shotcreting equipment shall be capable of feeding materials at a regular rate and ejecting shotcrete from the nozzle at velocities that will allow adherence of the materials to the surface being shotcreted with a minimum of rebound and maximum adhesion and density.

d) Equipment shall be leak proof with respect to all materials.

GL - Supplementary Specification - Tunnel - Shotcrete Lining GLTSP102

e) Equipment shall be thoroughly cleaned at least once per shift, or more frequently at appropriate intervals if hydration control admixtures are used, to prevent accumulations of residual deposits and/or deterioration due to the accelerators used.

f) Transport pipes consisting of hoses or pipes shall be laid straight or in gentle curves.

The transport pipes shall have a uniform diameter appropriate to the mix and fibre characteristics determined by field trials, and be free of any dents or kinks between the shotcrete machine and the nozzle.

g) Equipment shall allow application of shotcrete to all surfaces with the nozzle at the distances from the surfaces to be sprayed in accordance with this Specification.

h) Working areas for shotcreting shall be well illuminated. Cap lamps attached to safety helmets will not be accepted as sufficient illumination. Dust pollution shall be minimised by choice of appropriate equipment and by means of additional ventilation, water sprays, and by maintaining equipment in good order.

i) Dosing of admixtures by hand is not permitted. Each machine provided for the wet mix process shall incorporate:

i. A memory programmable control system to coordinate and control all functions of the machine including the dosing of all admixtures.

ii. An integrated proportioning unit to dispense admixtures at the required dosages as controlled by the throughput of concrete. The equipment shall be capable of delivering admixtures such that the approved dosages are dispensed to an accuracy of ±0.5% of the required dosage and shall be calibrated and operated in accordance with the manufacturer's instructions.

j) As far as practicable all shotcrete shall be applied using remote controlled spraying equipment appropriate to particular applications. Hand spraying of wet mix shotcrete is permitted.

k) Remote controlled spraying equipment shall be provided with as long reach as possible.

This shall ensure that the operator can observe the nozzle at all times during spraying from a position of safety under supported ground. The controls shall provide the operator with full and effective control of the nozzle articulation and other functions. The equipment shall be used, cleaned and maintained in accordance with the

manufacturer's instructions.

6.2 Proficiency of Nozzlemen

a) Nozzlemen shall have had previous experience and be proficient in the application of shotcrete. Production shotcrete shall be applied only by nozzlemen who have demonstrated their competence and their ability to produce either plain or steel fibre reinforced shotcrete by the method to be used. Nozzlemen shall hold certificates of competence issued by the Contractor Hold Point 2.

6.3 Production and Transport

a) The individual components for the production of shotcrete shall be measured by weight with an automatic batching device, except that admixtures may be measured by volume. The batching accuracy shall be within ±3% for all constituents except admixtures (refer to Section 6.1.i.ii.). Silica fume shall be weighed separately. The method of batching used shall ensure that the accuracy can be easily checked. All measuring equipment shall be maintained in a clean and serviceable condition and shall be zeroed daily and calibrated monthly.

b) Mixing shall be carried out in a mixer suitable for the efficient mixing and discharge of wet batched materials.

c) Regular checks shall be made to ensure that complete mixing is routinely achieved.

Tests for mix consistency shall be in accordance with ASTM C94-04 or similar approved international standard.

d) The addition of fibres shall be at a stage in the mixing suitable for the shotcreting equipment. The procedure for the addition of fibres shall be determined during the field trials. Fibres shall be added and mixed in a manner to avoid clumping and bending of the fibres. Any fibre clumps in the mix shall be diverted and removed by means of a screen placed over the shotcrete hopper. Fibres shall be uniformly distributed

throughout the mortar matrix without isolated concentrations. Fibres shall not be added to the mix at a rate faster than that at which they can be blended with the other

ingredients without forming balls or clumps.

e) The mixed base concrete for the wet mix process shall be applied within one and a half (1.5) hours of charging the mixer. This time may be extended by the use of retarders, plasticisers or hydration control admixtures in accordance with this Specification.

f) The base concrete for shotcrete produced by the wet mix process shall be transported by truck mixers, concrete pumps or other suitable containers and shall prevent

segregation or possible loss or gain of water. Remixing of material shall not be permitted, however, using a drop pipe to transfer the concrete from the surface

underground into an agitator truck is acceptable provided the material does not become overly segregated and remixing produces a homogenous sprayable mix. The mixture shall be effectively protected against any influence of the weather.

6.4 Application

The following requirements shall be achieved prior to and during the application of the shotcrete:

a) Method statement and procedures have been submitted and approval has been given by the Construction Certifier.

b) Checking and correction of the excavated cross section profile shall be carried out and rock surfaces and/or existing shotcrete shall be cleaned with compressed air and, as far as the local conditions permit, with an air-water mixture as necessary to remove all material which may prevent proper adhesion of the shotcrete to the surface. The surface to receive shotcrete shall be damp, but without free water prior to the

application of shotcrete. Treatment with an air-water mixture to ensure that the surface is sufficiently clean and damp shall be done shortly before the application of shotcrete.

c) Action shall be taken to control groundwater and prevent it adversely affecting the shotcrete lining. Adopted measures shall remain effective for at least 28 days. Water inflows which might cause deterioration of the shotcrete, or prevent adherence, shall be diverted as detailed on the Drawings, or otherwise proposed by the Contractor, by channels, chases, pipes or other appropriate means, to the invert or to the temporary groundwater drainage system.

d) Where necessary, pressure relief holes shall be provided through the primary lining to ensure that no hydrostatic pressure develops behind the lining.

e) Ensure the thickness control devices are in place

f) The distance between the nozzle and the surface to be shotcreted shall not exceed 1.8m for remote controlled spraying and 1.0m for hand spraying with the wet mix process. The nozzle shall, as a general rule, be held perpendicular to the application surface except as necessary to ensure proper embedment of steelwork such as lattice girders where shown on the Drawings.

g) Depending on the required final thickness the application of steel fibre reinforced shotcrete may be undertaken in two or more stages to minimise rebound, the first phase being as stated on the Drawings.

GL - Supplementary Specification - Tunnel - Shotcrete Lining GLTSP102

h) Each layer of shotcrete shall be built up by making several passes of the nozzle over the working area using good working practices and nozzle manipulation. The shotcrete shall emerge from the nozzle in a steady uninterrupted flow. Should the flow become intermittent for any cause the nozzleman shall direct it away from the work until it again becomes constant.

i) Where a layer of shotcrete is to be covered by succeeding layers, it shall first be allowed to set and loose material and rebound shall be removed. The surface shall be checked for soundness, repaired as specified, finally cleaned, and wetted using a blast of air and water.

j) No rebound material shall be covered with shotcrete. All rebound material shall be removed from the working area and shall not be used in the Temporary and Permanent Works. Disposal shall be undertaken with proper regard to the risks of environmental pollution by both the cementitious materials and/or the admixtures.

k) For vertical and near vertical surfaces application shall commence at the bottom. Layer thickness shall be governed mainly by the requirement that the material shall not sag.

Where thick layers are applied the top surface shall be maintained at a slope of

approximately 45 degrees. For overhead surfaces shotcrete shall preferably be applied from the shoulder to the crown.

l) Pockets, sags or other defects shall be cut out and resprayed. The area of respraying shall not be less than 300mm x 300mm.

m) Unless specifically required and appropriate mixes designed, finishing actions, such as trowelling or screeding, shall be avoided and may require remedial works to be

undertaken.

n) The temperature of the mix before spraying shall not be below 5ºC or above 35ºC unless special provisions are made to the approval of the Construction Certifier.

Spraying shall not be undertaken when the ambient temperature is below 5ºC.

o) Sprayed concrete shall not be applied in the Temporary and Permanent Works until the correct setting characteristics are observed during the start-up and a continuous shotcrete stream is ejecting from the nozzle.

p) Where two layers of reinforcement are used, the far face reinforcement shall be covered by sprayed concrete before the near layer is installed. The near layer shall be covered by sprayed concrete up to the required thickness with the minimum delay.

6.5 Thickness and Profile Control

a) Where specified on the Drawings the minimum layer thickness shall be controlled by depth pins attached to the rock bolt plates or lattice girders. Depth pins shall be used at a frequency of at least one marker per 5m² sprayed area. Where not specified on the Drawings suitable thickness control measures shall be implemented by the Contractor Witness Point.

b) Steel sets and/or other embedded steelwork shall be embedded as specified on the Drawings.

c) Control of the profile of the shotcrete lining as shown on the Drawings shall be by manual or electronic means. Laser based equipment shall comply with all necessary local health and safety legislation and shall be used in accordance with the

manufacturer's instructions.

d) The shotcrete thickness shall be determined by surveying the tunnel section before and after shotcrete application at intervals along the tunnel of not more than 5 m separation.

e) Tolerances are to be in accordance with those specified on the Design Drawings.

6.6 Curing

a) All final surfaces of shotcrete Types S1, S2, S3, S4, P1, P2 and P3 need not be subject to special measures unless the results of testing indicate that the performance

requirements of this Specification are not being consistently achieved and that such underperformance is attributable to poor curing, in which case the Contractor shall make a proposal for curing the shotcrete for acceptance by the Construction Certifier.