304.1. Spiling 1. Where spiling is employed to provide support for advancing the excavation, spiles shall be driven into the ground or placed in pre-drilled and grouted holes as specified on the contract drawings or by the Engineer.
2. The embedded length shall be not less than that specified by the Designer (typically 1 m beyond the proposed advance of the excavation).
3. The accuracy of installation shall be better than58 away from the alignment specified.
4. The number, location, overlap and angle of spiles shall be commensurate with the ground conditions and methodology specified on the contract drawings or by the Engineer.
5. Details of spiling shall be agreed with the Engineer in accordance with Clause 4 of Section 301.1.
6. Spiles shall be installed such that a tensile bond is formed between the spile, the ground ahead of the proposed excava-tion, and the sprayed concrete lining. Typically this may involve grouting the spile into the hole for pre-drilled and self-drilling spiles or hammering the spile in.
7. Care shall be taken during installation of spiles to ensure mini-mum disturbance of the ground due to the installation process.
8. Probing shall be carried out in conjunction with spiling in order that fully embedded spiles are installed prior to the required location.
304.2. Rock dowelling 1. Rock dowels shall be inserted into pre-drilled holes in the ground and grouted up. The number, location, lengths and angles of inclination shall be commensurate with ground conditions. The diameter of holes shall be designed to allow for installation of dowels and grout to ensure effective transfer of shear stress from rock to the dowel.
2. Holes for the installation of dowels shall be drilled straight and with an accuracy of 108. On completion of each hole, and prior to the installation of each dowel, holes shall be cleaned to remove debris. Where water-flush is employed, the amount of water shall be kept to an absolute minimum.
3. A regular surface shall be provided to seat the face plate by trimming rock surfaces or forming pads of quick-setting mortar. Where mortar pads are required they shall be of adequate thickness and extend beyond the face plate by 25 mm all round at that thickness before being chamfered at
458. Care shall be taken to ensure that the mortar does not interfere with the installed dowel.
4. Cementitious grouting material shall be injected starting from the furthest point of the drilled hole so that the dowel is com-pletely encased in grout. Grout shall not be used after a period equivalent to its initial setting time. Where cement grout is used, a set of six cubes of cement grout shall be taken when each series of rock dowels is in progress. Sampling, preparation, curing and testing shall be in accordance with BS EN 196. Half the cubes shall be tested at 1 day and the remainder at 28 days. The average compressive strength determined from any group of cubes shall exceed the specified characteristic strength by:
1 N/mm2for cement grout tested at 1 day 3 N/mm2for cement grout tested at 28 days.
5. Resin grouting capsules shall be installed as directed by the manufacturer.
6. The proposed pattern for dowels and full details of the dowels and installation thereof shall be agreed with the Engineer.
Where required, dowels shall be installed in the pattern and locations and manner shown on the Drawings.
304.3. Rockbolting 1. Where rockbolts are employed, full details of the bolts and installation shall be agreed with the Engineer. The pattern and type of rockbolt and the length and diameter of bolts shall be commensurate with the rock characteristics. Where required, rockbolts shall be installed in the pattern and locations and manner shown on the Drawings.
2. Where required by the Contract, the Contractor shall carefully inspect the excavation as it progresses, and if conditions arise that require a change in the excavation and/or support systems, then revised proposals shall be agreed with the Engineer.
3. Rockbolts shall be provided with an even and secure bearing for their face plates. Holes shall be drilled to produce straight holes of the required length, and with an accuracy of 108, and cleaned out by flushing with compressed air or with clean water to remove debris prior to fixing the rockbolt. The amount of water-flushing shall be kept to an absolute minimum.
4. Grouting of the rockbolts shall take account of the following:
(a) Inclined rockbolts:
. Flowing grouts may be placed by an injection pipe at the mouth of the borehole against packing material to seal the mouth and require a breather tube to prevent air-locks within the hole.
. Thixotropic grouts are typically placed by tremie pipe to the distal end of the borehole, with the grout flowing back down the annulus of the borehole.
(b) Declined rockbolts: a single tremie pipe to the base of the borehole for solid bars or a self-drilling hollow bar installed using simultaneous drill and grout.
(c) Horizontal rockbolts. Bolts should be108 to ensure that grout can be trapped in the borehole either by gravity or through the use of packers on inclined bores.
5. Rockbolts shall be fixed as soon as possible after excavation. A selection of rockbolts shall be tested. Where excavation is progressed by blasting, any rockbolts within 3 m of the face shall be retested. Any rockbolt which fails a test shall be adjusted to restore its nominated load or replaced as necessary.
6. The Contractor shall carry out in situ tests as agreed with the Engineer. Testing is to be generally in accordance with the procedures given in ISRM Document 2, Part 1 Suggested methods of rockbolt testing.
7. Unless otherwise provided for in the Contract, at least 5% of the first 100 bolts installed shall be subject to test. Thereafter 2.5% of subsequent bolts shall be tested. The remedial actions following any bolt test failures shall be agreed with the Engineer.
304.4. Load testing 1. Before commencing rockbolting or dowelling a test programme shall be undertaken to establish the capacity of the rockbolts/
dowels to provide the support required.
2. Suitability load testing and acceptance load testing for rockbolts and dowels shall be undertaken in accordance with an agreed quality control programme as set out in the Drawings or the Particular Specification.
304.5. Records 1. For each dowel or rockbolt installed, the following information shall be recorded:
(a) reference number (b) type of installation
(c) name of person taking record (d ) date of drilling
(e) length and orientation of drill hole
( f ) consistency, colour, structure and type of rock or material (g) rates of penetration and water flow if any
(h) date of dowel or bolt installation (i) length of installation
( j) details of tests, where carried out.