Section683 Soil Nail Walls

VicRoads

SECTION683 SOIL NAIL WALLS

##This section cross-references Sections 175 and 611.

If any of the above sections are relevant, they should be included in the specification.

If any of the above sections are not included in the specification, all references to those sections should be struck out, ensuring that the remaining text is still coherent:

683.01 GENERAL

This section specifies the requirements for the supply of materials, testing and construction of soil nail walls.

683.02 DEFINITIONS

For the purpose of this section the following definitions shall apply:

‘Soil Nail’ a component of a soil strengthening system consisting of a steel reinforcement bar(s) inserted centrally into a predrilled hole and grouted in place. A soil nail does not require post-tensioning.

‘Soil Nail Wall’ a soil strengthening system consisting of soil nails installed at appropriate intervals in both horizontal and vertical directions to provide a permanent support to the material retained by the wall.

‘Bonded Length’ The length of a soil nail along which passive resistance is developed.

683.03 STANDARDS

Design and construction of soil nail walls shall comply with the requirements of the Australian Standard for Bridge design - Foundations and soil supporting structures as listed in Section175. A soil nail wall designed to function as an earth retaining structure shall meet the requirements of the Australian Standard for Earth retaining structures as listed in Section175. Where the design requirements differ between the two Australian Standards, the requirements of the Australian Standard for Bridge design – Foundations and soil supporting structures shall take precedence over those of the requirements of earth retaining structures.

683.04 SOIL NAIL DESIGN

A soil nail shall have a minimum of 3m bonded length. The length of a soil nail within 1m (minimum) behind the shotcrete facing shall not be included in development of soil nail capacity.

HP The Contractor shall submit for-construction drawings to the Superintendent for review a minimum of two weeks prior to commencement of soil nail installation.

At each layer of soil nailing the for-construction drawings shall include but not be limited to the following information:

(a) full description of expected material types and groundwater levels;

(b) soil nail diameter, hole diameter, grout mix, etc.;

(d) length of the soil nail along which capacity of the nail is developed;

(e) design capacity of individual soil nails;

(f) horizontal inclination of soil nails;

(g) soil nail head and bearing plate details.

683.05 SOIL NAILS

(a) Soil nails shall consist of Grade500Y deformed high strength steel reinforcing bars complying with the requirements of the Australian Standard for Steel reinforcing materials as listed in Section175 and the requirements of Section611. The bars shall be detailed as shown on the drawings or as specified.

(b) Where a soil nail consists of two or more steel reinforcing bars joined by a coupler between bars, the couplers shall be of the same strength grade or higher grade than the bars.

683.06 CORROSION PROTECTION

(a) All soil nails including couplers shall be galvanized in accordance with the Australian Standard for Hot-dip galvanized (zinc) coatings on fabricated ferrous articles as listed in Section175.

(b) Centralisers shall be provided at intervals along a soil nail to ensure that a minimum grout cover of 40mm is maintained over the entire length of the soil nail. Centralisers shall be manufactured from a corrosion resistant material and shall be shaped to ensure achievement of the specified minimum cover during insertion of the nails, minimise disturbance of the hole during insertion, and minimise obstruction to the grouting.

(c) Prior to grouting, all soil nails shall be insulated from contact with grout/shotcrete at the interface between the ground and the underside of the shotcrete facing. The Contractor shall apply corrosion protection over the entire length of the soil nail to be embedded in the shotcrete facing. The protection shall be extended to a minimum of 300mm behind the underside of the shotcrete facing. Very heavy duty and robust wrapping tapes complying the requirements of the Australian Standard for Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings as listed in Section175 shall be used for the protection work.

683.07 TEMPORARY CASINGS

Temporary casings shall be placed for the full depth of the bored holes to support and prevent collapse of the drilled holes until supported by the anchor system itself. The casing shall be withdrawn progressively during grouting of the hole.

The thickness of the casings shall be determined by the Contractor who shall be responsible for its structural adequacy and the effects of any distortion which is likely to occur to the casings.

683.08 GROUT TUBING

Grout and bleed tubing of a minimum internal diameter of 12mm shall be provided. Tubing shall be made from high density polyethylene Type50 complying to requirements of the Australian Standard for Polyethylene(PE) pipes for pressure applications as listed in Section175. Tubing shall have a wall thickness of at least 2.0mm. Tubing shall be of adequate strength to resist damage both during installation and grouting.

683.09 SOIL NAIL DESIGN VERIFICATION TEST

The Contractor shall carry out testing on sacrificial nails in accordance with Clause683.10 to validate the soil nail design and to demonstrate that the proposed procedure will achieve the specified soil nail durability and load capacity:

HP Prior to commencement of sacrificial soil nail installation the Contractor shall submit to the Superintendent a procedure for soil nail design verification test.

The Contractor shall provide the following information:

(a) installation procedure for sacrificial nails including details of the plant and equipment to be used;

(b) the method of drilling and the proposed hole diameter;

(d) all details to be recorded on the soil nail lot register;

(e) proposed detailed construction procedure.

683.10 TEST ON SACRIFICIAL NAILS

(a) Pull-Out Test on Sacrificial Nails

A batch of at least three pull-out tests shall be performed on sacrificial nails for each type of soil profile. The soil nail configuration and length and the drilling, installation and grouting procedure shall be the same as proposed for the production nails. The test load on sacrificial nails, test procedures and acceptance criteria shall be in accordance with Clause683.13(a) to (d) inclusive.

(b) Exhumation Test on Sacrificial Nails

The batch of soil nails used for the sacrificial pull-out tests shall be exhumed to verify the adequacy of the grout cover. Precautions shall be taken to avoid damage during exhumation to the grout column. The exhumed nails shall be cut into 500mm lengths and the minimum grout cover at each section shall be photographed, measured and recorded.

If any section on any nail in the batch has a grout cover less than the specified minimum cover the Contractor shall amend the installation procedure and conduct further exhumation tests until the specified minimum cover is achieved at each section of each batch of three sacrificial test nails.

The Superintendent shall be notified at least 24hours in advance of each load test and each exhumation test.

HP Installation of production nails shall not commence until the soil nail design and the installation procedure have been validated by testing to the satisfaction of the Superintendent.

683.11 SOIL NAIL INSTALLATION

(a) General

Soil nails shall be installed as soon as practicable after completion of excavating each layer.

The soil nail shall be inserted and grouted on the same day as the completion of drilling the hole.

(b) Drilling

Drilling of holes for soil nails shall be in accordance with the drawings or as specified. Deviation in alignment shall not exceed 1in20. Deviation from straight shall not exceed 20mm in any 3metres. The holes shall be located within 100mm radius of the design nail position.

Where no protective sheathing is provided for permanent soil nails, the drill hole diameter shall be such that the steel bar shall have a minimum grout cover of 40mm.

Water or any other liquid shall not be used as drilling fluid or for flushing the holes.

HP All soil nail holes shall be inspected prior to inserting the soil nail. All drilling records shall be available for inspection prior to inserting the soil nail.

The soil nail shall be installed in one continuous operation to avoid damage to the nail and the drill hole and shall be positioned and secured to prevent movement.

(d) Bearing Plates

Soil nail bearing plates shall have the minimum dimensions in accordance with the drawings, and shall be hot dip galvanized to comply with the Australian Standard for Hot-dip Galvanized (Zinc) Coatings on Fabricated Ferrous Articles as listed in Section175. The plates shall be fixed to the nail head through use of a cupped washer and nut to accommodate variation in plate angle. The plates shall be bedded firmly onto the shotcrete face with non-shrink mortar/grout.

683.12 GROUTING

(a) General

Grout for filling soil nail holes shall be composed of cement, water and an admixture to reduce shrinkage and bleeding. Cement shall conform to the requirements for normal portland cement in accordance with the Australian Standard for Portland and blended cements as listed in Section175 and shall be free from calcium chloride. Admixtures shall not contain chlorides, nitrates or similar electrolytic conducting materials and shall only be used where they will increase workability or reduce shrinkage and bleeding. The water cement ratio shall be as low as possible, consistent with adequate workability and shall be between 0.38 and 0.45. All batching shall be by mass with an approved measuring device and to an accuracy of plus or minus1%. No chlorides will be permitted in the grout. The maximum proportion of chlorine shall not exceed 0.05% with not more than 0.02% in the cement and not more than 0.02% in the water. The maximum proportion of sulphur in the form of sulphites and sulphides shall not exceed0.2%.

The Contractor shall include full details of the grout proportions and additives, the equipment and methods which he proposes to use in the soil nail installation procedure specified in Clause683.09.

The Contractor shall not vary the grouting mixture without notifying the Superintendent.

The minimum compressive strength of test cubes made, cured and tested in accordance with the Australian Standard for Chemical admixtures for concrete, mortar and grout Part2: Methods of sampling and testing admixtures for concrete, mortar as listed in Section175 shall be 25MPa at 28days. At least one pair of cubes shall be taken from each five cubic metres or part thereof of grout. The bleeding of the grout shall not exceed 2% of the volume three hours after mixing and shall not exceed 4% of the volume at any time. All separated water shall be absorbed within 24hours. Bleeding shall be tested in accordance with the requirements of the Australian Standard for Chemical admixtures for concrete, mortar and grout Part2: Methods of sampling and testing admixtures for concrete, mortar, as listed in Section175.

(b) Tests

The Contractor shall provide test results for the proposed mix design including the 7day cube strength, water / cement ratio, bleeding and flow cone value in accordance with the Australian Standard for Chemical admixtures for concrete, mortar and grout Part2: Methods of sampling and testing admixtures for concrete, mortar, as listed in Section175.

At least one pair of cubes shall be taken from each five cubic metres of grout or part thereof. Cubes shall be made, cured and tested in accordance with the Australian Standard for Chemical admixtures for concrete, mortar and grout Part2: Methods of sampling and testing admixtures for concrete, mortar, as listed in Section175.

Details of the mixing and pumping equipment shall be included in the soil nail installation procedure specified in Clause683.09.

Grout shall be mixed in a high speed mechanical mixer, for at least two minutes, until a uniform colloidal consistency is produced. Mixing by hand, or by a tumbling action, will not be permitted.

Water shall be added to the mixer first, then the cement shall be added gradually, and the grout stirred continuously until pumped into the soil nail hole. Grout shall be stirred for a minimum period of two minutes prior to being pumped into the soil nail hole. Admixtures shall be added to the mix in accordance with the manufacturer's recommendations. The hoppers to the pumps shall be fitted with 2.36mm sieve strainers. Grout shall not be used later than 1.5hours after the addition of cement to the mix.

Pumps shall be capable of continuous operation with little pressure variation, and shall have a system for recirculating the grout whilst actual grouting is not in progress. Pumps shall be fitted with a pressure gauge and shall be capable of delivery at pressures up to 1MPa. The use of compressed air will not be permitted.

All piping to the grout pump shall have a minimum of bends, valves and changes in diameter. All pipes and fittings shall have a minimum internal diameter of 25mm.

All equipment, especially piping, shall be thoroughly washed with clean water after each series of operations and more frequently if necessary.

(d) Grouting Operations

Grouting shall not be carried out while the air temperature is below5°C, or while the shade temperature exceeds35°C.

Just prior to grouting, the Contractor shall ensure that all loose soils in a soil nail hole are removed. The soil nail bar shall then be placed centrally in the drill hole. Where a soil nail hole is supported by a temporary casing, the casing shall be withdrawn gradually. A minimum of 0.5m of the bottom end of the casing shall be filled with grout until the casing is full withdrawn.

Grout shall then be injected into each sheathing at a speed of between 0.3m and 0.6m per second.

The Contractor's grouting procedure shall ensure that there are no air or water inclusions left in the grouted zone.