Quality Supervision for Soil Nailing Works

1. Quality supervision of soil nailing works should be provided by the RGE and his TCP T5 and T3, as well as by the AS of the RSC (Site Formation) and his TCP T4 and T1.

1. For all soil nailing works, at least one TCP T3 of the RGE and one TCP T1 of the RSC are required to be resident full-time on site during every stage of the works for each soil nail. The RSC is required to notify the RGE’s TCP T3 before the commencement of any stage of the works. The RSC is also required to prepare detailed inspection, measurement and testing records for each soil nail as per the approved plan requirements.

Table 6.2 Stages of Soil Nailing Works
Item No.	Stage	Description
N1	Pull-out test and any specified site trial	Check whether the test nails are being constructed and the test/site trial procedure is in accordance with the approved plans or as specified by the RGE, and the acceptance criteria for the test/site trial are met.
N2	Setting out of soil nails	Check whether the positions of the soil nails agree with the approved plans.
N3	Drilling of soil nail holes	Check whether the drillhole diameter, length, inclination and bearing are in accordance with the approved plans and any anomalies on ground and groundwater conditions and to report to the responsible person if necessary.

Table 6.2 Cont’d

N4	Assembly        of        soil        nail reinforcement	Check whether the assembly is in accordance with the approved plans, in particular, the length, type and corrosion protection provisions of the reinforcement, adequacy and tightness of any couplers  used, adequacy of centralizers to ensure minimum grout cover and the grout pipes are not twisted and free from blockage and are extended to the bottom of the soil nail holes in accordance with the approved plans.
N5	Insertion        of        soil         nail reinforcement	Check whether: cleaning of the hole, e.g. by air flushing is needed to remove any blockage or collapse, or there is any groundwater, which may require a change in construction method, andthe assembly is sufficiently rigid and the correct assembly of soil nail reinforcement is inserted.
N6	Grout and preparation of grout	Check whether the grout used, grout mix, preparation of grout and grout test results meet the requirements of the  approved plans.
N7	Grouting of soil nail hole	Check whether: grouting of soil nails is carried out on the same day as insertion of the soil nail reinforcement assembly,grout is injected into the drillhole through the grout pipe with sustained grout return of satisfactory cleanliness and viscosity from the top of the drillhole,grouting operation is carried out according to the approved plans, andexcessive grouting time or excessive grout volume consumed in any drillhole to maintain sustained grout return of satisfactory cleanliness and viscosity, or other anomalies such as excessive ‘settlement’ of grout (as measured along the length of the nail) on cessation of grouting, are reported to the responsible person and recorded.
N8	Construction of soil nail heads and structural supports between nail heads	Check whether the soil nail heads and structural supports are constructed in accordance with approved plans, including the dimensions, materials used, structural detailing and workmanship.

1. Key records on supervision of soil nailing works (Appendix IX) should also  be prepared and certified by the RGE’s TCP T3 who carries out the inspection, measurement or check. A full set of all certified records  should be  kept on site for the inspection by the BA.

1. The RGE’s TCP T5 personnel should verify the design assumptions and carry out design review during construction. He should check whether there are  any anomalies that may invalidate the functional requirements of his design during his periodic site inspections and follow them up. He should also  follow up any anomalies reported to him by the RGE’s TCP T3.  If  necessary, the RGE should make amendment submissions for the approval of the BA.

1. The extent of supervision required for different stages of soil nailing works is shown in Table 6.2.  Actual supervision requirements will be imposed at   plan approval stage by the BA on a case-by-case basis depending on the scale and complexity of the slope and the soil nailing works, and the anticipated construction difficulties. The RGE should nominate to the BA, an adequate number of qualified supervision personnel with suitable experience, taking into account the site conditions and the number of soil nails proposed and their lengths. During the construction stage, the RGE should review the adequacy of the supervision team taking into account the likelihood of concurrent construction requiring close supervision under the construction programme.

1. The RGE’s TCP T5 should provide supervision as necessary during all stages in Table 6.2. Moreover, he is required to provide the following supervision personally :
   1. pull-out test and any specified site test – at least 1 nail each of pull-out test and site trial;
   1. insertion of soil nail reinforcement – at least 2 working nails at early stage of nail construction;
   1. grouting of soil nail hole – at least 2 working nails at early stage of nail construction; and

• construction of soil nail heads and structural supports between nail heads – at least one soil nail head.

1. The RSC’s TCP T4 should also provide supervision as necessary during all stages in Table 6.2. Moreover, he is required to provide the following supervision personally :
   1. pull-out test and any specified site test – at least 1 nail each of pull-out test and site trial;
   1. insertion of soil nail reinforcement – at least 2 working nails at early stage of nail construction;
   1. grouting of soil nail hole – at least 2 working nails at early stage of nail construction; and
   1. construction of soil nail heads and structural supports between nail heads – at least one soil nail head.

1. On completion of installation of soil nails, the RGE shall submit to the BA key supervision records in the form of Appendix IX certified by his TCP T3. Upon review of the supervision records, if the BA considers that there is cause for concern in relation to the quality of soil nailing works, the BA will require the RGE to carry out non-destructive testing (NDT) of at least 1% of soil nails with a minimum of 2 nails per slope (including wall) to verify the length of the installed soil nails.

1. Several NDT methods for checking the length of installed soil nails are described in GEO Report No. 133 “Non-destructive Tests for Determining the Lengths of Installed Steel Soil Nails”. Alternatively, the RGE may propose other methods for BA’s agreement at the design stage of the project. A test report with the test results and their interpretations together with re-assessment of the adequacy of the installed soil nails (if needed) shall be submitted to the BA for acceptance.