Quality Supervision | Code of Practice for Site Supervision

Quality Supervision for Foundation Works

Quality supervision of foundation works should be provided by the RSE and his TCP T5 and T3, as well as by the AS of the RSC and his TCP T4 and T2. Depending on the nature of the various stages of foundation works, TCPs should either be full-time on site or inspect certain percentage of the works as specified in this Code.

The stages of the various types of foundation works are shown in Table 6.3. Actual supervision requirements will be imposed by the BA at plan approval and consent stage on a case-by-case basis depending on the scale and extent of the foundation works.

Table 6.3 Stages of Various Types of Foundation Works
Item No.	Stage	Description
F1	Driven Piles Setting out of piles	Check that the locations of piles agree with approved plans.
F2	(ii) Driving test	Check that design assumptions agree with actual site conditions during driving tests.
F3	(iii) Driving of piles	Check that the accepted working procedures of pile driving are followed and anomalies rectified during pile driving.
F4	(iv) Splicing of piles	Check the accuracy of design details during pile splicing.
F5	(v) Final sets	Check that the required final set has been achieved and the capacity of each pile complied with approved plans.
F6	(vi) Proof test (Verification on the performance of the as-constructed piles by the imposition of test load)	Check that the testing procedures and acceptance criteria of proof tests are in accordance with PNAP APP-18 (previously PNAP 66) and measurements are properly recorded during the test.

Table 6.3 Cont’d

F7	Large Diameter Bored Piles, Barrette Piles and the like Setting out of piles	Check that the locations of piles agree with approved plan.
F8	(ii) Pre-drilling (To determine the proposed founding levels of piles)	Supervise the pre-drilling operation; the logging of soil/rock samples, and to measure the depth of drillholes. Ensure that the retrieved samples are not tampered.
F9	(iii) Verification of founding stratum	Measure the depth of excavation and check the quality of retrieved materials at the founding stratum.
F10	(iv) Installation of piles (Grouting operation when required)	Check that proper working procedures of pile installation are followed and anomalies rectified. Check the correct grout mix, grout pressure and grout volume are being used and the adjacent building structures are not adversely affected.
F11	(v) Preparation of pile base	Ensure that pile base is clean.
F12	(vi) Fabrication and installation of rebar cage and placing of concrete	Check that sufficient and correct amount of rebars are provided and proper concreting method is used.
F13	(vii) Interface core-drilling	Check that the quality of concrete and foundation rock conforms with that specified in the approved plan and that concrete and rock are in good contact at the interface.
F14	(viii) Proof test (Verification on the performance of the as-constructed piles)	Supervise the core drilling operation of the proof test and the logging of concrete/rock samples and measure the depth of drillhole. Ensure that retrieved samples are securely stored and delivered to laboratory for testing.
F15	Mini-piles, Socketted H-piles and the like Setting out of piles	Check that the locations of piles agree with approved plan.

Table 6.3 Cont’d

F16	(ii) Pre-drilling (To determine the proposed founding levels of piles)	Supervise the pre-drilling operation; the logging of soil/rock samples, and to measure the depth of drillholes. Ensure that the retrieved samples are not tampered.
F17	(iii) Verification of founding stratum	Measure the depth of excavation and check the quality of retrieved materials at the founding stratum.
F18	(iv) Installation of piles (Grouting operation when required)	Check that proper working procedures of pile installation are followed and anomalies rectified. Check the correct grout mix, grout pressure and grout volume are being used and the adjacent building structures are not adversely affected.
F19	(v) Installation of rebar and grouting	Check that sufficient and correct amount of rebars are provided and proper grouting method is used.
F20	(vi) Proof test (Verification on the performance of the as-constructed piles by the imposition of test load)	Check that the testing procedure and acceptance criteria of the proof tests are in accordance with PNAP APP-18 (previously PNAP 66) and measurements are properly recorded during the test.
F21	(vii) Post-installation borehole drilling	Verify the rockhead profile and socket length of piles during post-installation borehole drilling.
F22	Rafts and Spread Footings Setting out of rafts and spread footings	Check that the locations and sizes of rafts and spread footings agree with approved plan (or the submitted plans for minor works).
F23	(ii) Inspection of bearing stratum	Check the compliance of ground bearing stratum with approved plans (or the submitted plans for minor works), site investigation reports and design assumptions.
F24	(iii) Fixing of rebars and checking of concrete covers	Check that sufficient amount of rebars and good workmanship are provided.
F25	(iv) Placing, compaction and curing of concrete	Ensure the quality and workmanship of concrete works.
F26	(v) Plate loading test (where required) (To verify the adequacy of ground bearing stratum)	Check that the accepted testing procedures of plate loading test are followed and measurements are correctly recorded.

Note : Foundation unit inspected should be shown in the checklist by each member of the supervision team.

The AP, RSE and RSC should jointly submit a supervision plan, specifying the name of the TCPs appointed and frequency of inspection and/or extent of supervision, and carry out inspections and supervisions in accordance with the plan. The plan should be submitted prior to or at the same time as consent application for the foundation works. However, no prior approval of the TCPs is required before commencement of the foundation works. The AP/RSE/RSC are responsible to ensure that their TCPs satisfy the qualification and experience requirements specified and should notify the BA of any subsequent changes of TCPs. The plan should be kept on site for the inspection of the BA when required.

The RSE should provide supervision as necessary during all stages in Table 6.3.

The AS of the RSC should provide supervision as necessary during all stages in Table 6.3.

Pre-drilling, interface core-drilling, post-installation drilling and proof test core-drilling for foundation works must be carried out by a Registered Specialist Contractor in the Ground Investigation Field Works category and be supervised by the site supervisors responsible for the quality supervision of foundation works. There is no need to submit a separate supervision plan for the pre-drilling and post-installation drilling works.

Quality Supervision for Soil Nailing Works

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.

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.

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.

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.

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.

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.

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.

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.

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.

Code of Practice for Site Supervision

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CODE OF PRACTICE FOR SITE SUPERVISION – Quality Supervision for Foundation Works

CODE OF PRACTICE FOR SITE SUPERVISION – Quality Supervision for Soil Nailing Works