Single-Level Tied-back Walls

The factors which influence the behaviour of tied-back or anchored flexible walls were reviewed by Bjerrum et al (1972) and are discussed in the Section 7.1.1 of GCO Publication No. 1/90. For anchored walls with sloping anchors, the effect of the vertical component of the anchor force should be considered in design (Figure 35). The vertical force may cause possible downward movement of the wall when the wall has not been driven to refusal and the point resistance is low.

In the design of anchored walls, there are four primary areas of geotechnical consideration:

(a) ultimate limit states,

(b) serviceabiliy limit states,

(c) earth pressures for structural design, and

(d) design water pressures.

The consideration of ultimate limit state rather than serviceability limit states usually governs the design.

Ultimate Limit States

(1) Overall Stability. Possible failure mechanisms of anchored sheet pile walls are shown in Figure 36.

(a)《作业备考》APP-22基础及地库挖掘工程中的地下水位降低情况；

(a) PNAP APP-22 on Dewatering in Foundation and Basement Excavation Works;

(b)《作业备考》APP-24铁路的防护措施－《铁路条例》，《地下铁路（收回土地及有关规定）条例》及《建筑物条例》附表5所列地区的第3号地区；

(b) PNAP APP-24 on Railway Protection under Railways Ordinance, Mass Transit Railway (Land Resumption and Related Provisions) Ordinance and Area Number 3 of the Scheduled Areas in Schedule 5 to the Buildings Ordinance;

(c)《作业备考》APP-30附表所列的半山区地区内发展的岩土工程管制；

(c) PNAP APP-30 on Geotechnical Control on Developments in Mid-levels Scheduled Area;

(d)《作业备考》APP-49地盘勘测及土地勘测；

(d) PNAP APP-49 on Site Investigation and Ground Investigation;

(e)《作业备考》APP-61附表所列地区第2号及4号地区内发展的岩土工程管制；

(e) PNAP APP-61 on Geotechnical Control on Developments in Area Numbers 2 and 4 of the Scheduled Areas;

(f)《作业备考》APP-62保护污水和排水隧道；

(f) PNAP APP-62 on Protection of Sewage and Drainage Tunnels;

(g)《作业备考》APP-97处理同意展开建筑工程及街道工程的程序；

(g) PNAP APP-97 on Consent Procedures for Building Works and Street Works;

(h)《作业备考》APP-134大屿山北岸指定地区的发展；以及

(h) PNAP APP-134 on Development in the Designated Area of Northshore Lantau; and

(i)《作业备考》APP-137打桩和类似操作所引致经地下传送的震动及地面沉降。

(i) PNAP APP-137 on Ground-borne Vibrations and Ground Settlements Arising from Pile Driving and Similar Operations.

2.认可人士／注册结构工程师／注册岩土工程师并应遵守以下与基础工程相关的设计、建造、行政及程序的规定。

2. AP/RSE/RGE should also observe the following design, construction, administrative and procedural requirements relating to foundation works.

基础设计及建造

Design and Construction of Foundations

浅基础

Shallow Foundations

3.无钢筋混凝土填料常用于台阶式开挖不平坦或倾斜的岩石表面，以建造浅基础。不过，置于基脚或筏式基础之下的大型无钢筋混凝土填料（即最深处超过1米）应视为结构构件，并按照《2013年混凝土结构作业守则》设计。

3. Mass concrete fill is often applied for benching uneven or sloping rock surface for construction of shallow foundation. However, mass concrete fill of significant size (i.e. with a maximum depth greater than 1 m) placed beneath the footing or raft foundations should be regarded as a structural element and designed in accordance with the Code of Practice for Structural Use of Concrete 2013.

进行建造前及建造后验证钻探的注册专门承建商

Registered Specialist Contractor for Pre and Post-construction Proof Drilling

4.所有预钻、接合部位取芯钻探、装置桩柱后的钻探及藉取芯钻探以进行验证测试的工作必须由注册专门承建商(现场土地勘测工程类别)进行。受聘进行《建筑物（建造）规例》第20条所要求藉取芯钻探以进行验证测试的工作的承建商，应声明与基础承建商的关系，包括其公司是否为基础承建商的控股、附属或联营公司，或是否有财务上关系（例如交错董事），或是否与该基础工程有财务利益关系。

4. All pre-drilling, interface core drilling, post-installation drilling and proof test by means of core drilling must be carried out by a registered specialist contractor in the Ground Investigation Field Works category. The contractor who is appointed to carry out proof test by means of core drilling required under section 20 of the B(C)R should make declaration on its relationship with the foundation contractor, including whether or not it is a holding, subsidiary, or an associated company of the foundation contractor, or has financial relationship with it e.g. cross-directorship, or has financial interest in such foundation works.

大直径钻孔桩取芯钻探

Core drilling for Large Diameter Bored Pile

5.就大直径钻孔桩、矩形桩及其他类似的桩柱而言，混凝土与基岩在接合部位应接触良好，而且桩底部以下的岩石应全部达到所需的级别。为方便在接合部位进行取芯钻探，可预留直径不少于150毫米的管道，以接合部位上方大约1米为止在接合部位取芯钻探过程中观察到的轻微缺陷，例如沉淀物薄层、接合部位的混凝土分隔或桩底部以下的岩石有风化缝是可以接受的，前提是注册结构工程师／注册岩土工程师认为可以接受，并提供论证理由，以及在有需要时进行额外验证钻探。另一种做法是，注册结构工程师可以在基础图则中载列纠正以上缺陷的补救工程建议。建议应提供详细的施工方法说明，以及注册结构工程师要求采取的监督措施。

5. For large diameter bored piles, barrettes and the like, the concrete should be in good contact with the bedrock at the interface and the rock should be consistently of the required grade beneath the pile base. To facilitate successful core drilling at the interface, a pipe of not less than 150 mm diameter may be left in and stopped at about 1 m above the interface. Minor imperfection observed during the interface core drilling, such as a thin layer of sediment, segregated concrete at the interface or weathered seam in the rock beneath the pile base, may be considered acceptable provided that the RSE/RGE can demonstrate the acceptance with justifications and additional proof drilling, if required. As an alternative, the RSE may include in the foundation plans the proposed remedial works for rectifying any such imperfections. The proposals should provide details of the method statement and the supervision required by the RSE.

呈交图则及申请展开工程同意书

Plan Submission and Consent Application

6.呈交基础图则或记录时，如须提供岩土报告及辅证文件，该报告及文件应由注册岩土工程师拟备及签署。

6. When geotechnical reports and supporting documents are required for submission of foundation plans or records, such reports and documents should be prepared and signed by the RGE.

7.沿地盘界线安装桩墙及灌浆帷幕可提供额外预防设施，保护对沉降敏感的构筑物、道路或地下设施，以避免受在其邻近安装嵌岩工字钢桩期间的不良影响。为此，除非已呈交安装相关桩墙及灌浆工程的记录图则及评估报告，否则建筑事务监督可能不同意展开位于地盘界线10米以内的桩柱工程。为方便处理该展开工程同意书的申请，注册结构工程师可同时呈交有关桩柱的表格BA8，以及相关桩墙及灌浆工程的记录图则及评估报告。如属大型地盘，展开嵌岩工字钢桩工程的同意书的申请可分阶段呈交，注册结构工程师／注册岩土工程师应呈交额外的评估报告，以证明在展开工程同意书的申请时，地盘有足够预防设施。

7. Installation of pile walls and grout curtain along the site boundary would provide additional precautionary measures for safeguarding settlement sensitive structures, roads or underground services against possible adverse effects imposed upon them during the installation of the socketed steel H-piles at close proximity. In this respect, the consent for the commencement of works for those piles located within 10 m from the site boundary may not be granted unless the record plans and assessment report for the installation of related pile wall and grouting works have been submitted. To facilitate the processing of such consent application, the RSE may submit the Form BA8 for the piles together with the record plans and assessment report for the related pile walls and grouting works concurrently. In the case of large sites where consent application for those piles may be submitted in stages, the RSE/RGE should submit an additional assessment report to justify the adequacy of the precautionary measures at the time of consent application.

8.除了在某些情况下须先符合附加条件（例如为敏感建筑物进行施工前状况勘测、为毗邻建筑物提供撑柱等），屋宇署会考虑同时批准基础工程图则及同意展开有关工程。如果认可人士／注册结构工程师希望善用同步申请批准和展开工程同意书的简化程序，则应确保在呈交基础图则申请的32天之后才呈交要求同意展开工程的申请，以免不必要地使行政工作变得复杂。

8. Except in cases where there are imposed conditions to be met first, for example, pre-construction condition survey to sensitive buildings, shoring to adjoining buildings, etc. the Buildings Department (BD) may grant approval of plans for foundation works and consent for the commencement of such works at the same time. If the AP/RSE wishes to take advantage of the streamlined procedures for concurrent applications for approval and consent, the application for consent for the commencement of works should not be submitted before the 32nd day after the date of submission of the corresponding foundation plans for approval, so as not to cause unnecessary administrative complications.

9.为减少建筑地盘停工的时间，挡土构件（例如板桩/管桩墙）可与基础工程同时进行。当所有挡土构件均已妥善安装，便可在完成基础工程之前，呈交挖掘工程监督计划及申请展开地下结构挖掘工程的同意书。这程序容许在审查基础记录图则及准备验证测试期间进行地下结构挖掘工程。

9. To minimise the idling time on construction sites, earth-retaining elements such as sheet/pipe pile walls may be installed concurrently with the foundation works. Once the earth-retaining elements have been satisfactorily installed, a consent application may then be made and the corresponding supervision plan be submitted for the commencement of excavation works for substructures prior to the final completion of foundation works. This would allow excavation works for substructures be carried out while foundation record plans are being scrutinised and proof tests are being arranged.

10.在下述事项完成之前，建筑事务监督不会同意展开桩帽及上盖结构工程：

10. Consent for the commencement of the pile cap and superstructure works will not be given until:

(a)呈交令人满意的基础记录；

(a) the foundation records have been submitted and found satisfactory;

(b)呈交表格BA14，证明基础工程已竣工；

(b) the Form BA14 certifying the completion of foundation works has been submitted;

(c)成功完成所需的验证测试；以及

(c) the required proof tests have been satisfactorily carried out; and

(d)符合所有相关的附加条件，包括物料测试的规定。

(d) all relevant imposed conditions including material testing requirements have been complied with.

表格BA14、基础记录图则及报告

Form BA14, Foundation Record Plans and Reports

11.基础工程完成后，应按照《建筑物（管理）规例》第25条，呈交证明基础工程竣工的表格BA14。特大地盘的基础工程可适当地分阶段进行，并分别进行验证测试。如有此类分阶段安排，应尽早与屋宇署磋商。为加快验证测试的选桩过程，可以在呈交表格BA14之前，先呈交打桩记录图则及报告。

11. Upon completion of the foundation works, a Form BA14 certifying the completion of the foundation works should be submitted according to regulation 25 of the Building (Administration) Regulations. For exceptionally large sites, foundation works may be suitably phased and separately considered for proof testing. BD should be consulted as early as possible on such phasing arrangement. To expedite the selection of piles for proof tests, piling record plans and reports may be separately submitted prior to the submission of the Form BA14.

12.如所呈交的记录图则及报告具备足够数据，屋宇署会在收到基础工程的表格BA14的14天内通知认可人士／注册结构工程师所选择用于验证测试的具代表性桩柱。为避免不必要的延误，认可人士／注册结构工程师应确保打桩记录图则及报告已齐备所有有关建成桩柱的资料。

12. If sufficient information is available in the submitted record plans and reports, BD would within 14 days of the receipt of the Form BA14 for foundation works inform the AP/RSE of the representative piles identified for proof tests. To avoid unnecessary delay, the AP/RSE should ensure that full information on the completed piles is included in the piling record plans and reports.

13.如桩柱整体的实际基础深度与经批准桩基础图则显示的预期基础深度有差异，在以下情况下须就桩基础设计以反演分析进行复审及重新呈交桩柱荷载表︰

13. Should the overall actual founding levels of piles differ from the anticipated founding levels shown on the approved piling plans, review of piling design with back analyses and resubmission of pile loading schedule plan would be required in the following circumstances:

(a)桩柱整体的实际基础深度与经批准桩基础图则显示的预期基础深度相差多于桩柱长度的±5%；或

(a) the overall founding levels differ by more than ± 5% of pile lengths; or

(b)邻近桩柱之间的长度差异导致桩柱荷载明显重新分布或显示有陡斜的基岩地形。

(b) the difference in pile lengths among piles within close proximity results in significant redistribution of pile loads or implies the existence of a steep bedrock profile.

如果差异显著，须进行额外土地勘测证明偏差合理。屋宇署会视乎个别情况订定额外土地勘测的要求。就附表所列地区的第2号地区和第4号地区的基础工程，应留意《基础守则》第7.8条及《作业备考》APP-61所载的规定。

If the variation is significant, additional ground investigation (GI) may be required to justify the deviation. Such requirement of additional GI will be determined by BD on a case-by-case basis. For foundation works in Area Numbers 2 and 4 of the Scheduled Areas, attention should be drawn to the requirements stipulated in clause 7.8 of the Foundation Code and PNAP APP-61.

14.就大直径钻孔桩基础工程，当至少85%的建成桩完成混凝土及岩石接合位的验证钻探后，认可人士可向屋宇署呈交表格BA14。此外，如在此阶段具备足够证明，可无须呈交所有28天龄期混凝土立方块的测试结果。倘若已呈交在审批基础图则时所要求的其他资料，而有关资料亦令人满意，在余下的验证钻探及混凝土立方块测试进行期间，屋宇署会同步拣选具代表性桩柱进行验证测试。如其后发现不正常情况，屋宇署可能要求进行额外验证测试。只有所有呈交的验证测试结果及所需文件令人满意，屋宇署才会认收表格BA14。

14. For large diameter bored pile foundations, AP may submit Form BA14 to BD after completion of proof drilling at the concrete and rock interface for at least 85% of the completed piles. In addition, the submission of all test result for concrete cubes at 28 days is not necessary if sufficient justification is available at this stage. Provided that other information as required in the approval of the foundation plans have been submitted and found satisfactory, BD would select representative piles for proof tests while the remaining proof drilling and concrete cube testing are still in progress. In case there are irregularities found thereafter, BD may require additional proof tests. The Form BA14 would only be acknowledged when the results of all the proof tests and required documents are submitted and found satisfactory.

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