NWDSM Section 04 - Civil Engineering_A5 (18 Apr 2013).pdf

Section 4: Civil Engineering

D/MTRC/NW/DSM/ST/400/A5

New Works Design Standards Manual Section 4: Civil Engineering Revision Record Sheet

Version

Date of Issue

Clause No(s)

A1

Jan 1997

All

First issue

PEM

A2

Apr 1997

All

Underground openings, grout pressures, water loads, ground definitions and references amended

PEM

A3

March 2008

All

General update. See TMSG paper dated 19 March 2008 for details.

PjD on behalf of TMSG

A4

April 2009

All

General update. See TMSG paper dated 15 April 2009 for details.

HPE on behalf of TMSG

A5

April 2013

All

General update. See TMSG paper dated 18 April 2013 for details

HPE on behalf of TMSG

NWDSM-Section 4(Cover)-A5

Brief Description of Change

Approved By

April 2013

Section 4: Civil Engineering

D/MTRC/NW/DSM/ST/400/A5

CONTENTS 4.1

4.2

INTRODUCTION

4.1/1

4.1.1

General

4.1/1

4.1.2

Definitions

4.1/1

4.1.3

Synopsis

4.1/1

4.1.4

Design Deliverables

4.1/3

4.1.5

Abbreviations

4.1/4

GENERAL DESIGN CRITERIA

4.2/1

4.2.1

Scope and General Requirements

4.2/1

4.2.2

Design Life, Standards, Codes, and Regulations

4.2/1

4.2.3

Structure Gauge, Headroom and Setting Out

4.2/3

4.2.4

Structure Movements

4.2/4

4.2.5

Hazard on Existing Buildings and Structures

4.2/4

4.2.6

Structure, Ground and Temporary Works Movement Monitoring

4.2/7

4.2.7

Drainage and Flood Protection

4.2/9

4.2.8

Design for Fire

4.2/12

4.2.9

Design for Durability

4.2/12

4.2.10

Water Tightness Control

4.2/17

4.2.11

Void Access and Void Ventilation

4.2/19

4.2.12

Precast Parapet Finishes

4.2/20

4.2.13

Perimeter Fence and Parapet Requirements

4.2/20

4.2.14

Utility and Services Connections

4.2/21

4.2.15

Design For Collision From Railway

4.2/21

4.2.16

Electrical and Mechanical Services Requirements

4.2/22

4.2.17

Specialised Construction Elements

4.2/24

4.2.18

Envisaged Method and Sequence of Construction

4.2/24

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Section 4: Civil Engineering

D/MTRC/NW/DSM/ST/400/A5

Figure Number

4.3

4.2.9.F1

Stray Current Monitoring Point

4.2.9.F2

Overhead Line Mast - Foundation Details

4.2.9.F3

Corrosion Monitoring

4.2.12.F1

Precast Parapet

4.2.15.F1

Collision Protection – Wall Details

4.2.15.F2

Collision Protection – Pier Details

SPECIFIC DESIGN CRITERIA

4.3/1

4.3.1

Scope

4.3/1

4.3.2

Cut and Cover Structures

4.3/1

4.3.3

Underground Openings

4.3/2

4.3.4

Immersed Tube Tunnels

4.3/16

4.3.5

Ground Level and Overhead Structures

4.3/23

4.3.6

Structural Movement Joints

4.3/28

Figure Number

4.4

4.3.5.F1

Abutment Movement Joint - Access and Details

4.3.6.F1

Structural Movement Joint Details

DESIGN LOADS

4.4/1

4.4.1

Scope and General Requirements

4.4/1

4.4.2

Combination of Loads and Partial Safety Factors

4.4/1

4.4.3

Dead Loads

4.4/3

4.4.4

Imposed Loads

4.4/4

4.4.5

E&M Loads

4.4/6

4.4.6

Railway Live Loads

4.4/8

4.4.7

Highway Live Loads

4.4/10

4.4.8

Soil and Water Loads

4.4/11

4.4.9

Flotation Loads

4.4/13

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Section 4: Civil Engineering

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4.4.10

Wind Loads

4.4/15

4.4.11

Temperature, Shrinkage and Creep Loads

4.4/16

4.4.12

Collision and Impact Loads

4.4/16

4.4.13

Earthquake Loads

4.4/18

4.4.14

Parapet Loads

4.4/20

4.4.15

Crowd Loads

4.4/20

4.4.16

Air Pressure

4.4/21

4.4.17

Construction Loads

4.4/22

Figure Number

4.5

4.6

4.4.5.F1

Not Used

4.4.5.F2

Not Used

4.4.5.F3

Escalator Hoisting Hooks - Arrangement of Cast-in-Sockets

4.4.6.F1

Nominal Rolling Stock Loading

4.4.6.F2

Derailment Loading Configuration

SITE INVESTIGATION

4.5/1

4.5.1

Scope

4.5/1

4.5.2

Definitions

4.5/1

4.5.3

General

4.5/2

4.5.4

Extent

4.5/3

4.5.5

Contaminated Land

4.5/3

4.5.6

Pumping Test

4.5/3

GEOTECHNICAL DESIGN

4.6/1

4.6.1

Scope

4.6/1

4.6.2

Reclamations

4.6/1

4.6.3

Waste Landfills

4.6/2

4.6.4

Slopes and Embankments

4.6/5

4.6.5

Surface Excavation

4.6/6

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Section 4: Civil Engineering

4.7

4.8

D/MTRC/NW/DSM/ST/400/A5

4.6.6

Underground Excavations

4.6/9

4.6.7

Retaining Structures

4.6/10

4.6.8

Foundations

4.6/11

4.6.9

Trackform Substructure

4.6/12

4.6.10

Ground Bolts and Anchors

4.6/14

4.6.11

Blast Design and Vibrations

4.6/16

INSTRUMENTATION AND MONITORING

4.7/1

4.7.1

Scope

4.7/1

4.7.2

Instrumentation & Monitoring Design

4.7/1

4.7.3

Monitoring

4.7/3

STRUCTURAL DESIGN

4.8/1

4.8.1

Scope

4.8/1

4.8.2

Dynamic Analysis

4.8/1

4.8.3

Earthquake Analysis

4.8/1

4.8.4

Fatigue Analysis

4.8/4

4.8.5

Design For Flotation

4.8/5

4.8.6

Design for Durability - Steelwork

4.8/7

4.8.7

Design for Durability - Concrete

4.8/8

4.8.8

Prestressed Concrete Structures

4.8/13

4.8.9

Reinforced and Prestressed Concrete Detailing

4.8/14

Figure Number

4.9

4.8.9.F1

Column Tie Details for Seismic Design

4.8.9.F2

Ductility Detailing Provision for Seismic Design

DRAINAGE

4.9/1

4.9.1

Scope

4.9/1

4.9.2

General

4.9/2

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Section 4: Civil Engineering

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4.9.3

Drainage Water Volume Estimation

4.9/6

4.9.4

Drainage System – Hydraulic Analysis

4.9/8

4.9.5

Station and Ancillary Buildings

4.9/10

4.9.6

Tunnel, Shaft and Cavern Systems

4.9/12

4.9.7

Bridges and Elevated Structures

4.9/13

4.9.8

Building, Line and Portal Sumps

4.9/14

4.9.9

Culverts

4.9/15

4.9.10

Surface Water Groundwater and Foulwater Pumps

4.9/16

4.9.11

Viaducts

4.9/16

Figure Number

4.10

4.9.2.F1

Drainage Channel at Diaphragm Wall and Slab Connection

4.9.5.F1

Trackbed Drainage – Stations Base Slab

4.9.5.F2

Trackbed Drainage – Stations Intermediate Slab

4.9.7.F1

Viaduct Drains Emergency Overflow

4.9.8.F1

Drainage – Pump Sump Arrangement

4.9.8.F2

Tunnel Drainage – Sump Pump Arrangement (Sheet 1)

4.9.8.F3

Tunnel Drainage – Sump Pump Arrangement (Sheet 2)

TEMPORARY WORKS

4.10/1

4.10.1

Scope

4.10/1

4.10.2

General

4.10/1

4.10.3

Design Interfaces with EBS

4.10/2

4.10.4

Design Interfaces with New MTR Structure

4.10/2

NWDSM-Section 4(Contents)-A5

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Section 4: Civil Engineering 4.1 Introduction

D/MTRC/NW/DSM/ST/401/A5

4.1

INTRODUCTION

4.1.1

GENERAL

4.1.1.1

All subsections of this Section 4 of the New Works Design Standards Manual (NWDSM) shall be read in conjunction with each other and all other sections of the NWDSM. In some subsections guidance is given with regard to the work to be undertaken in each stage of the design. However, it shall not be assumed that the work in previous design stages has been completed or that deliverables required by the NWDSM or Scope of Services Document are available. In this respect, reference shall be made to the documents forming the Contract or Agreement for the design of the Works, where any previously produced and available documents will be noted.

4.1.2

DEFINITIONS

4.1.2.1

Civil Engineering and Building terms used within this section of the NWDSM are in accordance with BS 6100 “Glossary of Building and Civil Engineering Terms”, unless noted otherwise. Where terms are apparently contradictory or their use is unclear, clarification from the Corporation shall be sought before proceeding with the design.

4.1.3

SYNOPSIS

4.1.3.1

Section 4 of the NWDSM sets out the design requirements for all underground, surface and above ground civil engineering and building works. It is divided into subsections as listed below: i)

Subsection 4.2 - General Design Criteria This subsection defines the general criteria and lists the principal design standards, codes of practice and government regulations to be used for the design of all civil engineering and building works. It includes the minimum design requirements for the following: a) b) c) d) e) f) g) h) i) j) k) l)

surface and groundwater flood protection; fire resistant design; durability of structures; stray current and corrosion; crack control; void access; precast parapet finishes; perimeter fence and parapet; utilities and services connections; collision from railway vehicles; electrical and mechanical services provisions; and construction sequence.

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Section 4: Civil Engineering 4.1 Introduction ii)

D/MTRC/NW/DSM/ST/401/A5

Subsection 4.3 - Specific Design Criteria This subsection defines additional requirements for the design of specific underground, surface and above-ground structures such as tunnels, shafts and bridges.

iii)

Subsection 4.4 - Design Loads This subsection defines the particular requirements for loadings to be used in the design of all civil engineering and building structures.

iv)

Subsection 4.5 - Site Investigation This subsection defines the amount of ground investigation required, sampling pattern for contaminated land, supervision and data format to be used in investigations for all civil engineering and building works.

v)

Subsection 4.6 - Geotechnical Design This subsection defines the particular requirements for geotechnical design standards and methods to be used in the design of all civil engineering and building works which include geotechnical processes, slopes and earthworks.

vi)

Subsection 4.7 - Instrumentation and Monitoring This subsection defines the particular requirements for instrumentation and monitoring of structures and structural movements as well as ground and water movements for all civil engineering and building works.

vii)

Subsection 4.8 - Structural Design This subsection defines the minimum requirements for the design, detailing and analysis of reinforced or prestressed concrete, steelwork and other materials for all civil engineering and building works.

viii)

Subsection 4.9 – Drainage This subsection defines the specific requirements for civil engineering groundwater, surface water and foul water drainage systems and construction details, including the parameters to be used in the selection and sizing of surface water pumping systems. It also contains the general requirements for the estimation of surface water flows.

ix)

Subsection 4.10 - Temporary Works This subsection gives general guidance on the design and construction of temporary works. This subsection is also intended to assist in the assessment of submissions from contractors for temporary works design.

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4.1/2

Section 4: Civil Engineering 4.1 Introduction

D/MTRC/NW/DSM/ST/401/A5

4.1.4

DESIGN DELIVERABLES

4.1.4.1

The requirements for design deliverables are defined in the Scope of Services Document. These shall be produced during the design process along with the drawings, calculations and other deliverables required under the particular agreement or contract.

4.1.4.2

The purpose of the sequence of reporting required is to provide sufficient information for the design to progress through the design process in a sequential, logical and controlled manner. This is to ensure that the design development from the Works conception to completion of construction is adequately undertaken, documented, follows the usual design process and thereby reduces the possibility of unnecessary redesign.

4.1.4.3

Each and every report shall be cross-referenced to the preceding and corresponding reports where these are available. Reports from previous stages shall not be assumed to be available unless specifically noted as such by the Corporation before the start of each new design stage.

4.1.4.4

The Scope of Services Document defines the scope of each deliverable and give the required format and content. It is anticipated that the outline of the report deliverables will be developed from the given format in the appendices. Allowance shall be made for flexibility of format to meet the specific demands of the Works. For the case of protracted and/or complex Works the report deliverables may be divided into sections for clarity. Item headings and numbering shall be developed to suit both the quantity of information available and the stage of the Works. Where amendments to the requirements are requested, these shall be approved in writing by the Corporation.

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Section 4: Civil Engineering 4.1 Introduction 4.1.5

D/MTRC/NW/DSM/ST/401/A5

ABBREVIATIONS AASHTO AIP CADD CPF CSF DES DSD DFT E&M EBS ECS EPB EPD FOS FRP GGBS GEO HAT HKPWDM HKSDM HKSWDM IMT M&W NATM NDL NSF NWDSM OHL PIP RMJ RPM SCLM SCR SGI SLS SMJ SPC TBM TE ULS WSD

American Association of State Highway Transport Officials Approval In Principle Computer Aided Design and Drafting Controlled Permeability Formwork Condensed Silica Fume Design Statement Drainage Services Department Dry Film Thickness Electrical and Mechanical Existing Buildings and Structures Environmental Control System Earth Pressure Balancing Environmental Protection Department Factor of Safety Fire Resistance Period Ground Granulated Blast furnace Slag Geotechnical Engineering Office Highest Astronomical Tide Hong Kong Port Works Design Manual Hong Kong Structures Design Manual Hong Kong Stormwater Drainage Manual Immersed Tube Tunnel Materials and Workmanship New Austrian Tunnelling Method Net Downward Load Negative Skin Friction New Works Design Standards Manual Over Head Line Packed-in-place Piles Rail Movement Joint Railway Protection Manual Sprayed Concrete Lining Method Station Control Room Spheroidal Graphite Cast Iron Serviceability Limit State Structural Movement Joint Seismic Performance Category Tunnel Boring Machine Tunnel Element Ultimate Limit State Water Supplies Department

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Section 4: Civil Engineering 4.2 General Design Criteria

D/MTRC/NW/DSM/ST/402/A5

4.2

GENERAL DESIGN CRITERIA

4.2.1

SCOPE AND GENERAL REQUIREMENTS Scope

4.2.1.1

This subsection defines the general design criteria and the principal design standards, codes of practice, and government regulations to be used for the design of all civil engineering works and building works.

4.2.2

DESIGN LIFE, STANDARDS, CODES, AND REGULATIONS General

4.2.2.1

The design life and principal standards given in this subsection and the Functional Requirements Manual shall be complied with, except where these are amended by other clauses or in specific written instructions from the Corporation.

4.2.2.2

The Corporation may direct that different or further criteria be adopted in additional to those laid down in this subsection, or other documents it refers to, at its discretion. However, the clauses, or other documents it refer to, may not be modified or waived without the prior written approval of the Corporation.

4.2.2.3

Any reference to a Standard, Code of Practice or Manual shall be the latest issue thereof including all amendments, unless noted otherwise. Design Life

4.2.2.4

In the design of structures for loadings, durability, and safety within a given return period, the design life shall be taken as 120 years for all structures. In the design for durability of all structures reliance shall not be placed solely on the recommendations of International Standards. In selecting materials and taking measures for durability due account shall be taken of the generally aggressive environment in which the Corporation's structures are placed. Due consideration shall be given to the monitoring and maintenance works required to maximise the life of the structure.

4.2.2.5

Where elements of the structures are to be maintained and/or are replaceable within the overall design life of the structure, the design shall include provision for ease of inspection, maintenance and replacement during ‘non-traffic hours’. These hours are generally from 0100 hrs to 0500 hrs on any day, except several “special days” during the course of a year in which 24-hour train service is required. Such maintenance or replaceable elements shall be minimised providing that the life cycle cost of the structure is also minimised.

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Section 4: Civil Engineering 4.2 General Design Criteria

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Hong Kong Standards and Regulations 4.2.2.6

In certain cases the design shall comply with Hong Kong Government Regulations, Standards or Ordinances in addition to the requirements of this NWDSM.

4.2.2.7

For structures subject to the requirements of the Buildings Ordinance and Building Regulations, the most onerous structural design requirements of the Buildings Ordinance, the Building Regulations or the provisions of the NWDSM shall apply. Principal Design Standards, Codes, and Regulations

4.2.2.8

Underground structures, shall be designed in accordance with “Hong Kong Code of Practice for the Structural Use of Concrete”, and, BS EN 1992-3: Liquid retaining and containment structures.

4.2.2.9

Bridges shall be designed in accordance with BS 5400: “Steel, Concrete and Composite Bridges” and the Hong Kong Structures Design Manual (HKSDM).

4.2.2.10

Surface and above ground structures, other than bridges, shall be designed in accordance with “Hong Kong Code of Practice for the Structural Use of Concrete”.

4.2.2.11

Structural Steel within Stations, Depots and Ancillary Buildings shall be designed in accordance with “Hong Kong Code of Practice for the Structural Use of Steel”.

4.2.2.12

Foundations shall comply with “Hong Kong Code of Practice for Foundations”,. Limit state philosophy, using BS 5400, “Hong Kong Code of Practice for the Structural Use of Steel” or “Hong Kong Code of Practice for the Structural Use of Concrete” as appropriate, may be used for the design of the foundation structures.

4.2.2.13

The design of highway and pedestrian structures, including parapets and associated pedestrian ways (other than those supported by structures), miscellaneous road works, traffic signs, and road markings shall be in accordance with the relevant sections of the HKSDM.

4.2.2.14

The design of seawalls associated with reclamation and miscellaneous marine works shall be in accordance with relevant sections of the Hong Kong Port Works Design Manual (HKPWDM).

4.2.2.15

The design of geotechnical works, which support or are adjacent to railway structures, such as embankments or cuttings and the like, shall be in accordance with the various references given in the NWDSM and relevant GEO Guides published by Geotechnical Engineering Office (GEO).

4.2.2.16

Drainage of surface water and foul water shall be designed in accordance with the NWDSM and the following codes and regulations as appropriate:

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Section 4: Civil Engineering 4.2 General Design Criteria

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i)

BS EN 752: “Drain and Sewer Systems Outside Buildings” Parts 1 to 4 (successor to BS 8005: “Sewerage”);

ii)

Hong Kong Buildings Ordinance and Building Regulations;

iii)

Hong Kong Government Drainage Services Department’s Stormwater Drainage Manual (HKSWDM) and Sewerage Manual;

iv)

PNAP183: “Keeping Buried Services out of Slopes”;

v)

Hong Kong Code of Practice on Inspection and Maintenance of Water Carrying Services Affecting Slopes; and

vi)

Environmental Protection Department (EPD) requirements.

4.2.2.17

In certain circumstances, the recommendations of other internationally recognised design standards and codes of practice may be adopted with the prior written approval from the Corporation.

4.2.2.18

Due cognisance shall be taken of the requirements of the Corporation’s Railway Protection Manual (RPM) when constructing works adjacent to the existing MTR railway system.

4.2.2.19

The Designer is expected to be fully conversant with all proposal/contract documents and other sections of the NWDSM. The Designer shall be required to reflect the intentions of these documents in the design, but shall also draw the Corporation's attention to any special conditions or developments which may require modification of these documents. Where requirements are duplicated and are required to be applied, the more onerous shall be adopted.

4.2.3

STRUCTURE GAUGE, HEADROOM AND SETTING OUT

4.2.3.1

All structures, permanent or temporary, adjacent to the track shall be designed and constructed such that no part of any structure, cladding or finish shall at any time under any condition of loading, settlement or creep, encroach within the structure or construction gauge as defined in Section 3 of the NWDSM.

4.2.3.2

Apart from the general clearances to areas adjacent to track, the provision for minimum headroom shall be in accordance with Section 5 of the NWDSM for stations and ancillary buildings; Section 3 of the NWDSM for bridges over railways and HKSDM for any other bridge, viaduct or elevated structure. Allowance shall be made for foundation movement, shrinkage and creep, where appropriate, in the determination of minimum headroom.

4.2.3.3

Railway structures shall be set out relative to the railway alignment. Full account of the constraints imposed by the railway alignment shall be allowed for in designs. Any change to the proposed setting out of a railway structure shall be cross-referenced to the alignment and shall be submitted for the approval of the Corporation before implementation. Due allowance shall be made in the setting out details and design for the movement of the works during the

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Section 4: Civil Engineering 4.2 General Design Criteria

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operational stage and that may occur during the construction of the works.

4.2.4

STRUCTURE MOVEMENTS General

4.2.4.1

The design shall include an assessment of movements induced by the works on Existing Building and Structures (EBS), new Permanent Works and Temporary Works movements. Recommendations from the movement assessment shall be incorporated into the Tender and Contract documents. Railway Structure Movements

4.2.4.2

The adopted designs and construction methods shall limit new Permanent Works structure movements to less than those specified in the RPM after commencement of trackform installation in new railway structures, or at any time in existing railway structures. Other Structure Movements

4.2.4.3

Detailed assessments shall be carried out on EBS based on the available records so as to evaluate the structural implications and required movement / distortion limits from the proposed Works. Differential Settlements

4.2.4.4

The general requirement for differential settlement analysis shall be taken into consideration in the structural design calculations and details for all structures. This is particularly important where restrictions in ground support systems and ground parameters can lead to large changes in support stiffness.

4.2.5

HAZARD ON EXISTING BUILDINGS AND STRUCTURES General

4.2.5.1

All Corporation structures, particularly underground structures, shall be designed so that they can be constructed in a practical manner which minimises any ground movements arising from construction works which are liable to cause damage to any EBS, slopes and utilities. In order to demonstrate that this is the case, ground movements shall be estimated using methods which have been approved in principle by the Corporation and the likely effects on structures reported in the EBS reports defined in the Scope of Services Document or Contract documents. Ground movement shall mean movement or distortion of the ground in any direction, subsidence or collapse.

4.2.5.2

Although the following clauses are specifically for EBS, a similar procedure shall be used for identifying the risks of damage to all other civil engineering works and features which may be sensitive to ground movements such as slopes, retaining walls, services, utilities, drainage, pavements and street

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Section 4: Civil Engineering 4.2 General Design Criteria

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furniture and reported in a similar manner to that required for EBS. 4.2.5.3

4.2.5.4

Each design stage will require an increased level of detail to reflect the development of the project with the aim of eliminating from further consideration: i)

those EBS which fall into a damage assessment category which are of acceptably low risk;

ii)

those EBS which fall into a damage assessment category which is considered to be totally unacceptable such that the design or method of construction must be changed.

The design of Permanent Works and Temporary Works shall ensure that the degree of damage to EBS falls within the limits set in Risk Category 0, 1 or 2 of the Building and Structure Damage Classifications given in Table 4.2.5.T1. The empirical nature of the classification should be noted. Buildings should be reviewed to ensure that the theory is applicable, and the application of the classification made primarily with respect to the ease of repair.

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Section 4: Civil Engineering 4.2 General Design Criteria Table 4.2.5.T1

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Building and Structure Risk Categories

Building and Structure Damage Classification

Approximately Equivalent Ground

(after Burland et al (1977) and Boscardin and Cording (1989)

Settlements and Slopes

Risk Category

Description of Degree of Damage

Description of Typical Damage and Likely Forms of Repair for Typical Masonry Buildings

0

Negligible

Hairline cracks

1

Very Slight

Fine cracks easily treated during

Approx Crack Width (mm)

Max. Tensile Strain (%)

(after Rankin (1987)) Max. Maximum Slope Settlement of of Ground Building (mm)

Less than 0.05 0.1 to 1

normal redecoration. Perhaps

0.05 to

Less

Less than

0.075

than

10

isolated slight fracture in building.

1:500

Cracks in exterior brickwork visible upon close inspection. 2

Slight

Cracks easily filled. Redecoration

1 to 5

probably required. Several slight

0.075 to

1:500 to

0.15

1:200

10 to 50

fractures inside building. Exterior cracks visible: some repointing may be required for weathertightness. Doors and windows may stick slightly. 3

Moderate

Cracks may require cutting out and

5 to 15 or

0.15 to

1:200 to

patching. Recurrent cracks can be

a number

0.3

1:50

masked by suitable linings. Re-

of cracks

pointing and possibly replacement

greater

of a small amount of exterior

than 3

50 to 75

brickwork may be required. Doors and windows sticking. Utility services may be interrupted. Weather-tightness often impaired. 4

Severe

Extensive repair involving removal

15 to 25

Greater

1:200 to

Greater than

and replacement of sections of

but also

than 0.3

1:50

75

walls, especially over doors and

depends

windows required. Windows and

on number

frames distorted. Floor slopes

of cracks

noticeably. Walls lean or bulge noticeably, some loss of bearing in beams. Utility services disrupted. 5

Very Severe

Major repair required involving

Greater

Greater

Greater than

partial or compete reconstruction.

than 25

than 1:50

75

Beams lose bearing, walls lean

but also

badly and require shoring.

depends

Windows broken by distortion.

on number

Danger of instability.

of cracks

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Section 4: Civil Engineering 4.2 General Design Criteria Table 4.2.5.T1 Notes:

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Building and Structure Risk Categories (Continued)

1)

The table is based on the work of Burland et al (1977) and includes typical maximum tensile strains for the various damage categories (column 5) used in the Building and Structure Classification.

2)

Crack width is only one aspect of damage and should not be used on its own as a direct measure of it.

3)

Columns 6 and 7 also indicate the 'green-field' settlements and settlement trough slopes and are based on the methods of Rankin(1987). Risk Categories using the Rankin method are approximately equivalent to those proposed by Burland, although in some cases there may be significant differences.

EBS Condition And Structural Surveys 4.2.5.5

The Corporation will arrange for a detailed condition survey to be carried out by an independent surveyor on all EBS in Risk Category 1 to 5 inclusive, primarily for insurance purposes. However, a review by the Designer of these surveys shall be carried out and advice be given on the implications/considerations, if any, with respect to the proposed construction options and designs, if different to those contained within the detailed evaluations carried out previously.

4.2.5.6

The Corporation will arrange for a condition survey to be carried out for EBS adjacent to the work sites. Generally, EBS subject to at least 10mm ground movement or induced vibrations of 13mm/s will be surveyed, but exceptional buildings and structures outside such zone of influence should be considered on their merits.

4.2.6

STRUCTURE, MONITORING

4.2.6.1

Materials and Workmanship (M&W) Specification requires movements of all major temporary works including cofferdams, excavations and adjacent EBS as specified in the Contract to be monitored within and adjacent to the Works during the Contract period. Therefore Temporary Works, new Permanent Works, ground areas and EBS adjacent to new Permanent Works equivalent to or defined as Category 2 to 5 shall be defined as requiring monitoring (hereafter referred to as 'monitored elements') in the Design and Tender or Contract documents as appropriate.

4.2.6.2

In accordance with the M&W Specification the Contractor is also required to establish survey reference points on both sides of the front and back, top and bottom of adjacent EBS forming at least 8 reference points per building identified as requiring monitoring. Readings of all monitoring points at regular (at least weekly) intervals are required to be taken and submitted to the Corporation promptly throughout the duration of the Contract. However where it is considered that the building sensitivity or the predicted rate of movement warrants more stringent requirements, the extent of monitoring and frequency

GROUND

AND

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TEMPORARY

WORKS

MOVEMENT

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shall be subject to the approval of the Corporation and specified in the Design and Tender or Contract documents as appropriate. 4.2.6.3

The frequency and extent of monitoring for monitored elements shall be defined and shall be in all cases sufficient to give a comprehensive picture of overall movements. Measures shall be subject to the approval of the Corporation.

4.2.6.4

Structure, ground and Temporary Works movement monitoring drawings shall be produced for both the Tender and Contract documentation. The drawings shall incorporate the various movement control levels and requirements of the M&W Specification. These drawings will form the basis for monitoring and define the minimum requirements that the Contractor shall undertake.

4.2.6.5

Movement control levels for the monitored elements shall be defined accordance with the following criteria.

4.2.6.6

4.2.6.7

in

i)

Alert Level

-

Remedial measures agreed.

ii)

Alarm Level

-

Remedial measures instituted and revised Alert and Alarm levels set.

iii)

Action Level

-

Serviceability limit, stop work.

"Alert Level" shall initially be set as 0.5 times the serviceability limit movement for the monitored elements. The serviceability limit movement for a monitored element shall be the lesser of: i)

the calculated design value for the serviceability limit movement for the Temporary Works element;

ii)

the Temporary Works element movement which would theoretically cause services disruption, RPM, Buildings Ordinance (BO), EBS allowable structure or ground limits as defined in Cl.4.2.5.4 and Table 4.2.5.T1 to be compromised; and

iii)

allowable movement of the monitored element in accordance with RPM, BO, EBS or ground limits as defined in Subsection 4.2.5 and Table 4.2.5.T1.

The M&W Specification requires that following "Alert Level" movement at any location the Contractor shall immediately submit a written report to the Corporation reviewing all total and differential movements/distortions to date, assessing the effects of the movements/distortions on monitored elements and predicting further movements and their effect on monitored elements based on the trend to date. Where it is considered and agreed by the Engineer that movement trends indicate that "Alarm Level" may be reached during the course of the Works, the Contractor is required to submit proposals for remedial measures to limit further movement for the approval of the Engineer. The remedial proposals shall be reviewed and the Engineer advised as to their likely efficacy. Notwithstanding the above a change between consecutive readings greater than 5mm shall necessitate the imposition of "Alert Level" status

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regardless of the global movements. 4.2.6.8

"Alarm Level" shall be set at 0.7 times the serviceability limit movement for the monitored element. In accordance with the M&W Specification "Alarm Level" of movement at any location requires the Contractor to immediately instigate the approved remedial measures in accordance with the Contractor's method of construction and Temporary Works, agreed at the "Alert Level" status. Work may then only proceed if the remedial measures have been implemented and are in the opinion of the Engineer shown to be effective.

4.2.6.9

Upon reaching "Alarm Level' status the Contractor is required by the M&W Specification to submit an updated report reviewing the movements including differential movements and distortion. The report shall assess the effects on monitored elements and predict further movement and their subsequent effect on monitored elements. In addition, revised "Alert Level" and "Alarm Level" values which take into account the implemented remedial works shall be submitted and approved by the Engineer before work may continue.

4.2.6.10

"Action Level" shall initially be set at the serviceability limit movement for the monitored element. In accordance with the M&W Specification movement greater than the "Action Level" at any location will, subject to agreement by The Engineer, necessitate an immediate cessation to work. Requirements for building resumption, resumption of construction and a complete review of the Temporary Works and construction methods will be required as instructed by the Engineer.

4.2.6.11

Upon reaching "Action Level" status in accordance with the M&W Specification the Contractor will be required to provide a report detailing the full history of movements and remedial measures adopted in relation to the actual construction sequence. The report shall contain a review and interpretation of the events and give recommendations for enabling the work to proceed. Work may only resume upon the written instruction of the Engineer.

4.2.7

DRAINAGE AND FLOOD PROTECTION Flood Protection to Structures

4.2.7.1

All openings into underground or surface structures shall be located above the 1 in 200 year flood level. The effects of burst water mains and blocked surface water drainage systems shall be included in the determination of the design flood level. An analysis of the flood paths for the area surrounding the structures shall be carried out in order to determine the appropriate design flood level. In general, structures located on flat land shall have a minimum flood protection of 1.2 m above the surrounding ground level or natural ground water level. Flood protection requirements for structures located on slopes shall be assessed individually.

4.2.7.2

Structure entrances shall be protected by a combination of steps or slopes as appropriate up to a landing of at least 450 mm above street level, combined with removable flood boards to provide the remaining minimum margin to the

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design flood level. Standard flood board and the associated cast in fixing details are given in Section 5 of the NWDSM. 4.2.7.3

Entrances to underground structures shall be protected by flood doors designed to withstand the full head of water to the design flood level. Such doors shall be designed to be operated manually by a maximum of two persons.

4.2.7.4

Vehicle ramps into underground structures shall have a crest at or above the design flood level. A separate drainage system leading to the structure drainage system shall be provided on the structure side of the crest.

4.2.7.5

All civil engineering and building works shall be provided with drainage systems designed to cope with water from all sources such as rainfall, seawater overtopping, broken services, nominal seepage through underground structures and track wash down water in accordance with Subsection 4.9. Flood Protection for At-Grade Tracks

4.2.7.6

At grade tracks shall be protected against groundwater flooding by raising the railway formation (underside of sub-ballast) to above the 1 in 200 year flood level. Where the railway formation is unavoidably below this level or where the sub grade softening or movement may otherwise occur then, sumps, pumps, and subsurface drainage system shall be provided to prevent water levels rising exceeding 1 meter below the formation level.

4.2.7.7

Notwithstanding the above, a drainage system shall be incorporated into the design for draining surface water. Flood Protection Adjacent to Seawalls

4.2.7.8

The location of the 'Railway Boundary' and the necessity for protection against seawall overtopping shall be agreed with the Corporation at the start of the design process.

4.2.7.9

Where the Railway Boundary may be affected by seawall overtopping water, measures shall be adopted to ensure the following are complied with: i)

emergency personnel/detraining and accessing to/from the landward side of the Railway Boundary during storm events shall be provided where possible. Where this is not possible, overtopping protection shall be provided to the emergency access path, as defined in (iii) below, on the seaward side to the same degree as required within the Railway Boundary, as given in Cl.4.2.7.11;

ii)

no maintenance access shall be allowed during storm events from the seaward side of the Railway Boundary; and

iii)

a paved promenade/maintenance path with a minimum width of 4 m (or up to the Railway Boundary, whichever is less), shall be provided

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at the back of the seawall. 4.2.7.10

If any of the requirements of Cl.4.2.7.9 cannot be complied with, more stringent criteria than those given in Cl.4.2.7.11 may be required and specific approval from the Corporation shall be obtained. Reference should also be made to Cl.4.9.2 for the provision of drainage inside the Railway Boundary.

4.2.7.11

Measures shall be adopted to ensure the following limitations on wave and wind driven overtopping water volumes are complied with: i)

Operational limit (no damage) Up to 1 in 10 year event return periods: Railway Boundary average overtopping limit ≤ 0.001l/s/m.

ii)

Normal storm (limited damage) 1 in 10 year to 1 in 100 year event return periods: Railway Boundary average overtopping limit ≤ 0.02 l/s/m.

iii)

Extreme storm (significant damage) 1 in 100 year to 1 in 200 year event return periods: Seawall Crest average overtopping limit ≤ 200 l/s/m.

4.2.7.12

The terms and values given above have been determined from the guidance given in CIRIA Special Publication 83, Manual on the Use of Rock in Coastal and Shoreline Engineering.

4.2.7.13

When designing sensitive / fragile components within the Railway Boundary, it should be noted that instantaneous overtopping rates over a single wave period can be 500 to 1000 times average rates (derived over a period of 100 to 1000 waves) given in Cl.4.2.7.11.

4.2.7.14

Areas of the Railway shall be identified which may be particularly sensitive to the risks of overtopping for reasons of :

4.2.7.15

4.2.7.16

i)

coastline geography and seabed hydrography;

ii)

seawall structural form; and

iii)

transitions between structures and the like.

The Corporation shall identify similar particularly sensitive locations due to provision of : i)

E&M equipment, which is more sensitive than usual;

ii)

sensitive operational requirements; and

iii)

sensitive maintenance requirements.

The probability of inundation in the areas noted in Cl.4.2.7.14 and Cl.4.2.7.15 and the desirability for more stringent mitigation measures than those stated

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in Cl.4.2.7.11 shall be identified. The provision of any mitigation measures shall be agreed with the Corporation for each situation. 4.2.8

DESIGN FOR FIRE

4.2.8.1

All structures shall be designed to satisfy the fire safety requirements as specified in Section 5 of the NWDSM.

4.2.8.2

Materials specified for the Works shall be non-combustible and do not emit toxic fumes when subject to heat or fire, except where specifically allowed within the NWDSM, for example pipework. In all cases where there is a significant fire risk, materials shall be self-extinguishing, low flammability, low smoke and low toxicity type.

4.2.8.3

The detailing of structural elements shall be in accordance with “Hong Kong Code of Practice for the Structural Use of Concrete” to achieve the Fire Resistance Periods specified in Section 5 of the NWDSM, or those required under the Buildings Ordinance, whichever is more onerous.

4.2.8.4

The minimum thickness of reinforced concrete walls or slabs separating railway structures from structures owned or controlled by any other party shall be 200 mm.

4.2.8.5

Fire protection steel mesh is required within the nominal concrete cover zone for the concrete cover greater than 40mm according to the Code of Practice for Fire Safety in Buildings. The fire protection steel mesh shall be either hot dipped galvanised steel or stainless steel. However, fire protection steel mesh shall not be used in the soffit of tunnel lining above running tunnels to which there is no access during traffic hours. In this case the risks to train operation of spalling concrete due to mesh corrosion are considered more likely to occur than fire damage.

4.2.8.6

With respect to the condition as stated in CI.4.2.8.5 where fire protection steel mesh shall not be used, to prevent the threat of concrete spalling during a tunnel fire, a passive fire protection system by the addition of monofilament polypropylene fibres (PPF) in the concrete shall be provided in lieu of the required fire protection steel mesh. PPF shall be complied with the requirements of BS EN 14889-2:2006.

4.2.8.7

Acceptance for the use of PPF including material properties and concrete mix shall be obtained from the Corporation and relevant government authorities.

4.2.9

DESIGN FOR DURABILITY General

4.2.9.1

Particular care should be taken to ensure that: i)

designs and details are capable of being executed to the required

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standard, with due allowance for dimensional tolerances and the capabilities of the workforce;

4.2.9.2

ii)

there are clear instructions on permissible deviations; and

iii)

elements which are critical to workmanship, structural performance, durability, and appearance are clearly identified on the drawings.

In carrying out structural designs, the Designer shall ensure that both the ultimate and serviceability limit-states have been checked in accordance with the NWDSM and other adopted relevant standards and codes of practices. Soil and Groundwater Conditions

4.2.9.3

The Designer shall take full account of the prevailing soil and groundwater conditions and those predicted to occur within the design life of the Works, in designing to achieve durability.

4.2.9.4

Table 4.2.9.T1 gives indicative values from which the Designer can assess the degree of severity of soil and groundwater conditions. Table 4.2.9.T1

Soil and Groundwater Criteria

Chloride (Cl) NON AGGRESSIVE Soil or groundwater must satisfy all criteria AGGRESSIVE Soil or groundwater exceeding any limit

4.2.9.5

SOIL Sulphate pH (SO4)

Resistivity Ohm/cm

Chloride (CI)

GROUNDWATER Sulphate pH (SO4)

Resistivity Ohm/cm

〈0.05%

〈0.24%

〉5.5

〉10 000

〈200 ppm

〈0.4 g/L

〉5.5

〉10 000

〉0.05%

〉0.24%

〈5.5

〈10 000

〉200 ppm

〉0.4 g/L

〈5.5

〈10 000

Notes: 1)

Sites with low pH or where sulphate reducing bacteria or industrial pollutants occur require special consideration.

2)

This table should not be confused with the ground conditions for earthing mat design where high resistivity (>10,000 Ohm/cm) implies ‘aggressive’ conditions requiring a larger earthing mat and a low resistivity implies ‘non aggressive’ conditions (