I.S. 420:2004(R2023)

Foreword 1
Declaration 2
CLAUSES
1 Scope 5
2 Normative references 5
3 Terms and definitions 7
4 Symbols 8
5 General requirements 8
6 Special requirements 21
7 Conformity evaluation 26
8 Marking 27
Annexes
A (informative) Information to be supplied in an enquiry or order 28
B (normative) Standards relevant to I.S. EN 1917:2004 28
C (normative) Surface void tests 29
D (normative) Dimensional tests 30 Figures
1 – Use of corbel slabs in conjunction with double steps or ladder 7
2 – Square and rectangular openings in circular cover slabs 14
3 – Square openings in rectangular cover slabs 15
4 – Typical adjusting unit 15
5 – Typical corbel slabs 16
6 – Circular openings in cover slabs 17
7 – Typical reducing slabs 18
8 – Typical landing slabs 19
9 – Loading arrangements for cover slabs 23
10 – Loading arrangements for reducing slabs 25
11 – Loading arrangements for landing slabs 25
12 – Loading arrangements for corbel slabs 26
C.1 – Gauge for assessing surface voids 29
D.1 – Gauge for measuring deviation from straightness 32Tables
1 – Symbols 8
2 – Cementitious content 9
3 – Cement groups 10
4 – Nominal sizes, internal manufacturing diameters and
tolerances of circular units 12
5 – Nominal sizes, internal manufacturing sizes and tolerances
of rectangular units 12
6 – Shape, size and position of square or rectangular openings
in cover slabs, adjusting units and corbel slabs 137 – Shape, size and position of openings in reducing and
landing slabs 13
8 – Strength classes and corresponding minimum crushing
loads for circular and rectangular chamber and shaft units 21
9 – Vertical proof loads for cover, reducing and landing
slabs to fit chambers greater than DN 1250 and corbel slabs 22
B.1 – Standards relevant to I.S. EN 1917:2004 28