The new DWA-A 127 worksheet

# Structural analysis of sewers and drains – what will change?

Worksheet A 127 is currently under revision, analogously to the already completed DWA-A 161. The aim of this paper is to discuss briefly the most significant changes in DWA-A 127-1, which correspond to the editing status of December 2017. Publication of the preliminary yellow copy is planned for 2018.

## A number of minor changes

The material properties for all related DWA regulations are transferred to DWA-A 127-10. The semi-probabilistic safety concept with partial safety factors will be introduced analogously to the European standards and  DWA-A 161. General notes are given for application of numerical analyses (finite element method). The new designations A0 instead of A4, and B0 instead of B4, are purely formal to achieve a logical sequence (decreasing compaction) of the installation conditions. Sub-groups analogous to DWA-A 161 are introduced for designating in-situ soils. Classification of backfill remains as it is. The internal friction angle for G4 (cohesive soil) is reduced from 20° to 15°.

## Intermittently flowable, self-compacting backfilling materials (ZfsV)

Utilization of self-compacting backfilling materials (ZfsV) can be calculated only with A 127, if behavior similar to soil exists even after complete hardening. This condition must be verified based on a data sheet (for example, deformation module EB as a function of time). Additional as-built checks for buoyancy and safety against buckling must be performed. The design supporting angle is 2α = 120° or 90° when using sheet piling. As a benefit, αB = f1 = f2 = 1 may be applied. A calculated minimum limit applies to a trench width of bg = da + 2 x 0.15.

## Consideration of underramming in sheet piling

Until now, attention was called to worksheet ATV-AG 1.5.5 for taking this effect into account. Now the increase projection is limited to as ≤ 2 and as ≤ ar + bg/da. The latter limits the maximum influence of underramming to the center of the trench. Factor as increases the load concentration on the pipe. In addition, factor ks is limited: it takes into account the reduction of the support angle and the load concentration in the center of the top of the pipe. Factor ks = 1.3 is replaced by ks = 1 for ≤ DN 800 and ks = 1.2 for  ≥ DN 1200. Interim values may be interpolated. This measure favors all pipe dimensions by at least 8%, and smaller pipes by significantly more.

## Summary

A revision of DWA-A 127 became necessary to establish conformity with the current European body of regulations (e.g., partial safety coefficients and live loading), to take account of changes in railroad regulations, to make improvements (for example for underramming), and to include supplements (e.g., Zfs backfill materials and pipelines laid parallel to railroad tracks).

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