Report No. : GEO Report No. 257

Report Title : Study on Masonry Walls with Trees (2011), 154 p.

Author : C.M. Wong & Associates Limited

Abstract

The study on the methods of upgrading masonry walls with the objective of preserving the masonry blocks and existing trees thereon as far as possible commenced in November 2004. Professor C.Y. Jim of the Department of Geography, HKU, was appointed as the tree specialist for this study.

This study aims to assess the effects of wall trees on masonry walls. The stability of wall trees was not studied. This study included literature review, site inspections and information search. Based on the study, if trees grow on masonry walls, tree roots have minimal harmful effect and some beneficial effect on the stability of masonry walls. Due to the difficulty in quantifying the effect of roots, it may be ignored during stability analysis of masonry walls with trees. Surcharge of wall trees were found to have adverse effect on the stability of masonry walls. Wind forces on wall trees may cause additional sliding forces and overturning moments to act on the masonry walls. In the assessment of stability of retaining wall with trees, professional judgement should be exercised regarding whether the root anchorage is strong enough to sustain the design wind forces. If not, the effects of wind forces on wall trees could be ignored as far as the consequential effect on masonry walls is concerned.

Safety standards for checking the stability of masonry walls with trees are recommended in this report.

Special measures should be carried out during the upgrading of masonry walls that deserve preservation of the existing trees and the existing masonry patterns. The recommended special measures are presented in this report.

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