LAYMAN'S GUIDE TO LANDSCAPE TREATMENT OF SLOPES AND RETAINING WALLS

Transcription

1 LAYMAN'S GUIDE TO LANDSCAPE TREATMENT OF SLOPES AND RETAINING WALLS Geotechnical Engineering Office Civil Engineering Department

2 For orewor ord This Layman s Guide, intended for the use of the general public, provides general guidance on landscape treatment for man-made slopes and retaining walls. It is Government s policy to make slopes look as natural as possible. We have committed to landscape every existing slope upgraded under the Landslip Preventive Measures Programme and every newly-formed Government slope. With this commitment and effort, we believe that our living environment will be greener and more harmonious. With the experience gained from providing landscape treatment to Government slopes, we have prepared this document with the assistance of Urbis Limited. We hope that it will help and encourage private slope and retaining wall owners to provide landscape treatment to their slopes and walls when planning maintenance or upgrading works. 1 For more detailed guidance, the reader may refer to GEO Publication No. 1/2000 Technical Guidelines on Landscape Treatment and Bio-engineering for Man-made Slopes and Retaining Walls published by the Geotechnical Engineering Office of the Civil Engineering Department. R.K.S. Chan Head, Geotechnical Engineering Office July 2002

3 Contents Page Foreword 1 Contents 2 Why Do We Need Landscape Works on Slopes and Retaining Walls? 3 "Before" and "After" Look of a Landscaped Slope 4 Examples of Soft Landscape Treatments 5 Examples of Hard Landscape Treatments 6 2 Seven Landscape Design Objectives 7 Some Tips for Landscaping Slopes 12 Tip 1 - Preserve trees in your community 12 Tip 2 - Create planting opportunities 15 Tip 3 - Provide Ornamental planting 20 Are Landscape Works Costly? 21 Are Landscape Works Difficult to Maintain? 21 Seven Things to Remember 22 Assistance 23 Selected Publications Related to Slopes 24

4 Why Do We Need Landscape Wor orks on Slopes and Retaining Walls? To Enhance Proper operty Value To Improve Appearance ance To Crea eate a Greener Envir vironment 3

5 "Befor ore" and "After" Look of a Landscaped Slope BEFORE 4 AFTER More examples...

6 Examples of Soft Landscape Trea eatments Ornamental planting of shrubs and herbaceous plants at the toe of a slope with ferns covering the slope face Well maintained mature trees and ornamental shrubs on a slope 5 Climbers on a retaining wall with palm trees and decorative shrubs in a planting strip immediately in front

7 Examples of Hard Landscape Trea eatments Decorative designs on the face of a retaining wall enhanced by trees and shrubs in a toe planter Artificial rock and stone facing used to decorate a large-scale retaining wall 6 Artificial rock used to blend a steep slope into the surrounding natural landscape

8 Seven en Landscape Design Objectives es 1 Limit impacts on the natural environment Where possible, as much existing vegetation on and around the feature should be retained. 7 2 Fit with surrounding landscape/ natural topography Where possible, the creation or restoration of features should respond to the broad variations in surrounding landform and vegetation.

9 3 Achieve naturalness Solutions involving natural materials (rock and vegetation) are almost always visually preferable to those using artificial ones. 8 4 Maintain simplicity The fewer the number of different engineering or landscape techniques used on a feature, the more likely it is to look coherent.

10 5 Mitigate visual impact 6 Where artificial or built elements are used, efforts should be made to blend the built elements into their surroundings in order to create harmony between the artificial and natural landscape. Contribute to environmental sustainability 9 Vegetation on features helps to eliminate greenhouse gases and can provide ecological habitats and sources of food for insects and birds.

11 7 Aesthetically pleasing The landscape design of features should conform to general principles of good aesthetic design. i. Unity and coherence 10 Planting at the toe and top of a retaining wall and fill slope successfully creates a unified appearance to the whole slope. ii. Proportion and scale The buttresses with masonry facing are suitably sized and dispositioned in relation to the retaining wall with ribbed finish to create a sense of proportion.

12 iii. Pattern and texture This design solution employs a variety of techniques in a co-ordinated manner, resulting in a composition having both pattern and texture. 11 iv. Rhythm and complexity Ribbed finish and plain concrete create a scene with both rhythm and complexity.

13 Some Tips for Landscaping Slopes: Tip 1 - Preserve trees in your community Use protective fencing to screen construction works from areas of existing vegetation 12 Use tree rings to retain existing trees where a hard surface is required (Professional advice should be sought as necessary) Protect existing tree trunks with wooden pallets and/ or hessian wrapping during construction works Locate soil nails and other engineering features away from tree trunks and roots Use toe walls to retain existing trees where the slope surface has to be re-graded

14 Examples of tree preservation on slopes and retaining walls Tree rings are provided to protect existing trees 13 Rings formed in the slope surface around tree trunks and roots allow retention of existing woodland trees

15 14 Existing trees are retained after upgrading works using soil nails Use of soil nails to stabilise an existing masonry wall allows attractive wall trees to remain undisturbed Soil nail heads concealed behind blocks in the wall face

16 Tip 2 - Crea eate planting opportunities 15 Slope Angle θ 35 o 35 o < θ 45 o 45 o < θ 60 o 60 o < θ 90 o Possible Planting on Slope Face grass hydroseeding with pit planting of trees and shrubs grass hydroseeding with erosion control matting and pit planting of trees and shrubs grass mix with erosion control matting with wire mesh reinforcement and pit planting of groundcovers, climbing plants and ferns use of new method including proprietary systems

17 Examples of vegeta etation tion on slopes and retaining walls Ornamental shrubs and groundcover at the toe of a retaining wall 16 Climbers on a retaining wall Self-clinging climbers on a steep rock slope Erosion control mat supporting a grass surface

18 Toe wall planter supporting colourful flowering shrubs 17 Combination of trees and shrubs on a slope Trees on a slope Grass surface on a slope

19 Species Commonly Planted in Hong Kong Trees 18 Casuarina equisetifolia (Horsetail Tree) Melaleuca leucadendron (Paperbark Tree) Groundco oundcover er and Cree eeper pers Eucalyptus citriodora (Lemon-scented Gum) Wedelia trilobata (Wedelia) Ficus pumila (Creeping Fig)

20 Shrubs Calliandra haematocephala (Red Powderpuff) 19 Ligustrum sinense (Chinese Privet) Hibiscus rosa-sinensis (Chinese Hibiscus) Rhododendron spp. (Azalea)

21 Tip 3 - Provide Ornamental planting Ornamental low shrubs on a slope 20 Clipped shrubs used in combination with flowering shrubs and mature trees to provide an attractive appearance to a slope

22 Are e Landscape pe Wor orks s Costly? The typical unit cost for a rang ange of products in 2001 are as below: Groundcovers Hydroseeding Shrubs Climbing Plants Tree: light standard Planter Hole Toe Planter (HK$10-15 each) (HK$10-20 per sq m) (HK$15-30 each) (HK$25-40 each) (HK$ each) (HK$200 each) (HK$ per linear m) Rates given are indicative only and may vary according to scale and site conditions. 21 Are Landscape Wor orks Difficult icult to Maintain? Typical maintenance wor orks for soft landscape wor orks: Regular inspections of plants to check their healthy growth Replacement planting where necessary Control of pests Trimming of vegetation as necessary Watering of ornamental planting Inspection of hard landscape works in relation to planting Clearance of drainage channels Typical maintenance wor orks for hard landscape wor orks: Check for damage of surface finishes and make necessary repairs

23 Seven en Things to Remember 22

24 Assistance More guidance can be found in GEO Publication No.. 1/2000 "Tec echnical Guidelines on Landscape Trea eatment and Bio-engineering for Man-made Slopes and Retaining Walls", which h is availa ailable le from : Government Publications Centre, Ground Floor loor,, Low Block, k, Queensway y Government Offices ices, 66 Queensway,, Hong Kong ong. "Layman's Guide to Slope Maintanence", and other leaflets and booklets on slope safety can be obtained from om District Offices ices.. For or more e informa ormation on slope related matters, please contact: Community Advisory Unit, Geotechnical Engineering Office ice, Civil Engineering Department Tel. No.: or browse the following web-sites: Civil Engineering Department Hong Kong Slope Safety Hong Kong Institute of Landscape Architects 23

25 Selected Publica lications Rela elated to Slopes 24