A slope being cleared up prepared for the installation of the rock bolts. The provision of access to a working slope poses certain difficulties in

Transcription

1 A slope being cleared up prepared for the installation of the rock bolts. The provision of access to a working slope poses certain difficulties in most cases.

2 A preliminary treated slope with the surface protected by a layer of sprayed concrete. The polypropylene net pegged on the slope surface is used as the background to hold the grass usually planted using hydroseeding process.

3 A large-sized slope formed after the site formation process. Note the turfed surface and the surface channel system provided as a means to prevent erosion of the slope by storm water.

4 Another formed slope in Tiu Keng Leng area with height more than 50m and set back in 8 benches. Due to the steepness, the upper 4 benches are stabilized using soil nails.

5 A 30m newly formed slope in a residential development project making use of buttress wall as a means of stabilization. The buttress wall is constructed of in-situ reinforced concrete.

6 A 35m slope protected with rock bolts and spray concrete. To provide a better appearance, in-situ concrete planter boxes are built on the benches for the planting of vegetations.

7 An occasionally used method to stabilize an earth slope by the provision of a simple gravity retaining structure piled up in rock masses as toe to a benched slope.

8 The scaling process - immediately after the forming of the slope, loose rock or boulders are removed from the exposed faces, usually using manual method.

9 Appropriate landscaping provision is often carried out to large area of slope after treatment in order to provide better appearance. The one as shown here is turfed with grass on sprayed mortar surface with planting beds provided at certain locations.

10 The provision of drainage is of paramount importance in ensuring continual stability of slope. The drainage system should collect and safely convey run-off from the catchment from and above the slope to appropriate points of discharge. The photo shows the casting of a stepped channel on a steep slope.

11 The construction of a large in-situ cascade in reinforced concrete as the main trunk to a large slope drainage / catchment system.

12 One common method to stabilize a fractured rock slope is by the use of rock bolts. The photo shows a simple air-driven boring machine stationed on a temporary scaffold platform for the forming of holes for the insertion of the bolt.

13 Close up of the boring machine to form holes for the rock bolt.

14 A slope stabilized by rock bolts. Rock bolts are tensioned steel bars which comprise a short anchorage zone in sound rock and an unbonded zone in which tension is developed. Usually the head of the bolt is threaded and fitted with a torque nut used to develop tension while some are tensioned using hydraulic method

15 Detail of the set-up arrangement to tension a rock bolt using hydraulic jack. Note the tension gauge to monitor the extension of the bolt during the stressing process.

16 Insertion of the steel bar into the drilled hole. Note the bar centralizer at the front of the bar which is made of expanded PVC sleeve.

17 A typical set-up of a work platform composed of tubular steel to provide access for slope treatment works. The slope as shown in this photo is stabilized using soil nail. Note the heads of the soil nail at various levels of the platform.

18 Detail of the soil nail head before applying the concrete cover.

19 Detail of a removable galvanized steel head cover for a rock bolt which allows continual monitoring of the bolt.

20 A section of the treated slope with the concreted nail head in position.

21 Applying of the spray concrete to the bolted slope surface. Sprayed concrete can be used to provide surface protection for zones of weak or highly fractured rock. Steel fabric is often used as a reinforcement to span between rock bolts. Sufficient weepholes should also be provided to prevent building up of water pressure behind the surface.

22 Section showing the typical arrangement of a rock bolt with monitoring provision.

23 Soil nail head details for sprayed concrete slope surface.

24 Common methods of providing vegetation and green treatment to slopes.

25 Example of visual treatment to retaining wall.