Soil Conditions
Ground information for the site showed the excavation to be in medium, dense marine sands , underlain by completely decomposed granite.

Solution
AOKI investigated the use of anchor systems knowing the benefits that an open cut could offer to unhindered access for the construction of the four RC tunnels required by MTR.

This section immediately followed the submerged segment Victoria Harbour Tunnel.

The main works involved the design, drilling, installation, stressing and removal of 460 No. SBMA anchors up to 67m long. Using 5 rows of anchors the top two rows, founded in the marine sands had working loads of up to 1400kN and the lower three rows, founded in very dense silt, had working loads of 2000kN.

Preliminary testing demonstrated that loads up to 3000kN were achievable.

Construction
Up to 5 No. drill rigs using duplex drilling techniques produced the average 39m long hole for installation of the multiple-strand anchors which were stressed using specially developed twin strand multi-jack stressing heads.

The open excavation allowed by the anchor solution enabled the RC tunnels in this section to be completed 4 months ahead of those sections where struts were employed.

Wall movement amounted to less than half that predicted. The anchors were removed during the next 6 months in co-ordination with the permanent construction.

 

Client	Mass Transit Railway Corporation
Engineer	Robert Benaim & Associates
Main Contractor	Aoki Corporation
Specialist Sub-contractor	Austress Freysinnet Freysinnet Hong Kong JV