Reclamation Ground Settlement Monitoring by Using GPS and Other Positioning Technologies at ShenZhen Airport.

Abstract

Hong Kong is a small territory of about 1070 km2 . There is an ever-increasing demand for land to cope with her increasing development. Typical geology in Hong Kong under the seabed comprises a layer of soft marine deposit of variable thickness of up to 20 m, overlying alluvium, residual soil, decomposed rock and bedrock. However, the marine deposit is too soft to support any structures. Conventional reclamation practice in Hong Kong is to dredge the marine deposit, build the seawalls and fill the enclosed space by sand. This conventional approach has many shortcomings. A research project was undertaken by The University of Hong Kong to develop a vacuum preloading technique that is environmentally safe to improve the engineering properties of the thick layer of soft marine deposits so that they can be kept in place during land reclamation. As a result, the environmental problems relating to dredging can be completely eliminated. A vacuum preloading test near the Shenzhen Airport was carried out as part of a very large research program. Sub-surface field instrumentation comprised piezometers, inclinometers, extensometers and pressure cells to monitor the performance of the vacuum system and the physical changes of the marine deposit during vacuum preloading. Surface settlement was monitored using 3 units of high precision GPS equipment throughout the test for checking against the sub-surface monitored movement. It is necessary to use a fully automatic system like GPS for replacing conventional survey because the test was carried out over water, which was difficult to access and the test was carried out over a very long period of 4 months. This paper reports the use of GPS for reclamation ground settlement monitoring and demonstrates cm-level positioning results through experimental trials. The results also agree very well with the sub-surface settlement readings.