Investigation of a GPS multi-antenna system for slope stability monitoring

Abstract

Recently, the use of Global Positioning System (GPS) in slope deformation monitoring has received great attention in various countries. However, in Hong Kong, this application is still in planning and testing stage. The reasons may be the high expenses of purchasing several receivers for various monitored points and the reduction of GPS accuracy due to biases such as multipath effect. A GPS multi-antenna system was developed by Ding et al. (2000) for the monitoring of slopes. This system links several antennas to one receiver so that the cost of a monitoring system will be diminished dramatically. The aim of this study is to review the state of art of this system and suggest improvements in views of software and hardware. Three aspects of the system are studied. They are the GPS algorithms and software, system configuration design, and the GPS multipath effect in slope monitoring surveys. Two programs are developed for the improvements of software for the system. One is the automatic alarm system which is capable of checking the real time GPS data against a pre-defined threshold value and sending warning message by email and SMS message to mobile phones to prevent problems. The other is the automatic data extraction program that can automatically divide the single GPS data file collected from the GPS multi-antenna system into different sections to ease the data computation. A low cost GPS long distance data communication method is introduced in which it links a 200 m long cable with only a 40 dB signal amplifier to provide accurate and low cost GPS solutions. To demonstrate the effectiveness of this method, experiments are conducted in the Ho Hai University in Nanjing. Finally, the multipath effect on GPS measurements is studied by making use of its day-to-day repeatability characteristic. From the successful experimental results in this study, it is contemplated that this enhanced system may be applied widely in Hong Kong and many parts of the World to identify potential slope failures and also can be used to study the stability of many other engineering projects such as dams, high-rise buildings and structures. At the end of the research, the limitations of the enhanced GPS multi-antenna system are pointed out. It is the hardware constraint and restriction in static application. Improvements in these two aspects are suggested to further enhance the system.