Deformation features of the Yinshuigou deposit at Xiaowan Hydropower station were presented in this paper. Based on the factors of excavation, rainfall, drainage and reinforcement treatment, quite a lot of monitoring information is analyzed, the deformation mechanism of the slope is verified, and synchronized reinforcement effect is also evaluated. It provides much scientific reference for many aspects such as making hazard elimination plans, adjusting reinforcement parameters, optimizing construction organization and speeding the job schedule. It is also a typical case in the successful warning making and highly effective treatment of slope's large deformation which may provide reference for similar projects.
Xiaowan hydropower station is located in the midstream of Lancang Rive of Yunnan province in China. The 292m high Xiaowan arch dam that is the highest concrete arch dam under construction in the world. Yinshuigou deposit is located in front of the dam on the left bank between EL.1130m and EL.1590m, with a wide top, slender bottom and a total volume of about 4 million m3. The deposit rock's structure is compact and is mainly composed of rock blocks and boulders, debris-contained sand loam and debris. At the bottom where the deposit rock and the bedrock contact, there is usually a layer of slope wash, with the thickness between 0.15m and 2.45m; and in local areas, there are layers of diluvial deposit. When the slope was excavated from the top to EL.1276m, obvious deformation was detected by monitoring since Figure 1. Distribution of deformation of the deposit rock and layout of main monitoring points. Dec. 4, 2003. After the rainfall on Jan. 9, the deformation increased and on Jan. 29, the rate of deformation increased and the slope between EL.1245m and EL.1480m became deformation body with a clear boundary. On Jan. 29, 2004, the abnormalcy of the slope's stability raised the alarm again which drew great attention from all parties.
Fifty two surface survey points, 14 GPS measurement points, 20 inclinometer holes, 34 anchorage load cells, 12 sets of multi-point extensometers and 7 underground water level holes were arranged on the deposit. The layout of the primary measurement points is shown in Fig. 1. One high-precision TCA2003 monitoring robot is used for surveying. According to the actual conditions at the site and the requirements for precision, the measurement distance is kept within 100–700m and the horizongtal and vertical errors are within ±3.5 mm. The internal deformation was observed by deformation monitoring instruments provided by Sinco, Geokon, RocTest, etc. The most advanced GPS position monitoring system was installed By adopting multi-antenna technique, data were transmitted by GPRS and solved by GPS Single Epoch Algorithm. The observing-time period of each solution is 1–2 h and the precision is 1.0–3.5mm and thewhole-day unattended monitoring was realized.
