| Case studies on landslide monitoring, by newly developed IT Ground Tiltmeter System (below, “IT Ground Tiltmeter”), using accelorometers based on MEMS (Micro Electromechanical Systems) are reported. PWRI installed IT Ground Tiltmeters, that has been developed through the Joint Research with Akebono Brake Industry Co., Ltd. and Kawasaki Geological Engineering Co., Ltd. in 2008-2009, to measure tilt of the ground surface of landslides accurately. Weare testing the monitoring systems in different types of slope conditions: (1) a juvenile primary landslide in a slope facing to a road in a mountainous area (Site-A), (2) underwater slopes of a dam resovior area (Site-B), (3) a remobilized landslide facing a river, (4) a potential juvenile secondary landslide behind a collapsed slope. Observation by IT Ground Tiltmeters in Site-A and Site-B are reported precisely in this report. IT Ground Tiltmeter is an embedded type equipped with an accurate tiltsensor which detects gravity acceleration. Its features are: (1) ability to measure many areal points by linking up to 100 sensors to one data logger , (2) large measurement range of ±20º and precision of ±0.01º, (3) remote monitoring ability using cell phone circuits, (4) rapid installation ability simply by inserting and fixing the sensor in a single pipe poured on site.It is often reported that natural slopes, without a history of sliding, have suddenly collapsed, with destructive results. They are called juvenile primary landslides. To prevent or mitigate destruction caused by such landslides, initial minute motions must be accurately detected. However, unclear points remain concerning this motion because juvenile landslides are not revealed by clear landslide topography, it is difficult to reliably identify them, and measuring techniques are still not established. This resulted in minute motion suggesting the progress of creep deformation; a phenomenon which is a precursor of a juvenile landslide. The following is an outline of this test.Site-A was selected by a topographical reading using aerial laser profiler data from a region where several juvenile landslides have occurred in the recent years. At the test site, ridge topography is enclosed between talus slopes, collapsed topography etc., and there are gentle gradients at the top of slopes, so it is a rock slope where, presumably, creep deformation has loosened mountain sides. Minute motion showing cumulative tilting towards the bottom of the slope was noted to began in the N-S composition of the IT Ground Tiltmeter K-4 from August 27, i.e. 17days after heavy rainfall up to 212mm for 3 days long. Other compositions of the IT Ground Tiltmeters acceralated the tilting motionat the same time with the extensometer S-1, so that the deformation detected by the extensometer S-1 was proceded by the IT Ground Tiltmeter about 10 days.Monitoring under water of about 10m-depth was conducted in Site-B, by 3 IT Ground Tiltmeters. Adaptability of the IT Ground Tiltmeter to the underwater condition up to 30m will be confirmed by this field test in 2010.IT Ground Tiltmeter system, which is more appropriate to detect accumulation of slope movement earlier than ground extensometers, is expected to lead to measuring method to predict sudden juvenile landslide movement. We will continue performance of this measurement. |
