CONTRIBUTION OF D.M.S. MONITORING SYSTEMS IN THE ANALYSIS OF SLIDE MICRO-MOVEMENTS FOR EARLY WARNING MANAGEMENT, RISK ASSESMENT AND EVALUATION OF MITIGATING ACTIONS D.M.S. IUE Auto Blocking 3D D.M.S. 3D system (Figure 2) has been specifically studied for 3 dimension measurement in drilling holes, so as to record deformations directly on rocks or soils, and to execute multi- piezometric/multi-pore pressure measurements in the same monitoring hole. The system is composed of modules (E.D. 80 millimeter, with packers for direct hole anchorage), linked by special 3D flexible joints with high traction resistance (up to 100 KN) and maximal extension between 10 and 140 mm.. The system is particularly effective in the analisys of very fractured rocks and of consolidation and subsidence cases. D.M.S. IU 2D D.M.S. IU is composed of a sequence of hard tubular modules (stainless steel elements AISI 304 diam. 48.3mm), each containing one or more geotechnical sensors and electronic boards for data control, A.D. conversion and transmission. D.M.S. IU monitoring system (Figure 3) requires a casing with a minimum diameter of 60 mm. No intrinsic limits exists to the number of measurement modules. The use of a pressure sensor requires a slotted pipe. The modules are linked by flexible joints that allow strong, continuous adaptability to bends and twists of the casing whilst maintaining rigorously the orientation with respect to a reference system defined during installation. It is possible to use different types of joints with traction resistance between 10 and 50 KN. The system maintains the correct direction also without the inclinometric casing grooves or with damaged ones, so monitoring is possible also inside smooth casings (diam > 2”). To protect the system, D.M.S. is equipped with internal special cables for power and signal. APPLICATIONS: 1) Contextual multi-parametric monitoring on the inside of the same drilling hole 2) Possibility to recover the column 4) Forecasting of landslide movements by analysis of micro-movements - Civil protection applications 5) Possibility of rehabilitation of strongly deflected inclinometric casings which are no more measurable with traditional inclinometric system 6) High space resolution of the measurements 7) Modular structure and cost reduction 8) Multiparametric monitoring for landslide 2D/3D modelling 3) High adaptability of the monitoring column to deformations D.M.S. ADVANTAGES D.M.S. MONITORING EXAMPLES: Figure 1. D.M.S. System Figure 3. D.M.S. IU 2D Figure 2. D.M.S. IUE Auto Blocking 3D Slope stability, landslides Dams monitoring Cuttings Roads stability Ground and buildings response to tunneling Ground and buildings response to tunneling 0 5 10 15 20 25 30 -10 -8 -6 -4 -2 0 2 4 6 8 10 Error - mm 0 5 10 15 20 25 30 -10 -8 -6 -4 -2 0 2 4 6 8 10 Error - mm D e p t h m Field Accuracy inclinometer Probe Survey (Total Error) (Mikkelsen) Inclinometer Probe Survey (Random Error) (Mikkelsen) IPI Accuracy Criterion (Dunnicliff,La Fonta; La Fonta & Beth) DMS Accuracy Comparison of accuracy and precision of monitoring data Knowing the accuracy and precision of inclinometric data in landslides and engineering works is very relevant, particularly when even the smallest indication of displacement is a matter of concern for an early warning in public safety, risk analisys/assestment and evaluation of mitigating actions in the shortest time . relevant precision increase, depending on the statistically redundant data collected by sensors, the increase in vertical discretization and the good coupling of the modules with the casing (see Figure 4 CMEM 2005, Malta). D.M.S. monitoring data reveal The results of 'in situ' test performed with D.M.S. I IU columns equipped with inclinometric biaxial sensors, 30 m string length, 30 sensors evidence an accuracy in equal to ±0.5mm. L.S.T. (long stability tests-3 months) Albera Landslide Albera-Vendersi Landslide Slip surfaces micromovements 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6 6.4 6.8 7.2 7.6 8 01/01/06 03/01/06 05/01/06 07/01/06 09/01/06 11/01/06 13/01/06 15/01/06 17/01/06 19/01/06 21/01/06 23/01/06 25/01/06 27/01/06 29/01/06 31/01/06 02/02/06 04/02/06 06/02/06 Date Micromovements (mm) Slip surface I (Depth 23m) Slip surface II (Depth 14m) Cumulative Displacements (g.l.) D.M.S. Monitoring Control Unit GSM - GPRS GSM - GPRS Photovoltaic cells Control Unit GSM - GPRS GSM - GPRS Photovoltaic cells Technical service / Project Engineer / Monitoring Engineer D.M.S.( ) is a new multi-parametric in-place instrument for stability control and differential monitoring of soils, rocks, engineering works, in casing or borehole (Figure 1), designed mainly to evaluate danger levels of potentially instable areas. D.M.S. can be assembled 'in situ' forming an instrumented column, connecting the required number of modules, each containing one or more sensors and the electronic boards for data collection and transmission. The modules are linked by special 2D/3D flexible joints that allow strong, continuous adaptability to bends and twists of the drilling hole, whilst maintaining rigorously the orientation with respect to a reference system defined during installation. The link between sensors and control unit is realized with the digital mode protocol RS 485, for a maximum of 128 sensors linked to the central unit basic configuration. The control unit provides for the readings at regular time intervals, according to the requested program (default sampling: 1 reading/min/sensor, recording 1 average value/h per sensor). Remote control, download, storage and processing of data are made with a remote control station, equipped with GSM/GPRS integrated transmission and specific software “GEOMASTER”. The “D.M.S. Report”software enables data processing and the graphic display. Patent pending and trademark application C.S.G. S.r.l. - ITALY The Albera landslide (Northern Apennines) is of a complex-composite type involving the Vendersi village with an intermittent cinematic. The dimensions are relevant: length: 1,370 m, width: 519 m max, difference in height: 380 m, surface area: 51 x 10 4 m² and estimated volume: 11 x 10 6 m³ circa) and concerns the medium slope (Figure 5), crown altitude 950 m. a.s.l., toe altitude 570 m a s.l. A DMS IU column was installed in dicember 2005 by means of an helicopter (Figure 6), inside a 40 m deep drilling hole, rigged with a 3” slotted casing. The continuous monitoring is active with one reading/min/ per sensor, 1 averaged values each hour, GSM transmission. This system monitors the displacememt of the landslide body and the water table variations, making it possible to define and design urgent remediation activities and to compare phenomena and define critical precipitation thresholds for early warning. The continuous monitoring shows clearly (Figure 7) depth and velocity of 2 main rupture surfaces just a few days after installation, due to a rapid snow melting phase in winter season; this results is not achievable with traditional instrumentation (see Vendersi-Slip Surfaces Micromovements). Figure 4. Accuracy comparison Figure 5. Albera Landslide Figure 6. Albera D.M.S. installation Figure 7. D.M.S. Albera, slip surfaces Figure 8. S.Stefano Displacement - Water level vs Time The D.M.S. in S.Stefano Belbo (Langhe area) was installed to monitor a sector of a complex-composite landslide in a high risk area that envolves the unique access to the Belbo Valley during main flood events. In order to start urgently a remediation activity, a continuous monitoring program was started, financed by the National Civil Protection. D.M.S. column has been installed close to the road along the unsafe sector in June 2005, using 11 biaxial inclinometric modules, each long 1m, and 1 piezometric module, inside a slotted PVC, 80 mm diameter casing. The reported data refer to january to march 2006 monitoring period along the 9 months of continuous recording, with one reading/min/ per sensor, and 1 average values each hour. The column shows a main sliding surface occurring at 7.5 m bgl (Figure 8) with intermittent activity (V2=0.3 mm/d period 31/01- 11/01; V4=1.65 mm/d period 22/02-03/03, V5=0.4 mm/d period 03/03-07/03). A main displacement phase starts with a delay time of 4.5 days after water table raise during february; triggering factor: snow melting mixed to rain. S.Stefano Belbo landslide L. Foglino, (1) M. Lovisolo (1) A. Della Giusta (2) (1)C.S.G. S.r.l. (2) University of Padova 1/2/06 1/6/06 1/10/06 1/14/06 1/18/06 1/22/06 1/26/06 1/30/06 2/3/06 2/7/06 2/11/06 2/15/06 2/19/06 2/23/06 2/27/06 3/3/06 3/7/06 3/11/06 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Slip surface displacement (mm) -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 Water table(m bgl) Water table Slip surface displacement D.M.S. S.STEFANO BELBO LANDSLIDE TRIGGERING - DISPLACEMENT ANALYSIS MONITORING PERIOD: JANUARY - MARCH 2006 V1=0 mm/d V2=0.3 mm/d V3=0 mm/d V4=1.65 mm/d V5=0.4 mm/d V6=0 mm/d 4.5 dd Cumulative Displacement Module 0.00 5.00 10.00 15.00 20.00 25.00 30.00 0.00 0.20 0.40 0.60 0.80 1.00 Displacement [cm] D e p t h [ m ] Report N. 4 Date: 17/02/2006 3.11.05 Report N. 3 Date: 06/02/2006 3.12.14 Report N. 2 Date: 01/02/2006 3.12.45 Report N. 1 Date: 15/01/2006 3.16.02 Report N. 0 Date: 30/12/2005 9.02.54 Surface of rupture 1 Surface of rupture 1 Surface of rupture 2 Surface of rupture 2 C.S.G. S.r.l. Centro Servizi di Geoingegneria C.S.G. S.r.l. Centro Servizi di Geoingegneria 15011ACQUITERME(AL)viaTogliatti8-ITALY-tel.+39144356177 fax+39144350344 web www.csg-geo.it email [email protected]