INTRODUCTION

Puente del Inca is a natural bridge located at 32° 49′ 34″ S, 69° 54′ 41″ W, Mendoza, Argentina (Figure 1). Its shape forms a natural arch that stands upon the Cuevas river, in the Central Andes (Figure 2). Currently, it is considered a Protected Natural Area and it is part of the QhapaqÑan Andean Roadway System, recently designated a World Heritage Site by the UNESCO. Puente del Inca is not only a rigid geological structure composed by hot mineral spring waters, but rather a “Systems Geobiology” related to biological, physical and chemical processes. The balance between erosion factors and the natural formation process establishes the current morphology of the structure. A l t hough Puen te de l I nca undergoes a natural processes of regression, it was not until human intervention that its structural integrity was severely impacted. In light of studies conducted on the structure, it becomes necessary to monitor and assess this delicate balance in order to protect the bridge's integrity. With the goal of contributing to Puente del Inca's

IANIGLA - CCT - CONICET- Av. Dr. Ruiz Leal s/n. Parque General San Martín - (5500) MENDOZA. ARGENTINA. TEL. 54-261-5244223E-mail: elannutti@mendoza-conicet.gob.ar/mlenzano@mendoza-conicet.gob.ar

ADVANCES IN REMOTE SENSING FOR CULTURAL HERITAGE: FROM SITE DETECTION, TO DOCUMENTATION AND RISK MONITORING”, ESA - ESRIN Frascati (Rome), Italy

1 2 3 1,2Lannutti, E. , Lenzano, M. G. , Barón, J. , Lenzano, L. 1 Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, (IANIGLA)-CCT, CONICET, Mendoza, Argentina.

2 Universidad Nacional de Cuyo-CONICET, Mendoza, Argentina

3 Instituto de Estudios del Ambiente y Recursos Naturales (IDEARN), UNCuyo, Mendoza, Argentina.

DATA AND METHODS

As a start of the monument's structural study, a 3D model was made from LIDAR techniques and a material testing from some samples extracted from the bridge. By means of the Finite Element Method, the structural analysis of the bridge was u n d e r t a k e n t o g e t h e r w i t h simulations of its behavior. These include static and dynamic loads; for example snow weight, hydraulic, pedestrian, seismic, etc., tension studies, strains, security factors, modal parameter estimation, simulation of both aeolian and fluvial erosive factors, and thermal studies. Figure 3 and 4 show examples of the simulation of the structure's modal parameters and of the most affected areas by Aeolian erosion.

1. FEM

Structural health monitoring of the natural bridge Puente del Inca, Mendoza, Argentina

restoration and conservation, the structure's behavior and evolution were studied through SHM (Structural Health Monitoring) techniques. These nondestructive methods include: a) the structure's FEM (Finite Element Method) model through material testing and m e a s u r e m e n t s 3 D L a s e r Scanning; b) Measuring the bridge's surface velocities (N, E, U) and displacements building a GNSS (Global Navigation Satellite System) network; c) GPR (Ground-penetrating radar) techniques to analyze the internal structure; d) Estimate modal parameters using o u t p u t - o n l y r e s p o n s e s measurements with seismometers and System Identification software.

Universidad Nacional

Departamento de Geomática

Figure 1: Map of relative location of Puente del Inca Natural Structure on National Road 7, distant 183 km from Mendoza city.

Figure 2: View of Puente del Inca natural structure

3. GPRGPR measurements were made on the bridge's surface with 200-Mhz and 16-80-Mhz equipment. The use of the 200 MHz frequency relates the behavior of the electromagnetic signal in the presence of activity and inactivity of hot spring waters. By using TWT (Two-way travel-time) measurements taken with 20 MHz frequency, we estimated the propagation velocity in the medium and from it, determined the depth profile of radargrams. Besides, us we measured we made GPR-GPS measurements, following two longitudinal and three transverse profiles with 20 MHZ frequency. Each profile was referenced and related to the 3D model of the structure intending to improve interpretations of the obtained radargrams. We were able to differentiate reflectors along the

2. GNSSA GNSS net was built on the monument, consisting of 14 points (Figure 5), to obtain the structure's m o v e m e n t s a n d s u r f a c e deformation velocities. By means of differential GPS post-processing with the software Bernese, the

4. Modal parameter estimationMeasurements with seismometers were made to obtain the structure's dynamic characteristics. With the goal of reducing this study's impact on the monument we used wind and the Cuevas River as an excitation source, and we also opted for the opera t iona l moda l ana lys is techniques. 16 points over the bridge surface were measured with two seismometers. Using these series of data we estimatated the natural frequencies, vibration modes and damping utilizing modal parameter identification in the time domain and frequency domains.We may emphasize that the obtained parameters not only gave us a view of the bridge's state but did also provide a better adjustment of FEM model contrast ing the measured values with the simulated dynamic values of the computational model.

Figure 3: Modal Parameters

Figure 4: Aeolian erosion

position and velocity values for the installed points were obtained. Until now three series of discontinuous measurements have been done, once a year since 2013.

Figure 5: GNSS net

structure, such as an inner cavity, higher saturation areas, changes in interface and incrustations (Figure 5).

Figure 6: Longitudinal profile on the bridge's northern edge with 20-Mhz measurements

CONCLUSIONS

All these techniques, methodologies and tools will be integrated to obtain a diagnosis and a continuous follow up of the monument's condition, as well as a model to simulate the behavior and evolution of the bridge that will be worth analyzing. This research project will also contribute to the labors of preservation and restoration of this magnificent natural monument.

ACKNOWLEDGMENTS

We thank the Dirección de Recursos Naturales Renovables of the Province of Mendoza and their staff for their support. We also acknowledge the cooperation of Adalberto Ferlito, Robert Haroldo, Mario Rosas, Robert Smalley Jr, Demian Gomez and Geomatics Group Ianigla Conicet.