A customized resistivity system for monitoring saturation and seepage in earthen levees: Installation and validation

This work is based on the assumption that a resistivity meter can effectively monitor water saturation in earth levees and can be used as a warning system when saturation exceeds the expected seasonal maxima. We performed time-lapse ERT measurements to assess the capability of this method to detect areas where seepage is critical. These measurements were also very useful to design a prototype monitoring system with remarkable savings by customizing the specifications according to field observations. The prototype consists of a remotely controlled low-power resistivity meter with a spread of 48 stainless steel 20 Ã 20 cm plate electrodes buried at half-meter depth. We deployed the newly-designed permanent monitoring system on a critical levee segment. A weather station and an ultrasonic water level sensor were also installed in order to analyse the correlation of resistivity with temperature, rainfalls and water level seasonal variations. The preliminary analysis of the monitoring data shows that the resistivity maps follow a very reasonable trend related with the saturation/drying cycle of the levee caused by the seasonal variations of the water level in the irrigation channel. Sharp water level changes cause delayed and smooth resistivity variations. Rainfalls and, to a lesser extent, temperature seem to have an influence on the collected data but effects are apparently negligible beyond 1 m depth. The system is currently operating and results are continuously monitored

A challenging GPR investigation to assess the state of damage of a water tunnel

reserved3mixedS. Munda; L. Zanzi; D. ArosioMunda, Stefano; Zanzi, Luigi; Arosio, Dieg

Quality control of stone blocks during quarrying activities

Early detection of fractures and internal defects can help quarry owners in cutting quarrying costs and reducing the amount of waste products. Valuable stones used in construction industry such as marble, porphyry, granite, travertine, are usually extracted from quarries by cutting blocks whose size normally varies between 5 and 15 m 3. Transportation of these blocks from quarries, often located at high altitudes in mountainous environments, down to the headquarters of the stone industry where big machines are installed to transform the big size blocks into slabs or small size stones, can be quite expensive. Money could be saved by checking on-site the big size blocks with NDT methods able to detect internal fractures and other defects (voids, clay inclusions, etc.). A detailed map of fracture extension and orientation can be also very profitable in optimizing the production line. For example, the final destination of a block (i.e., production of slabs rather than small size blocks or other) and the orientation of the cutting planes can be more properly assigned. Currently, Ground Penetrating Radar is the most promising method for this type of application. It can be applied on-site, it can generate high resolution 3D reconstructions of fractures and defects, quasi-real-time results are feasible. Thus, it can be a cost-effective tool, worth being introduced into the quarry industry. To evaluate the potential of this technology for the quarry industry we have been testing the method on marble and porphyry blocks from a couple of quarries belonging to the Brescia stone district (North Italy). Results are very encouraging: all type of defects and fractures that might have an impact on the production line can be detected by 3D surveying the block with a 2GHz GPR system. A dual-polarized antenna is a plus that makes acquisitions faster and easier. Data processing must include two-dimensional filtering to cancel the artifacts generated by side reflections and 3D migration to generate accurate reconstructions of the target geometries. \ua92012 IEEE

A case study where dual-polarization was essential for correct interpretation of GPR results

The 19th century restoration works of the Basilica of Sant'Andrea in Mantua consisted of important modifications of pronaos and facade. According to historical documents, the use of metal reinforcements was planned to tie the facade with the counter-facade but designs and details are missing and since no external evidences of the tie-rods can be observed, the existence of these reinforcements was a fundamental open issue. The problem has been recently addressed with a GPR survey. Some tie-rods have been confirmed. The location of some of them has been problematic because of plaster decorations that reduced the survey area to narrow corridors. The dual-polarization was a benefit because some reinforcements, oriented parallel to the survey corridor, were detected only by the parallel-broadside polarization. In addition, for the exact location of these elements, 3D migration was needed because the reflection was generated out-of-plane. Some other unexpected reinforcements were also detected within the counter-facade wall. The complex geometry of these reinforcements was finally understood by composing the results of GPR investigations on orthogonal faces of the counter-facade. However, a tricky question arose on one side of the wall where an unexpected anomaly in GPR response seemed to reveal the presence of an additional set of metal bars. Again the dual-polarization was essential to exclude this misinterpretation and to understand the real origin of these unexpected signals

GPR investigations to assess the state of damage of a concrete water tunnel

Erosional voids developing around concrete-lined tunnels can compromise the safety of the surrounding areas, as well as of the tunnels themselves. In this study, ground penetrating radar (GPR) was used to assess the condition of a water tunnel built to channel a river under a mountain road. The tunnel is lined with 60-80 cm thick concrete and has a semicircular crosssection with a diameter that varies between 3 m and 4 m. The concrete structure has been damaged from erosion beneath the concrete floor, creating a sequence of pools and waterfalls, which further extend the erosive action below the floor and side walls

Damage assessment and identification of defects in reinforced masonry walls

none4In the framework of the DISWall research project, funded by the European Commission, quality assessment procedures for modern reinforced masonry buildings, based on the use of non-destructive test methods, are under development. Different testing techniques were applied on two reinforced masonry systems, based on the use of perforated clay units, typically designed for construction in areas characterized by low to high seismic hazard. In this contribution, the results of radar tests, applied in laboratory on two masonry specimens built by including known defects into the masonry, are reported. The main aim of the testing campaign was that of evaluating the effectiveness of the proposed non-destructive technique for localizing the position of vertical and horizontal reinforcement, evaluating the presence of the rebars overlapping, identifying the non-proper filling of vertical and horizontal joints and the absence of proper cover for the reinforcement. Subsequently, real scale reinforced masonry walls were tested on-site. Radar tests were again applied. Furthermore, dynamic tests were carried out on 6 m high walls, tested under cyclic out-of-plane loading, at different stages of the tests, in order to evaluate the influence of the damage on the structural response of the system. In the present contribution, the first results of the experimental tests are presented and discussed.noneDA PORTO F.; ZANZI L.; MOSELE F.; AROSIO D.DA PORTO, Francesca; Zanzi, L.; Mosele, F.; Arosio, D

Georadar investigations and monitoring of the wall structures and vault system of the Sala delle Asse, in Leonardo da Vinci - The Sala delle Asse of the Sforza Castle

In 2011, the engineer Giuseppe Albano studied the geometry and state of conservation of the structures of the vault system of the Sala delle Asse to assess any damage and instabilities in the room and proposed a series of studies and monitoring for the cracks that had been detected on the extrados of the lower vault and on the vertical structures, with the aim of identifying any movement that might be un­der way. Currently, a diagnostic campaign is in progress, targeted towards understanding the build­ ing technique and structural behaviour of the vault system. Radar studies were conducted to reconstruct the stratigraphy of the system comprising the lunetted cloister vault, the depressed arch cloister vault above and the floor of the room on the upper floor. Other radar studies were conducted to characterize the raised wall structures, which are of notable thickness (even as much as aver 2.5 m) and to identify cavities and a flue that runs along the full height of the north-east wall. A topographical/diagnostic laser scanner survey will make it possible to reveal the critical points of the structures and types of instability and provide understanding of the dynamics of the crack pattern. The stratigraphic reading will make it possible to codify the archaeological sequence of the built structure, the deterioration and state of damage (the contribution The Diagnostic Survey: The Sala delle Asse and its Context in the present volume).The need to speed Up the time spent collecting information that would be useful for safeguarding and protecting the room forced the immediate installation of a system far monitoring cracks based on the information available at the time, which derived from a preliminary survey and the results of thermographic studies (see the contribution The Preliminary Thermo-Hygrometric Research and Environmental Monitoring of the Sala delle Asse in this volume), which revealed a few structural cracks. It will be possible to review or integrate the arrangement of the transducers based on the results of the above-described survey

A customized resistivity system for monitoring saturation and seepage in earthen levees: installation and validation

This work is based on the assumption that a resistivity meter can effectively monitor water saturation in earth levees and can be used as a warning system when saturation exceeds the expected seasonal maxima. We performed time-lapse ERT measurements to assess the capability of this method to detect areas where seepage is critical. These measurements were also very useful to design a prototype monitoring system with remarkable savings by customizing the specifications according to field observations. The prototype consists of a remotely controlled low-power resistivity meter with a spread of 48 stainless steel 20 × 20 cm plate electrodes buried at half-meter depth. We deployed the newly-designed permanent monitoring system on a critical levee segment. A weather station and an ultrasonic water level sensor were also installed in order to analyse the correlation of resistivity with temperature, rainfalls and water level seasonal variations