This particular condition is related to the geological multi-stratum composed of lake deposits (essentially based on silt with high contents of consolidated organics) and fluvial deposits based on sand and gravel. At the beginning of the century the lake border was extended into the lake with deposits of incoherent materials of different origins, with an extreme slope· The project foresees a diaphragm of piles anchored at the head. To optimize the anchorage technique in the various soils of the lake borders (lake deposits and sand/gravel) a monitoring campaign has been launched. The limited financial budget and confined place allowed only the execution of 4 anchorages, all with an anchored part of 7 m installed as follows: Anchored part realized with multiple injections in the lake deposits. The anchored part was realized with a Jetting bulb in the lake deposits. The anchored part was realized with multiple injections in the sand and gravel soil. The anchored part was realized with a Jetting bulb in the sand and gravel soil.·
Aim of monitoring:
The optical fiber sensors SOFO from Smartec were installed in the anchored part and have been placed in this position to verify the optimal length of the anchorage and determine the force transmission from the bulb to the soil. This allows us to study its behavior either in the short or long term. Instrumentation: Three chains of 3 SOFO sensors each have been attached to the anchorage part during its assembly in the factory (the anchorage injected traditionally in sand and gravel has not been monitored). The measuring points for all sensors start from the head of the bulb. The length of each sensor is 1.5m 5.5m and 7.0m. The measurements have been carried out during the load test and after some weeks to determine the correlation between the load loss on the head and the behavior of the anchored part.
| INSTALLATION PERIOD | TYPE OF SENSORS | NUMBER OF SENSORS |
| 1998 | SOFO | 9 |
Main results:
The figure shows an example of the results obtained during the cable tension. In particular, it has to be noted that the head of the bulb gets in compression while the parts of 5.5m and 7m are not transferring any load as no difference between the two sensors is detected. There is a good correlation between the behavior of the bulb and the load measurement on the head of the anchorage.
