Details/description:
CLIENT: Municipality of Montefiorino.
USE: Public Nursery School.
CONFIGURATION OF THE DAMAGE: The building presented widespread cracks in almost all of its parts, partly due to differential subsidence phenomena affecting the foundations and partly connected with structural problems.
The cracks detected penetrate the entire thickness of the walls and, on average, measure around 2-5 mm.
LITHOLOGICAL CONTEXT (from Z=0): heterogeneous surface filling materials, masses with a fine silt/sand matrix and masses of clayey silt, irregularly distributed.
FOUNDATION STRUCTURE: direct continuous foundation.
EXTENT OF PROCEDURE: approx. 45 lm of foundation.
DIAGNOSTIC SYSTEM: analysis of the loads (P,Q,Con,Dis), survey of the crack pattern, penetrometric tests and ERT. All the diagnostic tests were performed in two separate sessions: prior to the procedure for planning purposes, and a few days after the procedure for data comparison purposes.
DIAGNOSTIC CRITERIA: overlapping analysis of all the data measured.
DESCRIPTION OF PROCEDURE: The compaction and consolidation of the bed was carried out using the traditional technique, injecting resin into the foundation ground/structure interface.
Prior to the procedure, surveys were carried out to enable the development of the injection project: determination of the geometry (x,y, Z = ground/structure interface), determination of the quantities of resin required for consolidation and compaction, on the basis of previous experience.
CONCLUSIONS: With the final measurements it was possible to reconstruct the resistivity values also for a certain portion underneath the building where the aforementioned horizontal irregularities and the deriving heterogeneity of the ground on which the foundations rest are still evident.
At the end of the work carried out in the days that followed, after the resin injections, we took post-procedure measurements testifying to considerable increases in the original values observed, with peaks of over 200% existing up to 2.50 m from ground level.
It may also be observed that the lateral irregularities shown in the background created a watershed between the areas showing an increase and the adjacent areas, with a slight decrease in resistivity values. The initially unsaturated portions filled up with water displaced by the compression of the resin, following sub-vertical preferential directions linked to geomorphological characteristics.
We also observed how the effect of the injections tends to be greater in areas presenting higher porosity and permeability, initially more conductive because damp and mixed with a fine matrix, with peaks around 1.50 – 2.00 metres depth.
