Structure of the building and historical vicissitudes

It is a building of 1916, with 6 floors, a basement, four floors above ground and an attic used as an attic, with a rectangular plan measuring approximately 30.00x12.00, with an eaves height of almost 17.00 m. The supporting structure is in masonry. The floors consist of reinforced concrete slabs with unidirectional reinforcement. The foundations are in non-reinforced concrete conglomerate. The warping of the floors was detected by means of a pacometric survey.

Hydro Buildings Consolidation s.r.l.
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Main crack pattern

In the following documents the minutes of the cracking state surveys carried out during the inspections are directly reported. The most evident and significant cracks were marked, floor by floor, in order to identify probable movements of the building and identify any other phenomena that are co-responsible for the cracking state in progress. The survey carried out made it possible to ascertain the coexistence of lesions of various genesis. Cracks can be recognized, almost always diagonal, directly attributable to mechanisms of subsidence of the foundations, located more or less on all the walls (external, spine, transverse) and, "perhaps", more accentuated in the extremities and on the side of Via Loderingo. It should be borne in mind that the various real estate units have undergone renovations and adjustments at different times and in different ways so that it is not immediate to correlate the extent of the cracking state between one portion of the building and another. During the inspections (and subsequently detected by the thermographic inspection) portions of plaster cracked due to phenomena of shrinkage, swelling and detachment from the support, both on the walls and on the ceilings, were identified. On the mezzanine floor, following the inspection carried out, the plaster from the ceiling of a room was removed because it was dangerous, as it was almost completely detached. In the past, the plaster fell on an entire ceiling in the adjacent property. This is a problem common to the entire building and is due to the fact that the floors are made of reinforced concrete and, moreover, highly deformable. Even the plaster of the walls is affected by a bad adhesion on the concrete blocks, even more so where we have modern cement-based and thick plasters. Another type of damage concerns the floors and is due to poor load-bearing capacity and excessive deformability (poor quality concrete, poor reinforcement, low thickness). The cracked state detected, as can be seen from the related documents, practically affects the two wings of the building in equal measure, it cannot be said that it concerns a preferential part. From the analysis of the cracked state it is evident, as already noted in the previous studies, that there is a phenomenon of differential subsidence of the foundations which are the cause of the most significant lesions found in the building.


Geological and geotechnical framework

By examining the results of the geotechnical tests performed, summarized in the following table, some circumstances are immediately identified that allow us to circumscribe the causes of the cracking phenomenon. The Geologist took 6 soil samples, three on the north side and three on the south side, at similar depths respectively, and subjected them to some laboratory tests including the determination of natural humidity and consistency limits. These are homogeneous samples for lithological characteristics; both in the south and in the north, fine clayey-silty soils were found. Also important is the fact that the samples were taken in September (late summer, dry period).

Analyzing the table the following considerations arise, also in relation to the presence of the drainage channel that runs parallel to the south side of the building at a depth of about 5 m and to its presumed influence on the cracking state. Samples S1C2 (south) and S4C2 (north), both taken at a depth between 5.00 and 6.00 m (immediately below the channel), have the same natural humidity detected in September. If the presumed dispersions of the channel actually influenced the behavior of the soil, we would have had to find significantly different values ​​of natural humidity for the two samples; the "south" sample, taken in correspondence with the channel and immediately below it, should have been much wetter than the "north" one taken at the same depth, even more so in a dry period. Also the relative humidity values ​​of the other samples comparable for depth, S1C1 with S4C1 and S1C3 with S4C3, are very little different. Finally, the maximum humidity values ​​measured are just above the plastic limit and just below the saturation value, given to me by the laboratory, equal to 28, as can be expected for clayey soils that are not immersed. Therefore, any dispersions of the channel do not influence the static behavior of the building in any way. Instead, what caused the settlements was the extreme drying of the soil immediately below the foundation plane, as evidenced by the natural humidity values ​​measured in the samples S1C1 (south) and S4C1 (north) which are close to the limit withdrawal. Furthermore, the strong propensity of that soil to vary its volume according to the moisture content is evident. That the building is also subject to movements due to swelling of the ground is evident from the fact that some lesions found have closed having substantially expelled the grouting.


Stratigraphy of the site under examination

Boundary conditions and probes positioning


Change in humidity with depth

Project of the intervention

The project involves the consolidation through the installation of a soil moisture control system (patented HBC system). As can be seen from the drawings shown in the following illustrations, six sub-horizontal pre-drilled polyethylene pipes are provided at a suitable depth, which have the function of diffusing the water necessary to keep the humidity constant regardless of the building's ground. from all external conditions that may intervene. They will be laid with the use of a horizontal drilling machine (No-Dig technique) working exclusively from the parking lot adjacent to the condominium without intervening in any way inside the rooms in the basement. The water supply will come from the garden irrigation system on the north side. The control of the system is entrusted to special float cocks installed in the inspection wells. The floor plan and section of the system are shown below.

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