In Situ Testing And Laboratory Investigation

In order to better characterize the materials, to justify the observed damage and to define corrective measures, an experimental in-situ and laboratory testing program was carried out.

5.1 Soil and foundation survey

This survey consisted of seven boring holes and three pits to define the mechanical and physical

Figure 10. Aspects of the wall movements: (a) separation between wall and vault (intrados of 1st level); (b) detail of previous separation; (c) separation between wall and vault (extrados of 2nd level) and (d) horizontal movement inwards to the court.
Figure 12. Material deterioration: degradation of stone carving and biological colonization.
Stone Biological Colonization

Figure 13. Examples of stone deterioration survey: (a) stone detachment in West wing; (b) SEM images of salt crystals.

Figure 11. Mechanical deterioration: crushing/shearing of the stone brackets of the 1st level and decohesion of the bricks.

characteristics of the soil and foundations. It was possible to define a layered soil consisting of an infill of clayey nature (1.1 m), organic soil (0.30 m), alluvial soil with medium large stones, naturally wounded and worn by the action of water (0.60), alluvial soil with pebble (0.50 m). Between 2.5 and 2.7 m depth, the soil is granular with some clay and below 2.7 m depth large stones, with a size of 0.30 m to 0.40 m are found (Fig. 14).

Figure 13. Examples of stone deterioration survey: (a) stone detachment in West wing; (b) SEM images of salt crystals.

The foundation soil exhibits moderated resistance and large heterogeneity for depths between 1.0 and 1.8 m, were supposedly all the cloister foundations are set. The foundations for the walls seem to be medieval and of good quality, but the foundations of the cloister columns are inadequate. These irregular masonry foundations are unable to distribute the loads over a significant soil area and the foundations depth around 1.0 m seems to indicate that the foundations were built on top of the original pavement level, directly on organic soil.

Figure 16. Flat-jack testing: (a) aspect of one test; (b) stress-relative displacements results.

Figure 14. Soil characterization: (a) identified layers; (b) inspection pit 2; (c) inspection pit 3.

Figure 15. Aspects of the inspection with rigid endoscope.

5.2 Internal characterization with rigid endoscope

In order to characterize the inner constitution of vaults and walls, a few bore holes and several cracks were inspected with a rigid endoscope (Fig. 15). The inspection allowed several conclusions, among which: (i) vaults are made with clay brick masonry with 0.22 m thickness. Infill material in the 1st level is soil and infill material in the 2nd level is a sort of rubble masonry. Separation between the two materials was not found; (ii) walls are made with large granite stones, with dry joints or a thin clay joint. The clay joint seems to be washed out around the cracks and in the external part of the wall due to weathering. An internal core of weaker mechanical characteristics was not found; (iii) internal longitudinal cracks that would compromise the stability of the walls under vertical loading were not found.

Figure 16. Flat-jack testing: (a) aspect of one test; (b) stress-relative displacements results.

As a result of the inspection with the rigid endoscope, it was concluded that the granite walls of the cloister are adequate and there is no danger of collapse due to desegregation under vertical loading. Coring and other techniques to estimate the strength of the walls were considered not necessary and it was decided to carry out two simple flat-jack tests.

5.3 Flat-jack testing

The results of one test are shown in Figure 16. The average in-situ stress obtained is 1.2 MPa and no indication of bending in the walls was found. The value expected is around 0.6 MPa. The difference between these values might be due to the irregular shape of the masonry blocks, indicating that only half of the stone block is active. It is stressed that the value of 1.2 MPa obtained can be considered as relatively low for the particular type of masonry.

5.4 Coring

In order to confirm the internal constitution of the vaults and to characterize the mechanical behavior of the brick masonry, three ^>75 mm cores were extracted from the vault (Fig. 17). The cores confirmed the borehole observation.

5.5 Chemical, physical and mechanical characterization

The plaster, vault infill and mortar from the brick masonry of the vaults were characterized with X-ray diffraction, non-soluble residual and burn loss tests (Fig. 18a). The bricks were characterized with absorption tests and uniaxial compression tests

Figure 17. Samples for visual identification and mechanical testing.

(Fig. 18b, c, d). The mortar from the brick masonry was also characterized with uniaxial compression tests. The representative samples were extracted from the construction or the cored samples.

The tests indicated the composition of the plaster and mortar (1:3 in volume) and the composition of the vault infill. The bricks are of low quality and nondurable, with an absorption in cold water around 20% and a volume mass of 1560 kN/m3.

The uniaxial compression tests were carried out in samples of 45 x 45 x 45 mm3, tested with greased Teflon layers to avoid the plate confining effect. The obtained Young's modulus and strength for the bricks were Eb = 7300 MPa and fb = 5.2 MPa, respectively. These values are quite low and confirm the poor quality of the bricks. The obtained Young's modulus and strength for the mortar were Em = 8600 MPa and fm = 3.8 MPa, respectively. This strength value can be considered normal for the mortar composition.

With these results it is possible to estimate the strength of the brick masonry as:

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