PSI - Issue 5

Annamaria Cividini et al. / Procedia Structural Integrity 5 (2017) 1072–1077 Cividini / Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 2. Shear resistance envelope and data from direct shear and unconfined compression tests.

In particular they allow to draw the failure envelope for the peak condition of the 'intact' adobe material (dashed blue line in Figure 2). The field investigation on Aliano adobe included also two diagonal compression tests carried out on adobe panels. For comparison, considering the measured tensile state at failure, the Mohr circles at failure are shown in Figure 2. It is worthwhile to note that the shear resistance of the adobe walls is highly influence by the presence of mortar, leading to an overall reduction of the wall resistance as frequently observed (see for instance Chaimoon and Attard, 2007). Unfortunately, the Aliano adobe data from the unconfined compression tests do not include those on the elastic properties. Among the data available in the literature, it was decided to refer to the extensive investigation presented by Silveira et al. (2012). Adobe specimens were recovered from several different house and land dividing walls, then they were subjected to displacement controlled, uniaxial compression tests. The variation of average values of the modulus of elasticity E with the compressive strength q max (see Table 1 in Silveira et al., 2012) is presented in Figure 3. The data lie on a straight line, the ratio E/q max varies between 77 and 220 and it is comparable with the one observed for saturated and dry laterite samples, recovered from blocks used for erecting two main buildings, known as “quadrangles” , in the archeological VatPhu area in Laos (Cividini et al., 2014). In addition, as expected, the adobe is more compressible than soft rocks, considered, for instance, in Tatsuoka et al. (1994). In order to roughly estimate the value of the ratio E/q max for the Aliano adobe on the basis of the data from the DS tests, the approximated value of the Young modulus is obtained on the basis of the oedometric modulus E ed evaluated in stage 1 of each direct shear test and assigning the Poisson ratio value (for instance equal to 0.25). Then the deviatoric stress q max is estimated considering the Mohr circle that includes the stress state at failure ( DS pk ). On the basis of the roughly estimated values, it appears that the Aliano adobe is more compressible with respect to those used in the buildings and land dividing walls in the Aviero district (Portugal). 2.4. Mechanical properties from unconfined compression tests