Stone construction elements are frequently in moist environments or in direct contact with water. Design and test standards have traditionally ignored the water impact on rock materials. However, several studies have shown that moisture can cause drastic strength reductions and deformability increase in some sedimentary rocks. For that reason, the main objectives of this work are: a) to quantify and understand the influence of water saturation on strength and deformability of four porous calcarenite building stones widely used in SE Spain ; b) to establish correlations between physical and mechanical properties of these rock materials in dry and saturated states and c) to compare the results with previous findings. The results showed a very significant reduction of mechanical properties such as unconfined compressive strength, Young´s modulus and point load strength index when these stones undergo saturated. In addition, significant correlations between physical properties (density, porosity, P wave velocity and dynamic elastic parameters) and the mentioned mechanical properties were established in dry and saturated conditions. Additionally, relationships among the mechanical properties of stones in both states are also proposed.

The preparation of standardized soft rock specimens to perform unconfined compressive strength (UCS) tests is typically difficult, expensive and time-consuming. Needle Penetration Test (NPT) was originally developed in Japan as an alternative for the indirect estimation of UCS of soft rocks. The needle penetrometer is a simple, portable and non-destructive testing device that measures applied load and penetration depth for the rock to calculate the needle penetration index (NPI). A complimentary, portable and widely used destructive test is the point load test (PLT), which measures regular and irregular specimens by the application of a concentrated load using two coaxial conical platens that yield the point load strength index (IS(50)). We investigated and compared the NPT and PLT in terms of measuring changes induced by water saturation and obtaining UCS and the static Young's modulus (Est) for dry and saturated soft sedimentary rocks. The results point to significant correlation functions from which to infer UCS and Est in terms of NPI and IS(50) in dry and saturated soft rocks. Furthermore, both NPT and PLT are suitable tests for evaluating changes in strength and deformability induced by water saturation. We also found a good correlation between the NPI and Is(50) .

Several studies have found that water can cause substantial reductions of mechanical properties of building stones such as unconfined compressive strength, tangent Young´s modulus or tensile strength. However, the influence of water content on shear strength parameters, triaxial compressive strength and modulus of elasticity under different confining pressures has been scarcely examined. For this reason, the present paper assesses the impact of water on peak and residual compressive strength and tangent Young´s modulus of three porous building geomaterials widely used in civil and architectural constructions under different confining pressure through triaxial compressive tests. Furthermore, the corresponding peak and residual shear strength parameters computed from Mohr-Coulomb (c and ϕ) and from Hoek-Brown (σci and mi) failure criteria are obtained under dry and saturated conditions. Complementary physical and petrological analyses are performed in order to understand the main causes of the effect of water observed in these rock materials. The results indicate that water causes significant reductions of peak and residual compressive strength and tangent Young´s modulus in the tested porous building stones for all the different applied confining pressures. Additionally, important changes of peak and residual shear strength parameters (c, ϕ, σci and mi) are exhibited by the studied stones when become saturated. This could be related to physicochemical changes such as the hydrolysis of quartz and silicates in crack tip region inducing subcritical crack growth (stress corrosion), the decrease of the cement quality and the deterioration of the intergranular bonds due to the dispersion or dissolution of some minerals (calcite or chlorite) and the formation of microcracks caused by the swelling of the clay minerals present in these materials when they come into contact with water.

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An accurate evaluation of the shear strength of discontinuities is frequently a key aspect for determining the safety of mining and civil engineering works and for solving instability issues at rock mass scale. This is usually done by using empirical shear strength criteria in which the basic friction angle (φb) is a relevant input parameter. Tilt testing is probably the most widespread method to obtain the φb due to its simplicity and low cost, but previous research has demonstrated that the results are strongly affected by several factors (e.g. surface finishing, cutting speed, specimen geometry, wear, time and rock type). In this connection, despite it is well known that water significantly reduces the mechanical properties of sedimentary rocks, very scarce research has focused on assessing the impact of the variations in water content on tilt test results. With the aim to fill this gap, saw-cut slabs of three limestone lithotypes were tilt tested in dry state, wet condition (fully water saturated, non-submerged samples) and under exposure to an environmental relative humidity (RH) of 90%. The results revealed that full water saturation caused moderate φb reductions in two lithotypes and a φb increase in one lithotype. This can be explained by their different microstructure and mineralogy, which makes that lubrication effect prevails over suction effect or vice versa. However, the exposure to a high RH environment did not cause significant φb variations. In addition, some important considerations related to tilt testing are provided and discussed, such as the intrinsic variability of the sliding angle (β) and the impact of multiple sliding on the same rock surfaces on β.

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