Irrigation appears as the most important technique to improve agricultural production in dry weather marginal areas. Utilization of not qualified water could increase either, soil and underground water salinization or sodification risk. Actual figures related to good quality water resources, show that in the future, a concurrence with human consumption could easily be hypothesized. Several research articles have shown negative consequences on agricultural production, due to soil salinity-sodicity levels. Spite of this, knowledge related to these chemical levels and soil physicals properties relationships, is still lacking. The hypothesis of this thesis was that soil chemic alteration due to irrigation with bad quality water, diminishes its compressibility and increases its shear stress resistance, changing Coulomb and Critical State Lines position. The main objective was to improve knowledge in order to explain soil behavior irrigated with waters of different qualities. Another objective was to develope a method to evaluate soil compressibility and shear strength, quantifying the incidence of irrigation water quality in these properties. In Facoltà di Agraria e Forestale of Florence, Italy, test of uniaxial compression and direct shear strength at constant normal stress were made in 4 soils, artificially irrigated with diverse quality waters. Three treatments were used. For 1-5 (3) treatment, soils we immerse 3 times in solution with 1mmol/liter concentration and 5 of SAR. In 100-45 (3) soils were immerse 3 times in solution with 100mmol/liter concentration and 45 of SAR. Finishing, the 100-45 (5) treatment soils were immerse 5 times in solution with 100mmol/liter concentration and 45 of SAR. The soils were dried, grinded and sieved through a 2 mm sieve, wetted till reach 23% (w/w) water content and compressed in successive steps arising 600 kPa of normal tension. Classical Mohr-Coulomb and Critical State theories frameworks, were used and a prediction of agronomical impact included as well. During compression, height sample were measured in order to quantify bulk density. After compression, the samples were unloading for 24 hours and dried till 20% (w/w) water content was reached. The samples were sheared at three normal tensions: 60, 240 and 480 kPa. In the shear test, were measured, not only shear resistance, but horizontal and vertical movement of samples, as well. After statistic treatment, in the compressive behaviour were found only few differences among treatments. The bigger shear strength of sodic treatment could be explained by its bigger content of dispersed clay. After outline Coulomb straights, was verify that, larger shear stress in the sodic treatment was due to increase in the cohesion parameter, without changes in friction internal angle. In the critical state theory framework no significative differences between normal consolidation lines position of diverse treatment, were finded, in agreement with compressive analysis. On the other hand, evident displacement of critical state line toward the normal consolidation line of the sodic treatment with respect of 1-5 (3) was found, increasing supercritical domain. The small possibility of compression post shear of sodic soil is due to small pores, unabled to lodge big particles or microaggregate, avoiding too, the possibility of particle rearrangement. Having these results in mind, some agricultural predictions could be made. The sodic soils demands higher energetic costs for tillage and the effect is highlighted in fine texture soils. Likewise, the big shear strength of sodic soils gives greater load capacity, then better trafficability could be predicted, due to it higher strength to be sheared. Consequently lesser slipage could be expected. We have evidence indicating diminishing of friability of sodic soils, limiting their tillage opportunity. The largest tendency from expansion of sodic soil after tillage will result in limited effectiveness due to one structure with massive aggregates and interaggregate pores of short life. The indiscriminate irrigation, without exhaustive analysis of quality of the irrigation water and soil capacity, could lead to a non sustainability system in short-term. Finally, developed method allows suitably assessment of the studied properties. These properties depend on water irrigation quality, being the sodium the responsible of cohesion increase and consequently of shear stress increments. On the other hand, the bulk density is less sensitive parameter than shear strength. Finally, the critical state properties of soil are affected by chemical degradation, increasing supercritical space.