No abstract

Determining and mitigating landslide risk is a technical-scientific objective, particularly for the protection and proper territorial management and planning. The slope stability depends on the pore pressure distribution, which is influenced by the saturation front propagation through the unsaturated zone, whose monitoring is useful to understand any possible instabilities. Such monitoring may be undertaken by sensors based on the measurement of the relative dielectric permittivity. Reliable relationships between the measurement and the soil moisture are necessary. The main objective of this study is to assess a laboratory calibration protocol for a specific capacitance sensor (Drill & Drop, Sentek Sensor Technologies). Two monogranular sands have been selected for the calibration purpose. The laboratory tests were performed under three relative density values (D_R equal to 40%, 60% and 80%) for seven volumetric water content values (θ_v ranging from 0.00% to 36.26%). Based on the experimental measurements, the soil-specific calibration curves were determined at an assigned relative density value; in particular, a simple power law is adopted to describe the probe’s reading as a function of the volumetric water content. The results point out that the relative density values slightly affect the tests, thus, the soil-specific calibration curves are derived based on a simple regression analysis fitting the whole set of the laboratory tests validated for each sand. The calculated coefficient of determination (R² = 0.96÷0.99) and root mean square error (RMSE = 1.4%÷2.8%) values confirm the goodness of fit. In order to propose more general fitting curves, suitable for both the investigated sands, multiple linear regressions are performed by considering θ_v and the mean grain size, D₅₀ as independent variables; again, the R² and RMSE values equal to 0.97 and 2.41%, respectively, confirm the suitability of the calibration curve. Finally, the laboratory calibration curves are compared with the manufacturer-supplied curves, thus, enhancing the need for the soil-specific calibration.

The issue of concrete strength often arises in civil engineering practice, either due to quality control of new constructions or due to the assessment of existing structures. To this aim, one of the most widely spread techniques is the rebound hammer (Schmidt hammer) test, for which calibration is still related to the original Schmidt curve dating back to the early 50’s. In spite of the large amount of research work performed in the last decades, the uncertainties of the rebound test are still not clearly quantified and open to further insight. This paper presents and discusses a wide research campaign on laboratory specimens and on third-party specimens delivered to the Laboratory for Building Materials of the University of Genoa, Italy, for standard quality controls. While it is well known that moisture content, surface finishing, and concrete maturity strongly affect the test result, the effect of the stress state has not yet been studied and is found in this research to be a further parameter affecting the test reliability. The final outcome of all the uncertainties is variability in estimated concrete strength as large as ±70%; additionally, some issues are discussed on the intrinsic uncertainty of this test. As already demonstrated by many authors, the results of this research also show that a universal calibration curve to be used for any concrete, in any condition, conceptually does not exist.

A new method for the evaluation of the ultimate load of piles by tests not carried to failure is proposed. It allows, by a proper use of the experimental results, a complete analysis of a pile behavior. In fact, the total, shaft and base load-settlement curves can be evaluated. It can be applied when shaft friction is fully mobilized during the test