## 1 _Editorial_ Sustainability in Geotechnics
The fourth, fifth, sixth, and seventh contributions study sustainable ways of improving the mechanical behavior of different soils. The fourth and fifth contributions propose the use of bio-inspired techniques (enzymes and biopolymers) to replace the use of cement in soil stabilization, while the sixth contribution proposes a sustainable solution by partially replacing Portland cement with industrial by-products and/or biochars; the seventh contribution proposes the potential use of coarse aggregate crushing waste to improve the geotechnical properties of a silty sand soil. [PERSON] et al. (Contribution 4) propose an innovative method that uses hybrid enzyme carriers (copper-carbonic anhydrase) to catalyze the bioprecipitation of calcium carbonate, aiming to increase the efficiency and sustainability of the bioccmentation process. [PERSON] and [PERSON] (Contribution 5) study the effects of soil's organic matter content on the biostabilization induced by the biopolymer xanthan gum. The results showed a detrimental effect in terms of unconfined compressive strength and stiffness, as well as an increase in compressibility and primary consolidation time for organic matter contents higher than 5.5%. [PERSON] et al. (Contribution 6) study viable alternatives (four biochars, including demolition wood and sewage waste, and five industrial by-products, including ashes and slags) as a partial replacement of Portland cement for the stabilization of three soils (a soft clay, a quick clay, and one peat). The results suggest that the stabilization effect of Portland cement combined with biochars increases with the increasing water content of the soils, while the opposite effect was observed for Portland cement combined with industrial by-products. Further studies should be carried out to establish the correlations between the mineralogical and chemical composition of these additives, as well as the mechanical performance of the stabilized soils. [PERSON] et al. (Contribution 7) investigate the reusing of coarse aggregate crushing waste mixed with Portland cement to improve the geotechnical properties of soil when applied in road construction. It was found that a combination of 10% coarse aggregate crushing waste with 2% Portland cement increases the undrained shear strength, the California Bearing Ratio (CBR), and the P-wave velocity, making such a soil improvement approach almost carbon neutral. [PERSON] et al. (Contribution 8) propose a framework to assess soil liquefaction based on the ratio between the shear wave velocity and the peak undrained deviatoric stress. The authors state that such a ratio can be accurately used to define a boundary between liquefaction and strain hardening for sands and between strain softening and strain hardening for silty sands and silts. This tool has the potential to assess the liquefaction of in situ soils, including natural deposits or mine tailings, contributing to safer and more sustainable geotechnical structures. The ninth and tenth contributions (Contributions 9 and 10, respectively) study the interaction of soil-sustainable reinforcement elements under monotonic and cyclical loading. The ninth contribution focuses on geogrids, while the tenth contribution focuses on wooden frame beams and bamboo anchor rods. [PERSON] et al. (Contribution 9) study the pullout apparatus scale (small and large) effect on the characterization of the soil-geogrid interface shear behavior. It was found that the pullout apparatus scale effect is small for confining stresses greater than or equal to 50 kPa, so the adoption of small-scale equipment is less material- and time-consuming, making it a more sustainable way of characterizing such interfaces. [PERSON] et al. (Contribution 10) conducted a series of model tests in embankment slopes supported by wooden frame beams and bamboo anchor rods under train loadings complemented with three-dimensional numerical simulations. The stresses acting on the support/reinforcement elements depend on loading magnitude and frequency, as well as the slope depth.