One of the fundamental techniques for road subgrades is soil stabilization. Considering the high emission of carbon dioxide during the production of binders, novel techniques to reduce the binder are being studied. Thus, we investigated dispersed reinforcement in stabilized soils. A study was conducted to determine the ultrasonic pulse velocity in nine mixtures of soil, cement, and polypropylene fibers and then correlate the results with other destructive tests. The results show a decrease in wave velocity in mixes with fiber addition by up to 18.5%. The result is dependent on the curing time and whether the samples were stored in a water tank. Immersion in water increases the obtained results by about 6.3%. Based on the analysis, for mixtures with fibers, boundary velocities of waves above which lower values of modulus of elasticity were obtained were determined. Depending on the mix and the module analyzed, the limits range from 2194 m/s to 2498 m/s.

Stabilized soils are commonly used as part of pavement construction in highway engineering. The everyday use of this material makes it necessary to classify it. One of the basic methods of determining the mechanical properties of a material is the unconfined compressive strength (UCS) test, from which the material elasticity can be determined. The scope of the research included the design and making of soil mixtures stabilized with polypropylene fibers modified cement. This paper presents the effect of the amount of dispersed reinforcement on the maximum compressive strength, the secant modulus at half the ultimate stress (${\mathrm{E}}_{50}$), the secant modulus at the ultimate stress (${\mathrm{E}}_{\mathrm{s}}$), and the tangent modulus (${\mathrm{E}}_{\mathrm{t}}$). The materials chapter characterizes the soil, cement, and dispersed reinforcement used. The test methods section describes the tests performed and the procedure for interpreting the results. The results section describes the relationship between elastic modulus and compressive strength. The discussion section compares the obtained results with the works of other authors. The work is concluded with a summary containing the most important conclusions resulting from the work.

Soil stabilization with hydraulic binders like cement is widely used in road construction but significantly contributes to CO₂ emissions. This study investigates a more sustainable alternative involving the use of dispersed polypropylene fiber reinforcement to improve the mechanical properties of stabilized soils while reducing cement consumption. Nine clay sand mixtures with varying cement (2–6%) and fiber (0–0.5%) contents were tested using unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) methods. Fiber addition improved UCS by 5.59% in a mix with 2% cement and 0.25% fibers and by 25.45% in one with 4% cement and 0.25% fibers. This shows that fibers can improve strength at different cement levels. A novel reinforcement index ($R_i$) was introduced to predict UCS empirically. The model showed that using 0.5% fibers ($R_i=1.0\%$) enabled a 25.12% reduction in cement without compromising strength. However, this improvement came at the cost of stiffness: deformation modulus $E_{50}$ decreased by up to 67.51% at 0.5% fiber content. Statistical validation using MAE, RMSE, and MAPE confirmed the model’s accuracy. Although the results were based on a single soil type, they showed that polypropylene fibers can support decarbonization efforts by reducing cement demand and represent a technically feasible approach to more sustainable geotechnical engineering applications.

Stabilized soils are used as structural components in pavement construction and highway engineering. Due to their broad application, practical methods for predicting their strength are essential. The unconfined compressive strength (UCS) test is a fundamental technique for assessing mechanical properties. This study focuses on the development of a new method for predicting the strength of cement-stabilized soils. The analysis was based on three series of tests. The first series examined the effect of variable initial moisture content, ranging from 6% to 13%. The second series focused on the impact of cement content, ranging from 1% to 9%. The third series examined the effect of cement content on strength increase over a period of 1 to 56 days of curing. Based on the collected data, an empirical relationship was developed to predict strength using three key parameters: porosity (n), cement index (C_i), and curing time (T_C). Nomograms were created using this relationship, allowing strength to be easily predicted. Additionally, the study presents correlations between the proposed model and deformation parameters, as determined by both destructive testing (DT) and non-destructive testing (NDT), including the E₅₀ modulus, E_UPV, and G_UPV. The statistical validation of the determined empirical relationship showed a MAPE value of 15.928% and an RMSE value of 0.318 MPa. The results confirm the accuracy of the developed model and the derived correlations.

Geotechnics, as a fundamental field of civil engineering, influences every stage of a construction project – from subsoil investigations, through design, earthworks, and foundation construction, to monitoring and durability analysis. This article presents a synthetic overview of key geotechnical issues from the perspective of global literature (DOI), juxtaposed with the contributions of the faculty of Civil Engineering at the Warsaw University of Life Sciences. It discusses their input into the development of foundation methods in challenging geotechnical conditions, soil stabilization, dynamic and cyclic testing, as well as modern techniques for predicting geotechnical parameters and engineering education.