Bruna de Carvalho Faria Lima Lopes

Accurate quantification of calcium carbonate (CaCO3) in soil is critical for geoenvironmental engineering, influencing soil stabilization, carbon sequestration, and climate-resilient design. This study compares four commonly used analytical methods—Loss on Ignition (LoI), Total Inorganic Carbon (TIC), X-Ray Diffraction (XRD), and a Calcium Carbonate Analyzer (CCA)—over CaCO3 concentrations from 0.3% to 50%. Controlled sand samples with known carbonate contents were tested to assess each method’s accuracy, precision, and reproducibility. Although LoI proves the most practical due to its simplicity and throughput, all methods face marked difficulties at low concentrations. Root Mean Square Error (RMSE) analysis shows that small discrepancies at low CaCO3 levels can produce disproportionately large relative errors, obscuring actual measurement uncertainties. Factors such as sample representativeness, operator handling, and instrument resolution further amplify inconsistencies, emphasizing the need for more rigorous protocols. Crucially, none of the evaluated methods consistently captures very low CaCO3 concentrations, posing significant challenges for soil carbon capture initiatives, regulatory compliance, and soil management practices. These findings highlight the urgent need to refine existing procedures or use alternative approaches to more accurately quantify CaCO3 content at low levels, thereby enhancing confidence in research outcomes and applied engineering solutions.

This study investigates an innovative application of microbial-induced calcium carbonate precipitation (MICP) for enhancing erosion control on unpaved roads, leveraging the unique capabilities of native microorganisms. Aiming to advance disaster-resilient infrastructure, this research employs bio-stimulating treatments to facilitate calcium carbonate (CaCO3) precipitation by way of a novel bio-weathering pathway. Unlike the conventional urea-hydrolysis method commonly used in MICP studies, which generates toxic ammonia as a byproduct, the bio-weathering approach in this study consumes CO2, offering a potentially carbon-negative solution while effectively reducing erosion. Granular material from an unpaved road embankment underwent comprehensive geotechnical characterisation. Inderbitzen tests, which simulate rainfall and runoff, were used to assess erosion resistance. Undisturbed samples were treated either with a bio-stimulating MICP solution or with distilled water as a control. Results indicate significant reductions in soil loss and enhanced stability in bio-stimulating treated samples. While the study primarily focuses on erosion control, it also acknowledges the potential for long-term CO2 sequestration as a beneficial byproduct of the CaCO3 precipitation process. The findings suggest that MICP can be effectively integrated into geotechnical practices to improve the durability and performance of unpaved roads, contributing to sustainable and resilient infrastructure development.

This paper discusses the potential of gamification as a tool for teaching and learning in geotechnical engineering. Gamification involves incorporating elements of gameplay such as challenges, rewards, competition, and cooperation into teaching and learning environments to make the process more interactive and engaging. Although gamification is widely used in many fields, it is still relatively new in geotechnical engineering. This paper presents the ‘Soil Character’ board game developed by the GeoFUN group as an example of successful gamification in geotechnical engineering education. The game focuses on basic soil characterization, including soil classification systems, index properties, and geotechnical characterization tests such as sieving, sedimentation, and Atterberg limits. The paper provides background information on the development of the game, and a description of the game components. The online Portuguese version of the game was tested with eight civil engineering undergraduate students who had successfully undertaken the introductory soil mechanics module. Student’s satisfaction in terms of game design, rules, and gameplay was measured via a questionnaire. Results of the questionnaires showed that the game was well evaluated in all aspects. Student volunteers reported that they felt very motivated, and that they wished they had been able to play the game when they were learning the topic. Thus, results presented in this paper suggest that gamification has the potential to make geotechnical engineering education more interactive and engaging. Exploring the effectiveness of the game in various contexts and with diverse student populations constitutes a key direction for our future research.

There are many historical bridges around the world whose crucial information regarding their foundations is unknown. Such information is essential for an accurate safety assessment regarding scour hazard. Current methods for identification of bridge foundation characteristics are typically expensive, potentially disruptive, and limited in their applications. Thus, the numerical feasibility study described in this paper assessed whether a nondestructive geophysical technique such as electrical resistivity tomography (ERT) could be used for this purpose. Synthetic scenarios were created accounting for different combinations of material resistivity. Two standard measurement sequences (dipole–dipole and Schlumberger) and an optimized one (“Compare R” method) were tested. Results showed that the depth of the bridge foundation was roughly well represented in all cases. However, the optimized sequence revealed slightly better results. Although this small improvement observed did not significantly affect the results of the simplified scenarios assessed by this study, it could be decisive for more complex scenarios. These findings demonstrated that ERT can be used to identify the depth of bridge foundations in an inexpensive, rapid, and nonintrusive way, allowing for more accurate assessment of bridge safety and scour risk ratings.

Soil compaction is one of the most common techniques used to engineer the soil. It is especially appealing to developing countries for its cost-effective and sustainable attributes for improving the soil's geotechnical characteristics. The compaction process along with the complexity of residual soils, abundant in the tropics zone, can have an impact on the performance of geotechnical structures built with these soils. Therefore, it is important to understand the influence that certain compaction conditions have on the structure of these materials. To investigate that, mercury intrusion porosimetry tests were performed on compacted samples of a tropical residual soil from Brazil under different conditions of water content and compactive effort. Results show that the compacted soil under all studied conditions presents a bimodal pore-size distribution (PSD). It appears that the low availability of water within the macro-pores, hence suction, could have played a decisive role in maintaining the bimodal framework of the PSD. In this respect, this study contributes to a better understanding of the tropical residual soils’ structure when subjected to different compaction conditions, thus providing means to improve field applications.

The aim of this paper is to evaluate the relationship between pore-size distribution and compressibility of a lateritic soil. Soil fabric was analysed under different conditions of preparation: compacted, reconstituted and intact, by means of mercury intrusion porosimetry tests on loading to different stress levels. The results show that all samples present bimodal pore distribution. However, the conditions of preparation and loading affected macropores more intensely, with subtle effects on micropores. This behaviour was attributed to the presence of aggregations with cementation. The compression curve of macro and micropores were determined and it was observed that the compression curve of macropores is very similar to the compression curve of the samples. In addition, it was observed that the fabric parameter regarding the uniformity of macro and micropores changed during loading. The new fabric parameter proposed captures the change in pore uniformity with loading. This parameter appears to be related to the soil compressibility, indicating that the most compressible samples also show greater changes in the uniformity of macropores.

The paper presents an analysis of the long-term stability of a large unsupported cave excavated in granular cohesionless material in Ficulle, Italy. The stability of the cave arises from a ‘cohesive’ term in the shear strength criterion and this paper investigates the source of this cohesive term. Contrary to expectations, the material appeared to be granular (cohesionless) at the touch. The investigation started by determining whether the stability of the cave was attributable to any cementation bonding the soil particles. Microstructural analyses, together with geomechanical testing, produced enough evidence to suggest that the material was not naturally cemented. On the other hand, water-undrained direct shear tests on unsaturated intact specimens indicated the presence of significant apparent cohesion, which was then linked to the existence of suction in the material. In this way, the stability of the cave was assessed accounting for the beneficial effects of suction and partial saturation on shear strength. A three-dimensional analysis based on the upper bound theorem of plasticity was successful in confirming the stability of the cave in terms of the state of the structure at the time of field investigation. In addition, it was shown that 24 and 48 h rainfalls of 100 years return period are not sufficient to relieve suction sufficiently to bring the cave to collapse, thus justifying the observed long-term stability of the cave. Suction is rarely included in geotechnical design under the assumption that it cannot be relied upon owing to the potentially adverse effect of rainwater infiltration. This case study demonstrates that suction can indeed remain ‘active’ naturally for a long time, contributing to the long-term stability of geo-structures.