Abstract Mohr’s circle is a convenient geometric method to solve two-dimensional stress and strain problems in geotechnical engineering and materials engineering. The pole point is such a special point that can help readily find stresses and strains on any specified plane by using a diagram instead of complex computations. This paper first presents two conventional pole point methods of a Mohr’s strain circle, i.e., the parallel line method and the normal line method. A new method of determining the pole point of strain, called the ray method, is then proposed. It was found that the parallel line method and the normal line method are two special cases of the ray method; however, the parallel line method was proved the most efficient way to determine the strains for a specified plane. The uniqueness of the pole point was proved by using an indirect proof; and the pole point method was verified by a theoretical method. Results also show that Mohr’s strain and stress circles can be drawn in a concentric circle. Based on the relationship between the pole points of stress and strain, any relatively complex stress and strain states can be determined by using the pole point method rather than using the theoretical method.

Abstract This work uses a new cementitious agent composed of porcelain polishing waste and hydrated lime in the mitigation of static liquefaction in a loose dune sand. The undrained behavior of the soil was investigated in 16 triaxial tests under four confining stresses (50, 100, 200 and 400 kPa), on loose samples (relative density of 25%) compacted with two levels of waste (10% and 30%) and lime contents (3% and 7%) cured at 28 days. Stress-strain behavior, ultimate strength and critical state parameters were evaluated. The results showed a brittle response of the stabilized sands, dilatant tendency and low liquefaction potential, however, the behavior changes with the increase in the confining stress. A friction angle of up to 42.6° and a cohesion intercept of up to 108.1 kPa were found for the stabilized sand. When compared to the pure sand, stabilization caused an increase in strength, of up to 17 times, and in brittleness with a change from contractive to dilatant behavior. For tests up to 200 kPa, the liquefaction potential reduced to values below zero. Therefore, the cementation of the grains by using porcelain polishing waste and hydrated lime was efficient in mitigating the static liquefaction potential of the dune sand.

Abstract This work compares the effectiveness of different biogrout agents to improve the mechanical properties (strength and stiffness) of two sandy soils. Based on the results of unconfined compressive strength tests for different curing times (3-180 days), the results obtained from microbial induced calcium carbonate precipitation using two bacteria (Sporosarcina pasteurii and Idiomarina insuliasalsae) are compared with employing urease to promote calcium carbonate precipitation and the use of the biopolymer xanthan gum (3-28 days). Additionally, the methodologies of calcite precipitation and the use of xanthan gum are also analyzed by examining scanning electron microscopy images. For a curing time of 28 days, the results show that the use of urease is the best of the three bio-based methodologies to improve sand, while the least efficient methodology is the use of the biopolymer xanthan gum. The use of both bacteria increases the unconfined compressive strength during the curing time (until 180 days); regarding the use of urease and xanthan gum, the unconfined compressive strength remains approximately constant for a curing time longer than 7-14 days. In terms of stiffness, the use of the bacteria Idiomarina insuliasalsae and urease result in a better improvement, while the use of the bacteria Sporosarcina pasteurii and xanthan gum has only a marginal effect on the stiffness.

Abstract The advent of construction informatization technologies and the success of the BIM (Building Information Modelling) methodology in the infrastructure market have increased the need for collaboration between different areas of knowledge, professionals, and agents involved in an infrastructure or civil project. For this collaboration to be effective, the correct standardization of procedures is essential to ensure efficient communication between the parties involved in these complex processes. The field of geotechnics and geotechnical investigations has the AGS (Association of Geotechnical and Geoenvironmental Specialists) standard for electronic transmission of files produced during drilling and laboratory tests. However, there is a gap regarding the standardization of a digital structure that can be used for the implementation of geotechnical databases. This paper proposes a logical model for the demands of the geotechnical market, which can be used by the entire community. The proposed model allows for easy access to large-scale data and the possibility of performing mathematical operations more easily.

Abstract The paper addresses the stability analysis of a circular tunnel face driven by a pressurized shield by means of the limit analysis kinematic approach implemented in the context of the Mohr-Coulomb strength condition. Emphasis is given to the assessment of the effects of seismic loading on the value of face support pressure that is required to prevent failure. The approach relies upon the pseudo-static method to model the destabilizing effects induced by the inertial forces associated with the passage of seismic waves in the ground. Rigorous limit analysis solutions for the limit face supporting pressure are derived from the analytical implementation of 3D and 2D failure mechanisms specifically devised for dealing with such a stability analysis problem. Indeed, original analytical expressions are provided and allow the evaluation of the pressure stabilizing the tunnel face. The accuracy of the approach predictions is assessed by comparison with available experimental and analytical results as well as with 2D finite element solutions. The influence of some relevant problem parameters in the context of tunnel face stability analysis is finally investigated, thus providing some preliminary guidelines for practical use in tunnel engineering.

Abstract Extensive and accurate data from on-site testing is increasingly fundamental in determining design geotechnical parameters of offshore structures. As a novel method for assessing offshore soil, the T-bar penetrometer offers benefits such as high precision, reliability, ample data acquisition and cost-effectiveness, but its application in offshore projects remains limited. In this research, a set of approaches are used to analyze the evaluation of penetration rate effects in a kaolin and bentonite mixture prepared to reproduce Brazilian offshore soil conditions aiming the development of in situ testing technology in the marine engineering area. Miniature T-bar penetrometer tests (10 mm diameter and 50 mm length) at constant driving penetration rate were performed at 0.05; 0.1; 0.25; 0.5; 1.0; 2.5 and 5.0 mm/s. In addition, three variable rate tests (twitch tests) were performed aiming to analyze the penetration rate reductions at each twitch stage. The measured resistances and the drainage conditions were interpreted using the normalized velocity (V), and the results show a strength increase by viscous effects of 10% for each logarithmic cycle of penetration rate increase. The results suggest that the transition between the undrained and partially drained penetration occurs at normalized penetration rates between 20 and 50. These results agree with values previously published in the literature and unequivocally demonstrate how the influence of penetration rate can impact the measured undrained shear strength for T-bar tests. It is concluded that the influence of the test penetration rate on the measured resistance cannot be disregarded in intermediate permeability soils.

Abstract Energy geostructures are a cost-effective solution for low enthalpy geothermal installations. Heat exchanger pipes are attached to the reinforcing cages of geotechnical structures to combine structural and geothermal roles. However, the installation of a group of multiple energy structures, such as a pile group, can lead to a heat cluster effect, which tends to decrease the efficiency of the heat pump (COP factor). This phenomenon is amplified by the number of grouped energy geostructures. However, energy geostructures are often installed in areas with groundwater flow. This induces a thermal washing effect, which decreases the risk of multi-year thermal shifts and preserves heat pump efficiency. In this paper, we evaluate the heat cluster effect in a group of piles, its influence on heat pump COP, the benefit of thermal washing due to underground water flow, and the effect of various seasonal scenarios. For this purpose, we present and use a specific numerical process that allows for modeling energy geostructure installations and interactions between groundwater flow models and thermal models. The heat pump COP is then estimated according to variable heat load, which depends on soil temperature.

Abstract A subject of great relevance for geotechnical engineering is the search for economical solutions to improve soil mechanical characteristics. Due to the constant evolution of the industry and the regular launching of new products – developed to compensate for various soil deficiencies - the need for applied research continually arises. Geosynthetics are reinforcement materials that increase soil strength and its traction features. Among them, microgrids have been used as a separating element for distinct materials, but studies on microgrids as reinforcement materials are still not quite common in the literature. This research aimed to evaluate on a small scale the mechanical behavior of microgrids as reinforcement materials in sandy soils by analyzing the strength parameters obtained through consolidated-drained triaxial tests (CD) of specimens with none to 3 layers of the material. The study also compared the performance of sandy soil reinforced with microgrid and non-woven geotextiles of different weights (200 g/m2 and 300 g/m2). Results showed that the insertion of microgrid layers in sandy soils increased the strength parameters, and the behavior of reinforced soil has changed from strain-softening to strain-hardening. The sample reinforced with one layer of microgrid had improved cohesion and friction angle compared to samples with one layer of non-woven geotextiles.

Abstract Understanding the effects of installation method on a deep foundation is fundamental for analyzing load test results and improving foundation design based on soil profile characteristics. This study analyzed 40 load-displacement curves of driven piles and piles bored using a manual auger, measured 20 cm in diameter and 3 or 6 m in length. Piles were constructed at the Experimental Field of Geotechnical Engineering, State University of Londrina. The soil is classified as silty clay, exhibits collapsible behavior up to a depth of 7 m, and has low resistance in surface layers, according to the results of particle size analysis and the standard penetration test. Load tests were carried out under static conditions using mixed loads. Natural moisture conditions were used in the test, and pre-wetted conditions in the retest. For three bored piles, these conditions were reversed. Pre-wetted conditions resulted in loss of failure load, highlighting the collapsible nature of the soil. Conversely, piles tested under natural moisture conditions exhibited higher failure load. Load-displacement curves showed shapes consistent with the expected for the analyzed pile types. This consistency supports the discussion on the effect of the construction method on pile behavior, demonstrating that soil removal during excavation for pile boring mobilizes side friction, whereas, in driven piles, soil compaction enhances toe resistance, particularly for piles constructed by concrete pounding as compared with concrete casting.

Abstract Point load strength index (PLSI) and slake durability index (SDI) are two important indices of rocks used to evaluate strength and durability for various engineering applications. This research investigates these two indices in sandstones from the Amile formation coupled with petrography, aiming to determine the strength and durability of rock, and test for correlations among mineral constituents, texture, PLSI, and SDI to develop empirical relationships among them. The study provides insights into the geotechnical properties of an important geological formation in the Lesser Himalayan Zone, contributing valuable data for infrastructure development. The methodology involved field sampling, petrographic analysis of thin sections, SDI testing over two cycles, and PLSI testing on irregular lump samples. Correlations between SDI, PLSI, water absorption, packing density, and packing proximity were statistically analyzed. Quarztose sandstones have extremely high durability (SDI: 99.17–99.78%), very strong to extremely strong compressive strength (PLSI: 5.94–14.81 MPa), and low water absorption values (WAV: 0–2.17%). Very high positive correlations were found between SDI and PLSI with R2 =0.804. Based on this correlation, future research can use the equation SDI = 0.0712PLSI + 98.727 to estimate durability from strength for similar sandstones, saving time and resources.

Abstract Downhole Seismic Testing (DST) is utilized for estimating low-strain shear damping ratio (ηs). Estimates of low strain η s values are very important for predicting and assessing ground amplification during earthquakes. The low strain ηs estimates also provide for a reference of laboratory tests such as the resonant column test. The Spectral Ratio Technique (SRT) is one of the most utilized analysis techniques for processing seismic data to obtain ηs. The SRT is applied in the frequency domain where the spectral ratio of two data sets and relative arrival times are calculated to obtain the quality factor. The quality factor is inversely proportional to the damping ratio. One of the limitations of the SRT is that it doesn’t account for the raypaths of the source waves. In DST the raypaths are of particular importance due to the fact the source waves will refract as they travel from the surface down to the seismic receiver. This paper outlines a technique, so-called FMDSM-SRT, which facilitates adjusting estimated SRT absorption DST values so that source wave raypaths are accounted for. It is of paramount importance to first implement newly optimal estimation algorithms on extensive test bed simulations prior to processing real data sets. This paper outlines the results from processing a challenging test bed simulation with the FMDSM-SRT algorithm.

Abstract The application of loading tests allows us to evaluate the behavior of shallow foundations under real conditions. This article addresses the application of a constitutive model based on Mohr-Coulomb with a cap failure criterion that simulates the compaction of the material and limits its shear strength to describe the behavior of a footing resting on tropical climate soil composed of silt-clay sand. The foundation was tested in terms of axial compression through a static and slowly maintained loading test (SML) until its failure was characterized by significant settlement. A two-dimensional axisymmetric finite element numerical model was used to process the numerical analyses. The numerical model used was able to simulate with high similarity the load-settlement behavior of the footing tested in the loading test, under different water content conditions and preload imposed in the field tests. Additionally, the experimental results facilitated the successful guidance of the numerical analyses, providing parameters to safely analyze similar foundations under other conditions.

Abstract The paper studies the effect of sample reconstitution for three commonly employed procedures, namely static compaction and standard and modified moist tamping methods, in the context of laboratory testing of mine tailing materials. The effect of initial water content and compaction energy on the resulting densities and uniformity of the samples are examined. Equivalencies between different reconstitution methods were established to attain a given target density. Then, the effect of the resulting fabric was investigated by means of isotopically consolidated undrained triaxial tests, on samples prepared with similar densities and water contents but with different reconstitution techniques. The results showed that all reconstitution techniques studied produced samples with acceptable uniformity and good repeatability. Although similar results were obtained across the different methods, the modified moist tamping technique yielded slightly higher undrained peak strengths and exhibited a more pronounced hardening behavior upon reaching the critical state line compared to the static compaction method. In contrast, the moist tamping and static compaction methods produced comparable responses in loose specimens. These results suggest that dynamic and static reconstitution methods may create subtle differences in the fabric of the samples, influencing their behavior under shearing.