Recent studies have highlighted the potential benefits of allowing inelastic foundation response during strong seismic shaking. This approach, known as rocking isolation, reduces the moment at the base of the column by transferring the plastic joint beneath the foundation and into the soil bed. This mechanism acts as a fuse, preventing damage to the superstructure. However, structures with a low static safety factor against vertical loads (FSv) may experience unacceptable settlements during earthquakes. To address this, shallow soil improvement is proposed to ensure sufficient safety and mitigate risks. In this study, a small-scale physical model of a foundation and structure (SDOF model, n = 40) was placed on dense sandy soil, and seismic loading was simulated using lateral displacement applied by an actuator. A group of short-yielding piles with varying bearing capacities (QU/NU = 0.1-0.8) was installed beneath the rocking foundation. The results of the small-scale tests demonstrate that the use of short-yielding piles during seismic loading reduces the settlement of the shallow foundation by up to 50% and increases rotational damping by 59%. This is achieved through the frictional yielding of the pile wall and the yielding of the pile tip, which dissipate energy and enhance the overall seismic performance of the foundation. The findings suggest that incorporating yielding pile groups in the design of rocking foundations can significantly improve their seismic performance by reducing settlement and increasing energy dissipation, making it a viable strategy for enhancing the resilience of structures in earthquake-prone areas. The optimal bearing capacity ratio (QU/NU = 0.25-0.5) provides a straightforward guideline for designing cost-effective seismic retrofits.

As a potential source of damage, earthquake-induced liquefaction is a major concern for embankment safety and serviceability. Densification has been a popular method for improving the performance of liquefiable soils. Understanding embankment settlement mechanisms plays a fundamental role in determining densification remediation. In this work, nonlinear dynamic analysis of embankments on liquefiable soils is conducted by the finite-difference program FLAC3D (version 6.0) with the simple anisotropic sand constitutive model. Numerical models are validated via dynamic centrifuge test results reported in the literature. The effects of densification countermeasures on the mean and differential settlements are explored in this study. Furthermore, the effects of the densification spacing and width are investigated to optimize the geometry of the densified regions. The development of pore pressure and the movement of the surrounding loose soil are discussed. The results show that both the mean settlement and differential settlement should be simultaneously utilized to comprehensively assess the overall effectiveness of densification treatment. The mean settlement is influenced by the densification spacing and width, but the differential settlement is highly associated with the inner edge of the densified region. This study provides insight for improving the design of the location and lateral extent of densification regions to prevent excessive embankment settlement.

Biogrouting, a method to enhance soil properties using microorganisms and mechanical techniques, has shown great potential for soil improvement. Most studies focus on small sand columns in labs, but recent tests used 0.5 m plastic boxes filled with sand stabilized with microorganisms and fly ash. The experiments, conducted over 30 days, applied injection and infusion methods with microbial fluids, maintaining groundwater levels to simulate field conditions. Mechanical properties were analyzed through unconfined compressive strength (UCS) tests on extracted samples. Researchers also assessed calcium carbonate distribution and shear strength. Results showed water saturation significantly influenced vertical stress (qu), while UCS correlated with the permeability of sand containing varying calcium carbonate levels. Bacillus safensis, a resilient bacterium used in this process, can withstand extreme conditions. After completing its task, it enters a dormant state and reactivates when needed. The bacteria produce calcium carbonate by binding calcium with enzymes, which cements soil particles, enhancing strength and stability. center dot Testing enzymes on microbes and natural soil center dot Installation settings for drip tools using infusion center dot Soil resistance testing after stabilization using UCS

Due to the environmental pollution caused by the production and consumption of cement, the demand for new and environmentally friendly methods to improve and strengthen the soil is increasing. In addition, reinforcing the soil with steel fibers improves the mechanical properties, including the formability and bearing capacity of the soil. The purpose of this research is to evaluate the effect of zeolite on the behavior of cemented sand soil reinforced with steel fibers. In the following, the unconfined compressive strength (UCS) test was used to check the compressive strength, and the flexural strength (FT) test was used to check the flexural. It should be mentioned that to improve the soil from cement in the amount of 5% by weight, zeolite in the amount of 0, 25, 50, 75 and 100% was used instead of cement, as well as steel fibers in the amount of 2% and random distribution in the curing of 28-day. In the results of unconfined compressive strength tests, the best replacement percentage of zeolite instead of cement in sandy soil was 25%, which initiated an increase in unconfined compressive strength and an increase in the failure strain of the sample. In the results of flexural strength tests, 25% of zeolite to replace cement in sandy soil affected the greatest increase in flexural strength and increased soft behavior. In addition, with the addition of steel fibers, the samples endured much more displacements than those without fibers. [GRAPHICS]

This study investigates the effectiveness of deep soil mixing (DSM) in enhancing the strength and modulus of organic soils. The research evaluates how varying cement types, binder dosages, water-to-cement (w/c) ratios, and curing durations affect the mechanical properties of two different organic soils that were used; natural soil from the Golden Horn region of Istanbul with 12.4% organic content, and an artificial soil created from a 50/50 mixture of Kaolin clay and Leonardite, which has an acidic pH due to high organic content. The specimens were cured for four durations, ranging from seven days to one year. The testing program included mechanical testing; Unconfined Compression Tests (UCS), Ultrasonic Pulse Velocity (UPV) measurements, and chemical analyses; XRay Fluorescence (XRF) and Thermogravimetric analyses (TGA). The UCS tests indicated that higher binder dosages and extended curing durations significantly improved the strength. Higher w/c ratios resulted in decreased strength. Long curing durations resulted in strength values which were four times the 28-day strength values. This amplified effect of strength gain in longer durations was evaluated through Curing time effect index, (fc). The results were presented in terms of cement dosage effect, effect of cement type, effect of total water/cement ratio (wt/c), standard deviation values, E50 values and curing time effect index (fc) values respectively. Results of UPV tests were used to develop correlations between strength and ultrasonic pulse velocities. Quantitative evaluations were made using the results of XRF and TGA analyses and strength. Significant amount of data was produced both in terms of mechanical of chemical analyses.

This paper attempts to enhance the mechanical properties of weak kaolin soil, partially replaced by calcined sepiolite (CS). The CS is highly reactive due to its high concentration of CaO and SiO2 oxides. This characteristic is chemically required to form polymeric bonds, which basically improve the mechanical properties of weak soil. Systematic analytical methods were employed to distinguish the textural and mineralogical properties of soil, sepiolite, CS, and new products. A series of geotechnical tests were conducted to examine the effects of varying percentages of CS admixture on Atterberg limits, standard Proctor test, and unconfined compressive strength (UCS). Samples were cured until the ages of 3, 7, and 28 days. The maximum UCS value was obtained after 28 days of curing when 3 wt% of CS was mixed with the primary soil. Also, replacing 3 wt% of CS lowered the soil plasticity index (PI) to about 60%. Further, incorporating 5 wt% CS into the soil increased the modulus of elasticity by 6.82 times compared to the control sample. Microstructural investigations indicated that the strength enhancement of kaolin soil was yielded by filler effects and chemical reactions/exchanges, including flocculation, carbonation, and solid solution reactions. Collectively, the results showed that CS could effectively enhance the strength properties of kaolin soil due to its high specific surface area (SSA), reactivity, and alkalinity.

Microbial induced carbonate precipitation (MICP) is a promising method for improving the performance of geotechnical engineering materials. However, there has been limited research on the creep characteristics of expansive soil treated with MICP. Therefore, this study investigated the improvement of consolidation creep characteristics of expansive soils using the MICP method through one-dimensional consolidation creep tests. The microstructure of the treated soil was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate that the MICP method effectively enhances the resistance of expansive soil to creep deformation. Compared to untreated expansive soil, the creep deformation of the treated soil decreased by 3.85%, 22.62%, and 18.40% for cementation solution contents of 50 mL, 100 mL, and 150 mL, respectively. Additionally, the creep curve of the improved expansive soil exhibits significant nonlinear characteristics. The creep process of the improved expansive soil can be divided into three stages: instantaneous deformation, decay creep, and stable creep. SEM images and XRD patterns reveal that the calcium carbonate precipitates generated during the MICP process can wrap, cement, and fill the voids between soil particles, which is the fundamental reason why the MICP method improves the deformation resistance of expansive soil. On the basis of the creep test results, a fractional-order creep model for MICP-treated expansive soil was established. Compared to traditional integer-order creep model, the fractional creep model can more accurately describe the entire process of consolidation creep of expansive soil improved by MICP method. The findings of this study provide a theoretical basis for analyzing the deformation of MICP-treated expansive soil under long-term loads.

Soil stabilization is a method of improving weak soils by adding different additives. Nano additives and materials represent a new technology and a revolution in soil mechanics and geotechnical engineering, used for soil stabilization, a branch of soil improvement. This research evaluates the particles of Nano- and Pico-Typha solution as a new biomaterial for soil improvement using nano and pico scales, bio, and soil mechanics tests. The research investigates the changes in soil mechanical properties after the addition of Nano and Pico Typha solution as a Nano-Bio Geotechnics (NBG) technique, comparing the properties of the soil before and after stabilization. To control and characterize the size and nature of the particles studied in this research, SEM tests were performed after the nano production process. To check the particle dimensions and structure before and after the nano production process, XRF and XRD tests were performed. After converting particles from micro to nano scale, there are also smaller pico particles. The research studied the properties of Khavaran clay soil by adding Typha and Nano Typha as a Nano-Bio additive in different percentages of 3%, 5%, and 7%, and in curing times of 1, 7, and 28 days. The results showed that the uniaxial resistance of clay increased from 50 kPa to 12 times its initial value by adding 7% Nano-Typha after 28 days of curing. The maximum deviator stress of the soil increased by 10.1, 14.07, and 15.9 times its initial value in confining stresses of 100, 200, and 300 kPa, respectively, by adding 7% Nano-Typha after 1 day of curing. The cohesion and friction angle of the soil stabilized with 7% Nano-Typha solution increased by 2.22 and 6.3 times, respectively, compared to clay soil after 1 day of curing.

Soil improvement is one of the most important issues in geotechnical engineering practice. The wide application of traditional improvement techniques (cement/chemical materials) are limited due to damage ecological environment and intensify carbon emissions. However, the use of microbially induced calcium carbonate precipitation (MICP) to obtain bio-cement is a novel technique with the potential to induce soil stability, providing a low-carbon, environment-friendly, and sustainable integrated solution for some geotechnical engineering problems in the environment. This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy. It systematically summarizes and overviews the mineralization mechanism, influencing factors, improved methods, engineering characteristics, and current field application status of the MICP. Additionally, it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement. This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand. Furthermore, we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future. The current review purports to provide insights for engineers and interdisciplinary researchers, and guidance for future engineering applications.

The increasing demand for sustainable civil engineering solutions requires balancing present-day infrastructure needs with environmental preservation for future generations. This study explores the potential of xanthan gum, an eco-friendly biopolymer, for stabilizing clayey sand as an alternative to traditional soil stabilizers. Various concentrations of xanthan gum (0.25 % to 1.5 %) and curing durations (7, 14, and 28 days) were evaluated using standard geotechnical testing methods, including compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM) analysis. The soil samples comprised 80 % poorly graded sand and 20 % high-plasticity clay. Results showed a significant improvement in soil properties, with just 0.25 % xanthan gum after a 7-day curing period leading to notable increases in UCS and tensile strength. However, further increases in xanthan gum concentration yielded diminishing returns in strength enhancement. Extending the curing time from 7 to 28 days improved compressive strength and stiffness. Additionally, xanthan gum-enhanced samples exhibited increased energy absorption, stiffness, and brittle behavior, forming a denser soil matrix and improving the particle bonding, supported by UPV results and SEM imagery. Also, the relationship between the stiffness from UCS tests and the ultrasonic pulse velocity was obtained. The findings underscore xanthan gum's potential as a sustainable and effective soil stabilizer for geotechnical applications.