Buried pipes are subjected to static and dynamic loads depending on their areas of use. To mitigate the risk of damage caused by these effects, various materials and reinforcement methods are utilized. In this study, five buried uPVC pipes designed in accordance with ASTM D2321 standards were reinforced with three different ground improvement materials: Geocell, Geonet, and Geocomposite, and experimentally subjected to dynamic impact loading. Acceleration, velocity, and displacement values were obtained from the experiments. Subsequently, finite element analysis (FEA) was performed using the ABAQUS software to determine stress values and volumetric displacements in the pipes, and the model was validated with a 5-7% error margin. In the final stage of the study, a parametric analysis was conducted by modifying the soil cover height above the pipe and the Geocell thickness in the validated finite element model. The parametric study revealed that the displacement value in the pipe decreased by 78% with an increase in soil cover height, while a 16% reduction was observed with an increase in Geocell thickness. The results demonstrate that the soil improvement techniques examined in this study provide an effective solution for enhancing the impact resistance of buried pipeline systems.

Construction on silty sand soils on the riverbank, which are typically loose, can cause geotechnical problems. Therefore, it is essential to improve their short-term and long-term behavior. Sustainable development encourages geotechnical engineers to use eco-friendly materials in soil improvement. This study investigates the effect of Kenaf fibers (KF) and Persian gum (PG) biopolymer on stabilizing silty sand with low shear strength. Short-term behavior was assessed using standard Proctor compaction, unconfined compressive strength (UCS), and indirect tensile strength (ITS) tests, while long-term performance was evaluated through the direct shear test. The effects of initial moisture content, PG and KF percentages, curing time, and temperature on mechanical properties were analyzed. Additionally, ultrasonic pulse velocity (UPV) and scanning electron microscopy (SEM) tests examined the microstructure of the improved soil. Results showed that the optimum PG and KF contents were 2.5 % and 1 % by soil weight, respectively. The UCS of samples containing these additives increased by 75 % compared to unstabilized soil. The highest UCS was achieved at 50 degrees C, with 5.1 times increase, while at 110 degrees C, it decreased by 67 % due to thermal degradation. Direct shear tests confirmed that KF reinforcement consistently improved shear strength. The UPV showed a strong correlation with UCS, supporting its use as a non-destructive evaluation method. Also, SEM analysis showed that PG enhanced particle bonding, while KF reinforcement created a denser and more interconnected soil structure. This study highlights the effectiveness of PG and KF as sustainable alternatives for soil stabilization, showing improved soil properties and environmental issues.

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 assesses the performance of biopolymers (agar gum and guar gum) for soil stabilization and the self-healing properties of these materials using non-destructive ultrasonic pulse velocity (UPV) and unconfined compressive strength (UCS) tests. Scanning electron microscopy (SEM) tests were performed to investigate the microstructure of the stabilized soil during the self-healing process. The results showed that adding biopolymers to the soil significantly improved the soil's mechanical properties and self-healing properties. The self-healing indexes of sandy soil stabilized with 1% of guar gum and agar gum were 45% and 18%, respectively, at the curing time of 14 days. Increasing the internal bonds and reducing cracking caused by hydrogel swelling are the significant advantages of using biopolymers in soil stabilization. The UPV provides a quick and accurate estimate of changes in the properties of the stabilized soil. The UPV of the samples increased after the self-healing period. The UPV of the sandy soil stabilized with 1% guar gum and agar gum increased by 17% and 13%, respectively, at the curing time of 7 days. The SEM results showed that the swelling of biopolymers led to crack repair after the self-healing period, the creation of new bonds between grains, and the increase of the contact surface of soil particles.

This study used Persian gum (PG) as a sustainable anionic hydrocolloid to alternative traditional stabilizers to stabilize this soil. For this purpose, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and direct shear tests were performed after freeze-thaw cycles. The results show that biopolymers can improve UCS by creating stronger bonds between soil particles and effectively reducing the adverse effects of freeze-thaw cycles compared to unstabilized clayey soil. Also, the accumulative mass loss by adding 2% of Persian gum to unstabilized clayey soil decreased by about 70% due to the adhesive property and interaction of Persian gum hydrogel with soil grains. In addition, the moisture loss is reduced with the addition of biopolymer compared to the unstabilized sample. The UPV of the samples under the freezing phase is higher than in the thawing phase. The internal friction angle and cohesion of unstabilized and stabilized clayey soil with 2% Persian gum increased and decreased under freeze-thaw cycles. Overall, the findings show that anionic hydrocolloids such as Persian gum can effectively improve the performance and durability of CH clayey soil under severe freeze-thaw conditions.

Microbially Induced Calcite Precipitation (MICP) is an eco-friendly method for improving sandy soils, relying on micro-organisms that require nitrogen and essential nutrients to induce carbonate mineral precipitation. Given the substantial annual generation of chicken manure (CM) and the associated challenges in its disposal resulting in environmental pollution, the nutrient-rich composted form of this waste material is proposed in this study as a supplementary additive (along with more costly industrial reagents, e.g., urea) to provide the necessary carbon and nitrogen for the MICP process. To this end, different CM contents (5 %, 10 %, and 15 %) along with various concentrations of cementation solution (1 M, 1.5 M, and 2 M) are employed in multiple improvement cycles to augment the efficiency of the MICP technique. Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), and Water Absorption (WA) tests are performed to assess the mechanical properties of the samples before and after exposure to freeze-thaw (F-T) cycles, while SEM, XRD, and FTIR analyses are carried out to delineate the formation of calcite within the porous structure of MICP-CM-treated sands. The findings suggest that an optimum percentage of CM (10 %) in the MICP process not only contributes to environmental conservation but also significantly enhances all the mechanical properties of bio-cemented sandy soils due to markedly improved bonding within their porous fabric. The results also show that although prolonged exposure to consecutive F-T cycles causes a reduction in strength and stiffness of enhanced MICP-treated soils, the mechanical properties of such geo-composites still remain within an acceptable range for optimal CM-enhanced biocemented mixtures, significantly superior to those of MICP-treated sands.

The ultrasonic pulse velocity (UPV) correlates significantly with the density and pore size of subgrade filling materials. This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality. The study measures the changes in UPV across dry density and compaction characteristics. The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve, primarily influenced by internal water molecules. The maximum dry density exhibits a positive correlation with the rock content, while the optimal moisture content demonstrates an inverse relationship. As the rock content increases, the relative error of UPV measurement rises. The UPV follows a hump-shaped pattern with the initial moisture content. Three intelligent models are established to forecast dry density. The measure of UPV and PSO-BP-NN model quickly assesses compaction quality. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This research paper delves into self-compacting concrete (SCC), a type of concrete that consolidates without the need for vibration. However, external loading and chemical reactions often lead to the development of microcracks. Addressing this issue, the study concentrates on CaCO3 precipitation in SCC as a method for self-healing microcrack repair. The research encompasses five different concrete mixes, incorporating two supplementary cementitious materials (SCMs), microsilica (MS), and metakaolin (MK), with and without the inclusion of the bacteria Sporosarcina pasteurii. Experimental findings indicate that mixes SCCMSSP and SCCMKSP increased compressive strength by 15.32% and 21.29%, tensile strength by 12.1% and 16.14%, and flexural strengths by 15.62% and 21.88%, respectively, at 28 days compared to the corresponding control mix. Moreover, these mixes improved compressive strength by 10.86% and 20.28%, tensile strength by 15.34% and 20.82%, and flexural strength by 17.65% and 26.47%, respectively, at 56 days compared to the corresponding control mix. The concrete's integrity concerning self-healing ratio, damage level, and strength regain ratio was evaluated through an ultrasonic pulse velocity test. Results showed that mix SCCMKSP exhibited optimal reduction of damage level by 27.36%, and mixes SCCMSSP and SCCMKSP demonstrated healing efficiencies of 14.06% and 12.52% at 28 days and 14.84% and 15.64% at 56 days, respectively, compared to the corresponding control mix. The research also employed scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to examine the mobility and elemental composition of bacterial concrete. These analyses further bolster the positive effects of bacteria in enhancing the self-healing capabilities of SCC mixes when combined with mineral admixture.