To study the failure mechanism of high ductile coagulation (HDC) under sulfate attack in cold saline soil area, cement-based cementing material (cement: fly ash: sand: water reducing agent: water = 1:1:0.72:0.03:0.58) and 2 % polyvinyl alcohol fiber (PVA) were used to prepare HDC sample, to increase the density and ductility of concrete. a 540-day sulfate-long-term immersion test was performed on HDC specimens under two low-temperature curing environments and different sulfate solution concentrations (5 %, 10 %). Using a combination of macro and microscopic methods, according to the principle of energy dissipation, To study the relationship between the evolution of energy (total damage energy U, dissipated energy Uds, elastic strain energy Ues) and the deterioration of strength and the change of pore structure during the compression process of HDC. According to the characteristics of stress-strain curves during HDC compression, the damage evolution characteristics of characteristic stress points during HDC compression are summarized, establish energy storage indicators Kel to evaluate the degree of internal damage of HDC. The results show that during the compression damage process of HDC after long-term soaking in sulfate solution under low temperature environment, Uds and Ues of HDC at characteristic stress points both increase first and then decrease, Kel are reduced first and then increased. The development trend of elastic strain energy and dissipative energy of HDC in 10 % sulfate solution is more drastic than that in 5 % sulfate solution. Compared with the other three groups, the D group energy storage level rises and falls more violently, and the HDC has a smaller ability to resist damage under this condition. Through the study of the correlation between macro and micro changes of HDC in cold saline soil areas and energy evolution, to provide a reference for the stable operation of highly ductile concrete in cold saline soil areas.

This study addresses the cracking issue of airport foundations in marine and coastal regions by proposing an unsaturated reinforcement method based on Microbially Induced Calcium Carbonate Precipitation (MICP) combined with coconut fibers. Composite sand columns incorporating coconut fiber and bioslurry were prepared, and the effects of fiber length and content on the mechanical properties of MICP-treated sand columns were investigated. Experimental results revealed that the addition of short fibers (1-5 mm) significantly improved the unconfined compressive strength and ductility of the MICP-treated sand columns. As the bioslurry content decreases in the sand columns, the enhancement effect of short fibers on the unconfined compressive strength becomes more pronounced, with fiber addition improving compressive strength by up to 98 %. However, the inclusion of medium fibers (5-10 mm) and long fibers (10-15 mm) negatively affected the mechanical properties of the sand columns. Microstructural analysis further confirmed the synergistic reinforcement effect of short fibers and calcium carbonate precipitation. Short fibers acted as bridges, forming additional contact points between sand particles, which facilitated calcium carbonate precipitation at critical contact points, thereby enhancing the overall stability and strength of the sand columns. This characteristic was more pronounced under unsaturated conditions. This study provides a feasible technical solution for the effective reinforcement of airport foundations and demonstrates potential in unsaturated reinforcement and improving the ductility of sandy soil foundations.

In this paper, an extensive series of direct shear box tests (99 tests) were conducted to explore and compare the effects of raw and treated natural fibers, specifically Doum fibers on the mechanical behavior of three categories of sandy soils with distinct mean particle sizes (D50 = 0.63, 1, and 2 mm). Specimens from every soil category, containing 0 to 0.8% raw Doum fibers and 0 to 1% treated Doum fibers in incremental step of 0.2%, were reconstituted at an initial relative density of (Dr = 87 +/- 3%) and subjected to three different initial normal stresses (100, 200, and 400 kPa). The obtained results indicate that incorporating raw or treated Doum fibers improve the mechanical and rheological properties (internal friction angle, ductility, and maximum dilatancy angle) of the tested mixtures up to specific thresholds Doum fiber content (FD = 0.6% and FTD = 0.8% for raw and treated Doum fibers respectively). Beyond these limiting values, the mechanical and rheological properties decreased with further increases in Doum fiber content. Additionally, specimens reinforced with treated Doum fibers exhibit higher shear strength than that of the raw Doum fibers for all tested parameters. Based on the experimental results, it has been found to suggest a reliable correlation between Particle Size Distribution (PSD) characteristics and mechanical properties for all reconstituted specimens. The recorded soil trend is especially pronounced for the mean grain size (D50) ranging between 1 and 2 mm, where a notable increase in shear resistance is noticed. The analysis of the obtained outcome suggests the introduction of new enhancement factors (EF tau peak and EF phi degrees) as useful parameters for predicting the mechanical behavior of sand-fibers mixtures. Furthermore, new relationships have been developed to forecast changes in mechanical properties (peak shear strength, internal friction angle, and maximum dilatancy angle) of the tested mixtures under the impact of the selected parameters (FD/TD, D50, and sigma n).

Local buckling of pipeline walls is a common failure mode for buried pipelines crossing reverse faults. The damage evolution of pipelines from initial buckling to severe failure under reverse fault displacement is closely related to soil properties, fault mechanism, and pipeline geometry. The performance-based design methodology proposed by the Pacific Earthquake Engineering Research Center has become well-recognized worldwide. However, current safety-based design codes for buried steel pipelines generally provide operable limits corresponding to the initiation of local buckling of the pipeline walls, and cannot be used to effectively assess the damage states and performance levels of pipelines. To address the local buckling of pipeline walls under fault displacement, a performance criterion is proposed based on the critical compressive strain and the change rate of pipeline compressive strain. Three performance levels corresponding to pipeline wall local buckling are identified, namely, buckling initiation, buckling development, and buckling failure. Moreover, the ductility coefficient that characterizes the nonlinear behavior of the pipeline wall prior to buckling failure is proposed in this study to quantify the damage state threshold values. Three-dimensional finite element models of the largediameter pipeline crossing a reverse fault are developed and validated against the existing experiment study. Parametric analysis is performed to comprehensively assess the effects of pipeline burial depth, fault mechanism, and pipeline geometry on the performance of the buried steel pipeline under reverse fault displacement. Finally, the empirical equation for critical displacements between performance levels under different conditions is developed. The numerical results indicate that as the diameter-to-thickness ratio and burial depth of the pipeline increase, the structure ductility of the pipeline wall prior to buckling failure decreases. The structural ductility of the pipeline wall increases by 94.7 % as the fault dip angle increases from 30 degrees to 90 degrees. Moreover, the structural ductility increases when the internal pressure increases from 0 MPa to 6 MPa, but decreases as the internal pressure changes further from 6 MPa to 12 MPa.

In the recent 2023 major earthquake triggering one other large earthquake in Anatolia, the poor structural performance of buildings and the satisfactory performance of bridges remained relatively consistent compared to past observed earthquake experiences. Despite numerous building collapses, it is worth noting that no bridges collapsed during the event. Several engineering factors for poor building performance have been identified based on field building inspections in the recent and past earthquakes, such as the misuse of building design software without proper engineering judgment, the utilization of poor-quality construction materials, underestimation of earthquake forces, construction on inadequate soil conditions, design mistakes, and incorrect implementation of high ductility reinforcement details. In the aftermath of the earthquake, it was found that only a small percentage of bridges (1%) were closed, and approximately 50% of them were reopened to traffic within 24 h. Remarkably, no bridge collapses including the modern or old bridges were reported in the affected area. The focus of this paper is to identify the differences in the design philosophy between buildings and bridges and to understand the reasons behind the bridges' resilience during these rare earthquakes. The study involves analyzing past structural performances of buildings and bridges under different earthquake conditions and design requirements. Analytical results from a survived 90-year-old reinforced concrete arch railroad bridge, highlighting its resilience and design characteristics are also presented.

Sandy soils are a type of geomaterial that may require improvements due to lack of cohesion. In this study, first, the lack of cohesion of sand was resolved using clay, and the soil was stabilized with cement and lime (4% and 3% of the dry weight of materials, respectively) and finally reinforced with recycled tire fibers of 20 to 30 mm in length for improved strength and ductility. Next, 747 samples with different fiber contents at different curing temperatures and ages were prepared and a unconfined compressive strength (UCS) test was carried out. Next, a novel approach employing multivariate nonlinear regression techniques and obtained empirical data was applied to formulate a mathematical model for predicting the UCS and the modulus of elasticity (E-s) of the reinforced and stabilized soil. This model can serve as a valuable tool for building engineers in designing building foundations. The comparison of the obtained UCS and E-s results and those predicted using the proposed model showed a correlation of >95% (R-2 >= 0.95). The fibers effectively increased the failure strain, thus resulting in the greater ductility of the samples. As an example, in 14-day samples cured at 60 degrees C with 0%, 0.4%, 1%, 1.7%, and 2.5% fibers, the failure strain showed an incremental trend of 1.47%, 1.87%, 2.08%, 2.20%, and 2.92%, respectively. Scanning electron microscopy (SEM) was used to study the microstructure of the samples and to explain the strength experimental outcomes. SEM images showed a desirable interaction between the fiber surfaces with the soil mass and the reduction in porosity and the occurrence of pozzolanic reactions through stabilization. The results also showed that the reinforcement effectively improved the ductility, as desired for building foundations; however, it resulted in reduced strength, although a greater strength compared to the untreated soil was achieved. Although soil stabilization has been widely studied, limited research focuses on stabilizing soil with clay, lime, cement, and recycled tire fibers. This study offers design engineers an estimation scheme of the strength properties of stabilized and reinforced foundations.

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load-displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density.

In this research, a soil reinforcement approach was explored by introducing a polyvinyl acetate polymer treatment along with sisal fiber material, considering two mean particle sizes (D50 = 0.63 and 2.00 mm). The sand specimens were mixed with varying sisal fiber contents (Fs = 0 to 0.8%) and polyvinyl acetate polymer contents (PVAc = 6%, 9%, and 12%). A series of unconfined compression tests were performed to evaluate the compressive strength of the tested materials. The experimental findings indicate a positive correlation between the concentration of polyvinyl acetate polymer and the unconfined compressive strength within the tested range. The shear strength and of the sand initially increases with rising sisal fiber contents and then decreases with further increments in sisal fiber, peaking at a maximum value when the fiber content reaches a threshold of 0.6%. The findings validate the significance of the strain energy parameter as a reliable indicator for elucidating and forecasting the mechanical characteristics of soil reinforcement. New correlations have been developed to predict variations in unconfined compressive strength and peak strain energy based on the studied parameters (Fs, PVAc, and D50). The agreement between predicted and measured characteristics validates the effectiveness of these established relationships in accurately predicting UCS and strain energy factors.

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment-reinforced-concrete (RC) pile (IAP)-soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder-integral abutment-RC pile (GIAP)-soil system was conducted for an IAB in China. The experiment's results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of -8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP-soil system was better than that of the IAP-soil system. Therefore, to accurately reflect the seismic performance of GIAP-soil systems in IABs, it is suggested to consider the influence of the girder.

Purpose Straw fiber (SF) is a natural and environmentally friendly material, which has great potential in improving the hydro-mechanical behavior of cemented dredge sediment. However, the treatment mechanisms and optimum application dosage of SF in cemented sediment at high water content are unclear. This study investigates the effect of SF on the shear strength and permeability of cemented sediment at high water content (3 times the liquid limit). Methods Various SF contents (0%, 0.3%, 0.5%, 1%, 3%, 5%, 8% and 12% by mass) and curing ages (3, 7, 14, 28, 60, 90, 180 days) were considered to improve cemented dredged sediment. The effectiveness of the improvement was evaluated through unconfined compression and permeability tests. Results The test results show that there is an optimum SF content of 0.5%, below which the unconfined compression strength (q(u)) of SF-reinforced cemented sediment (SFCS) increased with SF content. Beyond this point, q(u) decreased with SF content. The brittleness index (I-b), which indicates the ductility behavior, increased with SF content across the entire SF range (0-12%). When SF addition was relatively low (< 0.5%), pore filling and bridge effects increased the interface force between SF and sediment particles, resulting in positive effects on the improvement of SFCS strength. However, when SF content exceeded 0.5%, the higher organic matter from SF could suppress pozzolanic reaction, leading to weaker cemented bonding between sediment particles and hence lower sediment strength. Conclusion This study suggests that 0.5% SF should be applied in cemented dredged sediment at high water content to optimize its strength.