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CONTENTS
Volume 43, Number 5, December10 2025
 

Abstract
In response to the challenges of high silt content, poor cohesion, and loose structure in the Yellow River floodplain, this study proposes a combined reinforcement method using enzyme-induced carbonate precipitation (EICP) and MgO to enhance mechanical properties. By adjusting the cementation solution concentration and MgO amount, the mechanical characteristics of the reinforced silt were systematically analyzed, and the reinforcement mechanism was thoroughly investigated. Results show that while cementation solution concentration significantly affects calcium carbonate precipitation during EICP, excessively high concentrations inhibit urease activity. The addition of MgO promotes magnesium carbonate hydroxide formation, improving mechanical properties and increasing unconfined compressive strength to a maximum of 5000 kPa, with distinct brittle failure characteristics. Residual strength, elastic modulus, and peak strength also improved. Although MgO delays flocculation and precipitation processes, it increases carbonate production. SEM and XRD analyses reveal that increasing cementation solution concentration and MgO content reduces inter-particle porosity and enhances soil microstructural stability. Overall, the combined EICP–MgO method shows exceptional strength improvement in silt, highlighting its practical applicability and innovative advantage over EICP alone.

Key Words
bio-cementation; enzyme-induced carbonate precipitation; ground improvement; MgO; silt

Address
Bao min Liu, Wan juan He and Lin xian Gong : Institute of Resource and Environment, Henan Polytechnic University, Jiaozuo, Henan 454000, China
Yan Xu: Construction Engineering College, Jilin University, Xin Min Zhu Street, Changchun, Jilin 130026, China

Abstract
This study introduces an innovative approach, utilizing the ultrasonic pulse velocity (UPV) test, to assess the strength of desert sand samples treated with biopolymers, including various combinations of pore volumes (PV) and biopolymer concentrations. Consequently, unconfined compressive strength (UCS) and split tensile strength (STS) tests were performed on the treated desert sand to gauge the effectiveness of different biopolymers, specifically Starch and Gum varieties. The objective of this research is to highlight the significance of biopolymers as environment pleasant solution for enhancing the mechanical qualities of desert sand. The study incorporates five different biopolymers, including Corn starch (CS), Potato starch (PS), Tapioca starch (TS), Xanthan Gum (XG), and Guar Gum (GG) in varying concentrations (1%, 2%, and 3%), and two distinct pore volumes, 1PV and 0.75PV. The outcomes of UCS, UPV, and STS tests demonstrated that the strength of the sand increases as the biopolymer interacts with it up to a certain concentration. XG exhibited superior performance compared to GG, while among the starches, CS delivered the best results. Moreover, the study finds that pore volume plays an important role when interacting with sand. It was found that the 0.75 PV performs better than the 1 PV. The highest recorded UCS value was 891 kPa for the 3% CS treatment with 0.75 PV, whereas the lowest UCS value was 135 kPa for the 3% PS treatment with 1 PV. Likewise, the maximum STS value was 201 kPa for the 3% XG treatment with 0.75 PV, while the minimum STS value was 31 kPa for the 3% PS treatment with 1 PV. Furthermore, the minimum and maximum values from the UPV test were 798 m/s and 1270 m/s, respectively, which showed that all samples have strength. SEM and EDX tests for microstructure analysis have been performed to show bonding among particles.

Key Words
biopolymers; desert sand; gum; starch; UPV

Address
Monika Dagliya: Department of Civil Engineering, Prestige Institute of Engineering Management and Research, Indore, India
\Neelima Satyam: Department of Civil Engineering, Indian Institute of Technology Indore, India

Abstract
This study presents a reliability-based optimization (RBO) framework for the internal stability of mechanically stabilized earth walls, addressing reinforcement rupture and pullout limit states. The target reliability is set to B = 3.09 (Pf = 10−3). The MSE wall, reinforced with steel strips, founded on cohesionless soil, with horizontal backfill and uniform live traffic surcharge is considered. Uncertain variables in rupture and pullout limit states are unit weight and friction angle of backfill soil; uniform live surcharge load; and yield strength of steel strips. The reliability index is calculated by the first-order reliability method (FORM). Constrained optimization with linear approximation (COBYLA) is used for determination of reliability index and optimization of reinforcement length. For rupture, optimizing horizontal spacing at fixed vertical spacing yields designs that satisfy B > 3.09 at every depth with minimum factor of safety FSRP = 1.7 to 1.8 and a near heightindependent B–FS relationship. For pullout, optimizing strip length shows the required length-to-height ratio decreases with wall height and tighter vertical spacing: representative maxima of L/Hare 1.27, 0.83, 0.5 for H = 10 m at vertical spacing Sv = 1, 0.75, 0.5 m; 1.01, 0.7, 0.48 for H = 15 m; and 0.83, 0.6, 0.43 for H = 20 , respectively. Across cases, designs meeting B = 3.09 deliver factor of safety FS PG =2.10 at critical depth, but no unique B–FS mapping emerges for pullout. The framework converges to B-compliant, materially efficient layouts and clarifies how wall height and reinforcement spacing jointly control optimal L/H for pullout while leaving rupture behavior chiefly governed by spacing rather than wall height.

Key Words
constrained optimization; first-order reliability method; internal stability; MSE wall; reliability-based optimization

Address
Zafar Mahmood: Department of Civil Engineering, Imam Mohammad Ibn Saud Islamic University, Riyadh, Saudi Arabia
Mohsin Usman Qureshi: Faculty of Engineering, Sohar University, Sohar, Oman
Ali Murtaza Rasool: National Engineering Services Pakistan, Lahore, Pakistan
Syed Bilal Ahmed Zaidi: University of Engineering and Technology Taxila, Taxila, Pakistan

Abstract
In the estimation of the design spectrum for sites with topographic irregularity, the instructions of the earthquake codes are to use the horizontal components of the motions. Although this approximation remains conservative for horizontally layered conditions, the effect of the P wave component at basins with 2D/3D bedrock geometry, due to the complicated interaction among different wave types, would affect the basin amplification behavior. The major contribution of this study is to present a quantitative ratio in terms of amplification factor for comparison between the simultaneous P+SV and only SV incident wave condition. To attain this goal, a fully nonlinear analysis method capable of simultaneously application of the P and SV incident motions in time domain is utilized. In this study, the effect of parameters such as clay type and basin depth is investigated. The results show the effect of the P+SV cases on the frequency content of the surface response with respect to the only SV case. It was seen that for the basin with 50m depth the aggravating effect of the P+SV incident wave remains under 20% for both soft and stiff clay types. This ratio reaches to 25% for 100 m depth basins. Along with the aggravating effect, the results show a 10% to 20% suppressive effect of the P+SV especially at basins' center with dominant 1D behavior.

Key Words
amplification factor; basin edge effect; dynamic behavior; in-plane waves; nonlinear analysis; numerical modeling; simultaneous P and SV wave's effect

Address
Hadi Khanbabazadeh: Engineering Faculty, Gebze Technical University, 41400 Gebze, Kocaeli, Turkey

Abstract
Shallow foundations are widely used where surface soils can sustain structural loads without excessive settlement. Various ground improvement methods, such as microbially induced carbonate precipitation (MICP), can increase bearing capacity in cases where soil strength is insufficient. MICP promotes the formation of calcium carbonate between soil particles, thereby improving interparticle bonding and enhancing soil strength. This study uses experimental testing and numerical analysis to examine the impact of a biologically treated thin layer on the ultimate bearing capacity and failure mechanisms of rectangular shallow foundations in sandy soils. Laboratory tests were conducted in a steel container measuring 100 cm in length, 70 cm in height, and 70 cm in width, examining the effects of different bacterial strains and varying treatment depths. Results show that bacterial inoculation and subsequent MICP treatment significantly increase the cohesion and strength of sandy soils. Introducing a biologically improved layer can increase the bearing capacity by up to three times. Positioning the treated layer at the surface yields a bearing capacity more than 10% higher than placing it at half the effective depth. Among the tested bacteria, Bacillus megaterium notably improves the soil's shear strength parameters compared to Sporosarcina pasteurii, resulting in an over 50% increase in foundation-bearing capacity. Numerical simulations using PLAXIS, based on the mohr-coulomb constitutive model, closely match the experimental findings, with a deviation of less than 10%.

Key Words
bearing capacity; MICP; PLAXIS; sandy soil; shallow foundation

Address
Javad Bidgoli, Ahad Bagherzadeh Khalkhali and Amin Bahmanpour: Department of Civil Engineering, SR.C., Islamic Azad University, Tehran, Iran
Ali Derakhshani: Department of Civil Engineering, Shahed University, Tehran, Iran

Abstract
Rock fracture is a process of energy accumulation and subsequent release, in which rock mass strength significantly influences this process. This study investigates the energy release and evolution of failure mechanisms in models with different compressive strengths through uniaxial compression tests, acoustic emission techniques, and digital image correlation. The experimental results indicate that during the yielding stage, there is a notable increase in the number of small-scale failures in the models. The failure of the models, initially dominated by shear failure, progressively involves more tensile cracks. Before global instability occurs, significant horizontal relative displacement and localized surface deformation are observed at the pre-existing fissures. As the strength decreases, the models tend to exhibit a larger number of small-scale failures, and the failure mechanism shifts toward a composite shear-tensile mode.

Key Words
energy; failure mechanism; local deformation; rock-like model

Address
Xianxiu Lu and Zeqi Hao: School of Disaster Prevention and Reduction Engineering, Institute of Disaster Prevention, Langfang, China, 065201
Zhandong Su and Jianyong Zhang: School of Disaster Prevention and Reduction Engineering, Institute of Disaster Prevention, Langfang, China, 065201;
Key Laboratory of Earthquake Disaster Prevention and Risk Evaluation of Hebei Province, Langfang, China, 065201
Xiaoli Liu: State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing, China, 100084
Mingdong Zang and Jinzhong Sun: College of Engineering and Technology, China University of Geosciences, Beijing, China, 100083
Wenqiang Chi: China Railway 24th Bureau Group Zhejiang Engineering CO., LTD. Zhejiang, China, 310001


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