Advances in Civil Engineering

The expansive soil swells significantly in the presence of moisture, which often leads to the failure of superstructures. Conventional stabilization techniques are applied in many instances, although environmental issues are of significant concern for such stabilization. Keeping this in mind, an attempt is made to apply a new approach for stabilizing different types of expansive soils, treated with a nonconventional binder geopolymer that utilizes fly ash as the main ingredient. A series of laboratory experiments are run to determine the engineering properties of treated soils with varying percentages of geopolymer from 0% to 30%. The experimental investigation involved tests such as unconfined compressive strength, compaction, Atterberg limits, and swelling pressure. Significant strength development occurs with increasing percentages of geopolymer, and their swelling pressures decrease considerably. Additionally, a series of California Bearing Ratio (CBR) tests were undertaken to assess the suitability for road construction. The optimum dosage of the stabilizing agent is found to be 20%, as justified by studies in the literature. Furthermore, scanning electronic microscope (SEM) images of the treated samples revealed microstructural changes in the soil matrix, which strongly correlate with the improvement of strength and swelling behavior. Hence, based on our experimental results, 20% geopolymer content is sufficient for enhancing the engineering properties of expansive soils, and the treated soils can directly be used as subgrade or sub-base material.

To improve the strength of red sandstone roadbed and elevate the utilization rate of solid waste materials, this study explored the enhancement of red sandstone using three types of solid waste materials: slag-micronized powder, fly ash, and waste incineration bottom ash. The mechanical properties of various solid waste materials, including compaction, unconfined compressive strength, and disintegration test results, were evaluated to assess the enhancement of red sandstone. Additionally, scanning electron microscopy was employed to analyze the microstructural alterations induced by these materials. The results indicated that the optimal moisture content of fly ash-improved soil and slag micropowder-improved soil gradually increased, whereas the maximum dry density decreased with an increase in the solid waste material admixture. At an 11% dosage of waste incineration bottom ash, the maximum unconfined compressive strength reached 2,386 kPa. The soil–water characteristic curves for the different solid waste materials exhibited a similar overall trend. Notably, the disintegration rate significantly slowed at a 9% dosage of fly ash, whereas at 11% dosage of waste incineration bottom ash, the disintegration rate nearly reached 0%, demonstrating optimal improvement effects. This suggested that the bottom ash effectively enhanced the water stability performance of red sandstone and increased its resistance to disintegration. Microscopic analysis revealed that slag micropowder and fly ash were comparatively less effective in enhancing red sandstone. The waste incineration bottom ash efficiently generated substantial cementitious material to fill pores. In summary, employing 11% waste incineration bottom ash was recommended to enhance red sandstone in practical roadbed improvement projects.

Before beginning construction on any civil structure, it is imperative to conduct a soil investigation to determine the soil’s parameters and to learn about the subsoil’s behavior. A thorough analysis must be performed, taking into account the foundation’s cost-effectiveness and any potential overdesign. In the early stages of a soil investigation, geophysical testing is used to find out about the subsurface. This is because geophysical tests are fast, easy to do, do not cause damage, and are cost-effective. In this study, subsurface profiling is performed using the inverse slope approach after resistivity tests are performed at numerous sites on varying terrain types. We generate a subsurface profile using inverse slope electrical resistivity testing and compare it with bore log data to identify any discrepancies. The results of the inverse slope method and the bore log data are comparable at different depths; further, the range of agreement of both results is determined by Bland–Altman analysis.

This study explores the impact of wetting and drying cycles on teff straw ash-stabilized expansive soil, with a focus on enhancing its mechanical properties for road subgrade applications. Expansive soil, characterized by continuous swell and shrink behavior, undergoes cyclic testing to establish equilibrium and critical density. The mitigating effects of teff straw ash on soil damage and its influence on expansive soil’s mechanical attributes are investigated. Laboratory results classify natural expansive soil as A-7-5 and CH according to AASHTO and USCS standards, respectively. Using a one-dimensional odometer apparatus, six wetting–drying cycles are conducted on teff straw ash-stabilized expansive soil to observe its behavior at equilibrium. Scanning electron microscopy reveals a disordered bond between soil particles and teff straw ash, intensifying with increased wetting–drying cycles. X-ray diffraction analysis is performed on samples subjected to different curing times, indicating heightened cation exchange and pozzolanic reactions as curing duration increases, thereby reducing soil expansiveness. A 96-hr socked California Bearing Ratio (CBR) test assesses subgrade strength. The CBR values for natural soil fall below the Ethiopian Road Authority (ERA) standards for low-volume roads. In contrast, expansive soil stabilized with teff straw ash at 10%, 15%, and 20% exhibits substantial increases in CBR values (3.7, 6.7, and 8.9, respectively), meeting the ERA standards. This suggests that teff straw ash stabilization renders expansive soil suitable for low-volume road subgrades, aligning with ERA standards. This comprehensive study provides valuable insights into the potential use of teff straw ash as an effective stabilizer for expansive soils, offering sustainable solutions for road construction in regions characterized by expansive soil challenges.

Limit equilibrium (LE) method is the most widely used method for slope stability analysis. Different methods based on the LE technique for the analysis of the stability of the slope have been developed. Some are based on satisfying the force equilibrium condition of the failing mass (Janbu’s method), while some focus on satisfying the moment equilibrium condition (Bishop’s method). Among these methods, the most accurate result is provided by the Morgenstern–Price method as it not only satisfies both moments as well as a force equilibrium condition but also considers the interslice shear forces (V_i) and interslice normal forces (E_i), which are neglected by most of the LE methods to avoid the condition of indeterminacy. To accommodate these forces, Morgenstern–Price (MP) gave a relation between the V_i and E_i which depends upon a scaling multiplier (λ). Thus, it becomes necessary to evaluate λ value along with the factor of safety (FS). There is barely any work discussing the detailed methodology of evaluation of λ along with FS. Method for obtaining λ along with FS have been developed and elaborated in details here. While calculating FS (MP method), evaluation of E_i is a must which is dependent upon the values of normal force at the base of each slice (N_i) and FS, which itself is dependent upon the value of E_i, making it a loop of interdependent variables. To avoid this interdependency of above stated variables, a separate formulation of E_i is given which reduces the calculations (run-time) involved. A VBA code-based platform has also been developed incorporating the generalized LE method, including Bishop’s, Janbu’s, and Morgenstern–Price methods which are represented in the form of flowcharts in this work.

Reservoirs are highly relevant infrastructure assets, and now, more than ever, they play an essential role in society’s welfare and national security. Their importance is related to regional socioeconomic development due to their capacity to store water for different uses, such as human consumption, agricultural irrigation, flood control, and hydroelectric energy production, among other important services. However, many reservoirs are reaching the end of their period of life, and others are showing undesired displacements and cracking. Four 3D surveys were conducted on a reservoir that serves the Metropolitan Area of Monterrey City in Mexico. These surveys were carried out over a period of 5 years using GNSS observation to assist in understanding the actual dam kinematics, i.e., the behavior of its longitudinal and transversal displacements and the possible correlation with the reservoir level. The high-precision leveling and close-range remote sensing data were assessed and then mapped. The high-precision geodetic and leveling techniques allowed us to locate and measure 84 established permanent control points with errors of about ± 0.003 m. The mapping of displacements was made possible by modeling the positive and negative translations. The highest uplifts (11 mm) occurred at the left riverbank, and the highest subsidences (−5 mm) occurred along the downstream piers from the middle of the dam crest to the right riverbank. A ground laser scanner (GLS) produced 3D digital models with geometrical and radiometric characteristics, detecting displacements among the dam crest elements. The synergy of GNSS and high-leveling techniques allows the possibility to measure displacements, while the use of geographical information system (GIS) and geomatic techniques allows a better visualization through 2D and 3D maps validated using traditional topographical methods.