Geohazards such as slope failures and retaining wall collapses have been observed during thawing season, typically in early spring. These geohazards are often attributed to changes in the engineering properties of soil through changes in soil phase with moisture condition. This study investigates the impact of freezing and thawing on soil stiffness by addressing shear wave velocity (Vs) and compressional wave velocity (Vp). An experimental testing program with a temperature control system for freezing and thawing was prepared, and a series of bender and piezo disk element tests were conducted. The changes in Vs and Vp were evaluated across different phases: unfrozen to frozen; frozen to thawed; and unfrozen to thawed. Results indicated different patterns of changes in Vs and Vp during these transitions. Vs showed an 8% to 19% decrease for fully saturated soil after thawing, suggesting higher vulnerability to shear failure-related geohazards in thawing condition. Vp showed no notable change after thawing compared to initial unfrozen condition. Based on the test results in this study, correlation models for Vs and Vp with changes in soil phase of unfrozen, frozen, and thawed conditions were established. From computed tomography (CT) image analysis, it was shown that the decrease in Vs was attributed to changes in bulk volume and microscopic soil structure.

The objective of the present study is to evaluate the performance of a levee when subjected to flooding and subsequent seepage through centrifuge model tests. For this, six centrifuge model tests were conducted on a 240 mm high levee model at 30g in a 4.5 m radius large beam geotechnical centrifuge available at the Indian Institute of Technology Bombay, India. A custom-developed flooding simulator is employed to induce identical flood rates on the upstream side of the levee models. Further, using (a) geocomposite (GC) and (b) sand-sandwiched geocomposite (SSGC) as internal chimney drain, the suitability of GC material for dissipation of pore-water pressure (PWP) is also studied. The results of the centrifuge tests are presented and discussed in terms of the development of upstream flood function, subsequent PWP development within the levee body, and the surface settlements observed at the levee's crest. Further, the influence of an internal chimney drain, the material used for its construction, and its type and composition on the seepage response of the levee is discussed in detail. The performance GC chimney drain placed within the levee subjected to flooding-induced seepage is compared with a conventional sand chimney drain. It is observed that a GC-based chimney drain with sand cushioning on both sides in the horizontal portion of the chimney drain performs well. Further, digital image analysis of SEM micrographs of exhumed GC after centrifuge tests and the analyzed PWP data during sustained flooding-induced seepage is found to corroborate well.

Centrifuge-based physical modeling is widely adopted for understanding the performance of geostructures, like reinforced slopes, clay liners of municipal solid waste landfills, geogrid-reinforced soil walls, earthen dams, soil nailed slopes, etc. This study aims to highlight the benefits of centrifuge-based physical modeling in order to comprehend the performance of different geostructures both prior to and during failure. Firstly, a discussion is made on scaling considerations along with modeling aspects of various types of phenomena like rainfall, flooding, etc. Further, details of four types of balanced/beam centrifuge equipment used for understanding the behavior of various types of geostructures at high gravity conditions, along with errors due to radial acceleration field, are also presented. In the process, innovative development of cost-effective actuators for simulating: (1) continuous differential settlements of landfill lining systems, (2) seepage of water through a slope, (3) seepage-induced flooding, (4) dynamic compaction, (5) rainfall-induced seepage, and (6) pseudo-static seismic loading along with flooding-induced seepage has been done. Different types of instrumentation units like potentiometers (P), linearly variable differential transformers, pore-water pressure transducers, load cells, accelerometers, strain gauges, etc., along with wireless data acquisition systems were used for monitoring the performance of the models during centrifuge tests. Additionally, the use of particle image velocimetry, digital image analysis, and the digital-cross correlation technique to evaluate the performance of several models evaluated at high gravity is covered. Lastly, it has been sufficiently shown that using digital image analysis/digital image correlation approaches in conjunction with centrifuge-based physical modeling analysis is a useful study tool. Insights gained in understanding the behavior of geostructures in a geotechnical centrifuge, especially subjected to climatic events like rainfall, flooding, and earthquakes, are highly significant and help in designing and constructing geostructures with confidence to engineers.

An emerging alternative to improve the mechanical properties of fine soils susceptible to cracking is the addition of fibers obtained from reused synthetic materials such as polyethylene terephthalate (PET). The technical literature on the fracture mechanics of PET fiber-reinforced soils is rather scarce, so there has been insufficient progress in determining fracture parameters and standardized procedures to find optimal reinforcement conditions. This research uses experimental techniques to induce tensile stresses in clayey silty soil samples from the Valley of Mexico reinforced with different fiber contents. By applying approaches based on linear elastic and elastoplastic theory, parameters useful for the study of fracture mechanics and flexural strength of PET- reinforced soil were estimated: tensile strength, critical energy release rate, critical stress intensity factor, and contour integral for crack propagation under plasticity. In addition, imaging techniques are used to measure the deformations generated in bending tests of reinforced soil beams and to study crack propagation from initiation to maximum stresses. The addition of PET fibers significantly improved soil response by reducing cracking, increasing tensile strength, and providing ductile behavior as cracking progressed. These effects indicate the great potential of recycled PET fibers as a subgrade improvement method for soft, cracking soil deposits, or even for earthworks and slope stabilization in clayey soils on road projects.

An experimental study is made to understand the deformation characteristics and failure mechanism of sands subjected to severe plastic deformation in the ploughing model setup of in-plane orthogonal cutting. The cutting experiments were performed on sands over 3 orders of strain rates. High-speed imaging and concomitant image analysis were performed using the Particle Image Velocimetry algorithm to obtain the whole field velocity measurements of the material flow. The velocity field maps of the near tool tip region demonstrate a sharp change in the motion of sand particles along with the formation of a dead zone. The effective strain rate maps show regions of intense localized plastic deformation- termed shear bands. The inclination angle of these bands evolved periodically with time and showed a decreasing trend due to an increase in the surcharge and effective depth of cut. The morphology and overall characteristics of these mesoscale structures (shear bands) do not change significantly with strain rate. The cutting force signatures were oscillatory and suggested cyclic material softening (dilation)-hardening (compaction) ahead of the tool, which is also reflected in the periodic repositioning of shear bands. The limit equilibrium-based model was adequate to predict the tool-cutting forces well, even with the significant variation in strain rates.

Desiccation cracking has a significant impact on the hydro-mechanical properties of soils, yet quantifying crack patterns remains challenging. This study presents a quantitative framework with a total of 26 parameters for characterizing the geometric and morphological characteristics of soil desiccation crack patterns, including soil clod parameters (soil clod area, soil clod perimeter, number of clods, and the probability density distribution of clod parameters, etc.) and crack network parameters (crack length, crack width, crack inter angle, number of crack segments, surface crack ratio, crack density, connectivity index, etc.). To implement this quantitative framework, the Crack Image Analysis System (CIAS) was developed to automatically identify and analyse complex crack patterns through image preprocessing, clod identification, crack network identification and batch processing. CIAS was then applied to quantify the crack images of soil with different thicknesses, validating its efficacy. To comprehensively describe the geometric and morphological characteristics of crack networks, it is recommended to use the number of soil clods per unit area, surface crack ratio, crack density, and connectivity index as key parameters. These metrics effectively capture information on crack spacing, area, length, width, and connectivity. This comprehensive framework for characterizing and quantifying crack images is of great significant for geological engineering. Moreover, it holds great potential for application in other different disciplines such as geotechnical, hydraulic, mineral engineering and material even planetary science.

Integrated crop-livestock production (ILP) is an interesting alternative for more sustainable soil use. However, more studies are needed to analyze the soil pore properties under ILP at the micrometer scale. Thus, this study proposes a detailed analysis of the soil pore architecture at the micrometer scale in three dimensions. For this purpose, samples of an Oxisol under ILP subjected to minimum tillage (MT) and no tillage (NT) with ryegrass as the cover crop (C) and silage (S) were studied. The micromorphological properties of the soil were analyzed via X-ray microtomography. The MT(C) system showed the highest values of porosity (c. 20.4%), connectivity (c. 32.8 x 103), volume (c. 26%), and the number of pores (c. 32%) in a rod-like shape. However, the MT(S), NT(C), and NT(S) systems showed greater tortuosity (c. 2.2, c. 2.0, and c. 2.1) and lower pore connectivity (c. 8.3 x 103, c. 6.9 x 103, and c. 6.2 x 103), especially in S use. Ellipsoidal and rod-shaped pores predominated over spheroidal and disc-shaped pores in all treatments. The results of this study show that the use of ryegrass as a cover crop improves the soil physical properties, especially in MT. For S use, the type of soil management (MT or NT) did not show any differences.

Expansive soil is a special soil type that undergoes volume expansion during hygroscopicity and volume contraction during dehumidification. In this study, the effects of rainfall-evaporation cycles on the microscopic pores and cracks of expansive soils under different rainfall intensities were analyzed by simulating light rainfall, medium rainfall, and high-temperature drought environments using nuclear magnetic resonance (NMR) technology and image processing methods. The results showed that the micropores and small medium pores of the expanded soil gradually evolved into macropores during the cycling process, especially under stronger rainfall conditions. In addition, as the number of cycles increased, the expanded soil showed irrecoverable pore changes, which ultimately led to the scattering damage of the soil. By processing the surface crack images of expansive soils, the process of crack development was categorized into four stages, and it was found that the evaporation cycle of medium rainfall intensity caused the main cracks of expansive soils to develop more rapidly. A quantitative relationship model between the average crack width and the number of cycles as well as porosity was constructed, and the regression coefficient of determination R2 reached 0.98, 0.96, and 0.84, respectively. This study simulates the effects of real rainfall conditions on expansive soils and investigates the mechanism and evolution of cracks in expansive soils, which is of great theoretical and practical significance.

During previous medium intensity earthquakes, several cantilevered retaining structures shoring waterfront areas experienced large deformations or even collapsed. This was in contrary to the caisson type quay walls which performed better even during the very strong 1995 Kobe earthquake. Within this realm, recent studies have highlighted that saturated backfill adjacent to retaining structures may not fully liquefy and has a strong potential for shear-induced dilation mechanics owing to the presence of substantial static shear. However, despite these negative excess pore pressures and absence of a full liquefaction state in the backfill, cantilevered retaining walls may still experience large deformations. In this paper, a deformation mechanism is proposed for an embedded cantilever retaining wall supporting a submerged backfill made of Ottawa F-65 sand using a geotechnical centrifuge experiment. The dynamic response of the soil-structure system was measured, and the intra-cyclic mechanics were investigated. The entire earthquake duration of 20 s was divided into three different phases. In phase I (comprising of initial 6 s), the retaining wall experienced sliding deformations owing to its inertia with negligible soil straining at the backfill. Under the application of subsequent seismic pulses in phase II, large suction drops in excess pore pressures were observed during the translation of the retaining wall toward the backfill, which caused the negative excess pore pressure to exceed the hydrostatic value. However, the temporary release of the suction drops during the deformation of the wall toward the seaside resulted in significant softening as soil crosses the phase-transformation line. This ultimately resulted in significant plasticization of the backfill, and the wall initiated a rotation type deformation mechanism with a pivot point located near its base. Intra-cyclic observations revealed an increase in the magnitude of the phase transition in excess pore pressures, which contributed to the increased accumulated soil straining along the backfill. Owing to this, the wall experienced increasing rotations with the application of subsequent cycles in phase II (until 14 s) until the passive resistance in front of the wall was fully mobilized. However, a sudden catastrophic collapse of the wall could be avoided owing to the re-dilation mechanism, during which the soil again underwent a phase transformation and generated negative excess pore pressures on the completion of the wall translation toward the seaside. With the reduction in the amplitude of the applied cycles toward the end of shaking (phase III), the effective stress path in front of the wall moved away from the origin, and the mobilized passive stress reduced, which eventually resulted in the retaining wall achieving a stable state with no additional deformations. The proposed deformation mechanism highlights that a state of full liquefaction is not a necessary prerequisite for an embedded cantilever retaining wall to experience significant deformations, and an understanding of suction mechanics during excess pore pressure generation is critical.

Cultural and environmental factors can place creeping bentgrass (Agrostis stolonifera) under extreme stress during the summer months. This stress, coupled with the growth adaptation of creeping bentgrass, can result in shallow, poorly rooted stands of turf. To enhance root zone oxygen and rooting of creeping bentgrass, golf courses use methods such as core and solid-tine aerification, and sand topdressing. An additional method of delivering oxygen to the soil could be irrigation with nanobubble-oxygenated water. The properties of nanobubbles (NBs) allow for high gas dissolution rates in water. Irrigating with NB-oxygenated water sources may promote increased rooting of creeping bentgrass putting greens during high-temperature periods and lead to a more resilient playing surface. The objectives of this study include comparing the effects of irrigation with NB-oxygenated water sources with untreated water sources on creeping bentgrass putting green root zone and plant health characteristics using field and controlled environment experiments. Treatments included NB-oxygenated potable water and irrigation pond water, and untreated potable and irrigation pond water. In the field, NB-oxygenated water did not enhance plant health characteristics of creeping bentgrass. In 1 year, NB oxygenated water increased the daily mean partial pressure of soil oxygen from 17.48 kPa to 18.21 kPa but soil oxygen was unaffected in the other 2 years of the trial. Subsurface irrigation with NB-oxygenated water did not affect measured plant health characteristics in the greenhouse. NB-oxygenation of irrigation water remains an excellent means of efficiently oxygenating large volumes of water. However, plant health benefits from NB-oxygenated irrigation water were not observed in this research.