Search Results (4)

Frequent agricultural irrigation events continuously raise the groundwater table on loess platforms, triggering numerous loess landslides and significantly contributing to soil erosion in the Chinese Loess Plateau. The movement of irrigation water within the surficial loess layer is crucial for comprehending the mechanisms of moisture penetration into thick layers. To investigate the infiltration and evaporation processes of irrigation water, a large undisturbed soil column with a 60 cm inner diameter and 100 cm height was extracted from the surficial loess layer. An irrigation simulation event was executed on the undisturbed soil column and the ponding infiltration and subsequent evaporation processes were systematically monitored. A ruler placed above the soil column recorded the ponding height during irrigation. Moisture probes and tensiometers were installed at five depths to monitor the temporal variations in volumetric water content (VWC) and matric suction. Additionally, an evaporation gauge and an automatic weighing balance measured the potential and actual evaporation. The results revealed that the initially high infiltration rate rapidly decreased to a stable value slightly below the saturated hydraulic conductivity (K_s). A fitted Mezencev model successfully replicated the ponding infiltration process with a high correlation coefficient of 0.995. The monitored VWC of the surficial 15 cm-thick loess approached a saturated state upon the advancing of the wetting front, while the matric suction sharply decreased from an initial high value of 65 kPa to nearly 0 kPa. The monitored evaporation process of the soil column was divided into an initial constant rate stage and a subsequent decreasing rate stage. During the constant rate stage, the actual evaporation closely matched or slightly exceeded the potential evaporation rate. In the decreasing rate stage, the actual evaporation rate fell below the potential evaporation rate. The critical VWC ranged from 26% to 28%, with the corresponding matric suction recovering to approximately 25 kPa as the evaporation process transitioned between stages. The complete evaporation process was effectively modeled using a fitted Rose model with a high correlation coefficient (R² = 0.971). These findings provide valuable insights into predicting water infiltration and evaporation capacities in loess layers, thereby enhancing the understanding of water movement within thick loess deposits and the processes driving soil erosion. Full article

Long-term irrigation promotes the infiltration of water in the thick, stratified loess layer, significantly raising the groundwater table and triggering a series of landslides in loess platform areas. The soil–water characteristic curve (SWCC) of loess buried at different depths affects the unsaturated infiltration process and is intricately connected to the soil’s microstructure. The SWCCs, scanning electron microscope (SEMs), and pore size distributions (PSDs) for five sets of undisturbed loess samples at depths ranging from 3.4 to 51.9 m are shown in this paper. The results indicate that the fitting parameter air entry value (AEV) of the SWCC rises from 13.67 kPa to 40.19 kPa as the depth increases from 3.4 to 51.9 m. And the saturated volumetric water content drops by 10.9%, with a notable SWCC shape difference between the transition and residual zones observed. Additionally, the total porosity of undisturbed loess falls by 12% when the depth increases from 3.4 to 51.9 m, while the macropores and mesopores reduce by 3.6% and 12.1%, respectively. These findings highlight the control of the pore structure on the SWCC and emphasize the correspondence between the SWCC and PSD. The conclusions also illustrate that the compaction effect changes the microstructure characteristics of loess, thereby affecting the soil’s water retention behavior. Full article

Loess has the characteristics of complex structure and reduced mechanical strength after encountering water. In Chinese loess areas, irrigation, water storage, and rainfall affect the stability of the original loess structure and cause damage to the foundation. This paper analyzes the results of in situ water immersion test (in order to study the permeability of water storage in undisturbed loess), rainfall test (in order to study the permeability of rainwater in the backfill loess), and water storage test (in order to study the permeability characteristics of water storage in backfill loess) on the filling site and studies the permeability law of water in unsaturated layered loess and backfill remolded loess. The results of the in situ immersion test show that the vertical seepage velocity of water was very fast, and the infiltration depth was close to 25 m after 9 days of water storage, and at the interface of the new loess, the paleosol, and the old loess, the water infiltration line appeared to be refracted. Finally, the vertical and horizontal penetrations of water in the loess are analyzed, and the range of water immersion and saturation are determined. Through the rain test and water storage test of a loess-filled surface, the relationship between the moisture content and depth of the backfill loess before and after rainfall and storage is obtained. The results of rain period test show that the water infiltrated into the loess about 3 m after 25 days of rainfall. A further 90 days storage test shows that the final infiltration depth of water was about 7 m. Full article

Extensive agricultural irrigation in the loess region of Northwest China has seriously damaged the local hydrogeological environment. To properly understand the hydrological processes and the hydraulic properties of the layered soil, the field soil column irrigation test, laboratory soil column infiltration test, and undisturbed soil sample hydraulic experiments were carried out. The results showed that the proposed infiltration model can continuously simulate the infiltration process of the loess–palaeosol sequence well. The layered structure may form a temporary groundwater table at the interface of the two different soils under irrigation conditions. This provides a scientific basis for proposing reasonable irrigation measures. Full article