Thin Soil Layer Research Articles

Effects of land cover on variations in stable hydrogen and oxygen isotopes in karst groundwater: A comparative study of three karst catchments in Guizhou Province, Southwest China

Studying the spatial and temporal variations of stable hydrogen and oxygen isotopic values (δD and δ18O, respectively) in precipitation and groundwater in catchments with different land cover is of great significance to understanding the hydrologic cycles within the catchments. This study is focused on three karst catchments, Banzhai, Chenqi and Dengzhanhe, in Guizhou Province, Southwest China, a region with a subtropical humid monsoon climate. We analyzed the spatial and temporal variations in the δD and δ18O of precipitation and groundwater in these areas from September 2007 to September 2009. Local meteoric water lines (LMWLs) for the study areas and their relationships with groundwater were established. The seasonal variations of δD and δ18O for both precipitation and groundwater were similar, being depleted in the heavier isotopomer in the rainy season and enriched in the heavier isotopomer in the dry season. The similarity of patterns between groundwater and precipitation indicates short groundwater residence times in the three catchments, typical of karst terrains. The isotopic values of the Banzhai catchment, which is covered by a thin soil layer beneath virgin forest floor, had the largest variation among the three catchments. The isotopic compositions of the Banzhai catchment groundwater were close to those of precipitation in the rainy season and responded rapidly to it, indicating that precipitation quickly recharges groundwater in this area. In comparison, in the Chenqi and Dengzhanhe catchments, the thicker soil layers and large numbers of paddy fields and dry lands in the catchments resulted in more intense evaporation, and therefore relatively higher isotopic values in the infiltration water. Consequently, the isotopic values of spring water in these two areas were higher and varied to a lesser extent in the rainy season than those of precipitation. The Rayleigh fractionation model based on the correlation between the deuterium excess (d) and evaporation was employed in this study. The model calculation results showed that the catchment evaporation was more intense in Dengzhanhe than in Chenqi, with 14 ± 1% and 6 ± 4% of the water evaporated in Dengzhanhe and Chenqi, respectively. The higher percentage of evaporation in Dengzhanhe was mainly due to the larger percentage of paddy fields in the catchment. In contrast, the effects of evaporation from free water surfaces or soil surfaces on groundwater in the virgin forest-covered Banzhai catchment were extremely weak. Based on the isotopic and high-resolution continuous meteorological and discharge data, the transpiration rates were estimated to be 78% for Banzhai, 10 ± 4% for Chenqi, and 24 ± 1% for Dengzhanhe, and the differences among these values are mainly attributed to differences in vegetation types in those areas. These results show that the variation in stable isotopes in groundwater can be used as a key index in evaluating the effects of different land cover changes and environmental changes on the water cycle in a catchment.

Novel egg life-stage test with Folsomia candida – A case study with Cadmium (Cd)

Toxicity of pollutants is known to have a different impact depending on the organisms' life stage. Standard tests are often based on one life stage, i.e. effects could be underestimated. We aimed here to develop and optimize a test system using eggs of Folsomia candida (4–5 days) instead of the juveniles (10–12 days old) required by the OECD standard test guideline No. 232 (2009). Accordingly, the exposure time and thus the test duration was extended. Tests with “standard” juveniles (10–12 days old) and, adults (21 and 28 days old) were also performed. Cadmium (Cd) was used as test substance. The extension to the test guideline starts as follows: 1) synchronization of eggs in a thin soil layer on plaster of Paris, 2) selection of viable eggs, 3) burying these eggs in groups of 5 in soil. Afterwards, the test procedure will follow the standard procedure as described in the OECD standard test. Cadmium caused ca. 50% effects on reproduction at 60 mg Cd/kg soil dry weight (DW) when exposing juveniles or adults. There was no significant impact of Cd on the eggs, the hatching process or the latter life stages until ca. 250 mg Cd/kg DW (Cd is stable during this exposure period). Hence, Cd seems to affect reproduction before egg laying, i.e., during egg formation or during juvenile-adult stages. In order to clarify whether other chemicals do act in a similar way testing with different chemicals is highly recommended. Testing of different life stages does provide insight on the mechanisms and effects of contaminants and offers important insight.

Impact of Pore-Scale Wettability on Rhizosphere Rewetting

Vast amounts of water flow through a thin layer of soil around the roots, the rhizosphere, where high microbial activity takes place – an important hydrological and biological hotspot. The rhizosphere was shown to turn water repellent upon drying, which has been interpreted as the effect of mucilage secreted by roots. The effects of such rhizosphere water dynamics on plant and microbial activity are unclear. Furthermore, our understanding of the biophysical mechanisms controlling the rhizosphere water repellency remains largely speculative. Our hypothesis is that the key to describe the emergence of water repellency lies within the microscopic distribution of wettability on the pore-scale. At a critical mucilage content, a sufficient fraction of pores is blocked and the rhizosphere turns water repellent. Here we tested whether a percolation approach is capable to predict the flow behavior near the critical mucilage content. The wettability of glass beads and sand mixed with chia seed mucilage was quantified by measuring the infiltration rate of water drops. Drop infiltration was simulated using a simple pore-network model in which mucilage was distributed heterogeneously throughout the pore space with a preference for small pores. The model approach proved capable to capture the percolation nature of the process, the sudden transition from wettable to water repellent and the high variability in infiltration rates near the percolation threshold. Our study highlights the importance of pore-scale distribution of mucilage in the emergent flow behavior across the rhizosphere.

Sap flow of black locust in response to environmental factors in two soils developed from different parent materials in the lithoid mountainous area of North China

Relative extractable water and reference evapotranspiration rate were the main environmental factors affecting sap flow in black locust trees in China, while soil parent material also influenced trees’ water use. Whole-plant water use is affected by meteorological factors, soil water availability, and soil texture. Although water use by plants growing in lithoid mountainous areas with thin soil layers has been studied, the effect of soil parent material on whole-plant water use remained unclear. In the present study, we used thermal dissipation probe sensors to examine the effects of soil water availability and various meteorological factors on black locust sap flow in cinnamon and brown soils, originating from different parent materials. The results showed that vapour pressure deficit (VPD) and reference evapotranspiration rate (ET0) were more closely correlated with sap flow than solar radiation (Rs) and relative humidity (RH), but that Rs and ET0 explained more of the variation in sap flow than did the other two factors. Decreasing ET0 and VPD was produced a more sensitive sap flow response in trees that were growing in the cinnamon soil than in those growing in the brown soil, whereas the sap flow response to relative extractable water (REW) was less sensitive in the cinnamon soil than in the brown soil. REW and ET0 were the main environmental factors affecting sap flow. Furthermore, soil water content in cinnamon soil was not the only water source available to trees, as the exponential curve explained only 56% of the relationship between sap flow and REW. This finding indicated that soil parent material may have an important influence on plant water utilization. Future studies of plant water use should devote more attention to soil parent materials.

Cone penetration testing in thinly inter-layered soils

The effect of a soft layer on the cone resistance of a sand layer has been studied extensively, but the same cannot be said for the case of multi-layered deposits with many (thin) alternating soil layers. For geotechnical analyses based on cone penetration test data it is difficult to estimate a representative value of the cone resistance when encountering alternating thin layers of clay or peat and sand. This paper presents physical modelling tests to understand the ‘value’ of the cone resistance in thinly multi-layered soil deposits. The test results are compared with existing analytical methods. It is concluded that the characteristic resistance of the individual layers, the layer thicknesses relative to the cone diameter and the number of layers within the zone of influence of the cone affect the cone resistance in deposits containing multiple thin soil layers. Suggestions for practical implementation are also given.

Infiltration into frozen soil: From core‐scale dynamics to hillslope‐scale connectivity

AbstractInfiltration into frozen soil is a key hydrological process in cold regions. Although the mechanisms behind point‐scale infiltration into frozen soil are relatively well understood, questions remain about upscaling point‐scale results to estimate hillslope‐scale run‐off generation. Here, we tackle this question by combining laboratory, field, and modelling experiments. Six large (0.30‐m diameter by 0.35‐m deep) soil cores were extracted from an experimental hillslope on the Canadian Prairies. In the laboratory, we measured run‐off and infiltration rates of the cores for two antecedent moisture conditions under snowmelt rates and diurnal freeze–thaw conditions observed on the same hillslope. We combined the infiltration data with spatially variable data from the hillslope, to parameterise a surface run‐off redistribution model. We used the model to determine how spatial patterns of soil water content, snowpack water equivalent (SWE), and snowmelt rates affect the spatial variability of infiltration and hydrological connectivity over frozen soil. Our experiments showed that antecedent moisture conditions of the frozen soil affected infiltration rates by limiting the initial soil storage capacity and infiltration front penetration depth. However, shallow depths of infiltration and refreezing created saturated conditions at the surface for dry and wet antecedent conditions, resulting in similar final infiltration rates (0.3 mm hr−1). On the hillslope‐scale, the spatial variability of snowmelt rates controlled the development of hydrological connectivity during the 2014 spring melt, whereas SWE and antecedent soil moisture were unimportant. Geostatistical analysis showed that this was because SWE variability and antecedent moisture variability occurred at distances shorter than that of topographic variability, whereas melt variability occurred at distances longer than that of topographic variability. The importance of spatial controls will shift for differing locations and winter conditions. Overall, our results suggest that run‐off connectivity is determined by (a) a pre‐fill phase, during which a thin surface soil layer wets up, refreezes, and saturates, before infiltration excess run‐off is generated and (b) a subsequent fill‐and‐spill phase on the surface that drives hillslope‐scale run‐off.

Some Remarks on Practical Aspects of Laboratory Testing of Deep Soil Mixing Composites Achieved in Organic Soils

This paper presents the results of laboratory testing of organic soil-cement samples are presented in the paper. The research program continues previously reported the authors’ experiences with cement-fly ash-soil sample testing. Over 100 of compression and a dozen of tension tests have been carried out altogether. Several samples were waiting for failure test for over one year after they were formed. Several factors, like: the large amount of the tested samples, a long observation time, carrying out the tests in complex cycles of loading and the possibility of registering the loads and deformation in the axial and lateral direction – have made it possible to take into consideration numerous interdependencies, three of which have been presented in this work: the increments of compression strength, the stiffness of soil-cement in relation to strength and the tensile strength. Compressive strength, elastic modulus and tensile resistance of cubic samples were examined. Samples were mixed and stored in the laboratory conditions. Further numerical analysis in the Finite Element Method numerical code Z_Soil, were performed on the basis of laboratory test results. Computations prove that cement-based stabilization of organic soil brings serious risks (in terms of material capacity and stiffness) and Deep Soil Mixing technology should not be recommended for achieving it. The numerical analysis presented in the study below includes only one type of organic and sandy soil and several possible geometric combinations. Despite that, it clearly points to the fact that designing the DSM columns in the organic soil may be linked with a considerable risk and the settlement may reach too high values. During in situ mixing, the organic material surrounded by sand layers surely mixes with one another in certain areas. However, it has not been examined and it is difficult to assume such mixing already at the designing stage. In case of designing the DSM columns which goes through a thin layer of organic soil it is recommended to carry out each time the core drilling which checks the degree of material mixing and their strength.

Isolation and characterisation of a rock solubilising fungus for application in mine-spoil reclamation

The soil and water loss in rock mining areas is an extremely serious problem, while microbes play significant roles in soil remediation of those areas. In this study, a fungal strain Gongronella sp. NF-15 was isolated from the abandoned dolostone mines, and its mechanism of promoting dolostone dissolution was explored by analyzing the changes of pH value, Ca2+ concentration, Mg2+ concentration, organic acid concentration, micromorphology of rock surface, and rock particle diameter under controlled experimental conditions. After incubation of strain NF-15 with dolostone, the pH value continuously decreased significantly within 15 d, while the concentrations of Ca2+ and Mg2+ rose rapidly (1.8–2.7 times higher than that of control group). High performance liquid chromatography (HPLC) analysis showed that organic acids (succinic acid, citric acid, oxalic acid, malic acid, and lactic acid) were secreted by the strain NF-15 in the process of dolostone dissolution, and succinic acid was found more effective than other organic acids in lowering the pH and accelerating dissolution of rocks by Pearson correlation and Structural Equation Model (SEM) path analysis. In addition, the ultrastructure observation of the rock exhibited the significant erosion by fungal hyphae. Thus, strain NF-15 was suggested to combine with environmental remediation technologies to solve the problems of thin soil layer and mineral deficiency in destroyed dolostone mines. These results not only enrich the available microbial resources but also provide a new strategy for rehabilitating abandoned land in rock mining areas.

Measuring erosion rates on exposed limestone residuum using erosion pins: a 10-year record

Erosion rates in residual limestone soils in a humid climate were measured for 10 years at one site, and for 4 years at another site, using erosion pins. Erosion pins were placed in gully floors and on convex divides between adjacent gullies, on abandoned land where vegetation had been removed. We measured an average erosion rate of 20 mm yr−1 over 10 years at one site and only 5 mm yr−1 over 4 years at another site where chert gravel was common on the surface. The 10-year average erosion rate of divides (26 mm yr−1) was significantly greater than the average erosion rate of gullies (14 mm yr−1), suggesting control by different processes, some of which may be seasonal. In winter, it was observed that frost action produced a thin layer of loose soil on the surface of divides. In summer, a hardpan developed on divides, as the soil loosened by winter frosts was transported to gullies, likely by rainsplash or dry ravel. The diffusive processes of frost action, rainsplash, and dry ravel appear to shape the convex divides in this study. Down-cutting of gullies requires channelized flow produced by intense rainfall, which is more common in summer for this location.

Dynamic geotechnical properties evaluation of a candidate nuclear power plant site (NPP): P- and S-waves seismic refraction technique, North Western Coast, Egypt

Determination of the dynamic geotechnical properties and Vs30 of soil and rocks from seismic wave velocities serves as essential inputs for a foundation design cognizant of seismic site response and rock strength. This study evaluates a site which was suggested for a Nuclear Power Plant (NPP) in El-Dabaa area, north western coast of Egypt. On the near subsurface geology is made up of a thick succession of limestone overlain by a thin layer of soft soil. Assessment of geotechnical materials and Vs30 of the near sub-surface lithological layers are required for design of the foundation of critical structures like turbo-generator and reactor buildings. Interpretation of ninety one shallow P-waves and S-waves seismic refraction profiles distributed within the study area in conjunction with data of 76 boreholes were undertaken to delineate the dynamic properties of shallow soil for construction NPP. The velocity of the P- and S-waves were acquired and interpreted using SeisImager Software Package, then the results were used to build a velocity-depth model to estimate the depth to the bedrock and the thicknesses of overburden layers. This model was verified using boreholes data dissected the seismic profiles to improve the final velocity depth model. The depth to bedrock was determined from both shallow seismic refraction profiles and boreholes. Vs30, elastic moduli and dynamic geotechnical parameters were calculated and the site was classified as a National Earthquake Hazard Reduction Program (NEHRP) class “B”. The values of seismic velocities, the engineering consolidations, and the strength parameters showed that the bedrock in the study area is characterized by more competent rock quality.

A technique for the calculation of evaporation from the soil surface based on moisture profiles

The problem of calculating the evaporation from the soil surface is formulated as an optimal control problem. The controlled process of the vertical water transfer in soil is described by a onedimensional nonlinear second-order parabolic partial differential equation. The objective function is the squared Euclidean distance between the calculated values of the soil moisture at various depths and certain prescribed values. To improve the efficiency of finding a numerical solution, the sensitivity of the soil moisture at various depths to the variations of evaporation is estimated by means of fast automatic differentiation. The analysis of these estimates made it possible to determine an effective thin subsurface soil layer in which the moisture is most sensitive to the variations of evaporation; it is in this soil layer where the objective function should be calculated.

Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing

AbstractThis study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses.We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion.We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows.The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd.

Centrifuge tests on strip footings on sand with a weak layer

Tests on small-scale physical models of a strip footing resting on a dense sand bed containing a thin horizontal weak soil layer were carried out at normal gravity (1 g ). The results, reported in a companion paper, point out that the weak layer plays an important role in the failure mechanism and the ultimate bearing capacity of the footing if it falls within the ground volume relevant to the behaviour of the sand–footing system. The same problem was also investigated by means of centrifuge tests on reduced-scale models at 25 g and 40 g . The results of these tests, reported and discussed in this paper, confirm that failure mechanisms are governed substantially by the presence of the weak layer if its depth does not exceed a critical value and highlight marked scale effects involving the ultimate bearing capacity related essentially to the mean equivalent stress level in the soil beneath and around the footing. Equivalent bearing capacity factors, [Formula: see text], for footings on a dense sand bed containing a thin weak layer are derived from experimental results and are proposed in the paper.

Characteristics of soil water movement in a grass slope in a karst peak-cluster region, China

Soil water is very important in hilly areas with thin soil layers and deep groundwater tables, such as the karst peak-cluster region of Southwest China. An investigation into soil water movement can provide insights into management of shallow water resources and soil nutrients, as well as prevention of groundwater pollution. In this study, O-18 and H-2 tracers were used to trace soil water movement in planar soil mass type microhabitats in the middle part of a steep hillslope covered by grasses in a karst peak-cluster region of China. From May 2008 to July 2009, samples of precipitation and two types of soil water, which had different integrated degrees of mobility and were of different depth intervals or depths, were collected. The hydrogeochemical characteristics were compared between precipitation and soil water, and these data were applied in convolution-based lumped parameter models. Our results indicated that vertical piston flow, rather than lateral flow along the soil-bedrock interface, played an important role in soil water percolation at least in the upper soil layer approximately 7cm over the permeable bedrock. The mixing effect and preferential flow might also play a role in soil water percolation. In general, the evaporation effect on soil water was weak except for the uppermost 10cm soil matrix water during winter. The lower limits of mean transit time of soil matrix flow passing through 5, 15, 25, 35, and 41.5cm depths were 4.81, 7.70, 16.19, 21.85, and 27.44days, respectively. Our study demonstrated the crucial functions of the soil reservoir in regulating the water cycle and could provide guidance on conservation of soil water and hydrological studies. The applied method was proved to be a suitable approach for investigating soil water movement on a monthly scale.

Influence of pre-event water on streamflow in a granitic watershed using hydrograph separation

For water resources management, many studies for investigating flow paths from rainfall to subsurface have been conducted for last half century. A hydrograph separation based on end member mixing was carried out to evaluate the importance of the hydrological pathways providing the main sources of a small granitic watershed, Dorim-cheon, Seoul. An analysis of chloride, oxygen-18 and deuterium isotopes from precipitation and stream water during three storms was conducted with high-resolution data using 129 samples. Stream water, collected in advance of rain event, was assumed as a pre-event water (baseflow) component according to its dry condition and isotopic values compared with the values of different time periods. The contribution from vadose water was ignored due to the thin soil layer covering the study area. Using a two-component mixing model, hydrograph separation of the stream water in Dorim-cheon was conducted based on weighted mean values of rain water and pre-event water component with the high-resolution datasets. As a result of the analysis with water isotopes, contribution of groundwater was dominant during the entire study period (73–74%) except of instant dominance of rainfall at the earliest period. Using chloride as a tracer for hydrograph separation, a significant difference for the amount of pre-event water contribution was identified. This might be caused by the large variation of chloride concentration during the rain event and the end member determination.

Le fasi neolitica ed eneolitica di Moscano di Fabriano (AN)

Recent excavations at Moscano in Fabriano have uncovered a double inhumation grave in a reused cavity, for which two 14C dates have been identified. The grave was found on the outskirts of a Copper Age settlement, featuring rough surface pottery similar to that discovered on layer 4 at Attiggio in Fabriano. The two burials at Moscano lay one above the other, with a thin layer of soil separating them. The lower inhumation is an incomplete female adult skeleton (Individual 1) and was probably laid in a huddled position. A flint arrowhead was probably part of the grave goods. The upper burial is of a young individual aged around 8 years (Individual 1A) laid out in a supine position. It is not clear whether a pottery fragment decorated with scales and found at the site is related to this individual. This burial is currently unique for several reasons, including its location in inland Marche, the laid out position of the upper body and the presence of pottery decorated with scales. Although problematic in several respects, the 14C dates of the two individuals are suggestive of end of 4th / early 3rd millennium BC. This would make these discoveries contemporary to the most recent burials at Fontenoce and the central phase of the settlement at Conelle in Arcevia.

Parnassia palustris population differences in three Korean habitat types

Parnassia palustris is an herbaceous perennial with a circumpolar distribution. In Korea it is found in three habitat types: low-altitude high-latitude habitat (LH), mountain stream habitat (MS), and high-altitude low-latitude habitat (HL). This classification is based on soil physicochemical properties and species composition. To find the best habitat type for the maintenance of P. palustris populations, we surveyed vegetation and environmental properties in the three habitat types. All three habitat types had moist soil with low N content. LH had a temperate climate and shallow calcareous soil with a high pH. MS had a thin soil layer with high Ca2+ content, a high pH and heavy disturbance. HL had a low temperature and deep soil layer with a low pH. Co-occurring species in HL were strong competitors compared to co-occurring species in LH and MS. Population increase in MS was higher than in LH and HL. Reproductive traits were also higher in MS than in LH and HL. Of the three habitat types, MS is regarded as the best for P. palustris. We suggest maintaining P. palustris habitats with a sufficient water supply and weak competition to sustain the population successfully. This may further restore the MS habitat to expand the distribution of this species. Our study also provides information relevant to the conservation and restoration of the MS habitat for vulnerable calcicole or early successional species, like P. palustris.

Thermal and water regime studied in a thin soil layer of green roof systems at early stage of pedogenesis

The potential heat load and stormwater reduction of the anthropogenic, lightweight soil systems, such as green roofs, are valuable to heat island effect mitigation and to urban water management. Benefits of extensive green roofs, as widely used vegetated roof system with very thin soil layer, could be threatened by temporal changes of the soil structure. Green roof raised beds filled with two different anthropogenic soils (artificially constructed stripped topsoil with admixed crushed bricks and a commercial mixture of a technogenic substrate) were built to investigate the benefits of such systems in a temperate climate. These two soils were chosen with the intent to compare their thermal and water regime. One soil is expected to be favorable for hydrological functioning, whereas the other one for the thermal performance. Temperature and water balance measurements complemented with meteorological observations and knowledge of physical properties of the soil substrates provide the basis for detailed analysis of a thermal and hydrological regime in green roof raised beds. Moreover, the state of pedogenesis was studied on undisturbed soil samples by means of X-ray computed tomography. The water balance of green roof raised beds was calculated for a whole vegetation season and individual rainfall events. Runoff from raised beds was 38 and 63 % of received rainfall. On the basis of a detailed analysis of individual rainfall events, rainfall-runoff dependency was found for both raised beds. The difference between measured actual evapotranspiration and calculated potential evapotranspiration was discussed on the period with contrasting conditions in terms of moisture stress. Thermal characteristics of soil substrates result in a highly contrasting diurnal variation of soil temperatures. Analysis of X-ray computed tomography-derived macroporosity profiles reveals significant temporal changes in the soil comprised of the stripped topsoil with admixed crushed bricks. Both green roof systems were able to reduce heat load of roof construction when comparing with the concrete roof construction. Similarly, received rainfall was significantly reduced. The extent of rainfall reduction mainly depends on soil, vegetation status, and experienced weather patterns. Methods used for non-invasive imaging proved to be beneficial for studying of soil structure changes.

Novel Approach to Measuring Tensile Strength of Compacted Clayey Soil during Desiccation

Desiccation of soil is the gradual process of moisture loss from a fully or partially saturated condition to a dry state. If the soil is constrained against shrinkage during desiccation, it will begin to crack when tensile stresses in the soil exceed the tensile strength. Fundamental to understanding desiccation crack development in clayey soils is the accurate determination of the tensile strength during desiccation. Although numerous published studies have focused on soil desiccation and soil tensile strength, very little has been focused on experimental determination of tensile strength during desiccation. This paper presents the first generation of a novel apparatus designed to determine tensile strength during desiccation. During drying the tensile forces in a thin compacted soil layer are measured while simultaneously monitoring moisture content changes and crack formation via time-lapse photography. Results are presented from desiccation tests performed on two clayey compacted soils of medium to high plasticity. Soil water characteristic curves (SWCCs) were determined to relate the tensile strength to suction. The results demonstrate that the tensile strength of compacted soil is influenced by initial water content, suction, dry unit weight, soil pore structure, and soil type. Measured tensile strengths compare favorably with results of a theoretical model that considers microstructural and macrostructural aspects of unsaturated compacted clayey soil.

Corrosion Behavior of X80 Pipeline Steel under Thin Electrolyte Layer of Acidic Soil Simulated Solution

Corrosion Behavior of X80 Pipeline Steel under Thin Electrolyte Layer of Acidic Soil Simulated Solution