Soil Compaction Conditions Research Articles

Development, fabrication, and validation of custom-built accelerometers to monitor wave propagation during vibratory soil compaction

Abstract Historically, accelerometers have been heavily utilized in the geotechnical community for applications such as earthquake ground motion monitoring, centrifuge testing, pile driving analysis, and continuous compaction control of soils. Industrial-grade accelerometers that are commonly used for these types of studies can be expensive for monitoring programs requiring a dense configuration of accelerometers. In the current study, a dense array of relatively inexpensive custom-built accelerometers, previously developed by the authors, were deployed along an earthen embankment and subjected to real-world vibratory soil compaction conditions. Several industrial-grade accelerometers were also installed along the embankment for comparison purposes. This study describes the fabrication, calibration, and installation process of these custom-built accelerometers and compares their performance against the industrial-grade accelerometers. Accelerations recorded by both sensors during compaction were generally consistent with one another ultimately indicating that these custom-built accelerometers could offer a cost-effective option for dense sensor arrays for future geotechnical monitoring programs.

ZmSPL12 Enhances Root Penetration and Elongation in Maize Under Compacted Soil Conditions by Responding to Ethylene Signaling.

Soil compaction poses a significant challenge in modern agriculture, as it constrains root development and hinders crop growth. The increasing evidence indicated that various phytohormones collaborate in distinct root zones to regulate root growth in compacted soils. However, the study of root development in maize under such conditions has been relatively limited. Here, we identified that the ZmSPL12 gene, belonging to the SPL transcription factor family, plays a crucial and positive role in regulating root development in the compacted soil. Specifically, the overexpression of ZmSPL12 resulted in significantly less inhibition of root growth than the wild-type plants when subjected to soil compaction. Histological analysis revealed that the capacity for root growth in compacted soil is closely associated with the development of the root cap. Further exploration demonstrated that ZmSPL12 modulates root growth through regulating ethylene signaling. Our findings underscored that ZmSPL12 expression level is induced by soil compaction and then enhances root penetration by regulating root cap and development, thereby enabling roots to thrive better in the compacted soil environment.

Evaluating Riparian Plant Communities After Restoration of Plains Bison in the Northern Great Plains of Montana

Restoration of plains bison (Bison bison bison) in the northern Great Plains has been controversial for a variety of reasons, including the public concern that bison will supplant cattle on public rangelands. Riparian zones are among the most biologically rich areas within rangelands, but they are highly sensitive to disturbances such as grazing, leading to the public perception that riparian vegetation communities will be negatively impacted by year-round bison grazing compared with the norm of seasonal cattle grazing. Our objective was to evaluate the vegetation community and soil compaction conditions of areas in the northern Great Plains of Montana, where bison have been restored 5−10 yr as year-round grazers, compared with adjacent sites where cattle have been retained as seasonal grazers. Out of the 24 variables we assessed, only 2 significantly differed between the grazer treatments within our study's time frame and stocking rates. Native species diversity was significantly higher in the bison-grazed treatment (F[1,1,5.98] = 8.16, P = 0.03), and woody height heterogeneity was twice as high in the bison-grazed treatment than the cattle-grazed treatment (F[1,5.97]= 5.81, P = 0.05). Although longer-term studies are required, our findings indicate that year-round bison grazing under the current stocking rates did not degrade riparian vegetation communities compared with seasonal cattle grazing and rather benefitted some aspects of the plant community.

Mechanical and biotic reclamation strategies for a post‐mine temperate grassland

AbstractGlobal energy production is in high demand and is expanding its development into new landscapes, including grasslands. This expansion has intensive impacts on aboveground and belowground components of grasslands which need to be addressed during reclamation to promote long‐term ecological integrity. This study was conducted to ascertain how alternative reclamation practices may improve soil structure (i.e., compaction) while aiding in the creation of conditions that are conducive to both the establishment and continued growth of native grassland plant species. The grassland was reclaimed with different combinations of seeding mixtures (grass or grass and forb), ripping techniques (subsoil ripping or topsoil ripping), and the integration of mulch into the soil profile. Year, seed mixtures, and ripping techniques and their interactions significantly affected community composition and species diversity. Topsoil‐ripping and grass‐forb treatment had a higher association with native, perennial grasses while subsoil‐ripping and grass treatment favor more short‐lived species. Similar trends persisted across penetration resistance and soil moisture readings where topsoil‐ripping and grass‐forb treatment were different from subsoil‐ripping and grass treatments (p ≤ 0.10). Additionally, Kentucky bluegrass, an invasive grass species, increased by 76% over 1 year and was more common in the topsoil‐ripping and grass‐forb treatments. While early in the reclamation process, results suggest topsoil‐ripping and grass‐forb treatment are promising combination reclamation practices that can establish a native grassland community and initiate the improvement of compacted soil conditions.

Parsimonious root systems and better root distribution can improve biomass production and yield of soybean.

Enhancing the acquisition of belowground resources has been identified as an opportunity for improving soybean productivity worldwide. Root system architecture is gaining interest as a selection criterion in breeding programs for enhancing soil resource acquisition and developing climate-resilient varieties. Here we are presenting two novel characteristics of soybean root system architecture that improve aboveground growth and yield. Eleven selected soybean genotypes were tested under rain-fed conditions in 2019 and 2020 at two locations in South Carolina, in which one of the locations was characterized by compacted soils. The elite SC breeding line SC07-1518RR, exotic pedigree line N09-12854, and slow wilting line N09-13890 were superior genotypes in terms of biomass production, seed yield, and/or water use efficiency. Genotypes N09-12854 and N09-13890 demonstrated reduced root development (based on total root count and length), likely to restrict belowground growth and allocate more resources for shoot growth. This characteristic, which can be referred as a parsimonious root phenotype, might be advantageous for soybean improvement in high-input production systems (characterized by adequate fertilizer application and soil fertility) that exist in many parts of the world. Genotype SC07-1518RR exhibited a similar strategy: while it maintained its root system at an intermediate size through reduced levels of total root count and length, it selectively distributed more roots at deeper depths (53–70 cm). The increased root distribution of SC07-1518RR at deeper depths in compacted soil indicates its root penetrability and suitability for clayey soils with high penetration resistance. The beneficial root phenotypes identified in this study (parsimonious root development and selective root distribution in deeper depths) and the genotypes that possessed those phenotypes (SC07-1518RR, N09-12854, and N09-13890) will be useful for breeding programs in developing varieties for optimal, drought, and compacted-soil conditions.

Bio‐tillage improves soil physical properties and maize growth in a compacted Vertisol by cover crops

AbstractBio‐tillage has recently been proposed as a measure to alleviate soil compaction through biopores created by cover crop roots. The objective of this study was to determine the effect of different cover crops on soil physical properties and the succeeding maize (Zea mays L.) growth in compacted soil. Four treatments, including no cover crop as a control (Con), alfalfa (Medicago sativa L.), oilseed rape (Brassica napus L.), and radish and hairy vetch mixture (Raphanus sativus L. and Vicia villosa Roth), were carried out under both compacted and noncompacted soil conditions. Soil physical properties, such as the volumetric soil water content (SWC), bulk density, saturated hydraulic conductivity (Ks) and air permeability at water potential of −60 hPa (Ka60), and maize root characteristics and yield were measured. The cover crops did not affect the soil bulk density but significantly decreased the SWC in both the compacted and noncompacted soils relative to the Con treatment. The alfalfa treatment presented significantly higher Ks in the noncompacted soil and Ka60 in both the compacted and noncompacted soils than the Con treatment in the soil layer depth of 20–50 cm. The three cover crop treatments improved the maize root biomass density (173.2% for 2018 and 35.6% for 2019) and root length density (50.9% for 2018 and 51.8% for 2019) relative to the Con treatment in the soil layer depth of 10–70 cm in 2018 and soil layer depth of 10–50 cm in 2019 in the compacted soil rather than in the noncompacted soil. Compared with the Con treatment, the radish mixed with hairy vetch treatment in 2018 and the oilseed rape treatment in 2019 significantly enhanced the maize yield in the compacted soil. Our results suggest that alfalfa is the best crop for improving air permeability; however, the oilseed rape and mixture of radish and hairy vetch lead to better maize growth in the compacted soil. Bio‐tillage using cover crops is effective in alleviating soil compaction.

Impacts of soil compaction and historical soybean variety growth on soil macropore structure

Soil compaction is the main form of soil degradation in agricultural systems. It leads to decreased infiltration and limited root growth. Plants can alleviate soil compaction through various mechanisms connected to root growth. However, it remains unclear whether plant breeding can improve the root traits of modern cultivars and their ability to alleviate compacted soil. The aim of this study was to determine the responses of soybean (Glycine max L. Merr.) roots to soil compaction and to observe the difference in soil alleviation by using soybean varieties bred before and after the development of mechanical agriculture in the Mollisol region of Northeast China. Five soybean varieties, bred from 1941 to 2003, were planted and subjected to either soil compaction or no compaction. Root traits and soil macropores were characterised by screening the root system (Shovelomics method) and by adopting dye-tracing methods. The properties of roots in soybean varieties showed noteworthy differences, although no clear breeding trends were detected. Compared with no compaction, the root lengths of all varieties decreased significantly when grown in compacted soil. Moreover, soil compaction decreased the vertical macroporosity and increased the heterogeneity of horizontal macropores. The modern soybean variety alleviated soil compaction by enabling the creation of more macropores, which were located deeper in the soil, compared to the older varieties. Overall, root growth was responsible for approximately one-third of macropore changes observed under compacted soil conditions, and the alleviation effects were greater in roots growing vertically than those observed in roots growing laterally. The observed variability of soil compaction alleviation among different soybean varieties could be considered in agriculture by breeders to select the varieties which decrease soil compaction.

Stochastic forestry harvest planning under soil compaction conditions

We present a study of annual forestry harvesting planning considering the risk of compaction generated by the transit of heavy forestry machinery. Soil compaction is a problem that occurs when the soil loses its natural resistance to resist the movement of machinery, causing the soil to be compacted in excess. This compaction generates unwanted effects on both the ecosystem and its economic sustainability. Therefore, when the risk of compaction is considerable, harvest operations must be stopped, complicating the annual plan and incurring in excessive costs to alleviate the situation. To incorporate the risk of compaction into the planning process, it is necessary to incorporate the analysis of the soil's hydrological balance, which combines the effect of rainfall and potential evapotranspiration. This requires analyzing the uncertainty of rainfall regimes, for which we propose a stochastic model under different scenarios. This stochastic model yields better results than the current deterministic methods used by lumber companies. Initially, the model is solved analyzing monthly scenarios. Then, we change to a biweekly model that provides a better representation of the dynamics of the system. While this improves the performance of the model, this new formulation increases the number of scenarios of the stochastic model. To address this complexity, we apply the Progressive Hedging method, which decomposes the problem in scenarios, yielding high-quality solutions in reasonable time.

Non-invasive Imaging of Rice Roots in Non-compacted and Compacted Soil.

Roots are the prime organ for nutrient and water uptake and are therefore fundamental to the growth and development of plants. However, physical challenges of a heterogeneous environment and diverse edaphic stresses affect root growth in soil. Compacted soil is a serious global problem, causing inhibition of root elongation, which reduces surface area and impacts resource foraging. Visualisation and quantification of roots in soil is difficult due to this growth substrate's opaque nature; however, non-destructive imaging technologies are now becoming more widely available to plant and soil scientists working to address this challenge. We have recently developed an integrated approach, combining X-ray Computed Tomography (X-ray CT) and confocal microscopy to image roots grown in compacted soil conditions from a plant to a cellular scale. The method is suited to visualize cellular responses of root tips grown in both non-compacted and compacted soils. This protocol presents a fully integrated workflow, including soil column preparation, creation of compaction conditions, plant growth, imaging, and quantification of root adaptive responses at a cellular scale.

Gas permeability in soil amended with biochar at different compaction states

Biochar amended soil (BAS) is widely studied to apply in green infrastructure, such as landfills and slopes. Presence of biochar improved soil hydraulic properties (e.g. water retention ability) in previous studies, while influence of biochar on gas permeability (k g ) under different compaction states is not clear yet. The main objective of this study is to investigate the k g of BAS under different soil compaction conditions. The soil selected for investigation was poorly graded sand. BAS was compacted in an in-house built 1-D column set up under three different soil density (65 %, 80 % and 95% degree of compaction) were considered in mixtures with 0% and 10% biochar content. The tests were carried out in a greenhouse at Shantou University. In tests, soil column was designed and subjected to drying-wetting cycles, during which soil suction, moisture content and k g were measured. Results showed that BAS (i.e. minimum water content 37.2% and 22.1%) had better water retention performance than bare soil (i.e. minimum water content 20.2% and 19.5%) at compaction conditions (65% and 80% degree of compaction). However, when the degree of compaction increased to 95%, bare soil and BAS shows similar water retention characteristic (i.e. minimum water content 15.7% and 15.9% respectively). The addition of biochar could decrease k g as compared with that of the bare soil, meanwhile, in the lower suction range, k g decreased with an increase of compaction (i.e. k g 65%>k g 80%>k g 95%).

Sensitivity of flood dynamics to different soil information sources in urbanized areas

This study focused on the sensitivity of flood dynamics to soil hydraulic properties derived from three different soil databases in urbanized area: (1) upscaled locally observed soil texture data based on the soil-landscape relationships (SMLS); (2) the SoilGrids250m open data source (SMSG); and (3) the FAO soil map (SMFAO). However, soil in the urban areas has two major conditions related to land cover and soil physical structure for which the information is not available in soil databases: the effect of fragmented vegetation cover and the effect of compaction of bare soil. Non-built-up areas can be covered by fragmented vegetation (grass and shrubs) which generally has high infiltration rates. In contrast, bare areas such as dirt roads and footpath can be heavily compacted and have typically low infiltration rates. We used Pedotransfer functions (PTFs) with satellite-derived vegetation cover and bare soil to predict soil hydraulic properties related to the uncompacted and compacted scenarios. Infiltration dynamics was derived from the predicted soil hydraulic properties for these soil information sources, which then determined the flood dynamics in the catchment. The flash flood modeling was done using the integrated flood modeling system using openLISEM (Bout and Jetten, 2018) for the whole of Kampala (Uganda) using the 25th of June 2012 flood event. In the distributed openLISEM hydrological model, these two urban soil conditions have been treated separately. We have evaluated the sensitivity of flood dynamics to three different soil databases under both uncompacted and compacted urban soil conditions by using different flood indicators such as catchment water balance, infiltration rate, flood depth and duration, flooded area and flood volume, and the average number of structures affected. The result of the study indicates that soil hydraulic properties needed for the distributed hydrological model are better predicted when using the SMSG and SMLS, which resulted in better infiltration simulation. Consequently, compared to an earlier simulation that was verified with stakeholders and accepted for drainage system design, the accuracy of the simulated flood extent map was better when using SMSG and SMLS. Moreover, soil compaction significantly reduces infiltration and consequently increases the flood depth and duration, and therefore, must be included in the urban flash flood modeling study.

Urban Residential Surface and Subsurface Hydrology: Synergistic Effects of Low‐Impact Features at the Parcel Scale

AbstractAccurately predicting the hydrologic effects of urbanization requires an understanding of how hydrologic processes are affected by low‐impact development practices. In this study, we explored how growing season surface runoff, deep drainage, and evapotranspiration on a residential parcel are affected by several low‐impact interventions, including three “impervious‐centric” interventions (disconnecting downspouts, disconnecting sidewalks, and adding a transverse slope to the driveway and front walk), two “pervious‐centric” interventions (decompacting soil and adding microtopography), and all possible “holistic” combinations. Results were compared to both a highly and moderately compacted baseline parcel under an average and a dry weather scenario for a temperate climate. We find that under reasonable assumptions for highly compacted soil, pervious areas are a major source of runoff and disconnecting impervious surfaces may be relatively less effective without improving soil conditions. Under both highly and moderately compacted soil conditions, combining efforts to decompact soil with impervious disconnection has a synergistic effect on reducing surface runoff and increasing deep drainage and evapotranspiration. All combinations of interventions enhance infiltration, but the partitioning of additional root zone water between deep drainage and evapotranspiration depends on the weather scenario. Importantly, when all low‐impact interventions are applied together, growing season deep drainage is higher than that from a vacant lot with no impervious surfaces. We infer that ecohydrologic interfaces between impervious and pervious areas are strong controls on urban hydrologic fluxes and that high‐resolution, process‐based models can be used to account for these interfaces and thereby improve predictions of the hydrologic effects of low‐impact interventions.

Effects of deep tillage and municipal green waste compost amendments on soil properties and tree growth in compacted urban soils

Large trees are often seen as a means of offsetting negative consequences of growing urban densification. To increase the tree canopy cover of dense urban landscapes, developers, planners and urban tree managers are often forced to plant into damaged and compacted sites. Compacted urban soils can hinder the establishment and growth of deep rooted, woody plants by: 1) impeding root exploration and development which is critical for water and nutrient acquisition; 2) reducing infiltration of water into the soil and the availability of water to plants; and 3) reducing gas exchange and the balance between anaerobic and aerobic conditions.At three sites in Melbourne, Australia with compacted and damaged soils, we established four soil remediation treatments: 1 & 2) tillage to 0.25 m with and without 50% (v/v) municipal green waste compost (MGWC) additions, and 3 & 4) tillage to 0.5 m with and without 50% MGWC addition, plus a non-remediated control. Each treatment was replicated (n = 3), and one Corymbia maculata (spotted gum) tree was planted into the centre of each 2 × 2 m treatment plot (n = 15), at all three sites (n = 45).Bulk density and field-saturated hydraulic conductivity were improved by tillage, at least in the short-term. The use of MGWC may maintain these changes for longer. Depending on site soil conditions tree growth may be improved by tillage alone. At one site, we found that additions of MGWC lead to nitrogen immobilisation due to site soil conditions. At another site, deep tillage (with or without MGWC) led to significantly improved tree growth.Compacted and degraded urban soils may be improved through simple tillage and/or organic amendment strategies for the successful establishment of deep rooted woody plants. However, site soil conditions will dictate whether the addition of MGWC is beneficial or not, as one site showed no positive response to any tillage or MGWC. This research has examined a technique that can be used by landscape managers to improve soil physical characteristics and, in certain circumstances, can improve deep-rooted woody plant establishment and growth in challenging compacted urban soil conditions.

Efectos de las actividades de labranza en el índice de área foliar en una plantación de Tectona grandis en la zona norte de Costa Rica

Tectona grandis es una de las especies más utilizadas en los proyectos de reforestación en Costa Rica y ha sido plantada en sitios con problemas de capas adensadas en el perfil del suelo que retrasan el crecimiento de las plantaciones; por esta razón se hace necesario el desarrollo de actividades de labranza que mejoren las condiciones del suelo y favorezcan la productividad. En el presente estudio se evaluaron los efectos en el diámetro, altura total e índice de área foliar (IAF) de ocho tratamientos de labranza (testigo, testigo con dolomita, labrado con uno, tres y cinco cinceles tanto a 25 cm como a 40 cm de profundidad en combinación con dolomita) aplicados durante 2013 en una plantación de T. grandis. Tres años después de la labranza, no se encontraron diferencias significativas en el diámetro y en altura de los árboles (en promedio 11,74 cm y 11,1 m respectivamente). En cambio, el IAF mostró la formación de dos agrupaciones de tratamientos, una conformada por el testigo y testigo con dolomita y otra por individuos con suelo labrado. La primera agrupación presentó IAF menores a 3,80 m2 m-2, con correlaciones de IAF-altura inferiores a 15% y modelos alométricos con errores estándar altos; esto se debió a la heterogeneidad de los individuos causada por el estrés generado por las condiciones de compactación en el suelo. En contraste, los individuos con suelo labrado presentaron IAF superiores a 4,5 m2 m-2, con correlaciones de IAF-altura superiores a 56% y modelos alométricos con errores estándar menores a 0,20; el aumento se atribuye al proceso de reactivación del crecimiento de los individuos producto del mejoramiento en las propiedades del suelo.

Interactions between soil physicochemistry and belowground biomass production in a freshwater tidal marsh

The success of tidal freshwater wetland restoration is typically gauged by the re-establishment of characteristics found in reference marshes. Although plant species composition may resemble reference marshes within a few years after the initiation of restoration, return of soil physicochemical properties may take much longer. We investigated soil characteristics in a post-levee breach freshwater tidal marsh restoration site (Liberty Island, California), and the impacts of soil compaction on the survival and growth of emergent macrophytes. In a field study, we examined soil physicochemical properties throughout 50-cm deep soil cores collected from locations at Liberty Island that differed in location and stage of vegetation colonization. In a controlled mesocosm study, we subjected three species that are commonly implemented in restoration plantings (Schoenoplectus acutus, S. californicus, and Typha latifolia) to two levels of soil compaction (control and high soil bulk density) to determine the influence of soil compaction on soil physicochemical properties and macrophyte response. Belowground biomass increased and soil bulk density decreased with time since vegetation colonization. The controlled study showed that both Schoenoplectus species exhibited greater survival than T. latifolia. The species explored are capable of ameliorating compacted soil conditions over time; this ability can facilitate the re-establishment of wetland structure and function at restoration sites.

Bioaccumulation of copper, lead, and zinc in six macrophyte species grown in simulated stormwater bioretention systems

Stormwater bioretention (BR) systems collect runoff containing heavy metals, which can concentrate in soil environments and potentially leach into groundwater. This greenhouse experiment evaluated differences among six plant species undergoing three varying hydraulic and pollutant loads in their bioaccumulation potential when subjected to continual application of low metal concentrations as a means of preventing copper, lead, and zinc accumulation in the BR soil. Results show that >92% of metal mass applied to the treatments via synthetic stormwater was removed from the exfiltrate within 27 cm of soil depth. Compacted soil conditions of unplanted controls retained significantly more Cu, Pb, and Zn than Carex praegracilis, and Carex microptera treatments. Differences in above and below ground plant tissue concentrations differed among species, resulting in significant differences in mass accumulation. In the above ground tissue, from highest to lowest, Phragmites australis accumulated 8 times more Cu than Scirpus acutus, and C. microptera accumulated 18 times more Pb, and 6 times more Zn than Scirpus validus. These results, and differences among species in mass distribution of the metals recovered at the end of the study, reveal various metal accumulation mechanisms.

Prediction model for non-inversion soil tillage implemented on discrete element method

In the present study the discrete element method is used for predicting forces reactions and soil behavior during non-inversion tillage. The numerical model at particle level works with a force system integrated by normal, shear, cohesion and friction forces. Macro parameters are defined as the soil mechanical properties obtained by soil mechanical tests. The behavior of soil–soil and soil–metal interface at different dry bulk densities and gravimetric water contents were determined by modified direct shear box and triaxial compression tests. A set of statistical regression equations feasible to estimate the macro values of Young’s modulus, shear strength, soil friction and soil cohesion were obtained. The relationship between macro and micro behavior of soil friction was investigated by means of the simulation of direct shear tests. The discrete soil model was used to simulate soil tillage at conditions called hard-dry, soft-wet and friable state. To calibrate the model, a soil-bin was filled with the soil previously characterized and equipped with a tool similar to the one used for the simulation. A National Instrument Data Logger system was configured aimed at measuring vertical and horizontal reaction forces. The comparison between draft forces from simulation and soil-bin tests showed a small under-predicted behavior of the model for loose soil with high moisture; this behavior was fixed toward compacted and dry soil conditions. Para-plough and moldboard were the tools used for non-inversion tillage simulation at different physical states of the soil. The result shows the pattern of movement and force distribution related with the geometry of the tool.

Modeling the pullout behavior of short fiber in reinforced soil

Fiber reinforcement is an effective method for improving engineering properties of soil. However, the interaction mechanism of the fiber and the surrounding soil is not well understood. Based on mechanical analysis of fiber-soil interface under pullout condition, a tri-linear model is proposed to describe the shear stress-displacement relationship. The progressive pullout process of a short fiber in soil is divided into five consecutive phases: (1) the initial pure elastic phase (Phase I); (2) the elastic-softening phase (Phase II); (3) the pure softening phase (Phase III); (4) the softening-residual phase (Phase IV); and (5) the final pure residual phase (Phase V). For each phase, the analytical solutions of the distributions of tensile force, interfacial shear stress and displacement are derived. Through a comparison between the pullout test results of polypropylene fiber (PP-fiber) and the predicted results, the effectiveness of the proposed model in capturing the progressive load-deformation behavior of a short fiber in soil is verified. Moreover, the effects of water content and dry density of soil on the model parameters are analyzed in detail. It is found that the interfacial peak/residual shear resistance and shear stiffness of fiber reinforced soil significantly depend on soil compaction conditions. In general, two transition phases (Phase II and Phase IV) are not evident during the whole pullout process of PP-fiber.

Molding water content of clay soils and hydraulic properties of mineral liners of waste landfills

Municipal landfills as engineering constructions highly dangerous to the natural environment have to be isolated by liners in order to prevent the anthropogenic pollutants transport, together with eg landfill leachates. Mineral liners, properly prepared and compacted, sealing the bottom, sides and the top of the landfills are one of the most popular manners of their isolation. The mineral liners are usually constructed of compacted clay soils to obtain, the required by the Polish Decree of the Minister of Environment of 3 April 2013 and the Council Directive 1999/31/EC of 26 April 1999 on the landfill of wastes, value of liner’s saturated hydraulic conductivity lower than 1 10 m s. The value of hydraulic conductivity of saturated soils is directly affected by the conditions of soil compaction, especially a molding water content. This paper presents an attempt of the determination of the effects of the molding water content of a selected clay soil on its saturated hydraulic conductivity and hydraulic properties of the sealing liner, constructed according to the actual standards, of the compacted clay material. Range of our studies covered the in situ and laboratory measurements as well as numerical modeling. Saturated hydraulic conductivity under natural conditions was measured by BAT probe, (GeoNordic) while the hydraulic conductivity of the compacted clay soils was tested by Humboldt Mfg. Co. permeameters for compacted soils, in accordance with ASTM D5856. The assessment of hydraulic properties of a bottom liner made of the clay material under study was performed by the method of numerical modeling of infiltration process with the assumed value of groundwater head with an application of the FEFLOW, DHI-WASY modeling software. The lack of validation in our modeling attempt influences the fact that our studies should be treated as preliminary.

Lunar Excavation Experiments in Simulant Soil Test Beds: Revisiting the Surveyor Geotechnical Data

The establishment of permanent bases on planetary surfaces is an important long-term goal of the space community. Understanding the geotechnical properties of planetary surfaces and their interaction with tools and implements will be essential in addressing the challenges of material-handling equipment for infrastructure development during surface missions. With this aim, a replica of the soil mechanics surface sampler, an extendable scoop with a bearing plate attachment, operated on some of the lunar Surveyor missions in the 1960s, was fabricated and used in a series of simulated bearing and excavation tests. Initially, a set of tests was performed on a small laboratory test stand using an acrylic soil bin with a 30.5×33.0-cm footprint. Subsequent tests were performed in a new large-scale soil bin facility (2.27×5.94×0.76 m) to minimize wall effects. Both test setups involved the use of JSC-1a lunar simulant soil beds and motorized actuators to drive the scoop into the simulant. Emphasis was placed on methods of repeatable soil bin preparation. The scoop was attached to a commercial six-axis load cell that provided time-resolved measurements of the three-dimensional forces and torques. In addition, simultaneous video provided detailed imaging of the flow behavior and surcharge formation of the regolith during excavation. A surface-profiling technique was developed to resolve the surface deformation as the scoop penetrated and trenched the simulant. Bearing test data in loose bed preparations in both bins compared well with the Surveyor flight data. The data also included the soil response under compacted soil conditions.