Hydraulic Conductivity Characteristics Research Articles

In Situ Rainwater Harvesting System Slows Forest Decline through Increasing Soil Water Content, Fine-Root Traits, and Plant Hydraulic Conductivity

Large-scale vegetation restoration campaigns have been implemented on the Chinese Loess Plateau, which have resulted in higher soil moisture deficits in this region. This, in turn, has hampered the healthy growth of planted trees, leading to a decline and, in severe cases, mortality of trees. Therefore, the rational regulation and utilization of rainwater, the primary water source in this region, may alleviate drought stress, ensuring the sustainability of the ecosystem. In this study, we investigated the impact of in situ rainwater collection and infiltration systems (IRCISs) on soil water, fine-root distribution, xylem vascular, and hydraulic conductivity characteristics in declining Robinia pseudoacacia forests. The results demonstrated that the application of an IRCIS can effectively increase plant available moisture content (0–5.0 m) of declining Robinia pseudoacacia forests. In particular, IRCIS treatment significantly increased xylem conduit diameter and plant hydraulic conductivity while substantially reducing the percentage loss of hydraulic conductivity in both roots and branches. Furthermore, IRCIS treatment significantly reduced the root biomass and distribution depth of Robinia pseudoacacia during both wet and dry years. This implies that IRCISs are beneficial for plant growth and survival. The findings of this study are significant for devising strategic methodologies for the planning and management of rainwater resources.

Effect of Leachate containments on Clay liners

Clayey soil is made up of extremely tiny clay particles that can be employed as a binding material and have a higher retention of water compared to other soils. A hydraulic barrier to fluid flow can be obtained by a clay liner. Clay liners serve a purpose in liner systems to regulate leachate release from the waste or in covering systems to reduce water infiltration. Long-term low hydraulic conductivity constitutes a demand for clay liners to accomplish these objectives. Clay liners were barriers designed to cover landfills and dispose of low and intermediate-level waste. clay sample of its index and engineering characteristics permeability will be examined in a laboratory. After adding Na, Cl (salts) and Mg,Cr,Zn,Pb (metals) at different percentages to the clay soil the Hydraulic conductivity and index characteristics are examined within lab conditions. The measured values of the sample’s including before and after the addition of chemicals at different percentages 0,2,4,6, and 8%, have been compared by the results of the present investigation.

Time-varying characteristics of saturated hydraulic conductivity in grassed swales based on the ensemble Kalman filter algorithm —A case study of two long-running swales in Netherlands

Saturated hydraulic conductivity (Ks) of the filler layer in grassed swales are varying in the changing environment. In most of the hydrological models, Ks is assumed as constant or decrease with a clogging factor. However, the Ks measured on site cannot be the input of the hydrological model directly. Therefore, in this study, an Ensemble Kalman Filter (EnKF) based approach was carried out to estimate the Ks of the whole systems in two monitored grassed swales at Enschede and Utrecht, the Netherlands. The relationship between Ks and possible influencing factors (antecedent dry period, temperature, rainfall, rainfall duration, total rainfall and seasonal factors) were studied and a Multivariate nonlinear function was established to optimize the hydrological model. The results revealed that the EnKF method was satisfying in the Ks estimation, which showed a notable decrease after long-term operation, but revealed a recovery in summer and winter. After the addition of Multivariate nonlinear function of the Ks into hydrological model, 63.8% of the predicted results were optimized among the validation events, and compared with constant Ks. A sensitivity analysis revealed that the effect of each influencing factors on the Ks varies depending on the type of grassed swale. However, these findings require further investigation and data support.

Modified expression for hydraulic conductivity according to Mualem–van Genuchten to allow proper computations at low‐pressure heads

AbstractWater retention and hydraulic conductivity characteristics are key input data in studies on soil water dynamics in the vadose zone. The most well‐known analytical functions to describe these characteristics are those given by Mualem and van Genuchten, where van Genuchten showed that both can be described by a limited set of shared parameters. Analytically, there are no restrictions on the range of pressure heads for which these characteristics can be used. Experience, however, has shown that for certain sets of parameters, the hydraulic conductivity cannot be computed accurately at low‐pressure heads. This is due to the accuracy of (double precision) floating point operations in computer code. It is shown that for low‐pressure heads, the Mualem function approaches a power function. An adapted version of the Mualem–van Genuchten (MvG) expression for the hydraulic conductivity is proposed: between saturation and a soil‐dependent critical pressure head, the classical Mualem expression is valid and below this critical pressure head a power function is used. The power function is defined such that it matches the Mualem value at the critical pressure head. No accuracy problems will occur when using the power function until the result approaches the smallest possible (double precision) floating point value that significantly differs from zero.

Hydraulic Conductivity, Microstructure, and Compositional Changes of Sand–Bentonite Backfill in Cutoff Walls Exposed to Organic Acids

Leachate, consisting of organic acids such as acetic acid (AA) and oxalic acid (OA), commonly is released into groundwater from municipal solid waste dumps and uncontrolled landfills. Slurry trench cutoff walls commonly are used to contain such contaminated groundwater, thereby protect the surrounding public and the environment. However, no studies have assessed comprehensively the effects of organic acid–laden groundwater exposure on the hydraulic conductivity and microscopic characteristics of sand–bentonite (SB) backfill in the cutoff walls. Several series of free swell, liquid limit, and flexible-wall hydraulic conductivity tests were conducted to quantify the effects of AA and OA exposure on the free swell index of bentonite and hydraulic conductivity and liquid limit of SB backfill. Results showed that the free swell index of bentonite and the liquid limit of SB backfill decreased with increasing concentrations of AA and OA. Exposure to AA yielded a lower free swell index of bentonite and liquid limit of SB backfill than those of OA with the same concentration. Increasing concentrations of AA and OA resulted in an increase in the hydraulic conductivity of SB backfills. Exposure to AA yielded higher hydraulic conductivity of SB backfill than OA with the same concentration. Mechanisms for increased hydraulic conductivity under organic acid exposure were ascertained based on the microstructure and compositional changes quantified by field-emission scanning electron microscopy (FESEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), X-ray fluorescence (XRF), cation exchange capacity (CEC), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR) analyses.

Characterizing the hydraulic conductivity of soil based on the moving average of precipitation and groundwater level using a regional database

Abstract Hydraulic conductivity is an important geological and geotechnical characteristic, necessary for flow-related problems and underground construction. In many countries, databases for hydrology parameters and groundwater level (GWL) are well established, often not fully utilized for directly estimating hydraulic conductivity characteristics. In this study, a method for estimating hydraulic conductivity based on a regionally established database of hydrological, geological, and geotechnical parameters is proposed. For this purpose, 68 databases of hydrological, geological and geotechnical parameters in different regions in Korea were collected and adopted to develop a data-based estimation method of soil hydraulic conductivity. The time response of GWL to precipitation was considered as a key influence factor on the hydraulic conductivity of soil, as it directly affected the infiltration process of rainfalls into soil deposits. Moving average (MA) of precipitation was introduced, which gave the best correlation to GWL, to account for the effect of accumulated precedent precipitation. Case examples were selected and used to check the validity of the proposed method.

Hydraulic Conductivity Characteristics of Iron-Ore Tailings–Bentonite Mixtures Exposed to Landfill Leachate

Landfill liner materials are required to provide reliable hydraulic performance for very long times after construction, and at least for the design lifespan of the facility. To meet this objective, liner systems must retain their low hydraulic conductivity over their service lives. In this paper, we report on the durability aspects of iron-ore tailings (IOT)–bentonite mixtures in extended hydraulic conductivity experiments. The hydraulic conductivity tests were conducted on mixtures containing 20%, 25%, 30%, 35%, and 40% bentonite, compacted at 2% wet of optimum by the British standard light (BSL) effort, and permeated with municipal solid waste (MSW) landfill leachate (electrical conductivity = 25.60 mS/m, pH = 7.94) with or without prehydration for a duration of 120 days. Under these influences, permeation with leachate showed no detrimental effect on mixtures with 25% and 30% bentonite, but was rather beneficial in reducing the hydraulic conductivity (k) values of the two mixtures at the end of testing by two orders of magnitude to 4.19 × 10−8 and 9.25 × 10−9 cm/s for the prehydrated specimens and 2.4 × 10−8 and 9.9 × 10−9 cm/s for the nonprehydrated specimens. For mixtures containing 20%, 35%, and 40% bentonite, k values representing a 1.6 times decrease from the average were recorded for both the prehydrated and nonprehydrated conditions at the end of testing. Further analysis showed that prehydration had a slightly substantial effect on those specimens containing 20%, 35%, and 40% bentonite, whereas it had a minor effect, if any, on mixtures with 25% and 30% bentonite. In terms of durability, only mixtures containing 25% and 30% bentonite that consistently maintained low k values up to the end of testing are projected to be effective as liner materials in the construction of geological repositories for MSW. Regarding the hydraulic conductivity characteristics of the mixtures upon exposure to the combined effects of leachate and the elevated temperatures expected in landfill conditions, all mixtures maintained relatively good hydraulic performance, exhibiting a decrease in hydraulic conductivity with time.

Experimental study on the reaction process and engineering characteristics of marine calcareous sand reinforced by eco-friendly methods

Calcareous sands are important building materials in ocean engineering. In order to ensure the stability of the island under the actions of wave and current, the marine calcareous sand was reinforced by two eco-friendly methods (Microbial and Enzyme induced carbonate precipitation, MICP and EICP). The concentrations of calcium and bacteria, shear wave velocity, global hydraulic conductivity, penetration resistance and microscopic characteristics of each test were evaluated systematically. The normalised shear wave velocity in EICP treated samples were smaller than those of MICP treated sand, but the response of EICP was faster at the same duration. The global hydraulic conductivity exhibited different degrees (46% of MICP and 28% of EICP) of exponential reductions with the increase of the time in dry environment. It exhibited less degrees (33% of MICP and 18% of EICP) of liner reductions in underwater environment. The cementation products of MICP in calcareous sand were mainly spherical calcium carbonate in both dry and underwater environments, and rhombohedral calcium carbonate also appeared in dry environment, leading to higher penetration resistance in P1-M than P2-M. For EICP-treated calcareous sands, calcium carbonate crystals in dry environment were mainly rhombic, and loose eggshell-like morphologies were formed in underwater environment. MICP was more suitable than EICP for the reinforcement of marine calcareous sands in underwater environments.

Hydraulic Conductivity Characteristics of a Clayey Soil Incorporating Recycled Rubber and Glass Granules

Recycled waste materials have been employed to stabilize clayey soil by many practitioners in geotechnical engineering. However, the effects on hydraulic conductivity and its underlying mechanism have rarely been explored. The study aims to examine the hydraulic conductivity characteristics of soil reinforced with the inclusion of selected recycled waste granules, rubber crumb (RC) and crushed glass (CG) under changing confinement. For this purpose, a series of consolidation tests were carried out by varying recycled waste type and additive contents (0%, 5%, 10% and 20% additive content by dry weight of soil). The confining stress was increased within a range of 6.25 kPa to 200 kPa. The results reveal that the addition of RC and CG, as well as the stress state, significantly impacted the soil’s hydraulic conductivity (k). The hydraulic conductivity of both RC/CG soil composites consistently declined with increasing applied stress. Moreover, as the concentration of recycled waste granules in the reinforced soil increased, the hydraulic conductivity value k initially increased, reaching a peak before subsequently declining. Additionally, the study utilized scanning electron microscope (SEM) imaging, which revealed that the inclusion of RC and CG significantly influenced hydraulic conductivity-related parameters by modifying pore size and distribution.

Assessment of engineering properties of slag mixtures as a bottom liner in landfills

This work examines the engineering properties and leachate characteristics of ground granulated blast-furnace slag (GGBS) blended with laterite soil–bentonite mixtures as a bottom landfill liner. In this study, laterite soil is considered a non-expansive and non-plastic clay; in contrast, bentonite is a highly expansive and highly plastic clay. Laboratory experiments were performed to quantify the effect of GGBS–laterite soil–bentonite mixtures on the liquid limit (LL), free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity (k) and leachate characteristics tests. As the GGBS percentage in the mix blend increased, the LL, FSI, optimum moisture content, k determined with deionised water/diesel oil contaminants and leachate concentration decreased, whereas the maximum dry densities and UCS value increased. Furthermore, X-ray diffraction analysis and energy-dispersive X-ray spectroscopy were performed on UCS samples to determine the occurrence of a hydration reaction in mix blends at 0, 14 and 28 days of curing. The test results revealed that an increase in the calcium (Ca)/silicon (Si) ratio and a decrease in the aluminium (Al)/calcium ratio enhanced the UCS during the curing period. Consequently, 20% GGBS combined with laterite soil–bentonite mixes proved to be the ideal material for landfill bottom liners in waste containment systems.

Changes in geotechnical properties of soil contaminated by methyl tertiary butyl ether (MTBE)

As an extensively used gasoline additive, methyl tertiary butyl ether (MTBE) can leak into the subsurface, and this not only damages the ecological environment but also affects the geotechnical characteristics of the soil. In this study, the geotechnical properties of MTBE-contaminated soil, such as the basic physical properties of strength, compressibility, hydraulic conductivity, leachability, electrical resistivity and microstructural characteristics, are comprehensively investigated. The results show that the Atterberg limits consistently decrease with increasing MTBE content in the soil. As the MTBE content increases from 0 to 10%, the specific surface area of the soil decreases by 28%, the sand content increases by 22%, and the clay and silt contents decrease by 3 and 18%, respectively. The soil compression index, hydraulic conductivity, leached MTBE concentration and electrical resistivity increase, while the unconfined compressive strength (UCS) decreases, with increasing MTBE content. Microstructural analysis shows that increasing the MTBE content results in mineralogical alterations that decrease the illite and kaolinite content of the soil. The aggregation and flocculated structures can be detected by an increase in the number and size of inter-aggregate pores. In addition, the electrical resistivity of the contaminated soil is used to assess the geotechnical properties of the MTBE-contaminated soil based on well-established empirical relations.

New insights into the seepage behavior of heavy metal-contaminated loess and its underlying geochemical mechanism

Heavy metal contamination in soils can pose severe challenges to the safety of geotechnical engineering projects. Loess, which is widely distributed in Northwest China, is a preferred engineering construction material for anti-fouling barriers. Therefore, research on the influence of heavy metal ions on its seepage performance is urgently required. To obtain new insights into the seepage behavior of heavy metal-contaminated loess and its underlying geochemical mechanism, laboratory investigations were performed on the saturated hydraulic conductivity (Ksat), leaching, and microstructural characteristics of loess contaminated with Cu2+ and Zn2+. The results indicate that the hydrolysis of Zn2+ creates an acidic environment, which promotes the dissolution of carbonate minerals in loess, enhances the leaching capacity, and leads to the quantitative transformation of small pores (2–8 μm) to mesopores (8–32 μm). Meanwhile, the alternating adsorption of Zn2+ and its diffuse double-layer effect compresses the diffusion layer, increasing the abundance of free water channels. Thus, the Ksat of Zn-contaminated loess increases by 81.2% during the seepage period. As for Cu-contaminated loess, its seepage behavior is the opposite of that of Zn-contaminated loess, with a Ksat decrease of nearly 50%. The primary factor controlling this phenomenon is the formation and enrichment of Cu2O in the lower part of the soil, which inhibits the enlargement of pores and reduces the effective connectivity of pores. The findings of this work provide insight into the seepage behavior of saturated loess under erosion by heavy metals and the underlying geochemical mechanism thereof.

Modification of Highway Sub-Grade Black Cotton Soil by using Nano Chemical: Terrasil Mixed with Fly-Ash and Rice Husk Ash

Abstract: As the population grows daily, the amount of excellent, solid ground available for development decreases, necessitating the use of weaker or softer soil for the construction of buildings and other civil engineering projects. The building of structures built on the problematic broad black cotton soil is fraught with difficulties. It has poor geotechnical subgrade features, including swelling and imperviousness. In this study, an attempt is made to improve the different geotechnical characteristics of black cotton soil by mixing it with waste products like river sand, fly ash, and marble dust. These properties include index properties, swelling characteristics, consolidation characteristics, hydraulic conductivity characteristics, and strength characteristics. Due to the best possible use of these waste materials in the enhancement of various aspects of black cotton soil, these techniques therefore minimised the impact of waste materials on the environment. There are many different types of soil stabilisation, but typically, mechanical, and chemical stabilisation procedures are used to accomplish traditional soil stability. Stabilizers are the additives that are used to stabilise substances. For stabilisation, a variety of stabilisers are utilised, including fly ash, bitumen, rice husk, lime, cement, and other chemicals. When dry, black cotton soils are extremely hard; yet, when wet, they entirely lose their strength. Widespread issues with expansive soils provide a number of difficulties for civil engineers. Numerous techniques are used to enhance the expanding soils' engineering properties. The study's findings are summarised as follows. By raising the percentage of Terrasil and maintaining the values of rice husk ash and fly ash, which are 10% and 20% respectively, unchanged, the liquid limit percentage lowers by 0% to 0.08% and grows. When Terrasil is changed while leaving the values of rice husk ash and fly ash, which are 10% and 20% respectively, unchanged, the plastic limit percentage falls from 0% to 0.10 percent. When rice husk ash and fly ash are kept at their constant values of 10% and 20%, respectively, the plasticity percentage drops from 0% to 0.04% and then rises to a high of 0.06% at 30.07. The maximum value is reached before the optimal moisture content (OMC) first increases, then declines. achieved after 0.10% addition of Terrasil while maintaining the 10% and 20% values for rice husk ash and fly ash, respectively, and were equivalent to 27.64%. The compressive strength first increases and then decreases, the maximum value obtained was at 0.06% addition of Terrasil keeping constant value of rice husk ash and fly ash, i.e., 10% and 20% respectively, and were equal to 1.69 gm/cm2. The maximum dry density (MDD percentage) first increases up to 0.06% of Terrasil and then decreases.. The greatest value achieved was at 0.06% addition of Terrasil retaining constant value of rice husk ash and fly ash, i.e., 10% and 20% respectively, and were equal to 0.861kg/cm2. The shear strength initially increases and subsequently drops. As Terrasil's percentage rises while the amounts of fly ash and rice husk ash remain constant at 10% and 20%, respectively, the permeability commonly drops.

Assessment of geotechnical and geo-environmental behaviour of recycled concrete aggregates, recycled brick aggregates and their blends

The infrastructure development involves the demolition of non-functional establishments and the construction of the desired infrastructure needs, which generates construction and demolition (C&D) waste in enormous volumes. The demolished concrete and brick wastes are found mixed together, if not separated before crushing. Therefore, the geotechnical behavior of blends of recycled concrete aggregate (RCA) and recycled brick aggregates (RBA) with different proportions should be identified in order to find their suitability in geotechnical applications. This paper presents the geotechnical and geo-environmental characterization of RCA, RBA, and their blends (75RCA-25RBA, 50RCA-50RBA, 25RCA-75RBA). The recycled waste aggregates and their blends under this study have excellent shear strength, hydraulic conductivity, and compaction characteristics. The values of cohesion intercept (c) and angle of internal friction (ф) are found in the range of 50 to 63 kPa and 55˚ to 71˚, respectively. It is observed that the optimum values of shear strength parameters (c = 63 kPa, ф = 64˚), hydraulic conductivity (3.12 × 10-5 m/s), and compaction characteristics (OMC = 11.50 %, MDD = 1.96 gm/cm3) are found for 50 % RBA content in RCA-RBA blends. The water absorption is found on the verge of upper bounds considering pavement applications. The impact and crushing resistance of blends are found comparably low and decrease with increased RBA content in RCA. Therefore, their applicability to the surface course, even to the base course in pavements, may be restricted. Based on experimental results current study suggested that up to 50 % RBA content in RCA-RBA blends may provide satisfactory performance in various geotechnical applications like: pavement base and sub-base, fill material in embankments and reinforced earth structure, etc.

Joint Estimation of Adsorptive Contaminant Source and Hydraulic Conductivity Using an Iterative Local Updating Ensemble Smoother with Geometric Inflation Selection

The joint estimation of groundwater contaminant source characteristics and hydraulic conductivity is of great significance for reactive contaminant transport models in heterogeneous subsurface media. The accurate determination of the sorption parameters of such contaminants is also a key prerequisite for estimating the parameters of the groundwater system. In this study, to investigate the impact of the sorption parameter field on the accuracy of hydraulic conductivity and source characteristics estimation, numerical experiments were conducted in a synthetic aquifer considering the contaminant sorption process in groundwater models with varying sorption parameter settings. Iterative local updating ensemble smoother with geometric inflation selection (ILUES-GEO) was employed to assimilate hydraulic head and contaminant concentration data to jointly estimate the contaminant source information and hydraulic conductivity in a heterogeneous aquifer. The results indicated that the ILUES-GEO successfully recovers contaminant source information simultaneously with hydraulic conductivity, and its performance improves as more accurate sorption parameters are introduced. Furthermore, the influence of the ILUES algorithm parameters and ensemble size is investigated to improve the estimation accuracy. Additionally, the characterization of contaminant sources and hydraulic conductivity fields is influenced by the number and locations of measurements. This study can help to understand the significance of sorption parameter setting for the joint estimation of reactive contaminant source and hydraulic parameters.

Predicting the hydraulic conductivity of frozen coarse-grained soils

Hydraulic conductivity is crucial to revealing the mechanisms of frost damage in cold regions, while the hydraulic conductivity of coarse-grained soils during freezing process has rarely been considered. In this study, a new pattern that ice grows from the pore wall is used to describe ice formation in coarse-grained soils. In this pattern, unfrozen water confined in the pore center provides flow channels for liquid water migration. The relationship between distribution characteristics of flow channels and hydraulic conductivity can be established by redefining parameters such as porosity ϕe, hydraulic radius RH¯ and tortuosity Γ in the Kozeny-Carman equation. It thus generates a new hydraulic conductivity model for frozen coarse-grained soils. Comparing with measured result in the literature, it shows that the proposed model gives a better prediction than existing models, especially for sand. The proposed model can provide a useful tool for simulating water-heat transfer process of coarse-grained soils in cold regions.

Experimental Investigation of Hydro-Mechanical Soil Properties of a Slope Failure

A sudden slope failure occurred in Manisa possibly due to the effect of water infiltration because of a slightly damaged sewage pipe. Considering that there was no other evidence such as rainfall or any loading conditions to trigger the slope failure, a laboratory investigation on the soil’s unsaturated hydro-mechanical properties was initiated. Slopes are naturally unsaturated soils, and they may lose their stability with increased saturation degrees with water infiltration. Thus, for a proper investigation, the unsaturated hydro-mechanical properties of soils should be determined. The results presented in this study are focused on determining the key parameters to evaluate the slope failure for unsaturated soil conditions. In this regard, hydraulic conductivity and suction characteristics and the shear strength parameters were determined as well as the classical geotechnical properties of the soil. Classification of soil was determined as silty sand which is known to have slight to moderate suction stresses and mostly affected suddenly by water infiltration. A flexible-wall permeability test was run with a falling head procedure and the saturated hydraulic conductivity of the soil sample was measured as 1x10-7 m/s. Suction characteristics were detected by filter paper method, besides, the soil water retention curve of the soil was constructed. The maximum matric suction of the soil was measured as 2887 kPa for an air-dried sample. Following, the shear strength parameters were measured by conventional direct shear test for both dry and soaked conditions. Finally, the friction angle due to suction was calculated to be 1.7 degrees from the results of dry and saturated shear strength parameters.

Crustacean polysaccharides for the geotechnical enhancement of organic silt: A clean and green alternative

Biopolymer-based soil stabilization offers a clean alternative to conventional stabilizers like cement and lime. This study investigates the possibility of using shrimp-based chitin and chitosan for stabilizing low plastic silt with organic content by investigating their effect on pH, compaction, strength, hydraulic conductivity (HC) and consolidation characteristics. X-ray diffraction (XRD) spectrum shows that no new chemical compounds were formed in the soil on additive treatment; however, results of scanning electron microscope (SEM) analysis indicate the formation of biopolymer threads that bridge the voids in the soil matrix leading to a stiffer soil matrix, with increased strength and lower HC. Chitosan showed nearly 103 % strength enhancement after 28 d of curing with no degradation. However, chitin failed as a soil stabilizing additive as it showed degradation owing to fungal bloom after 14 d of curing. Chitosan can therefore be recommended as a non-polluting and sustainable soil additive.

Effect of ammonia on the hydraulic conductivity and adsorption characteristics of lithomargic clay – bentonite barrier in landfills

Alteration of characteristic properties of the liner material occurs mainly due to interaction with contaminants present in the landfill leachate. The present study deals with the effect of inorganic contaminants on the behaviour of bentonite-based landfill liner material. Saturated hydraulic conductivity, unconfined compressive strength and compaction characteristics of the lithomargic clay and its blends permeated with an inorganic contaminant (ammonia) were evaluated. Experiments were conducted by blending lithomargic clay with 5%, 7.5% and 10% bentonite. The results showed that hydraulic conductivity decreased from an initial value of 3 × 10−8 m/s to 6.83 × 10−11 m/s. Unconfined compressive strength at wet of optimum and maximum dry density of blended lithomargic clay also reduced slightly. Adsorption studies were conducted, and the coefficient of distribution (Kd) for blended lithomargic clay with 5% and 10% was found to be 60.46 L/kg and 94.74 L/kg, respectively. The Kd values indicate good adsorption characteristics of bentonite-based material. Overall, the results showed that lithomargic clay blended with bentonite is a suitable alternative barrier for constructing engineered landfills to prevent environmental degradation and other health effects.

Characteristics of hydraulic conductivity in mountain block systems and its effects on mountain block recharge: Insights from field investigation and numerical modeling

• Potential flow paths of MBR process in mountain block were explored based on hydraulic conductivity up to ∼592.34 m depth. • Characteristics of hydraulic conductivity for bedrock and fault zones including core zones and damage zones were reported. • Spatial discontinuities in the permeability may exist for the same fault, which lead to its role can be either a conduit or a barrier in the MBR process. The process wherein groundwater flowing from mountain bedrock into lowland and adjacent alluvial aquifers, known as mountain-block recharge (MBR), is found across various climatic and geological settings. An understanding of the potential groundwater flow paths in mountain block systems is necessary for comprehending MBR spatial distribution. However, poorly characterized mountain block hydraulic properties, and especially a lack of direct measurements of hydraulic conductivity ( K ) at depths > 200 m, limit the characterization and quantifications of the MBR processes. In this study, we analyze hydraulic data set, namely 555 in-situ K measurements at various depths from two borehole sections extending from mountain block to mountain front in a potential disposal site for high-level radioactive waste. The K dataset was categorized into two groups: one for bedrock and another for fault zones, which was further classified into fault core K , damage zone K , and general fault zone K . Using a permeability conceptual model and multiple scenarios numerical modelling, this study examined the potential flow paths of MBR processes, mainly focusing on the characteristics of K in bedrocks and the hydraulic role of fault zones in mountain block systems. The distribution of Bedrock K supports the assumption of decreased trend with depth. A logarithmic fit through Bedrock K and depth pairs resulted in Log(K) = −1.62*Log(z) − 6.52, with low predictive power. This study illustrated the localized effects and spatially variable roles of fault zones in MBR within this particular hydrogeological configuration in Beishan, China. Our results provide insights into the MBR process in crystalline mountain block systems. Additionally, the hydraulic conductivity presented here provides data on the subsurface properties of mountain block systems in a crystalline area, and further facilitates the characterization and quantification of mountain-block recharge.