One-dimensional Soil Column Research Articles

Determining the unsaturated hydraulic conductivity of remoulded loess with filter paper method and soil column seepage test

Loess is very widely distributed, and the unsaturated hydraulic conductivity of loess is related to many engineering issues. To determine the unsaturated hydraulic conductivity of remoulded loess more conveniently and at a lower cost, filter paper test and soil column seepage test were carried out. The results indicate that in the one-dimensional soil column seepage process, the unsaturated hydraulic conductivity of loess increases with the increase of the volumetric water content, and as the seepage time continues, the unsaturated hydraulic conductivity of loess from the top to the depth of 40 cm gradually becomes uniform. The changes in the microstructure indicate that the collapsible settlement will occur during the seepage process, which will change the pore structure of loess, thereby reducing the unsaturated hydraulic conductivity of the underlying loess. Compared with the experimental results, the soil hydraulic conductivity curve (SHCC) obtained by the van Genuchten–Mualem model (VG–M model) underestimates the magnitude of unsaturated hydraulic conductivity in the part with a low volumetric water content (< 20%). and the Childs and Collis-George model (CCG model) has more consistent results with the experimental results, because it is based on more segments of the soil–water characteristic curve (SWCC).

Multi-scale simulation of wave propagation and liquefaction in a one-dimensional soil column: hybrid DEM and finite-difference procedure

Multi-scale simulation of wave propagation and liquefaction in a one-dimensional soil column: hybrid DEM and finite-difference procedure

Experiments and simulation of co-migration of copper-resistant microorganisms and copper ions in saturated porous media

Heavy metal (HV) pollutants may migrate to the groundwater environment through leaching, causing groundwater pollution. Compared with surface water pollution, groundwater pollution is complex and hidden. Existing methods for treating HV pollution in the vadose zone have had limited application owing to various problems. In recent years, microorganisms have been used in the field of pollution control and remediation owing to their outstanding adsorption and degradation properties and low cost, but their environmental safety and behavior in porous media are still poorly understood. This study aimed to investigate the migration behavior and mechanisms of copper ions in saturated porous media under the action of copper-resistant microorganisms and to establish a corresponding numerical model to simulate the results. The key parameters of adsorption and migration were determined through batch adsorption and soil column experiments. A one-dimensional soil column was used to conduct a co-migration experiment using copper-resistant microorganisms and Cu2+ in water-saturated quartz sand, and a co-migration mathematical model was constructed. It was found that the existence of microorganisms had an inhibitory effect on the migration of Cu2+ in quartz sand, and Cu2+ promoted the migration of microorganisms, reduced their adsorption, and increased their concentration in the column experiment effluent. The selected solute transport mathematical model had a good fitting effect on the breakthrough curves of copper ion and copper-resistant microorganisms during their co-migration. The results can provide parameters and a theoretical basis for the risk assessment and prevention of HV pollution in the saturated zone or aquifers.

Pile driving and submarine slope stability: a hybrid engineering approach

During pile installation into a submerged, sandy slope, liquefaction mechanisms including flow and cyclic liquefaction warrant attention. Because of the interconnection of these mechanisms, evaluating slope stability during and as a result of vibration-inducing construction activity is not trivial. This paper presents a practical approach to such an evaluation. The primary focus of any slope stability analysis must lie with flow liquefaction as the form of failure with the most hazardous potential. Given the importance of excess pore water pressure in giving rise to (delayed) slope failures due to cyclic loading events, excess pore pressure (EPP) generation and dissipation is the mechanism of most interest in modelling cyclic liquefaction. Currently, no engineering method exists which is able to capture the interconnected processes. Therefore, a hybrid model, consisting of a numerical tool which computes EPP generation and dissipation in time, is combined with empirical relations to describe the decay of EPPs generated due to pile driving in space and time. The proposed numerical tool predicts the evolution of EPP in a one-dimensional soil column close to a vibratory-driven pile, taking into account sustained static shear stresses, interim drainage, and pre-shearing. Radial EPP dissipation is considered the dominant mode of drainage. This engineering tool fits within a holistic slope stability analysis procedure, which is demonstrated for a submerged slope in the IJmuiden harbour of the Netherlands, where mooring piles and sheet piles are installed through a relatively loose layer of sand.

Experimental study on infiltration of unsaturated soil and solution of permeability coefficient

During the unsaturated infiltration, water content, infiltration rate, infiltration amount and other physical quantities are all related to the water supply approaches and intensities. In order to study the change of water migration and the permeability coefficient in vertical infiltration of one-dimensional soil column with different infiltration conditions, this paper designs an experimental device for a one-dimensional soil column infiltration model. Three sets of infiltration tests with different intensities were carried out in two ways: artificial rainfall infiltration and ponding infiltration. The results show that the infiltration under the conditions of rainfall infiltration and ponding infiltration presents a similar trend. The infiltration of ponding in the initial stage of infiltration has greater fluctuations than the infiltration of rainfall, but after the latter stabilizes, the infiltration capacity of ponding infiltration and rainfall infiltration tends to be the same. Finally, on the basis of the theory of soil water energy state and the law of conservation of energy, a new method for solving the permeability coefficient of unsaturated soil under free infiltration is obtained.

Study on the time effect of aeolian sand subgrade salinization in desert areas

Aimed at the salinization problem of aeolian sand subgrades in desert areas over time, which has not been sufficiently considered in the Ejina region, China, based on multifield coupled numerical simulations with COMSOL Multiphysics and indoor one-dimensional soil column tests, the water and salt migration process in aeolian sand subgrades under a temperature gradient was analysed. The temporal and spatial variations in the temperature, moisture, and salinity in the subgrade salinization process were determined. Selecting a salinization rate of 0.3% accumulated 10 cm below the top of the subgrade as a critical criterion, a regression equation between the salinization time of the aeolian sand subgrade and the initial subgrade moisture content and salinity was established via nonlinear regression analysis. The results show that the temperature inside the subgrade is nonlinear along the depth direction, and the transmission process is accompanied by the attenuation of energy, which establishes a temperature gradient. The moisture and salt contents of the subgrade gradually decrease from bottom to top and are influenced by the pavement coverage effect and temperature gradient. There is a water-salt accumulation zone on the surface of the subgrade. The measured salt content at points in the soil column test agrees well with the simulation results, and the distribution law of water and salt obtained by the model is in good agreement with the water and salt variations in the simultaneous heat and water transfer model. The salinization time of the aeolian sand subgrade is affected by both the initial moisture and salt contents of the subgrade, and the influence of the initial salt content is more notable. The research results have a theoretical guiding significance for the control and prevention of salinization in desert areas.

Site-specific ground response analysis at a site in the affected area of the 2016 Pidie Jaya earthquake

Analytical models have demonstrated that they are able to simulate reasonably well the seismic motions at the ground level. The most widely used model is the equivalent linear approach. This equivalent linear model was used to compute the free-field response of Meureudu-Pidie Jaya, Aceh Indonesia’s soft soils during the 2016 Pidie Jaya earthquake. The model computes the ground response of horizontally layered soil deposits subjected to transient and vertically propagating shear waves through the one-dimensional soil column. Each soil layer is assumed to be homogeneous, visco-elastic and infinite in the horizontal extent. The equivalent linear estimation of soil properties is taken to express the nonlinearity of the soil’s shear modulus and damping values. These values are assumed to be a function of shear strain amplitude and determined by an iterative process that must be consistent with the level of the effective strain induced in each sub-layer. Starting with the highest shear modulus and a low damping value, the shear modulus and the damping ratio of each sub-layer are modified. The modification is based on the applicable relationship between both properties and the shear strain. The calculation is repeated until strain-compatible modulus and damping values converge within a tolerance of 1%. This research reveals the ground motions of Pidie Jaya’s soils. The results of the analysis are presented.

Using the maximum entropy production approach to integrate energy budget modelling in a hydrological model

Abstract. Total terrestrial evaporation, also referred to as evapotranspiration, is a key process for understanding the hydrological impacts of climate change given that warmer surface temperatures translate into an increase in the atmospheric evaporative demand. To simulate this flux, many hydrological models rely on the concept of potential evaporation (PET), although large differences have been observed in the response of PET models to climate change. The maximum entropy production (MEP) model of land surface fluxes offers an alternative approach for simulating terrestrial evaporation in a simple way while fulfilling the physical constraint of energy budget closure and providing a distinct estimation of evaporation and transpiration. The objective of this work is to use the MEP model to integrate energy budget modelling within a hydrological model. We coupled the MEP model with HydroGeoSphere (HGS), an integrated surface and subsurface hydrologic model. As a proof of concept, we performed one-dimensional soil column simulations at three sites of the AmeriFlux network. The coupled model (HGS-MEP) produced realistic simulations of soil water content (root-mean-square error – RMSE – between 0.03 and 0.05 m3 m−3; NSE – Nash–Sutcliffe efficiency – between 0.30 and 0.92) and terrestrial evaporation (RMSE between 0.31 and 0.71 mm d−1; NSE between 0.65 and 0.88) under semi-arid, Mediterranean and temperate climates. At the daily timescale, HGS-MEP outperformed the stand-alone HGS model where total terrestrial evaporation is derived from potential evaporation, which we computed using the Penman–Monteith equation, although both models had comparable performance at the half-hourly timescale. This research demonstrated the potential of the MEP model to improve the simulation of total terrestrial evaporation in hydrological models, including for hydrological projections under climate change.

Soil column infiltration tests on biomediated capillary barrier systems for mitigating rainfall-induced landslides

Rainfall-induced landslide is a common geohazard in tropical and humid regions. Capillary barrier system (CBS) is a popular and widely studied mitigating measure for rainfall-induced landslides. However, several previous studies have shown that the performance of the conventional CBS under intense rainfalls has not been particularly convincing. This paper aims to explore the feasibility and effectiveness of a newly proposed system, known as “biomediated capillary barrier system” (B-CBS) in minimizing water infiltration into soil. A one-dimensional soil column was used to investigate the infiltration characteristics of the proposed system. The results showed that the B-CBS of biomediated residual soil overlying original residual soil (Test IV) could effectively control the infiltration into soil by taking advantage of the less-permeable biomediated soil cover. The B-CBS of biomediated residual soil overlying gravelly sand (Test V) and the three-layered B-CBS of fine sand overlying gravelly sand and biomediated residual soil (Test VI) showed the best performance in terms of minimizing the water infiltration. A suction of about 5 kPa still remained in the soil column after 60 min of infiltration from the ponded water on the soil surface.

A field evaluation of soil moisture modelling with the Soil, Vegetation, and Snow (SVS) land surface model using evapotranspiration observations as forcing data

To address certain limitations with their current operational model, Environment and Climate Change Canada recently developed the Soil, Vegetation, and Snow (SVS) land surface model and the representation of subsurface hydrological processes was targeted as an area for improvement. The objective of this study is to evaluate the ability of HydroSVS, the component of SVS responsible for the vertical redistribution of water, to simulate soil moisture under snow-free conditions when using flux-tower observations of evapotranspiration as forcing data. We assessed (1) model fidelity by comparing soil moisture modelled with HydroSVS to point-scale measurements of volumetric soil water content and (2) model complexity by comparing the performance of HydroSVS to that of HydroGeoSphere, a state-of-the-art integrated surface and subsurface hydrologic model. To do this, we performed one-dimensional soil column simulations at four sites of the AmeriFlux network. Results indicate that under Mediterranean and temperate climates, HydroSVS satisfactorily simulated soil moisture (Nash-Sutcliffe efficiency between 0.26 and 0.70; R2 ≥ 0.80), with a performance comparable to HydroGeoSphere (Nash-Sutcliffe efficiency ≥0.60; R2 ≥ 0.80). However, HydroSVS performed weakly under a semiarid climate while HydroGeoSphere performed relatively well. By decoupling the magnitude and sourcing of evapotranspiration, this study proposes a powerful diagnostic tool to evaluate the representation of subsurface hydrological processes in land surface models. Overall, this study highlights the potential of SVS for hydrological applications.

Site response analysis for estimating seismic site amplification in the case of Banda Aceh - Indonesia

The city of Banda Aceh is potentially exposed to a significant seismic hazard of seismic site amplification. Estimation of seismic site amplification of the city is urgently required for any mitigation efforts as the city is founded on a thick, soft layer. This study aims to estimate seismic site amplification of Banda Aceh's soil. Analytical models have demonstrated that they can simulate reasonably well the seismic ground motions amplification. The most widely used model is the equivalent linear approach. The approach computes the ground response of horizontally layered soil deposits subjected to transient and vertically propagating shear waves through a one-dimensional soil column. As aforementioned, this study focuses on Banda Aceh-Indonesia which is founded on thick alluvium. Three actual historical time histories and three developed sub-surface models were used to estimate the seismic site amplification of Banda Aceh's soft soil. The used time histories are of 2012 M8.1 Simeulue earthquake, 2013 M6.0 Mane-Geumpang earthquake and 2013 M6.2 Bener Meriah earthquake. Three sub-surface models of three separate sites across the city of Banda Aceh were developed. The site response analysis results reveal the ground motions amplification of Banda Aceh's soils of up to 4.3. Thus, applying the seismic site amplification for structural design at Banda Aceh can be further works.

Combined Functioning of Geotextile as Barrier and Drainage Material in Unsaturated Earth Retaining Structures

This article presents an insight into the effective functioning of geotextile as a barrier and drainage material when used in earth retaining structures under unsaturated conditions. A numerical model of the infiltration test on a one-dimensional soil column has been simulated and a finite element transient seepage analysis is conducted to determine the progression of saturated wetting front through the clay–geotextile interfaces. The barrier mechanism of a geotextile layer was highlighted in terms of the water accumulation over the soil–geotextile interface, and retardation of wetting front migration beneath the geotextile layer. It was observed that the barrier breakthrough time is substantially affected by the initial volumetric water content of the surrounding soil and the hydraulic characteristics of the geotextile. Rainwater infiltration analysis of a geotextile revealed that the barrier effect assures the geotextile to be functioning as horizontal drainage layer after exceeding the breakthrough suction of the geotextile. Provision of a facing drain channels the surface runoff, as well as the water emanated from the geotextile layers, to the toe drain. Such provisions resulting in an effective drainage system substantially lowers the lateral thrust and improves the stability of the soil wall, which inadvertently enhances the sustainability of the reinforced soil walls with marginal soil backfills.

Study of the water transportation characteristics of marsh saline soil in the Yellow River Delta

One-dimensional soil column water infiltration and capillary adsorption water tests were conducted in the laboratory to study the water transportation characteristics of marsh saline soil in the Yellow River Delta, providing a theoretical basis for the improvement, utilization and conservation of marsh saline soil. The results indicated the following: (1) For soils with different vegetation covers, the cumulative infiltration capacity increased with the depth of the soil layers. The initial infiltration rate of soils covered by Suaeda and Tamarix chinensis increased with depth of the soil layers, but that of bare soil decreased with soil depth. (2) The initial rate of capillary rise of soils with different vegetation covers showed an increasing trend from the surface toward the deeper layers, but this pattern with respect to soil depth was relatively weak. (3) The initial rates of capillary rise were lower than the initial infiltration rates, but infiltration rate decreased more rapidly than capillary water adsorption rate. (4) The two-parameter Kostiakov model can very well-simulate the changes in the infiltration and capillary rise rates of wetland saline soil. The model simulated the capillary rise rate better than it simulated the infiltration rate. (5) There were strong linear relationships between accumulative infiltration capacity, wetting front, accumulative capillary adsorbed water volume and capillary height.

Effects of straw size in buried straw layers on water movement in adjacent soil layers

Deeply buried straw retention can improve the soil content of organic matter, its capacity for moisture preservation, the agroecological environment utilization efficiency of water resources, ensuring a stable crop yield; at the same time, the quantitative effects of deeply buried straw retention on soil moisture have a direct influence on the promotion and application of the technology. Using an infiltration and evaporation experiment of a one-dimensional soil column, the effects of straw size on the water content of the straw and the adjacent soil were evaluated when the straw was deeply buried in soil; the infiltration and evaporation features of different sized straw and its adjacent soil were analyzed; the hydraulic conductivity, sorptivity and saturated water content of the straw were obtained; in the end, the water distribution laws of straw and adjacent soil under the same conditions were concluded. The experiment was comprised of rod-shaped straw (RS), segment-shaped straw (SS) and filament-shaped straw (FS) to control treatment (CK). The results indicated that from the perspective of infiltration, the infiltration rate of filament-shape straw was the lowest at the stage of straw unsaturation. The hydraulic conductivities of rod-shaped, filament-shaped and segment-shaped straws are 4.01 mm/min, 1.33 mm/min and 0.03 mm/min at the stage of straw and adjacent soil saturation, respectively. There is a strong effect on preventing infiltration from segment-shaped straw; with the help of the Philip model of long duration, the sorptivity of the soil with rod-shaped, filament-shaped and segment-shaped straws was 12.31 mm/min0.5, 11.02 mm/min0.5 and 24.26 mm/min0.5 at the unsaturation stage, respectively. The segment-shape straw improved the water absorption capacity of the soil and straw column. The water retention capacities indicated that the saturated water contents of sandy loam, filament-shaped straw, segment-shaped straw and rod-shaped straw were 0.38 cm3/cm3, 0.29 cm3/cm3, 0.26 cm3/cm3 and 0.13 cm3/cm3, respectively. Additionally, the evaporation rate indicated that the soil moisture content of soil below different straw layers retained approximately 30%; that the more crushed the straw was, the more moisture the straw layer lost; and that the cumulative evaporation of rod-shaped straw, filament-shaped straw and segment-shaped straw within 120 days was 1.5 mm, 13.5 mm and 25.5 mm, respectively. Keywords: deeply buried straw, straw size, soil moisture, infiltration, evaporation, water retention DOI: 10.3965/j.ijabe.20160902.2068 Citation: Yao M Z, Li B, Wang T L, Feng X. Effects of straw size in buried straw layers on water movement in adjacent soil layers. Int J Agric & Biol Eng, 2016; 9(2): 74－84.

Transport of ammonium and nitrate in saturated porous media incorporating physiobiotransformations and bioclogging

ABSTRACTThe vertical transport of nitrates from fertilizer application and wastewater irrigation through the subsurface and saturated zone is of major concern to assess the vulnerability of groundwater contamination. The present study addresses the transport of nitrogenous fertilizers such as ammonium and nitrate in the presence of organic carbon (acetate) in a one-dimensional soil column under saturated conditions, considering the effect of adsorption and biotransformation. The soil had a neutral pH range and was classified as loamy sand, with a 0.89% organic carbon content. Batch studies revealed that sorption occurred in the order of ammonium > acetate > nitrate following a Freundlich isotherm model. Mixed heterotrophic native soil bacteria for aerobic nitrification and anoxic denitrification were developed, and the growth kinetic parameters were simulated using a Haldane inhibition model for nitrification and a Monod inhibition model for denitrification. Results from biotransformation studies suggested that denitrification was the predominant process, with significant bacterial growth and clogging of pores occurring monotonously reaching a stationary phase by 12 days. Pore-clogging phenomenon not only reduces the permeability of the soil by 5 orders of magnitude but also increases the contact time of the contaminant with the soil microbe and thereby delays the transport process and decreases the effluent ammonium and nitrate concentrations. A tailing breakthrough in a leaching study illustrates that water flux variation (0.153 and 0.509 cm/min) did not influence the transport of solutes, rather irreversible chemical bonding retains more ammonium than nitrate in the soil matrix.

Infiltration into unsaturated reinforced slopes with nonwoven geotextile drains sandwiched in sand layers

The use of nonwoven geotextile drains in geosynthetic-reinforced soil (GRS) structures has been suggested to facilitate the dissipation of pore water pressure. It has also been recognised that the nonwoven geotextile may retard water penetration due to the capillary barrier effect under unsaturated soil conditions and can function as a drainage material only once the soil immediately above it is nearly saturated. In this study, numerical models of unsaturated slopes with nonwoven geotextile drains, subjected to rainfall infiltration were developed to investigate the unsaturated hydraulic behaviour and stability of slopes constructed with nonwoven geotextile drains in thin layers of highly permeable sand (i.e. sand cushions). The numerical models were first validated for their suitability for modelling water flow and the capillary barrier effect within unsaturated soils using the experimental results from a one-dimensional soil column infiltration test and full-scale infiltration tests. Next, a series of numerical simulations of unsaturated slopes with and without sand cushions and under different infiltration conditions were performed. The numerical results indicated that the sand cushions reduced the development of the capillary barrier effect by acting as an intermediate material between the backfill and the nonwoven geotextile, which bridged the gap between two materials with very different unsaturated hydraulic characteristics. The reduction of the development of the capillary barrier effect led to the accumulation of pore water pressure above the nonwoven geotextile being effectively dissipated downward. The sand cushions also acted as additional drain layers to facilitate the drainage of water within the slope system. Thus, the inclusion of sand cushions enhanced the local slope stability for soils above the top geotextile layer. Based on the numerical results, methods for determining the occurrence of the capillary barrier effect are identified from the literature and discussed.

Gas breakthrough and emission through unsaturated compacted clay in landfill final cover

Determination of gas transport parameters in compacted clay plays a vital role for evaluating the effectiveness of soil barriers. The gas breakthrough pressure has been widely studied for saturated swelling clay buffer commonly used in high-level radioactive waste disposal facility where the generated gas pressure is very high (in the order of MPa). However, compacted clay in landfill cover is usually unsaturated and the generated landfill gas pressure is normally low (typically less than 10kPa). Furthermore, effects of clay thickness and degree of saturation on gas breakthrough and emission rate in the context of unsaturated landfill cover has not been quantitatively investigated in previous studies. The feasibility of using unsaturated compacted clay as gas barrier in landfill covers is thus worthwhile to be explored over a wide range of landfill gas pressures under various degrees of saturation and clay thicknesses. In this study, to evaluate the effectiveness of unsaturated compacted clay to minimize gas emission, one-dimensional soil column tests were carried out on unsaturated compacted clay to determine gas breakthrough pressures at ultimate limit state (high pressure range) and gas emission rates at serviceability limit state (low pressure range). Various degrees of saturation and thicknesses of unsaturated clay sample were considered. Moreover, numerical simulations were carried out using a coupled gas–water flow finite element program (CODE-BRIGHT) to better understand the experimental results by extending the clay thickness and varying the degree of saturation to a broader range that is typical at different climate conditions. The results of experimental study and numerical simulation reveal that as the degree of saturation and thickness of clay increase, the gas breakthrough pressure increases but the gas emission rate decreases significantly. Under a gas pressure of 10kPa (the upper bound limit of typical landfill gas pressure), a 0.6m or thicker compacted clay is able to prevent gas breakthrough at degree of saturation of 60% or above (in humid regions). Furthermore, to meet the limit of gas emission rate set by the Australian guideline, a 0.6m-thick clay layer may be sufficient even at low degree of saturation (i.e., 10% like in arid regions).

Consolidation of unsaturated lumpy clays

Coupled flow-deformation analysis of consolidation in unsaturated lumpy clays is presented. The governing differential equations are discretised using the Galerkin method and the finite difference technique for space and time, respectively. Particular attention is given to the cross coupling coefficients arising from the pore scale deformation compatibility between micro and macro voids. Two examples are analysed: a one-dimensional soil column, and a strip footing acting on a two-dimensional medium of lumpy clay. A range of sensitivity analyses are preformed using different values of degree of saturation and volume fraction of macro voids. All results are carefully analysed and salient features of consolation in lumpy clays are highlighted. The significance of the cross coupling coefficients in the numerical results obtained are also examined.

Numerical Assessment of Rainfall Infiltration into Soil Column for the Unsaturated Layered Residual Forest Soil

Infiltration caused by rainfall leads to the changes of moisture content and pore water pressure of the soil. These changes indicate the behavior of the soil especially during wetting and drying due to rainfall. This paper describes the numerical analyses and result of rain water infiltration into soil column using SEEP/W (Geo-Slope International, 2004). The analyses were using three types of soils.Two types of soils were commercially obtained;siltyand gravelly sand, while another soilsample obtained from UniversitiKebangsaan Malaysia (UKM) forest. The main objectives are to describe the rainfall infiltration behavior into unsaturated residual forest soil, using one-dimensional soil column model, and the effect of rainfall intensity and duration to the infiltration process for the soils. The soil properties used for that analyses such as soil water characteristic curves (SWCC), and hydraulic conductivity were obtained from the laboratory works. The study was performed for one, three, and six hour flux for all types of soils.Results of volumetric water content show that water infiltration in silty and gravelly sand aremore rapidly than forest soil. The upper layer of soil column experienced greatly increased of volumetric water content compare to the other layers.In addition, pore water pressure for siltyand gravelly sand has also greatly increased from negative towards positive value for one and three hour rainfall compared to forest soil. Therefore, as the water infiltrates,initially dry soil will gradually increase both volumetric water content and pore water pressure as an event of rainfall is applied.

Coupling methodology and application of a fully integrated model for contaminant transport in the subsurface system

Summary An efficient integrated modeling approach is developed to simulate the contaminant transport in the subsurface system. The unsaturated zone is divided into a number of horizontal sub-areas according to the atmospheric boundary conditions, land use types and hydrological conditions. Solute migration through the unsaturated zone of each sub-area is assumed to be vertical and can be represented by the one-dimensional advection–dispersion equation, which is then coupled to the three-dimensional advection–dispersion equation representing the subsequent groundwater transport. The finite element method is adopted to discretize the vertical solute equation, while the hybrid finite element and finite difference method is used to discretize the three-dimensional saturated solute transport equation, which is split into the horizontal and vertical equations based on the concept of the horizontal/vertical splitting. The unsaturated and saturated solute transport equations are combined into a unified matrix by the mass balance analysis for the adjacent nodes located at the one-dimensional soil column and at the water table. Two hypothetical cases and two field cases are simulated to test the validity of the model with the results compared with those from HYDRUS-1D, SWMS2D and the measured data. The limitations of the model are discussed as well. The analysis of the four cases demonstrates that the proposed model can calculate the water flow and solute transport reasonably even with complex boundary and variable topography conditions. It also shows that the model is efficient to simulate the water flow and solute transport in regional-scale areas with small computational costs. However, the model will lose accuracy when the lateral dispersion effect is dominant in the unsaturated zone.