A Simulation of Salt Transport in NaCl-Laden Soil Barrier to Control Subterranean Termites in an Earth Embankment

Subterranean termite-induced damage to earth embankments in agricultural systems occurs globally. NaCl-laden soil barriers (NLSBs) are an environmentally sustainable termite control method, and have exhibited good potential in preventing termite-related tunneling damage in Zhejiang Province, China. The persistence of the NaCl concentration in NLSBs is a key characteristic for the long-term prevention of subterranean termite infestations. This study is a scientific attempt to estimate the field efficacy and barrier longevity of NLSBs in reservoir embankments based on the Richards equation and the convection–dispersion equation using HYDRUS (2D/3D). The observed and simulated NaCl concentrations at the end of a 1915-day simulation were compared. The results indicated that the proposed model performed well and can effectively characterize the water flow and salt transport in NLSBs. The salt desalination rate of the NLSB in the upstream slope was higher than that in the downstream slope, both of which were significantly higher than that at the embankment axis. Regardless of the type of embankment (homogeneous or core-wall), the barrier longevity of NaCl-laden soil against subterranean termites can reach 50 years with an optimized NaCl/soil ratio in different parts of the embankment.

Combined effect of hysteresis and heterogeneity on the stability of an embankment under transient seepage

Long-term effects of conventional tillage and no-tillage on saturated and near-saturated hydraulic conductivity – Can their prediction be improved by pore metrics obtained with X-ray CT?

Saturated and unsaturated seepage analysis of earth-fill dams using fractal hydraulic conductivity function and its verification

In the northwest, a lot of multi-stage high slopes with loess have been encountered in the construction of basic engineering. Slope engineering belongs to permanent project. So it is unavoidable to meet the conditions of rainfall. Under rainfall infiltration, the degree of saturation and mass of soil slope increase, which can further cause the change of slope matric suction and effective stress. As a result, the stability of the slope can be greatly influenced. In this paper, the coupling calculation model of seepage field and stress field is established. It considers the changes of the matrix suction as the rain water infiltration at the different depths of the slope body. Then, the stability of the multi-stage high slope with loess under the condition of rainfall infiltration can be analyzed. Then, according to an actual engineering and using the PLAXIS 3D geotechnical finite element software, the calculation model of slope stability is established. By setting the variation function of rainfall with the time and boundary condition, the stability calculation of multi-stage high slope with loess is carried out under the condition of rainfall infiltration. And then, The numerical calculation results are compared with the theoretical calculation results. According to the numerical calculation results, the changes of the deformation, matrix suction, effective stress, potential slip surface and safety factor of the multi-stage high slope with loess under the condition of rainfall infiltration are obtained. And the stability of the multi-stage high slope with loess under the condition of rainfall infiltration are analyzed. The study results can provide some guidance for the design of the multi-stage high slope with loess under the rainfall infiltration.

Study of soil hydraulic properties such as saturated and unsaturated hydraulic conductivity is required in the environmental investigations. Despite numerous research, measuring saturated hydraulic conductivity using by direct methods are still costly, time consuming and professional. Therefore estimating saturated hydraulic conductivity using rapid and low cost methods such as pedo-transfer functions with acceptable accuracy was developed. The purpose of this research was to compare and evaluate 11 pedo-transfer functions and Adaptive Neuro-Fuzzy Inference System (ANFIS) to estimate saturated hydraulic conductivity of soil. In this direct, saturated hydraulic conductivity and physical properties in 40 points of Urmia were calculated. The soil excavated was used in the lab to determine its easily accessible parameters. The results showed that among existing models, Aimrun et al model had the best estimation for soil saturated hydraulic conductivity. For mentioned model, the Root Mean Square Error and Mean Absolute Error parameters were 0.174 and 0.028 m/day respectively. The results of the present research, emphasises the importance of effective porosity application as an important accessible parameter in accuracy of pedo-transfer functions. sand and silt percent, bulk density and soil particle density were selected to apply in 561 ANFIS models. In training phase of best ANFIS model, the R2 and RMSE were calculated 1 and 1.2×10-7 respectively. These amounts in the test phase were 0.98 and 0.0006 respectively. Comparison of regression and ANFIS models showed that the ANFIS model had better results than regression functions. Also Nuro-Fuzzy Inference System had capability to estimatae with high accuracy in various soil textures.

Soil erosion is one of the main causes for the degradation of black soil in Northeast China. Understanding the differences of soil water and air transport under different land use patterns can provide scientific basis for efficient utilization and protection of soil and water resources in the black soil area. In this study, we examined the in-situ soil saturated hydraulic conductivity, air permeability and relative gas diffusion of 0-5 cm soil layer in three typical land use patterns (cropland, woodland, abandoned land) in the Northeast black soil area and explored the impacts of soil erosion and land use pattern on water and gas transport. Results showed that there were significant differences in soil water and air transport between different eroded croplands and between different land use patterns. Soil bulk density of serious erosion cropland was higher than that of other lands, and that of ungraded cropland was significantly lower than other lands. Compared with the ungraded cropland, soil bulk density in the light erosion cropland, the moderate erosion cropland and the serious erosion cropland increased by 12.7%, 17.6% and 39.2%, saturated hydraulic conductivity decreased by 84.4%, 53.7% and 12.7%, air permeability decreased by 94.6%, 64.4% and 14.0%, and relative gas diffusion decreased by 91.3%, 82.6% and 4.3%, respectively. The saturated hydraulic conductivity, air permeability and relative gas diffusion of pine forest decreased by 86.5%, 83.0% and 91.3% respectively compared with that of ungraded cropland, saturated hydraulic conductivity, air permeability and relative gas diffusion of sea-buckthorn forest decreased by 51.7%, 45.6% and 82.6%, and saturated hydraulic conductivity, air permeability and relative gas diffusion of abandoned land decreased by 16.2%, 1.4% and 73.9% respectively compared with that of ungraded cropland. In addition, the measured result of soil air permeability and relative gas diffusion could be used to estimate saturated soil hydraulic conductivity. Soil water and gas transport characteristics were significantly affected by soil erosion and land use pattern.

Statistical analysis of saturated hydraulic conductivity is the fundamental of engineering plans for water resource projects. In the other words, project solutions and designs depend directly on the accuracy of these statistical analyses and the methods that develop them to studied area. One of the recent methods was used to estimate the variables such as hydraulic conductivity is Kriging method. In this study, GIS software was used for this purpose and kriging method was used to estimate the saturated hydraulic conductivity of the soil. Spherical model with nugget effect of 0.0039 and sill of 0.0262 was the best variogram for determining soil hydraulic conductivity in this method, which expressed the high strength of regional variable structure in the studied area. The results showed that the simple kriging method with a regression coefficient of 0.82 has the highest accuracy in modeling the saturated hydraulic conductivity function. Also, the results showed that the geostatistical kriging method for modeling soil hydraulic conductivity index has a higher accuracy in determining saturated soil hydraulic conductivity than the traditional Thiessen method.

Equivalent salt solutions series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (E,) producing the same extent of clay swelling in a given soil. These equivalent salt solutions series values have yielded satisfactory predictions of changes in saturated hydraulic conductivity, with changes in salt solution composition and concentrations. In the present study, previously published data on changes in saturated and unsaturated hydraulic conductivities of Gilat soil in salt solutions of cationic ratio 0-50 (mmol dm-3)1/2 and electrolyte concentration 2-50 (m.e. dm-3) were used to compare the equivalent salt solution series values for hydraulic conductivities at different water contents. The equivalent salt solution series causing a given change in saturated hydraulic conductivity of a loamy Gilat soil were derived. These equivalent salt solution values were used to predict the unsaturated hydraulic conductivities of this soil at low water contents. Predictions of unsaturated conductivity at relative water contents (è) ranging from 0.80 to 0.20 agreed closely with the measured values. Coefficients log a1 and b1 for Gilat soil, in the equation log Ec = log a1+b1 log SAR, relating the Ec and SAR values of each equivalent salt solutions series were determined at è values between 1.00 and 0.20. The relationship between log a1 and bl was similar at all water contents, in agreement with the equivalent salt solutions concept. Therefore, equivalent salt solution parameters derived from saturated hydraulic conductivity measurements could be used to predict changes in unsaturated conductivities and hence flow rates of saline water under specified boundary conditions.

Subterranean termites (Odontotermes formosanus Shiraki) that build nests in the soil matrices of earth embankments may adversely affect the stability of these structures in paddy farming regions of southern China. An adult termite nest comprises a primary chamber, fungus gardens, passageways, and other shelter tubes. These porous architectures enable high hydraulic conductivity and rapid groundwater flow. In this study, we performed a field survey to characterize these termite nest architectures and proposed a simulation method that estimates seepage and associated stability in termite-infested earth embankments. Three types of nest architectures—straight, siphon, and string—were investigated in situ. Groundwater flow and its relationship with earth embankment stability were analyzed using a numerical model based on the two-dimensional Richards equation in the HYDRUS software package. Results indicated that the presence of termite nests affected seepage zone geometry and substantially affected its phreatic line, seepage flux, and global and local stabilities of the earth embankment. In the cases examined here, the presence of termite nests resulted in a maximum factor of safety reduction of 17% along the downstream slope. The local instability zones of earth embankment, resulting from clogged termite nest passageways along the downstream slope, were also assessed.

The estimation of hydraulic conductivity indicates how fluids flow through a substance and thus determine the water balance in the soil profile. In determining the saturated and unsaturated hydraulic conductivity of soil, five plots of 5.0 x 4.0 m were prepared with a PVC access tube installed in each plot. The plots were ponded profusely and surface covered with grass to prevent water loss by evaporation or water input by rain. The readings were taken twice daily for over a period of 5 days using capacitance probe with trade name Diviner 2000. The Diviner 2000 uses the method that utilizes the high dielectric constant of water compare to soil and air to determine water content of the soil. The trend lines of hydraulic conductivity has its linear regression r = 0.8296 - 0.9273 and its saturated hydraulic conductivity in the range of 5.09 cmh-1 – 14.03cmh-1 and unsaturated hydraulic conductivity in the range of 0.700 cmh-1 – 0.785 cmh-1. This reveals that soil water content can be obtained reasonably well from a capacitance probe which will allow for a determination of the pattern and use of the referred soil.

Interactive effects of environmental factors and fertilization practices on soil nitrate leaching and tea productivity in Tianmu Lake Basin, China

Abstract. Determining soil hydraulic properties is of major concern in various fields of study. Although stony soils are widespread across the globe, most studies deal with gravel-free soils, so that the literature describing the impact of stones on the hydraulic conductivity of a soil is still rather scarce. Most frequently, models characterizing the saturated hydraulic conductivity of stony soils assume that the only effect of rock fragments is to reduce the volume available for water flow, and therefore they predict a decrease in hydraulic conductivity with an increasing stoniness. The objective of this study is to assess the effect of rock fragments on the saturated and unsaturated hydraulic conductivity. This was done by means of laboratory experiments and numerical simulations involving different amounts and types of coarse fragments. We compared our results with values predicted by the aforementioned predictive models. Our study suggests that it might be ill-founded to consider that stones only reduce the volume available for water flow. We pointed out several factors of the saturated hydraulic conductivity of stony soils that are not considered by these models. On the one hand, the shape and the size of inclusions may substantially affect the hydraulic conductivity. On the other hand, laboratory experiments show that an increasing stone content can counteract and even overcome the effect of a reduced volume in some cases: we observed an increase in saturated hydraulic conductivity with volume of inclusions. These differences are mainly important near to saturation. However, comparison of results from predictive models and our experiments in unsaturated conditions shows that models and data agree on a decrease in hydraulic conductivity with stone content, even though the experimental conditions did not allow testing for stone contents higher than 20 %.

Probabilistic slope stability analysis considering the variability of hydraulic conductivity under rainfall infiltration–redistribution conditions

Wide-grade loose soils (WGLS) are common source materials for denuding hillslopes, mobilizing sediments, and causing geo-hazards. Although the effects of interstitial flow process on the shallow failure of WGLS materials are widely studied during rainfall, the combined effects of interstitial flow and surface runoff processes remain poorly understood. This in turn limits our ability to better understand the effects of fluid flow on the mechanical response of hillslope soils. In this study, flume model test was performed under rainfall infiltration and surface runoff conditions to further study the initiation process of WGLS failure. Based on the experimental results, a new mathematical model was then explored by incorporating hydrodynamic theory considering the surface runoff and fine particle migration effect. Experimental results shown that no significant slope failure was triggered only under the rainfall infiltration condition, but the slope materials could transform into continuous surface erosion under the thin surface runoff condition. Meanwhile, the back calculations and analyses of the mathematical model shown that the established model here proved to be better suited for describing WGLS failure.