Soil Matric Suction Research Articles

Hydrological and mechanical properties of plants to predict suitable legume species for reinforcing soil

Plants have considerable hydrological and mechanical impacts on soil. However, there are lack of documentation and limited understanding on the hydrological and mechanical impacts of tropical legume trees. Therefore, this study was aimed to investigate the hydrological and mechanical properties of three selected legume plants, Leucaena leucocephala, Adenanthera pavonina and Peltophorum pterocarpum. Regarding hydrological aspect, the study results indicated that soil on which the L. leucocephala was grown had the highest transpiration rate, water absorption rate (WAR) and soil matric suction (SMS). In terms of mechanical characteristics, L. leucocephala exhibited the highest root tensile strength and cellulosic components in the root. Interestingly, L. leucocephala also showed a higher root biomass, root length and fine roots than A. pavonina and P. pterocarpum. The leaf area index (LAI) strongly correlated with SMS (R2 = 0.74), indicating that high LAI improved SMS. The high root tensile strength and fine roots of L. leucocephala make this species special for growing as a soil reinforcing plant. Overall results suggested that L. leucocephala exhibited outstanding hydrological and mechanical properties and can be a potential plant for the soil reinforcement program.

Modelling of unsaturated ground behaviour influenced by vegetation transpiration

Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots.

Laboratory performance of reduced-scale reinforced embankments at different moisture contents

The paper describes instrumentation, testing, and detailed results of three 1-m high reinforced embankment models that were built in the laboratory at three different gravitational water contents (GWC). Each embankment model was subjected to a strip load near its crest until failure. The embankment models were constructed using lean clay at the GWC values ranging between OMC−2% and OMC+2% (OMC: optimum moisture content). Each embankment model included a single reinforcement layer which was placed 180 mm below the embankment surface. The location of the reinforcement layer was selected based on preliminary embankment tests and numerical simulations to ensure that it would intercept the failure surface that developed underneath the strip footing near the embankment slope. The embankments were instrumented with a total of 67 sensors to measure the soil GWC, matric suction and excess pore pressure, reinforcement strains, earth pressure and deformations of the embankment models, and the test box during the tests.The test setup and data described in this paper are part of a long-term study to validate a set of moisture reduction factors (MRF) introduced by the authors in their recent studies which involved pullout and interface shear tests on the same soil and reinforcement materials. Specifically, the data and discussions in this paper provide a basis for further in-depth analysis to verify or modify the authors’ proposed MRF values for actual embankment configurations. Furthermore, the test descriptions and results in this study will be used to validate numerical models to examine the influence of the soil matric suction and moisture content on the soil–geotextile reinforcement interface strength and internal stability of reinforced soil structures. The ultimate goal of the study is to develop a better understanding of the influence of matric suction on the performance of reinforced earthen structures constructed with marginal soils, and improved methodologies for their design.

A study on the effect of compaction on transport properties of soil gas and water. II: Soil pore structure indices

Experimental data on the effects of compaction and applied organic matter (OM) on macropore structure indices, more particularly on pore continuity, have yet rarely been documented. In this study, static compaction was simulated in the laboratory at 150, 225, and 300kPa upon rice husk, rice straw, compost, sawdust, and wood bark-mixed soils and control. Measurements of relative gas diffusivity (Dp/D0)100 and air permeability (ka100) were conducted at −100cm H2O soil matric suction after measurement of saturated hydraulic conductivity (ks). Corresponding dry bulk density (ρd), total porosity (f), and air content (ɛ100) values were also determined. Volume of macropores (ϕ≥30μm) and micropores (ϕ<30μm) were expressed as volume of air and water at −100cm H2O soil matric suction, respectively, relative to the volume of soil solid. Specific gas diffusivity (SD100) and specific air permeability (Ska100) were calculated as (Dp/D0)100/ɛ100 and ka100/ɛ100, respectively. Analogous to the SD100 and Ska100, specific hydraulic conductivity (Sks) was defined as ks/ɛ100. The results showed that compaction significantly increased ρd, which was followed by a reduction in f, and the mixed OM resulted in a significantly lower ρd and higher f than the control. The volume of macropores was reduced by compaction whereas the volume of micropores remained unaffected, for which the mixed OM tended to result in a higher volume of macropores than the control. Compaction resulted in more tortuous macropores for gas diffusion (lower SD100) and less continuous macropores for gas convection (lower Ska100) for which a significant difference was more pronounced between the 300 and 150kPa compactions. Compaction also resulted in fewer continuous macropores for water movement as indicated by lower Sks. The mixed OM was likely to result in a lower SD100, but except for rice straw tended to result in a higher Ska100 than the control. In addition, the mixed OM also seemed to result in a higher Sks than the control. Of the OM-mixed soils, the decrease in (Dp/D0)100 and ka100 was more sensitive to compaction (i.e., decrease in ɛ100) than that of the control whereas the decrease in ks acted conversely. Discussion of the measured (Dp/D0)100, ka100, and ks is presented in the companion paper.

A study on the effect of compaction on transport properties of soil gas and water I: Relative gas diffusivity, air permeability, and saturated hydraulic conductivity

Operation of farm machinery in agricultural fields is the main cause of soil compaction, which may have detrimental effects on soil gas and water transport. However, application of organic matter (OM) reduces the adverse effects of compaction and improves transport properties of soil gases and water. To date, experimental data on the effect of compaction on those transport properties and its relationship to the presence of applied OM remains scarce. The effect of compaction on relative gas diffusivity (Dp/D0)100 and air permeability (ka100) at a soil matric suction of −100cm H2O (soil pF 2.0), and saturated hydraulic conductivity (ks) were investigated using disturbed soil sample taken from 0–15cm layer mixed with rice husk, rice straw, compost, sawdust, and wood bark at a rate of 20% of the soil volume. The common compaction caused by farm machinery in agricultural fields was simulated in the laboratory using a static compression load of 150, 225, and 300kPa. The effect of compaction on total porosity (f) and air content at soil pF 2.0 (ɛ100) was also examined. Compaction reduced f, ɛ100, (Dp/D0)100, ka100, and ks, with the more pronounced significant difference between 150 and 300kPa compactions. The decrease in (Dp/D0)100 was likely attributable to a reduced air content, and the decrease in ka100 and ks was likely attributable to a reduced volume of macropores, as indicated by reduced ɛ100 values. Compared with the control, addition of sawdust and wood bark seemed to have the most positive effect on (Dp/D0)100, ka100, and ks in term of resistance to compaction, while rice straw had the opposite effect. The presence of OM was likely to block the soil pores and increase capillary water in the bottle-neck, leading to lower values of (Dp/D0)100 and ka100 for a given value of ɛ100 (“blockage effect”). These pores blocked by OM, however, seemed to allow the water to flow through the soil matric (“ceramic filter effect”). Further studies on the prolonged application of OM at field scale, taking into account the decomposition process, should be conducted.

Investigation of soil–atmosphere interaction in pyroclastic soils

This paper investigates the interaction between soil and atmosphere in pyroclastic soils with a view to understanding whether and to what extent the prediction of the hydraulic (and mechanical) behaviour of geotechnical problems (cuts, slope stabilities, embankments, foundation, retaining structures) regulated by rainfall-induced fluctuations of matric suction is influenced by evaporation phenomena. Evaporation fluxes are quantified and compared with other fluxes (precipitation, run-off, deep drainage) affecting soil water content and matric suction. This work is based on the data collected through a physical model over 2 years of experimental tests. The model consisted of a 1 m3 tank, filled in this case with pyroclastic soil and exposed to natural weather elements. The system was extensively monitored to record atmospheric and soil variables. The results provided by the experiments highlight the importance of the top-soil state in determining the intensities of infiltrating rainfall and actual evaporation. The results also bring to light the significance of evaporation which, during the dry season, largely prevails over infiltration, raising suction to very high values. Also during the wet season, evaporation gives rise to a non-negligible flux with respect to the infiltrated precipitation. The reliability of two pre-existing empirical models to estimate evaporation flux is also investigated and appraised within this paper.

Effect of Matric Suction on Resilient Modulus for Compacted Recycled Base Course in Postcompaction State

The demand for recycled material as the unbound base course in roadway construction has increased in recent decades because of the excellent mechanical properties of the recycled base course and inherent life-cycle benefits. However, concerns have been expressed about postconstruction changes in the resilient modulus (Mr) caused by moisture variation. This study investigated the relationship of Mr to soil matric suction (ψ) at an in-service stress state for recycled asphalt pavement, recycled pavement material, and recycled concrete aggregate compared with crushed limestone as a conventional base course control. Resilient modulus tests were conducted in accordance with NCHRP Project 1–28A Procedure 1a. Equipment modifications allowed for an applied ψ ranging from 1.5 kPa to 65 kPa during testing. A proposed model incorporated parameters from the soil–water characteristic curve to predict a summary resilient modulus (SRM), that is, the in-service Mr at a representative field stress state. The SRM increased with increasing ψ for all compacted base courses studied. An SRM ratio, defined as the ratio of the SRM at a particular ψ to the as-compacted SRM at optimum water content, was empirically quantified. The modulus ratio increased linearly with logarithmic ψ for the studied recycled and natural aggregates. The findings indicate that the Mr–ψ relationship is highly relevant for predicting in-service performance of pavement layers.

Estimating soil suction from electrical resistivity

Abstract. Soil suction and resistivity strongly depend on the degree of soil saturation and, therefore, both are used for estimating water content variations. The main difference between them is that soil suction is measured using tensiometers, which give point information, while resistivity is obtained by tomography surveys, which provide distributions of resistivity values in large volumes, although with less accuracy. In this paper, we have related soil suction to electrical resistivity with the aim of obtaining information about soil suction changes in large volumes, and not only for small areas around soil suction probes. We derived analytical relationships between soil matric suction and electrical resistivity by combining the empirical laws of van Genuchten and Archie. The obtained relationships were used to evaluate maps of soil suction values in different ashy layers originating in the explosive activity of the Mt Somma-Vesuvius volcano (southern Italy). Our findings provided a further example of the high potential of geophysical methods in contributing to more effective monitoring of soil stress conditions; this is of primary importance in areas where rainfall-induced landslides occur periodically.

THE INFLUENCE OF TREE INDUCE SUCTION ON SOIL SUCTION PROFILES

This study provided an investigation of active root tree zone located at the toe of the slope. This section of slope generated suction due to tree water uptake during dry season. A field mon itoring set up program was carried out to collect m atric suction data at slope with absent of a tree and with a tree located at toe of the slope. The installations of Jet-fill tensiometer and Gypsum blocks to measured matric suction were placed at vicinity of tree with certain depths and distances. The distribution in matric suction values and matric suction profiles responses to tree water uptake and rainfall were investigated. The decreased of soil matric suction after intense rainfall in this monitoring period as a function of an initial condition before the water uptake drive n by active root tree substantially increased matric suction (low moisture content). Ma tric suction significantly increased at vicinity of tree trunk located at toe of slope compared to the slope without tree. This exploratio n provides the viewed of mature tree can significan tly alter the suction distribution driven by transpiration in an unsaturated soil slop e. It takes consideration by preserved mature tree can improved soil properties in geotechnical slope design.

실내모형실험을 통한 TDR 함수량계의 현장 함수비 보정

지하매설구조물인 상수도관 주변 지반의 간극수 동결로 상수도관의 변형에 영향을 미칠 수 있다. 이에 최근에는 현장 계측을 통한 포장 하부구조체의 함수비를 주기적으로 측정하기 위해서 미국 Campbell사의 TDR(time domain reflectometry) CS616 함수량계와 독일의 IMKO사 제품의 TRIME FM를 이용한 수동 함수량계 TRIME P3, T3 Probe를 사용하고 있다. 일반적으로 TDR 함수량계와 TRIME 수동 함수량계는 흙의 종류, 입도, 다짐도, 온도 등에 의해 오차가 유발될 수 있기 때문에, 현장의 시료를 사용하여 TDR 함수량계의 실내보정실험을 반드시 수행해야 한다. 즉, TDR함수량계의 매뉴얼에서는 일반적인 흙의 보정방정식을 제안하고 있지만 현장 적용시에는 반드시 보정실험을 수행하도록 권고하고 있다. 본 연구에서는 상수관 등 지하매설구조물의 주변의 다양한 채움재료를 사용하여 실내 보정 실험을 수행하였으며, 이 결과로부터 TDR함수량계인 CS616, TRIME-T3, TRIME-P3의 보정모델식을 제안하였으며, 보정식에 대한 현장검증을 수행하였다. Water content of subgrade soil in water supply systems has a large effect on performance. Many researchers lately make use of time-domain reflectometry (TDR) probes to measure the soil water content of subgrade soil from monitoring. The laboratory calibration test of TDR probe should be performed with soil field, because TDR probe can cause an error by type, gradation, density, and temperature of soil. This study shows the laboratory calibration test using TDR CS616, TDR-P3, TDR-T3. The calibration equations of TDR were then proposed. It was confirmed from the study that the data of TDR probe monitored in field could be used to estimate the freezing, unfrozen water content, and matric suction of soil.

Infiltration-induced seasonally reactivated instability of a highway embankment near the Eisenhower Tunnel, Colorado, USA

Infiltration-induced landslides are major natural hazards. When they occur along highways they can impede traffic, damage infrastructure, and threaten public safety. This paper presents a case study of an active landslide on an embankment of Interstate-70 west of the Eisenhower Tunnel in central Colorado, USA. Records indicate that the hillslope under I-70 has moved episodically over the previous 40years. In the previous two decades the road surface has been displaced vertically by more than 60cm. The objective of this work is to develop a conceptual model capable of quantifying the seasonally reactivated landslide movement at the site. Inclinometer data of subsurface deformation and geologic and hydrologic mapping are used to develop the conceptual model as well as to constrain a numerical model. A two-dimensional hydro-mechanical numerical model is used to test the conceptual model under three different infiltration rates during the period of snowmelt in the spring. The framework used in the numerical model accounts for the major physical processes driving instability of the slope: time-dependent variably saturated flow, the resultant changes in stress, and induced deformation. When the snowmelt water infiltrates into the slope, the soil water content and the water-table level vary accordingly. These time-dependent variations result in changes in soil matric suction, effective stress, and consequently change in slope stability. The model calculates pore-water pressures, suction stress, and the distribution of effective stress in the embankment slope at different times. Global factors of safety as a function of time are calculated along the predetermined sliding surface using effective stresses calculated with finite elements. The slope stability assessment quantitatively confirms the conceptual model and is consistent with the displacements monitored at the site during the years of 2007–2009. It is shown that annual snowmelt infiltration of 60–100cm of water can reduce the factor of safety by 6%, enough to sustain landslide movement for as long as 8months each year.

A Study on Tensiometer Measurements in Salt Laden Soil Used for Irrigation Scheduling

Tensiometer is one of the most popular and simple instrument for in situ and laboratory measurement of negative pressure or suction in soils. Such measurements in the top soil or root zone are useful for automated optimized irrigation scheduling for different vegetation. The top soil accommodates various salts/contaminants whose main source is storm water runoff, irrigation water and application of crop fertilizers. These salts accumulate in the soil due to evaporation. It is an established fact that tensiometer measures only soil matric suction with the help of a ceramic interface. It is believed that osmotic effect of salts present in the soil does not influence tensiometer measurements. However, there is no systematic experimental verification in the literature to understand the influence of salt laden soil on tensiometer measurements. It needs to be ascertained that the pore size of the tensiometer ceramic will not exhibit semi-permeable membrane characteristics leading to osmotic effect. Such verification is important as it would influence the irrigation scheduling of crops. It is also of interest to know whether the osmotic suction (due to the salts) would increase the water retention characteristics and hence the irrigation requirement. If so, then the tensiometer based irrigation scheduling would be an underestimate of the actual irrigation requirement of crops. To investigate these issues, the present study has performed controlled laboratory suction measurements using tensiometer in a locally available soil, contaminated with known concentration of inorganic salt solution. The total suction of the same salt laden soil has been measured using the WP4 dew point potentiameter technique. The results indicate negligible influence of salts present in the soil on tensiometer measurements. The study demonstrates the incapability of tensiometer to assess the osmotic component of salt present in the soil. This would result in the under prediction of water retention and hence irrigation requirement of the soil.

Combination of artificial neural networks and fractal theory to predict soil water retention curve

Despite good progress in developing pedotransfer functions (PTFs), the input variables that are more preferable in a PTF have not been yet determined clearly. Among the modeling techniques to characterize soil structure, those using fractal theory are in majority. For the first time, fractal parameters were used as predictors to estimate the water content at different matric suctions using artificial neural networks (ANNs). PTFs were developed to estimate soil water retention curve (SWRC) from a dataset of 148 soil samples from North West of Iran. Including geometric mean (dg), geometric standard deviation (sg), and median diameter (Md) of particle size distribution as input parameters significantly enhanced the PTFs’ accuracy and increased the coefficient of determination (R2) by up to 5.5%. Fractal parameters of particle size distribution (PSDFPs) were used as predictors and it improved the accuracy and reliability by decreasing root mean square error (RMSE) by up to 30% for water content at h value of 5kPa (θ5 kPa) and by up to 12.5% for water content at h value of 50kPa (θ50 kPa). Entering the fractal parameters of aggregate size distribution (ASDFPs) in the models raised the accuracy at most soil matric suctions (h) and caused up to 6.7% reduction in the RMSE. Their impacts were significant at θ25kPa and θ50kPa. The network architectures were unique and problem specific with respect to the output layer transfer functions and number of hidden neurons. Adding PSDFPs and ASDFPs to the input parameters of the proper ANN models could improve the estimation of SWRC, significantly.

Analytical expressions for drainable and fillable porosity of phreatic aquifers under vertical fluxes from evapotranspiration and recharge

In shallow unconfined aquifers, the response of the water table (WT) to input and output water fluxes is controlled by two distinct storage parameters, drainable and fillable porosity, which are applicable for WT drawdown and rise, respectively. However, only the drainable porosity estimated from the hydrostatic soil moisture profile is in common use. In this study, we show that under conditions of evapotranspiration and/or recharge from or to a shallow water table, drainable and fillable porosity have different values. Separate analytical expressions are developed for drainable and fillable porosity accounting for dynamic soil moisture conditions through the assumption of successive steady state fluxes in the unsaturated zone. The equations are expressed in terms of soil hydraulic parameters and matric suction at the soil surface. Parametric evapotranspiration and recharge functions are used to estimate the suction at the soil surface. The final expressions are independent of evapotranspiration or recharge function, thus allowing the use of any appropriate function to estimate the storage parameters. It is shown that the occurrence of unsaturated zone fluxes can result in significantly different values of drainable and fillable porosity, even when hysteresis is neglected. Application of the two parameters in a Boussinesq‐type groundwater model resulted in significantly improved estimates of field‐measured water table dynamics compared to the hydrostatic, single‐parameter model.

Monitoring soil-water and displacement conditions leading to landslide occurrence in partially saturated clays

Shallow landslides frequently occur during transient rainfall infiltration and under partially saturated conditions. However, a detailed analysis of what triggers them, particularly in clayey soils, is often hindered by the lack of field measurements. It is uncommon, in fact, to capture their occurrence in an instrumented natural slope. This paper presents results from an integrated field experiment monitoring the soil-water and displacement conditions that lead to the occurrence of a shallow landslide in partially saturated clays. The integration of a variety of experimental techniques allowed for the examination of interplay between soil hydrological and mechanical properties. This research also evaluates a slope stability model based on the suction stress concept. Since the model was applied after the occurrence of the landslide, the results are interpreted as a hind-casting technique for model evaluation. Nevertheless, the detailed field measurements acquired during the monitoring activity and the occurrence of a landslide during the experiment provided significant information on model parameters and data interpretation. The station provides remote satellite monitoring of data on weather variables, soil water content and soil suction. A time domain reflectometry cable was installed vertically to detect potential soil failure. The experimental area had a high probability of landslide occurrence. Indeed, slope failure occurred during the observation period, showing the effectiveness of the station in detecting the occurrence, time and depth of landslides. The landslide was triggered in consequence of changes in suction stress. The failure plane occurred at a depth of 1.4m, corresponding to the interface between a superficial layer of higher permeability of 1 to 1.45m thickness, slipping over a compacted substrate having lower permeability. The analysis allowed for testing of the validity of the model and the description of the triggering mechanisms of the observed shallow landslide in unsaturated conditions, indicating that oscillations in soil matric suction were the dominant variables determining soil failure.

Experimental evaluation of mechanical behavior of unsaturated silty sand under constant water content condition

There are very few experimental data on the mechanical behavior of unsaturated soils, particularly in constant water content condition, because of the technical difficulties and time-consuming nature of measuring suction and deformation. This paper presents the results of a series of constant water constant triaxial tests on the specimens of an unsaturated silty sand. Constant water content tests correspond to a field condition where the rate of loading is much quicker than the rate at which the pore water is able to drain out of the unsaturated soil. The axis translation technique and a double-walled triaxial cell have been used to measure the soil matric suction and variation of pore air volume respectively. Test specimens were prepared at two different compaction conditions prior to testing to achieve different initial density. It is found that the mechanical behavior of the soil mainly depends on the initial density, the mean net stress and the initial matric suction. Also the volume and pore water pressure changes are significantly different in specimens with different initial condition. The results of tests indicated that the shearing strength of silty sand increases non-linearly with matric suction.

부분포화토의 침투와 흙의 거동에 따른 유효응력 계수 분석

열역학적 가정을 토대로 평형방정식을 이용하여 지반의 침투와 흙의 거동을 지배하는 불포화토 유한요소해석을 위한 수학적인 알고리즘을 개발하고, 여러 가지 유효응력 개념들을 수치해석을 통해 비교 분석하였다. 불포화토의 유효응력은 지반의 강도를 나타내며 지반이 함유하고 있는 수분과 모관흡수력의 중요한 구성관계를 표현한다. 특히, 불포화 지반내에서 물의 침투가 흙의 알갱이 거동을 예측하기 위해 여러 문헌에서 제안하고 있는 유효응력계수 <TEX>${\chi}$</TEX>의 특성을 지반의 잔류포화도와 변위에 관련된 구성방정식 조건을 이해하기 위해 분석하였다. 그 결과, 불포화토 유효응력계수 <TEX>${\chi}$</TEX>는 외부하중과 침투가 있는 지반내에서 모관흡수력의 분포를 변화시키지만, 지반의 잔류포화도에 따라 유효응력계수의 차이점을 보이며, 외부하중에 의한 지반 변위가 작아지면 유효응력계수 <TEX>${\chi}$</TEX>는 지반내의 모관흡수력에 대한 영향력이 작아진다는 것을 확인할 수 있었다. Based on thermodynamics, the mathematical framework governing the hydro-mechanical behavior of partially saturated soil is derived by using balance equations, and the numerical analysis through implementation of various effective stress definitions is performed. Effective stress on partially saturated soil describes the soil strength which is presented by the relationship between water content and soil suction. For the estimation of hydro-mechanical behavior on partially saturated soil, effective stress parameter <TEX>${\chi}$</TEX> defined from various literatures is especially analyzed to understand the conditions of constitutive equations regarding residual saturation and displacement of soil. As a result, effective stress parameter <TEX>${\chi}$</TEX> has an influence on the variation of matric suction in soil with an external load and seepage. However it was found that the effect of each parameter <TEX>${\chi}$</TEX> varies with residual degree of saturation, and that of each parameter <TEX>${\chi}$</TEX> decreased with decrease in displacement of soil caused by an external load.

Soil Water Characteristic Curve and its Applications in Tunnel

A soil water characteristic curve (SWCC) can describe the relationship between unsaturated soil matric suction and water content. By analyzing and researching the test data of the soil water characteristic curve researchers can initially establish the SWCC equation and apply this equation to the actual engineering analysis. In another words, this article is based on the fluid-solid coupling theory of unsaturated soil used to analyze and study the problem of land subsidence caused by tunnel construction. Numerical calculations show that the coupling results agree well with the measured curve works.

Study on the Test of Soil Water Characteristic Curve

The test of soil water characteristic curve (SWCC) and its mathematic model are present. The SWCC can describe the relationship between unsaturated soil matric suction and water content. Matric suction is an important parameter to address when studying the engineering properties of unsaturated soil. And while the measurement of substrate attraction is a very difficult issue, it is also one of the biggest obstacles in the engineering applications of unsaturated soil. By analyzing and researching the test data of SWCC researchers can initially establish the mathematic model which is the SWCC equation. The Van Genuchten model and the Fredlund and Xing model were used to simulate better the changes between the volume water content and the matric suction. Predictions were compared with experimental results to determine the simulation capability of the model for the soil of Beijing.

Improving the Predictive Capability of Popular SWCCs by Incorporating Maximum Possible Suction

Soil-water characteristic curve (SWCC) that represents the relationship between the soil moisture and matric suction is one of the important constitutive models required for numerical modeling of unsaturated soils. An effective SWCC model should be capable of calculating the moisture-suction variation for the entire range of degree of saturation. Applicability of popular SWCC models such as Brooks and Corey, van Genuchten, and Fredlund and Xing is limited, especially in low (< 20%) degree of saturation range. In this study, all these models are modified by incorporating maximum suction as one of the model parameters, so that these models can be effectively used over the entire range of degree of saturation. The Fredlund et al (1994) permeability function is also modified based on the modification to the Fredlund and Xing SWCC model. The applicability of the improved models is investigated by calibrating the SWCC of various types of soil and presented in this paper. Based on this study it can be concluded that the modified models are flexible enough to fit the experimental data for the entire range of degree of saturation.