Instantaneous Profile Method Research Articles

Development and Application of an IoT-Based System for Soil Water Status Monitoring in a Soil Profile.

Soil water content (θ), matric potential (h) and hydraulic conductivity (K) are key parameters for hydrological and environmental processes. Several sensors have been developed for measuring soil θ-h-K relationships. The cost of such commercially available sensors may vary over several orders of magnitude. In recent years, some sensors have been designed in the framework of Internet of Things (i.e., IoT) systems to make remote real-time soil data acquisition more straightforward, enabling low-cost field-scale monitoring at high spatio-temporal scales. In this paper, we introduce a new multi-parameter sensor designed for the simultaneous estimation of θ and h at different soil depths and, due to the sensor's specific layout, the soil hydraulic conductivity function via the instantaneous profile method (IPM). Our findings indicate that a second-order polynomial function is the most suitable model (R2 = 0.99) for capturing the behavior of the capacitive-based sensor in estimating θ in the examined soil, which has a silty-loam texture. The effectiveness of low-cost capacitive sensors, coupled with the IPM method, was confirmed as a viable alternative to time domain reflectometry (TDR) probes. Notably, the layout of the sensor makes the IPM method less labor-intensive to implement. The proposed monitoring system consistently demonstrated robust performance throughout extended periods of data acquisition and is highly suitable for ongoing monitoring of soil water status.

Characterizing water transfer in compacted soils in the context of energy storage, contribution of magnetic resonance imaging (MRI)

The concept of energy geostructures consists in enhancing existing civil engineering structures from an energy point of view thanks to the insertion of heat exchanger tubes. In order to consider the use of compacted soil embankments for heat storage [1], a good knowledge of water movement is required. Indeed, the increase in temperature of the exchangers leads to a migration of liquid/vapour water to the surface layers [2]. A loss of moisture may alter the thermal capacity of the soil [1] and therefore the system energy efficiency. To determine unsaturated hydraulic properties, the Instantaneous Profile Method (IPM) consists in inducing transient flow in a long cylindrical sample of soil and then measuring the resulting water content and/or pore water pressure profiles at various time intervals [3]. The unsaturated hydraulic conductivity (ku) is then computed using Darcy’s law.
 The direct evaporation technique allows the measurement of the suction profile in a soil column submitted to drying [4] using filter papers whose water retention curve is known. This method is quite reliable but requires long equilibrium time. Thus, the tests need several weeks and do not give accurate results at the early stages of drying, as the soil state is close to saturation. The analysis of the results when the soil retention capacity is low is therefore complicated, especially when the flow is coupled with temperature variations.
 In this study, this classical method was compared to a faster alternate method using nuclear magnetic resonance imaging (MRI) that allows for non-intrusive, continuous and small-scale monitoring of the effect of thermo-hydraulic solicitations on water transfer within the sample. The use of MRI for monitoring the drying/wetting front progression appeared in 1970 [5]. Simpson et al. [6] presented the successive studies that have made it possible to develop a method for monitoring the movement of water within a sample. These measurements can be 1D, 2D and 3D.
 The tests were performed on a sandy lean clay sampled in the Paris region in France. The soil was dried, pulverized, and sieved through a 2 mm sieve before experiments. The compaction state was selected to optimize the heat storage capacity [4] with a water content of 16.3% and a dry density of 1.79 Mg.m-3. Ten cylindrical samples of 70 mm in diameter and 20 mm in height were compacted and superimposed with introducing filter paper disks between them. The regular weighting of each sample and each filter paper during three months allowed the derivation of the ku curve by the IPM method.
 For the MRI method, 9 samples of 36 mm in diameter and 10 mm in height were compacted at the initial state then brought to different degrees of saturation. The measurement of the water proton relaxation time using a Bruker Biospec 24/40 superconducting magnet (100 MHz), allowed the definition of a calibration curve which connects MRI signal to the water content of the samples (Figure 1b). A Single Point Imaging pulse sequence [7] was used to obtain the signal intensity (encoding time 75 µs < t < 200 µs). In an image acquired with the SPI method, the intensity of each voxel (S) is :
 (1) Whereis the magnetization in a pixel and is the transverse relaxation time.
 The calibration curve is shown in Figure 1b. Then, a larger sample of 30mm in height was compacted and exposed to an air flow at 20°C and 30% relative humidity through using a remote humid air generation system. 27 measurements points were monitored with an interval of 1.1 mm along the sample. Four examples of the recorded profiles are shown in Figure 1c. The evolution of the water content inside the sample is then calculated using the calibration curve to interpret the water migration in the samples submitted to humidity- and temperature-controlled air (Figure 1a). The pre-established retention curve of the soil will be used to calculate its matric suction. At each depth, the flow velocity and the hydraulic gradient will be calculated from the water content profiles and suction profiles respectively in order to determine the unsaturated hydraulic conductivity. 
 These experimental developments allow the non-intrusive and continuous quantification of water movement in unsaturated soils during the application of coupled thermo-hydraulic solicitations. The understanding of these fundamental parameters is a key step for studying thermo-hydromechanical behavior of compacted soils considered for heat storage. The results provide insight into the feasibility of these structures in terms of their long-term energy efficiency and stability.

Fast-nondestructive measurement of axial slice water content and water distribution with NMR SFG-MSCPMG sequence

Measuring hydraulic conductivity by instantaneous profile method needs to detect the pore water content of soil at different positions, but most of the detecting methods will disturb the soil sample. In the study, the axial slice scanning of soil samples was carried out by using static filed gradient multi-slice Carr-Purcell-Meiboom-Gill (SFG-MSCPMG) sequence of nuclear magnetic resonance (NMR) technology, which can nondestructively determine water content and distribution at different positions of soil column. In this experiment, three clays were used to illustrate the relationship between NMR test results and oven drying results of water content. The results show that there is a good linear relationship between the NMR signal and water content. Combining mercury intrusion porosimetry (MIP) data, the transverse surface relaxivity parameters (ρ2) of clays are obtained. With ρ2 = 41.90 μm/s the T2 distribution curve of pore water in the ordinary clay can be converted into the pore water distribution curve, which is in good agreement with that obtained with MIP. Nevertheless, it is found that the T2 distribution curve of pore water in expansive clay obtained with NMR technique is more suitable for analyzing the average pore water distribution because of the fast exchange of pore water between the interlayers, intra-aggregates and inter-aggregates in expansive clay.

Temperature effects on the hydraulic properties of unsaturated rooted soils

Soil temperature of vegetated landfill earthen covers varies with time during their service, due to heat released by the degradation of municipal solid waste. In this study, an experimental campaign to capture soil water-retention curve (SWRC) and hydraulic conductivity function (HCF) of unsaturated rooted soils was conducted at different temperatures (25, 45, and 60 °C). Simplified evaporation tests were conducted by subjecting soil specimens to a prolonged drying period at maintained temperature. Based on the responses of matric suction and water content, SWRC and HCF were determined by the instantaneous profile method. It was found that increasing temperature reduced water-retention capacity, due to root shrinkage, thermal expansion of liquid phase, and reduction in forces of capillarity and adsorption. Soil hydraulic conductivity was enhanced by the increase in soil temperature due to reduction of water viscosity and potential preferential flow at root channels induced by root shrinkage. Temperature effects on SWRC and HCF of rooted soils are suction-dependent. A new nonisothermal SWRC model was developed to capture the dual effects of roots and temperature. By using the same set of calibrated parameters, the model demonstrates its ability to predict SWRCs reasonably well within the range of temperature investigated.

Numerical Investigation of Hydraulic Conductivity Variation on Highway Slopes Made of Expansive Yazoo Clay

Expansive soils cover more than 25% of the total area of the United States and are subjected to shrink-swell behavior with moisture variation. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of the expansive soil is subjected to change because of the development of shrinkage cracks which affect the vertical hydraulic conductivity, whereas the horizontal hydraulic conductivity remains negligibly constant. This affects the percolation behavior of the subgrade soil and, in turn, reduces the soil strength, as one of the major factors of slope failure. However, no study has been done on the change in the hydraulic properties of expansive soil with time and its effect on highway slopes. The current study intends to investigate the hydraulic conductivity and matric suction variation at different wet-dry cycles on highway slopes. An instantaneous profile method to investigate the changes in hydraulic conductivity during 1N to 5N wet-dry cycles was utilized. The finite element method in Plaxis was conducted to evaluate the effect of different frequencies and duration of rainfall on water intrusion, and the corresponding change in the matric suction of the highway slope. The selected rainfall pattern is evaluated at different intensities and durations of rainfall based on 100-years return periods. The flow analysis showed that the suction dropped at the highway slope with the presence of rainfall.

Using splines in the application of the instantaneous profile method for the hydrodynamic characterization of a tropical agricultural Vertisol

An important aspect in the study and understanding of the physical phenomena involved in water movement in the soil-plant system is the need to carry out the hydrodynamic characterization (HC) of non-saturated field soils. Studies of this type have been widely developed in soils of temperate climates, but they are infrequent in the tropics, hence there is a need for further research in tropical Vertisols under field conditions. Hydrodynamic characterization consists of finding the functional relationship between soil hydraulic [...]

New simplified transient method for determining the coefficient of permeability of unsaturated soil

The instantaneous profile (IP) method is widely used for determining the coefficient of permeability of unsaturated soils. IP method requires the measurement or control (i.e., zero flux) of flux at any one end of a soil profile. Besides, there are requirements of variations in volumetric water contents (VWCs) and pore-water pressures (PWPs) at various points from the above-mentioned one end of the soil profile to a particular point in which the unsaturated coefficient of permeability is derived. The measurement or control of flux at one end of the soil profile requires high accuracy which causes difficulty while performing tests in the laboratory and field. To overcome the difficulty of the IP method, this study proposes a new simplified transient method for determining the coefficient of permeability of the unsaturated soil. Variations in volumetric water contents and corresponding pore-water pressures at three points are required in the new simplified transient method. The intellectual advantage of this method as compared to the IP method is that there is no need to measure or control the flux at one end of the soil profile. Therefore, this new method is more practical and is expected to be widely used in both laboratory tests and field tests. The validity of the new simplified transient method is verified through numerical simulations considering a one-dimensional seepage for four different types of soils including coarse-grained soil, sand, clay, and silty sand with gravel. The applicability of the new simplified transient method is demonstrated by comparing the unsaturated coefficients of permeability of soils computed by the new simplified transient method and the IP method. Good agreements in comparisons prove that the new simplified transient method is effective for determining the unsaturated coefficient of permeability of soil regardless of soil types and hydraulic functions features.

Investigating unsaturated hydraulic conductivity and water retention characteristics of compacted biochar-amended soils for potential application in bioengineered structures

This study investigates the influence of biochar amendment on the water retention and unsaturated hydraulic conductivity (Kunsat) of compacted soils focusing on its potential application in bioengineered structures. Physical properties, water retention characteristics and Kunsat of two different soils, such as silty sand and pure sand and amended with 5% and 10% (w/w) biochar made from mesquite were measured with the help of instantaneous profile method (IPM). The water retention capacity of the biochar-amended soil was characterised by plotting soil water retention curve (SWRC) and estimating the saturated volumetric water content (θs), residual water content (θr), shape parameter ‘n’ and plant available water content (PAWC). The results revealed that the amendment of biochar in the soils increased the θs (by 20–30%), θr (60–370%) and PAWC (7–60%), and decreased the n (by 5–18%) and Kunsat (one-two order). The microstructural observation showed that the hydrophilic surface functional groups and intra-pores in biochar contributed to the improved water retention, while the altered pore size distribution and porosity of the soils due to biochar amendment increased the tortuosity of the water flow path and hence reduced the Kunsat. Based on the findings, biochar-amended soil is proposed to be used in bioengineered structures that could promote the growth of vegetation and improve the performance.

Flow exchange and unsaturated permeability of cracked clay: experimental and modelling

Cohesive soil was often submitted to the shrinkage when it is dried. Constrained shrinkage and heterogeneity of the soil in terms of density or porosity and water content conduct to cracks of the fine soil. The unsaturated permeability as a function of suction changes significantly with cracks number and opening. The paper aims to study the flow exchange flow in the unsaturated cracked clay flow, by measurement of the unsaturated permeability using tensiometer and hygrometer sensors in cracked specimens under drying and controlled in an environmental chamber. The instantaneous profile method was used to interpret these tests. Cracks were characterised by Image Analysis which conducted to define some known quantitative parameters as the Cracks Intensity Factor (CIF). Aiming at reproducing the experimental results, the paper presents a model which leads to the prediction of the suction field and the flow rate exchange. This model integrates analytical equations of the unsaturated permeability and water retention property of the cracked soil and also the shrinkage behaviour. A good agreement between numerical and experimental results is highlighted in terms of flow exchange rate.

Investigation of the hydraulic conductivity of an unsaturated compacted bentonite/claystone mixture

A pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed as a candidate sealing material in a French deep geological repository for high-level radioactive waste. An in-depth understanding of the hydraulic property of this material is essential for accessing the over-pack corrosion and nuclide migration along the gallery. In this study, water flow in the compacted bentonite/claystone mixture was investigated by carrying out infiltration and water retention tests under constant-volume conditions alongside detailed microstructure observation. The evolution of total water hydraulic conductivity with suction was experimentally determined based on the instantaneous profile method. It was observed that the measured total hydraulic conductivity increased slowly at high suctions, then quickly at low suctions and finally approached the saturated value. A new method was developed based on the evolving pore structure, accounting for both vapour and liquid-water hydraulic conductivities. The total hydraulic conductivity predicted by the proposed method agreed well with the measured value, indicating the reliability of the predictive method. The vapour hydraulic conductivity was larger than the liquid-water one at a suction larger than 15·2 MPa, while liquid-water hydraulic conductivity became dominant at a suction lower than 15·2 MPa. In addition, based on the predicted vapour and liquid-water hydraulic conductivities, a numerical model was set up to simulate the water infiltration process. Comparison between the simulation and the measurement showed close agreement, validating the two-phase water flow mechanism in the bentonite/claystone mixture.

Unsaturated Hydraulic Conductivity Variation of Expansive Yazoo Clay with Wet-Dry Cycles

Expansive soils are subjected to shrink-swell behavior with moisture variation in Mississippi, United States. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of expansive soil is subjected to change because of the development of shrinkage cracks, which can be as large as as 1.2 cm wide and 1.5 m deep in the field, affecting the vertical hydraulic conductivity (Kv), whereas the horizontal hydraulic conductivity (Kh) remains fairly constant. The current study intends to investigate the hydraulic conductivity of highly expansive Yazoo clay at different wet-dry cycles. To observe the changes in the hydraulic conductivity with different wet-dry cycles in the laboratory, an instantaneous profile method to measure the permeability was utilized. Compacted Yazoo clay samples at different initial moisture content instrumented with moisture sensors at different depths to monitor changes in the moisture content were investigated. The samples were subjected to one, two, and three numbers (1N, 2N, and 3N) of wetting and drying cycles. For the drying process, testing chambers are kept in a controlled high-temperature booth of about 37°C simulating high summer temperatures in Mississippi. After the end of the wet-dry cycles, the test is performed to investigate the changes in the hydraulic conductivity of soil with the presence of shrinkage cracks. The hydraulic conductivity of highly plastic clay is very low at a fully compacted state and was observed to be (1.0×10-8 cm/s) at the 1N wetting phase. However, with an increment in the wet-dry cycles, the Kv of Yazoo clay increases (3.70×10-4 cm/s) after the sample is exposed to three wet-dry cycles. Even though the changes in the Kv of highly plastic clay define the infiltration behavior, which mostly controls the slope failure and pavement distress, consideration of the climatic loads is ignored in the design phase of the highway embankment and levees. By inclusion of the climatic variation, and evaluating the performance, the design life and resilience of the structures can be significantly increased

Combining two methods for the measurement of hydraulic conductivity over a wide suction range

The hydraulic conductivity of unsaturated soils can span several orders of magnitude. The measurement of hydraulic conductivity over a wide suction range is a challenging task for decades. In this study, numerical tests are carried out to check the assumption, error sources, and applicable conditions of the wetting front advancing method and instantaneous profile method. Based on the numerical test results, a digital wetting front advancing method is proposed to measure hydraulic conductivity of unsaturated soils in the relative high suction range and the traditional instantaneous profile method is found to be robust in measuring hydraulic conductivity in the low suction range, e.g. for soil with a degree of saturation above 0.9. Further, a combination of the digital wetting front advancing method and the traditional instantaneous profile method is implemented in the same soil column test and leads to an accurate soil hydraulic conductivity function over a wide suction range. The proposed method is applicable to various soil types and the test duration is only 1 ~ 5 days, thus makes the measurement of hydraulic conductivity a routine experiment for unsaturated soil mechanics.

Improvement of three common methods for determining hydraulic conductivity curve of unsaturated soil upon wetting

Boltzmann transform method, wetting front advancing method and instantaneous profile method are widely used in measuring hydraulic conductivity of unsaturated soils. However, all the three methods are based on relatively strong assumptions. In this study, a new Boltzmann variable was proposed based on the experimental observation that the wetting front advancing distance is not always proportional to the square of time. The improved Boltzmann transform method incorporating the new Boltzmann variable can significantly improve the accuracy of hydraulic conductivity determination. For the wetting front advancing method, a new formula for calculating the hydraulic gradient using central difference was proposed to reduce the fluctuation of determined hydraulic conductivity curve while using data recorded with small time intervals. A series of numerical tests including the horizontal absorption test, vertical ponding test and vertical capillary rise test were performed to verify the accuracy of hydraulic gradient and water flow rate calculated by wetting front advancing method. Results show that the calculated hydraulic gradients in low suction range are far from the real values except for the vertical ponding test and only the vertical ponding test can give reasonable hydraulic conductivity in both low and high suction ranges. For the instantaneous profile method applied in infiltration test with one end of soil column maintained at saturation, using the connected linear line with consideration of the location of wetting front to represent profiles of water content and suction can improve the accuracy significantly.

A New Method to Simultaneously Measure the Soil–Water Characteristic Curve and Hydraulic Conductivity Function Using Filter Paper

Abstract The soil–water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are widely used to study the hydraulic conductivity behavior of unsaturated soil. This article proposes a filter paper–based instantaneous profile method to simultaneously measure the SWCC and HCF of unsaturated soil. The method uses a small soil column that comprises several vertically stacked soil specimens sandwiched with filter papers. The water content and matric suction of the soil column are measured by weighing the soil specimens and filter papers, respectively, at regular time intervals. Therefore, the matric suction profiles and water content profiles can be obtained, and the SWCC and HCF can be calculated with the profile data. The method was applied to intact loess soil. The measured suction range is 0 to 2×105 kPa, and the measured hydraulic conductivity range is 10−5 to 10−13 m/s. Both SWCC and HCF curves display a bimodal characteristic and are consistent with previous mathematical models. This method is an inexpensive method to measure the SWCC and HCF in a large suction range.

Applicability of wetting front advancing method in the sand to silty clay soils

The unsaturated hydraulic conductivity function is one of the keys to solve unsaturated seepage issues, and it is difficult to be obtained via the laboratory test considering the time involved. In this study, a series of laboratory tests, include capillary rise test and downward infiltration test, were conducted to obtain the unsaturated hydraulic conductivity function of six kinds of soils varies from sand to silty clay by using the wetting front advancing method. The similarities and differences between instantaneous profile method and wetting front advancing method were discussed. The interpretation of data, demand details and the aspect that notice in test process, and application of the capillary rise test and downward infiltration test were summarized and analyzed. The demerits and its countermeasures for the method were given.

Relationship between multifractal characteristics of particle-size distribution and hydraulic conductivity of unsaturated soils

In order to study the relationship between multifractal characteristics of particle-size distribution (PSD) and unsaturated hydraulic conductivity, taking the Hunan clay as the research object, we analysed the particle composition of the whole particle size range by a laser particle size analyser, and discussed the multifractal characteristics of PSD by using the fractal theory. The soil–water characteristic curve (SWCC) and unsaturated hydraulic conductivity were measured by the pressure plate instrument and instantaneous profile method, and the unsaturated hydraulic conductivity was predicted by the fractal model. The results show that the fractal dimension D is not a fixed value for the Hunan clay with the whole particle size range, which exhibits obvious multifractal characteristics. The value of fractal dimension D is closely related to the investigated particle size range. The larger the particles in the particle size range, the larger the corresponding fractal dimension D. By comparing the measured and predicted values of the unsaturated hydraulic conductivity, it is found that the prediction results of fractal dimension D for unsaturated hydraulic conductivity with different particle size ranges are quite different, and that those results with larger particle size ranges are more reasonable.

Utilizing Splintex 2.0 for estimating the soil hydraulic conductivity curve measured with instantaneous profile method

Soil hydraulic conductivity curve (SHCC) is a key-physical-function in hydrological and environmental studies. Measuring SHCC is a difficult and onerous task and often unfeasible in large-scale monitoring. Therefore, pedotransfer functions (PTFs) have been an alternative way for estimating SHCC. In this study, the novel version of Splintex model (Splintex 2.0) is analyzed to estimate the unsaturated soil hydraulic conductivity (K) as a function of water content (θ). Splintex 2.0 estimates the function K(θ) assuming that soil pores can be represented by equivalent capillary tubes and that the water flow rate is a function of pore size distribution. Then, the estimates of K(θ) data are fitted to the SHCC described by the van Genuchten (1980); Mualem (1976) (VGM) equation. In this study, the goodness-of-fit of K(θ) estimation was evaluated with selected 198 measured SHCCs by the instantenous profile method. Each data set contains measured information of textural composition, solid and bulk densities, total porosity, and K(θ) data. Estimated and measured SHCCs were compared dividing the analyzed soil data in four textures and computing Pearson correlation coefficient (r), mean error (ME), and root mean square error (RMSE) measures. The estimation using Splintex 2.0 revealed a mean RMSE of log10[K(θ)] of 1.17, ranging from 0.77 to 1.22, pointing for an acceptable performance for PTFs purposes.

Investigation of the hydro-mechanical behaviour of GMZ bentonite pellet mixtures

Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (> 10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (< 10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion.

Unsaturated hydraulic properties of vegetated soil under single and mixed planting conditions

Effects of plant roots on changes of soil hydraulic properties, including soil water retention curves (SWRC) and soil hydraulic conductivity functions (SHCF), are not well understood, especially when soil is unsaturated and vegetated with multiple plant species. The aim of this note is to quantify the root effects on both SWRC and SHCF of silty sand using the instantaneous profile method. Four types of vegetated soil, namely bare, grass-only, tree-only and mixed tree–grass silty sand, were subjected to a controlled drying–wetting cycle in a plant room. Plant roots affect the air-entry value, saturated hydraulic conductivity and reduction rate of unsaturated hydraulic conductivity (with respect to suction) most significantly, but the roots do not affect the reduction rate of volumetric water content much. When planted with single species (grass or tree), the air-entry value of silty sand increased, while the saturated hydraulic conductivity and reduction rate of unsaturated hydraulic conductivity with suction decreased. However, under the mixed planting conditions, opposite results are found.

A Fractal Approach for Predicting Unsaturated Hydraulic Conductivity of Deformable Clay

The relative hydraulic conductivity is one of the key parameters for unsaturated soils in numerous fields of geotechnical engineering. The quantitative description of its variation law is of significant theoretical and technical values. Parameters in a classical hydraulic conductivity model are generally complex; it is difficult to apply these parameters to predict and estimate the relative hydraulic conductivity under deformation condition. Based on the fractal theory, a simple method is presented in this study for predicting the relative hydraulic conductivity under deformation condition. From the experimental soil-water characteristic curve at a reference state, the fractal dimension and air-entry value are determined at a reference state. By using the prediction model of air-entry value, the air-entry values at the deformed state are then determined. With the two parameters determined, the relative hydraulic conductivity at the deformed state is predicted using the fractal model of relative hydraulic conductivity. The unsaturated hydraulic conductivity of deformable Hunan clay is measured by the instantaneous profile method. Values of relative hydraulic conductivity predicted by the fractal model are compared with those obtained from experimental measurements, which proves the rationality of the proposed prediction method.