Unsaturated Soil Profile Research Articles

Integrating downhole seismic testing into dynamic probing light (DPL): first results

Dynamic probing light (DPL) is available among a wide range of dynamic penetrometers. This equipment can be used in locations where conventional sounding equipment may have limited access. Here, the shear wave velocity (Vs) determination by the downhole seismic technique is incorporated to the DPL to develop a hybrid test, the seismic DPL test, for the preliminary characterization of tropical soils. The corresponding equipment, test procedure and data interpretation of the seismic DPL (S-DPL) test are presented and discussed. S-DPL test campaigns were carried out at two experimental research sites where crosshole seismic tests were conducted to provide reference Vs profiles. The Vs profiles determined with the S-DPL test are in accordance with those determined with the crosshole test for both sites. The proposed hybrid test (S-DPL) has the potential to serve applications in preliminary site characterization, particularly at sites including unsaturated tropical soil profiles.

Geotechnical site characterization by DMT and laboratory tests on an unsaturated tropical soil site for slope stability analysis

The slope stability is an important topic because it presents risks of socio-economic losses caused by eventual ruptures. It is necessary to identify the site profile, as well as obtaining soil strength parameters for the slope stability analysis. This paper presents and discusses the use of the Flat Dilatometer Test (DMT) in the geotechnical site characterization for slope stability analysis in an unsaturated tropical soil site. Six DMTs were performed to define the stratigraphical profile and estimate geotechnical parameters. Shear strength parameters were determined in the laboratory using saturated and unsaturated triaxial compression as well as soil water retention curves (SWRC) to support DMT data interpretation. A commercial software was used to perform the slope stability analysis a cut slope with 6.6 m height and a gradient around 55° to illustrate the application of DMT and triaxial test data. The DMT allowed the representative site profile to be identified, as well as estimating the design parameters that compared well to those interpreted from unsaturated triaxial test data for the in-situ soil suction. The DMT can be used as logging test in the preliminary characterization of studied site specially to define the stratigraphical profile, site variability, select the regions to collect disturbed and undisturbed soil samples and as the first attempt to estimate the geotechnical design parameters via correlations. It is important to emphasize that laboratory tests on undisturbed soil samples are essential in the slope stability analysis of unsaturated tropical soil profiles.

Liquefaction-induced flow-like landslides: the case of Valarties (Spain)

This paper examines a flowslide involving a glacial deposit of low-plasticity silty sand triggered by a karstic spring after a rainfall period. The work aims at explaining the triggering, propagation and kinematics of flow-like landslides in a unique framework. In particular, a material point method open-source code, able to solve coupled hydro-mechanical problems for saturated/unsaturated soils, was developed. Laboratory and field experiments revealed a liquefaction potential of the mobilised material. To simulate such potential, a recent liquefaction model (Ta-Ger), validated so far at a laboratory scale, was selected, extended to unsaturated conditions, implemented and calibrated. The analysis indicates a complex behaviour of the moving mass and explains the mechanisms developing sequentially in the flowslide. The impact of the upper unstable soil mass against the soil at lower elevations is a key phenomenon to generalise soil liquefaction in the entire slope. Patterns of soil velocity and displacements are far from being a uniform flow of liquefied material. The model developed is a powerful tool to interpret flowslides involving a saturated and unsaturated soil profile. The paper includes sensitivity analyses and discusses the discrepancies observed in the run-up of the flowslide climbing on the opposite slope of the valley.

Field and laboratory measurements of shear wave velocity in unsaturated soils

Shear wave velocity measurements in soil are important for assigning site soil profiles to seismic site classes and for calculating other dynamic soil properties. The seismic cone penetration test (SCPT) is commonly used to determine shear wave velocity profiles in the field. In the laboratory, bender elements provide an easy means to measure shear wave velocity of soil specimens from discrete depths. In this study, shear wave velocity measurements obtained from unsaturated soil profiles in the field and on field samples in the laboratory under similar stress conditions were analyzed and compared. Additionally, the influence of seasonal changes on the behavior of shear wave velocity was investigated. Comparisons of shear wave velocities from the field and laboratory were favorable for similar moisture and stress conditions. However, results showed that as the degree of saturation increases and suction decreases the shear wave velocity can decrease significantly.

Geomechanical parameters in the active zone of an unsaturated tropical soil site via laboratory tests

The seasonal variability of geotechnical parameters in the unsaturated zone is typically neglected in the design of geotechnical works. In most of the geotechnical projects the parameters are determined only for the saturated condition. Although it is known that this condition is the most critical to soil strength and deformability, this conservative approach may neglect a possible important contribution of the unsaturated condition, resulting in an increase in the cost of the geotechnical solution. This paper presents and discusses the site characterization of the active zone of an unsaturated sandy soil profile under different suction conditions. Laboratory tests with controlled suction (retention curves, triaxial compression with bender elements and oedometer tests) were carried out on undisturbed samples collected from 1.0 to 5.0 m depth. The results show that strength and deformability parameters are strongly affected by soil suction and are less influenced by confinement stress up to 5.0 m depth. All the investigated subsoil profile shows a collapsible behavior, more pronounced closer to the ground surface and under the effect of higher suction values. The findings highlight the importance of incorporating the suction influence in the site investigation, parameter determination, and geotechnical design for more economical, reliable, and environmentally sustainable solutions.

Irrigation quality and management determine salinization in Israeli olive orchards

Abstract. Olive (Olea europaea L.) orchard brackish water irrigation with incorrect irrigation management reduces soil fertility and degrades soil health through soil salinization. This study was conducted in the Beit She'an Valley, one of the main agricultural regions in Israel, in an olive orchard in which a combination of soil salinization and poor drainage conditions impedes plant development and causes severe economic damage. By combining various research methods, including soil salinity monitoring, field experiments, remote sensing (frequency domain electromagnetic – FDEM), and unsaturated soil profile saline water movement modeling, the salinization processes were quantified. Irrigation water conductance of 3.13 dS m−1 points to salinization within the tree upper root zone, whereas the modeling results suggest that salinization danger is greater with brackish treated wastewater rather than with lower-salinity brackish irrigation groundwater and that irrigation with potable water can help reduce salt accumulation and recover damaged plots.

Soil water and stable isotopes in the unsaturated zone profile – field observations and analysis

In this review, we provide research data emphasizing the role of groundwater table and hydrometeorological parameters variation on soil water fluctuations in the unsaturated soil profile. We focused on soil water content, air temperature, precipitation and groundwater table observations. The ThetaProbe Soil Water Sensors basing on changes in the apparent dielectric constant were used for soil volumetric water content measurements. The sensors were installed at the different depths of the unsaturated zone profile under natural atmospheric conditions. The observations lasted more than five years (14 November 2013 – 31 December 2018). Groundwater table data was obtained using Diver data loggers, which continuously recorded water pressure and temperature. For more detailed investigations of water and mass transport at the Maišiagala radioactive waste repository site water, stable isotopes as environmental tracers were used as well.

Factors Affecting Multiphase Benzene Breakthrough into Drainage Concrete Pipe in the Unsaturated Subsurface Profile

AbstractAnalyses presented herein explore transport aspects related to benzene breakthrough into gasketed subsurface concrete pipe embedded in an unsaturated soil profile. A series of three-dimensi...

Analysis of the bearing capacity of continuous flight auger piles in terms of their excavation energy and of rainfall data

Continuous flight auger piles (CFAs) are among the most common types of foundation executed in the tropical residual soil of Brasília, DF, Brazil. The bearing capacity of CFAs can be controlled according to the energy required to excavate each pile but is also influenced by seasonal conditions that affect the unsaturated soil profile. In the present article, a database of controlled execution of CFAs carried out at Brasília-DF was evaluated. The execution methodology enabled the full control of the drilling energy. Load tests were also performed and the pile bearing capacity was estimated by extrapolating the load-settlement curve using the van Der Veen method. As the site was excavated before the foundation was built, the morphology of the site was also considered in the analyses. Furthermore, by comparing the execution energies and climatological information, a relation between the moisture indexes and the execution energies was investigated. From these analyses, discussions regarding the relation between the bearing capacity of the piles tested and the rainfall regime they have been subjected to are presented. The changes observed in bearing capacity due to climatological effects may lead to economical savings and offer enhanced reliability in the design of CFAs.

Estimating the specific yield of the Pampeano aquifer, Argentina, using superconducting gravimeter data

Specific yield is a key parameter for the sustainable management of unconfined aquifers, since it relates water-table fluctuations to aquifer storage-changes and thus impacts water supply. However, estimating specific yield is still a challenge due to theoretical and methodological limitations. Water-storage changes in the aquifer and in the overlying unsaturated soil profile cause local changes in gravity that can be recorded by high-precision superconducting gravimeters. In this work, a novel methodology to estimate specific yield from superconducting gravimeter data is presented. The proposed methodology is based on a hydrogravimetric model that estimates the gravity response due to the loss and gain of water mass in the soil profile using rainfall, water-table and air-temperature data. The model is applied to a study site of the Pampeano aquifer in Argentina where a continuous 1-year record of superconducting gravimeter measurements is available. The specific yield value obtained using this methodology is 0.11 ± 0.039, which is validated by means of a long-term pumping test performed at the study site. The proposed method constitutes a promising alternative to the available tools for estimating specific yield, by taking advantage of superconducting gravity data.

A review on controlled vacuum lysimeter design for soil water sampling

Abstract Measuring water movement in unsaturated soil profile is inherently difficult. Equilibrium Tension Lysimeters have been introduced for collecting representative water samples (in terms of concentration and volume). In this method, suction level in sampler container is adjusted daily with soil matric pressure. Since soil–water tension changes over time, the vacuum level of sampler has to be adjusted accordingly. Automated Vacuum Lysimeters use electronic controllers as well as a set of vacuum sensors to keep the vacuum applied to porous plates in equilibrium with soil matric pressure. Automated Equilibrium Tension Lysimeter has no direct control on matric pressure right above the sampler. Therefore, accuracy of samples is questionable. Controlled Suction Period Lysimeter (CSPL) uses a tensiometer right above water sampler to address this issue. This method seems to be the most reliable method for collecting soil–water samples. However, it has some issues such as low energy efficiency and slow tensiometer response rate. In this review paper, different methods of measuring water movement in unsaturated soil profile are summarized and compared. A low resistance set up and a new controlling algorithm are suggested to significantly increase energy efficiency and accuracy of the system.

A method for predicting the influence of matric suction changes on CPT tip resistance

The Cone Penetration Test (CPT) is a valuable tool for continuous soil profiling and estimating soil properties. A CPT sounding will often pass through the active zone of an unsaturated soil profile, near the ground surface where moisture conditions and matric suction can vary considerably with depth and time. For many projects, the active zone is also significant to the support of shallow foundations and overlying embankments. However, the strength and stiffness of the unsaturated soils in this zone can be significantly affected by variations in the moisture content and matric suction. Likewise, the cone penetration tip resistance and sleeve friction will be influenced by the variations in moisture conditions and suction. Therefore, it is important to consider the soil moisture conditions when CPTs are conducted relative to the moisture conditions assumed for geotechnical design. This paper presents a method for predicting changes in tip resistance as result of changes in matric suction. The method extends the bearing capacity theory to predict changes in cone tip resistance due to changes in matric suction. CPT data collected at test sites, during wet and dry seasons and representing different soil types, are presented to demonstrate the viability of the proposed method.

Estimation of Conservative Contaminant Travel Time through Vadose Zone Based on Transient and Steady Flow Approaches

Estimation of contaminant travel time through the vadose zone is needed for assessing groundwater vulnerability to pollution, planning monitoring and remediation activities or predicting the effect of land use change or climate change on groundwater quality. The travel time can be obtained from numerical simulations of transient flow and transport in the unsaturated soil profile, which typically require a large amount of data and considerable computational effort. Alternatively, one can use simpler analytical methods based on the assumptions of steady water flow and purely advective transport. In this study, we compared travel times obtained with transient and steady-state approaches for several scenarios. Transient simulations were carried out using the HYDRUS-1D computer program for two types of homogeneous soil profiles (sand and clay loam), two types of land cover (bare soil and grass) and two values of dispersion constant. It was shown that the presence of root zone and the dispersion constant significantly affect the results. We also computed the travel times using six simplified methods proposed in the literature. None of these methods was in good agreement with transient simulations for all scenarios and the discrepancies were particularly large for the case of clay loam with grass cover.

Site Characterization of a Tropical Soil by In Situ Tests

This paper compiles experimental site characterization of an unsaturated tropical soil profile in an experimental research site in Bauru, Sao Paulo, Brazil. Several in situ campaigns comprised geophysical borehole tests (cross-hole, down-hole and up-hole together with the SPT), as well as mechanical tests (SPT, CPT and SDMT) have been performed. There is an unsaturated sandy soil at the studied site and, according to the MCT Classification System for tropical soils, the first 13 m depth is a colluvium with lateritic soil behavior (LA’) over the residual soil with non-lateritic behavior (NA’). The ratio between seismic ( G o ) and mechanical ( q n , N 60 , E D , K D and M DMT ) parameters was useful to identify the existence of microstructure and to confirm unusual soil behavior for this tropical soil site. CPT and SDMT were efficient for detailed stratigraphic logging, however, the estimative of geotechnical parameters cannot be solely been done base on just conventional correlations defined for sedimentary soil.

Updating the Coupling Algorithm between HYDRUS and MODFLOW in the HYDRUS Package for MODFLOW

Core Ideas The coupling algorithm between HYDRUS‐1D and MODFLOW is updated. Pressure head profiles are updated based on the groundwater table and bottom flux after each time step. This eliminates sudden variations in inflow and outflow fluxes with groundwater table changes. The HYDRUS‐based flow package for MODFLOW (the HPM or the HYDRUS package) is an existing unsaturated zone flow package for MODFLOW. In MODFLOW with the HPM, the groundwater modeling domain is discretized into regular grids that can be combined into multiple zones based on similarities in soil hydrology, topographical characteristics, and the depth to the groundwater. Each of these zones is assigned one unsaturated soil profile (the HPM profile). In this model, after every MODFLOW time step, the flux at the bottom of the HPM profile is given as an input recharge flux to MODFLOW. MODFLOW simulates groundwater flow, and the water table depth at the end of the MODFLOW time step is assigned as the bottom boundary condition in the HPM profile. The current coupling algorithm assumes that the groundwater table in the HPM profile remains constant throughout the entire MODFLOW time step. This results in unrealistic sudden inflow and/or outflow fluxes at the bottom of the HPM profile after every time step. The objective of this study was to develop a methodology to eliminate the error in the determination of the recharge flux at the bottom of the HPM profile. This was achieved by updating or modifying the pressure head profile in the HPM profile after every MODFLOW time step. The effectiveness and the applicability of the new coupling algorithm were evaluated using different case studies. The new coupling algorithm is effective in eliminating unrealistic sudden variations in the bottom flux in the HPM profiles.

An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones

ABSTRACTThe development of in situ vapour sampling methods to measure δ2H and δ18O in pore water of deep, unsaturated soil profiles, including mine tailings and waste rock, is required to improve our ability to track water migration through these deposits. To develop appropriate field sampling methods, a laboratory study was first undertaken to evaluate potential materials and sampling methods to collect and analyse vapour samples from unsaturated mine waste. Field methods were developed based on these findings and tested at two mine sites using either on-site analyses with a portable isotope laser spectrometer or sample collection and storage prior to laboratory analyses. The field sites included a series of deep (>50 m) multiport profiles within a coal waste rock dump and open wells installed in a sand tailings dyke at an oil sands mine. Laboratory results show that memory effects in sample bags and tubing require 3–5 pore volumes of vapour flushing prior to sample collection and sample storage times are limited to 24 h. Field sampling highlighted a number of challenges including the need to correct for sample humidity and in situ temperature. Best results were obtained when a portable laser spectrometer was used to measure vapour samples in situ.

Investigations of the unsaturated zone at two radioactive waste disposal sites in Lithuania

ABSTRACTThe unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium (3H) and stable isotope ratio (18O/16O and 2H/1H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater.

Estimating the effect of shallow groundwater on diurnal heat transport in a vadose zone

The influence of shallow groundwater on the diurnal heat transport of the soil profile was analyzed using a soil sensor automatic monitoring system that continuously measures temperature and water content of soil profiles to simulate heat transport based on the Philip and de Vries (PDV) model. Three experiments were conducted to measure soil properties at depths of 5 cm, 10 cm, 20 cm, and 30 cm when groundwater tables reached 10 cm, 30 cm, and 60 cm (Experiments I, II, and III). Results show that both the soil temperature near shallow groundwater and the soil water content were effectively simulated by the PDV model. The root mean square errors of the temperature at depths of 5 cm, 10 cm, and 20 cm were 1.018°C, 0.909°C, and 0.255°C, respectively. The total heat flux generated the convergent and divergent planes in space-time fields with valley values of–161.5W•m–2 at 7:30 and–234.6W•m–2 at 11:10 in Experiments II and III, respectively. The diurnal heat transport of the saturated soil occurred in five stages, while that of saturated-unsaturated and unsaturated soil profiles occurred in four stages because high moisture content led to high thermal conductivity, which hastened the heat transport.

Simplified Finite-Element Model for Site Response Analysis of Unsaturated Soil Profiles

AbstractA numerically stable and computationally efficient finite-element model for analyzing the dynamic response of unsaturated soil profiles in terms of total stresses is presented in this paper. The highly nonlinear, fully coupled governing differential equations are simplified by neglecting the relative accelerations and velocities of the pore fluids, and the simplified formulation is improved by incorporating an external viscous damping formulation for unsaturated soil. The surface spectral accelerations computed using the proposed model are qualitatively compared with that of DEEPSOIL and PLAXIS following a comparison of surface spectral accelerations computed using the underdamped and the damped simplified formulations. A detailed parametric study of the effect of viscous damping parameters and both elastoplastic and elastic constitutive models is also presented. A simplified soil–pile interaction study is presented to show the effect of soil–pile interaction on the computed responses. Analysis re...

Dye tracer visualization of flow patterns and pathways in glacial sandy till at a boreal forest hillslope

Dyes are valuable tracers in visualizing flow patterns and pathways in soil. We applied the dye Acid Blue 9 to unsaturated and saturated soil profiles at a boreal forest hillslope consisting of glacial sandy till, and determined the soil physical properties from soil samples. The objective was to characterize preferential flowpaths, investigate their porosity, extent and connectivity, and complement earlier findings on subsurface flow formation at the site. According to the results, preferential flowpaths were formed by roots, erosion related to soil water flow, freezing–thawing cycles, and soil fauna. The role of roots and stones in the formation of preferential flowpaths was emphasized. Porosity of preferential flowpaths was 5.1±1.8%, and they extended to a depth of about 55cm from the soil surface; the deepest roots reached the same depth. When the soil saturated, individual preferential flowpaths self-organized into continuous and well-connected lateral flow systems along the slope. At the slope shoulder, preferential flow network covering the entire soil profile, as well as preferential flowpaths on the underlying bedrock surface, were considered crucial for runoff generation. In the midslope area, runoff generation was characterized by lateral preferential flow and the transmissivity feedback phenomenon. At the slope foot, preferential flowpaths in soil below the eluvial horizon were the major runoff contributors. A full saturation of the soil profile at the slope is unlikely under natural conditions. However, lateral flow was found to occur also in unsaturated soil.