Zhong Han

State-of-the-Art: Prediction of Resilient Modulus of Unsaturated Subgrade Soils

AbstractIn this paper, equations that were proposed in the literature over the past four decades to estimate or predict the variation of the resilient modulus with respect to soil suction for pavement base-course materials and subgrade soils are summarized into three groups: (1) empirical relationships, (2) constitutive models incorporating the soil suction into applied shearing or confining stresses, and (3) constitutive models extending the independent stress state variable approach. Two equations selected from each of the groups (a total of six equations) are used to predict the resilient modulus–soil suction correlations for three compacted subgrade soils. Strengths and limitations of these widely used equations are discussed based on the comparisons between the measurements and predictions. The key objective of the state-of-the-art research summarized in this paper is for assisting practicing engineers to choose suitable equations for the rational prediction of the resilient modulus taking into accou...

Modeling Behavior of Friction Pile in Compacted Glacial Till

AbstractExperimental and numerical modeling studies related to the behavior of pile foundations are conventionally undertaken based on the assumption that the surrounding soils are in a state of saturated condition. Such an assumption may contribute to erroneous estimations of the stability and settlement behavior of pile foundations installed in unsaturated soils due to neglecting the influence of soil suction. In this paper, the behavior of a single friction pile loaded in drained and undrained conditions in a compacted glacial till is modeled using finite-element analyses (FEAs). The influence of the soil suction on (1) the shear strength and the modulus of elasticity of the soil and (2) the shear strength of the pile-soil interface derived from the experimental studies is discussed and considered in the FEA. There is reasonable agreement between the load-settlement behavior and the bearing capacity of the friction pile modeled using the FEA and the measured results from experimental studies. This stud...

Predicting the Variation of Resilient Modulus with respect to Suction Using the Soil-Water Characteristic Curve as a Tool

The resilient modulus (MR), which is a key parameter in the design of pavements, is significantly influenced by the seasonal moisture variations and the resultant suction fluctuations. Several relationships or models are available in the literature for predicting or estimating the MR taking account the influence of moisture content or suction. In this paper, two models from the literature are used for providing comparisons between the measured and predicted MR values of a fine-grained soil compacted at three different initial water contents. The strengths and limitations of the two selected models are discussed. In addition, a semi-empirical model is proposed for predicting the variation of the MR with respect to suction using the soil-water characteristic curve (SWCC) as a tool. The proposed model is promising and can be used in the reliable prediction of the variation of the MR with respect to suction.

Soil freezing process and different expressions for the soil-freezing characteristic curve

The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions ( i.e. , power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils ( i.e. , sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.

Normalizing Variation of Stiffness and Shear Strength of Compacted Fine-Grained Soils with Moisture Content

AbstractVariation of the resilient modulus (MR), elastic modulus (E), and unconfined compression strength (qu) with the gravimetric water content (w) and soil suction (s) for four compacted fine-gr...

A New Approach for Estimating the Influence of Soil Suction on the Resilient Modulus of Pavement Subgrade Soils

A new approach is proposed in this paper for estimating the resilient modulus (M sub R) of pavement subgrade soils taking account of the influence of the soil suction (ψ). This approach includes two steps: step (i) estimating the soil-water characteristic curve (SWCC) using one-point method, and step (ii) predicting the M sub R - ψ relationships using a simple model and the estimated SWCC from step (i). Estimations of the SWCC and the M sub R for two different subgrade soils using (i) the proposed approach, and (ii) the widely used mechanistic-empirical pavement design guide (MEPDG) approach are compared with the experimental measurements. The comparison results suggest that the proposed new approach provides reliable estimations of both the SWCC and the M sub R - ψ relationships. The proposed approach in this paper is relatively simple and is promising for use in the design of pavements.

Prediction of the Variation of the Resilient Modulus with Respect to the Soil Suction for Three Granular Materials Using Three Methods

Base-course layers of a pavement structure usually are composed of granular materials which are typically in an unsaturated condition during their service life. Pavements during the last decade have been encouraged to be designed based on the mechanistic methods which use the resilient modulus (M sub R) as a key parameter. The soil suction has a significant influence on the M sub R of granular materials. In this paper, various equations proposed for predicting the M sub R of unsaturated granular materials from the literature are summarized. Three equations proposed for predicting the M sub R of granular materials summarized in this paper are selected to provide comparisons between the measured and predicted M sub R values of three different granular materials. The strengths and limitations of the three equations are discussed. In addition, the relationship between the M sub R and the soil-water characteristic curve (SWCC) is highlighted with recommendation to use it as a tool in the prediction of the M sub R for granular materials.

Addressing Transportation Geotechnics Challenges Using Mechanics of Unsaturated Soils

Cost-effective and high-quality transportation systems are critical to the regional, national as well as international development. The design and maintenance of the pavements, which form a critical component of the transportation systems, should address the geotechnics challenges that arise from the influence of external environment, which include the seasonal drying–wetting and freeze–thaw cycles. Environmental factors influence on the pavements can contribute to their deterioration or even failure in certain scenarios. This paper presents recent advancements in the mechanics of unsaturated soils that can be used in the reliable mechanistic pavement design methods. Simple yet reliable approaches that have been developed for predicting the soil–water characteristic curve (SWCC) and the variation of the resilient modulus (MR) with moisture content and suction are introduced and integrated. The proposed integrated approaches provide reliable predictions of the SWCC and the MR using limited experimental data that can be determined from conventional geotechnical tests, and can be used in the rational pavement design practice.

Effect of montmorillonite content and sodium chloride solution on the residual swelling pressure of an expansive clay

Expansive clays may continue to swell even after obtaining fully saturated condition due to the continuing montmorillonite hydration process. Expansive clays in this case, if confined, will generate swelling pressure, which is termed as residual swelling pressure in this study. The residual swelling pressure poses significant impact on the long-term safety and stability of adjacent geotechnical infrastructure. Despite its significance, currently, there are very limited studies on the residual swelling pressure. In this paper, the influence of (1) the montmorillonite content and (2) sodium chloride (NaCl) concentration in the pore water on the residual swelling pressure of a compacted expansive clay was evaluated using constant-volume swelling tests. Scanning electron microscopy analyses were applied to investigate the influence of NaCl solution on the microstructure of the compacted expansive clay. Tests results showed that the residual swelling pressure increases with montmorillonite content and dry density of specimen and decreases with an increase in the NaCl concentration. The NaCl in the pore water used for compacting the clay influences the particle orientation and arrangement. High NaCl concentrated solution contributes to soil structures with higher integrity that exhibit lower residual swelling pressure. An equation is developed to interpret and predict the residual swelling pressure of expansive soils considering their montmorillonite content and dry density. The proposed equation is verified using experimental data determined in this study as well as data obtained from the literature.

Prediction of the Resilient Modulus of Unsaturated Base-Course Materials

Reliable design of pavement base-course is possible by taking account the variation of resilient modulus (MR) with respect to suction using mechanistic design methods. In this paper, a semi-empirical model is proposed to predict the MR-suction relationships for base-course materials using the soil-water characteristic curve (SWCC) as a tool. The proposed model is validated by providing comparisons with the experimental results of four base-course materials. The approach proposed in this study is simple and can be used in the rational design of pavement base-course extending the mechanics of unsaturated soils.