Characterization, Modeling, and Performance of Geomaterials: Selected Papers From the 2009 GeoHunan International Conference

Soil suction is one of the most important parameters describing the moisture stress condition of unsaturated soils, and its measurement is equally important for realistic applications of unsaturated soil mechanics. The thermocouple psychrometers, filter paper method and chilled-mirror device are three soil suction measurement techniques that have found their places in describing the behavior of unsaturated soils in geotechnical engineering practice. However, as it is inherent with all the suction measurement methods there are still difficulties and uncertainties associated with these soil suction measurement techniques. In this paper, the filter paper, chilled-mirror psychrometer, and thermocouple psychrometer methods are evaluated and compared based on some recent observations and test results. These methods are used to measure total suctions of some high plasticity clay soils under very strict temperature control conditions. From the test results, the capabilities and limitations of the three methods are analyzed.

A probabilistic analysis of the effects of stochastic soil compression index and hydraulic conductivity on one-dimensional finite strain consolidation is presented. Random field simulation and finite strain consolidation are combined to perform Monte Carlo simulations. Parametric study on the effect of the standard deviation of the stochastic soil properties on output statistics relating to total settlement and consolidation time is conducted.

More and more attention has been paid to account for the effects of hydraulic behavior including hydraulic hysteresis on the stress-strain behavior of unsaturated soils. Current trend is to have two elasto-plastic models for unsaturated soils, one is for the modeling of the mechanical behavior of the soil and the other is for the modeling of hydraulic behavior of the soil. However, few researchers have considered the consistency between these two models. In many existing constitutive models, main drying and wetting curves were assumed to be unique functions between degree of saturation and matric suction for the description of hydraulic hysteresis, in which the degree of saturation is a function of matric suction. In this paper, the Barcelona Basic Model (BBM) is selected to discuss problems associated with such an adoption.

Swelling characteristics of compacted cohesive soil were examined through laboratory tests from an absorbed energy perspective. A series of samples was prepared by a "compression procedure" in the laboratory, in which the energy or work absorbed by tested samples was derived from recorded forces and deformations. Swelling behavior of the compacted samples was found to correlate well with the absorbed energy of the samples. The testing results from this study also led to a correlation between swelling behavior and samples' basic properties (dry unit weight and moisture content), which will provide a quick approximation for swelling susceptibility in the field. The factors that significantly affect swelling characteristics of the compacted soil were also identified. Good correlations among swelling behavior, the absorbed energy, dry unit weights and moisture contents confirmed the viability of the absorbed energy approach in characterizing swelling aspects of compacted cohesive soils.

When the strain tensor, the scalar damage quantity and the Laplacian thereof serve as the state variables of Helmholtz free energy, the general expressions of elasticity-gradient damage constitutive equations are derived directly from the basic law of irreversible thermodynamics by constitutive functional expansion method at the initial state. When damage variable equals to zero, the expressions can be simplified to linear elastic constitutive equations, when the damage gradient vanishes, the expressions can be simplified to the classical damage constitutive equations based on the strain equivalence hypothesis.

It is essential to study the practicality of consolidation and simplified approach of unsaturated soils with high degree of saturation. The water and air in the pores can be regarded as a mixed fluid in unsaturated soils when degree of saturation is between 70% and 95%. Mass balance, mixed fluid continuity, modified water continuity equations are then established regarding the compressibility of the mixed fluid in the pores. The influence of permeability and initial degree of saturation of soils are analyzed with the new method. The conclusions are: there is a strong interaction between the pore-air and pore-water in the consolidation of unsaturated soils with low permeability; the degree of pore-air pressure influence on consolidation of unsaturated soils is related to initial degree of saturation of soils.

The purpose of this paper is to propose the geosynthetic soil reinforcing technique as a simple and cost-effective alternative of improving the bearing capacity of shallow foundations. It is also expected that the geosynthetic soil reinforcing technique presented herein can help prevent those buildings built on shallow foundations from excessive settlements. Over the last few decades, many pilot and full-scale tests have been conducted, and it has been confirmed that the geosynthetic soil reinforcing technique can improve the bearing capacity of shallow foundations. This paper summarizes the processes of the theoretical development, experimental work, and numerical simulation on the bearing capacities of shallow foundations built on soils reinforced utilizing the geosynthetic reinforcing technique.

Geosynthetic-reinforced pile-supported embankments have been used as an economic and rapid construction technique for earth structures, such as embankments and retaining walls over soft soil. They have limited total and differential settlements and increase load transfer from soft soil to piles thereby leaving less load to the soil. Two key mechanisms of this technique are: soil arching within the embankment fills when a differential settlement occurs to mobilize the fill shear strength and tension membrane effects of geosynthetic reinforcement when it deforms. This study focuses on understanding the complex load transfer mechanisms by performing a numerical study using the Discrete Element Method (DEM). The granular backfill material was modeled using cylindrical rods. The geogrid reinforcement was modeled using bonded particles. At the end of the simulation, the displacements of granular particles were plotted for the illustration of soil arching.

Laboratory large scale model tests for optimizing the geometrical conditions of geotextile in reinforced standard dry sand 161 (patterned in Iran) were carried out. Based on the results of the model tests, the number of reinforcement layers, critical depth of reinforcement and the dimensions of the geotextile layers for mobilizing the maximum bearing capacity were determined and the results were compared with the Plate Load Tests (ASTM-D1194). The total number of tests in this study was 45. The models dimensions were with 100 cm x 100 cm x 80 cm (length x width x depth) and the circular foundation had a diameter of 200 mm.

The dynamic response of Guanjiazhuang Bridge of Qinghuangdao-Shenyang passenger rail line was tested. The relations among dynamic stress and dynamic acceleration of road-bridge transition sections reinforced by geogrid, and the velocity of the train were studied, as well as the attenuation rule of the dynamic response versus the depth of the roadbed. Based on those test results, a dynamic model of the track-roadbed is built to numerically simulate the dynamic response of road-bridge transition sections. The simulation results are consistent with the obtained test results, which show that the road-bridge transition sections reinforced by the geogrid can effectively prevent the propagations of dynamic stress and dynamic acceleration in the roadbed, and reduce the dynamic load effects on the roadbed.

A centrifugal test of a geogrid reinforced embankment with lime-stabilized soil as backfill on soft clay was conducted to investigate the reinforcement mechanisms. A finite element model was developed to simulate the centrifugal test based on the test dimensions. Verifications of the numerical model were taken by comparing the numerical results with the measurements obtained from the centrifugal test, and it was found that both were in good agreement.

A granular geomaterial, known as sand-tire lightweight fill, was proposed by blending sand with disposed tire scrap in proportions. The geomaterial can be used as alternative backfill in many infrastructure works, where less overburdens and lateral loads are expected. The reuse of tire scraps may not only address growing environmental and economic concerns, but also help solve geotechnical problems associated with low soil shear strength. In this study, an experimental testing program was undertaken with the goal of evaluating the compression and shear behavior of the materials. Three tests were implemented, i.e., 1-D compression tests, direct shear tests and consolidated drained triaxial compression tests. A compression strain-load model was proposed to describe its compression behavior. Rebound-reload tests revealed that materials' plastic deformation was associated with the mixing ratios. The tire scrap content was found to influence the stress-strain and volumetric strain behavior of the mixtures. Mixtures underwent shear contraction during shearing processes, which is different from the shear dilation of compact sands. Effects of mixing ratios and stress conditions on shear deformation behaviors were also discussed.

To optimize utilization of the closed municipal solid waste (MSW) sites, there is a dire need to establish simple, reliable and cost effective testing methodologies. Characterization of MSW sites is difficult due to non availability of standard procedures and limited worldwide experience. The shear strength is probably the most important parameter for the design of any structure on the closed MSW sites. Direct Shear Test has been widely used for the evaluation of the shear strength of MSW. Because of the obvious limitations of lab testing of MSW samples, a Field Large Size Direct Shear Apparatus was designed. Numerous insitu direct shear tests were performed in a closed MSW sites with the designed apparatus and very encouraging results were obtained. While maintaining simplicity, the apparatus allows strict load and deformation control. This paper highlights the salient design features of the apparatus.

This research is based on three different views of the industry, academic and government. Our assessment criterion goals were five dimensions of "the utility aspect", "the economic aspect", "the adoption principle", "the working-method characteristic" and "the environmental condition". Using each representative detailed item from the experts' interviews and literature reviews, and utilizing Fuzzy Delphi Method ( FDM ) and Fuzzy Analytic Hierarchy Process ( FAHP ), we get the comprehensive performance with relative weighted index. Applying the Matrix Law of Value, we compare the comprehensive performance value of traditional method and ecological method which are applied to construct national roads. We find that the ecological method of building national roads is feasible and is better than the traditional method.

Based on discrete theory, this article tries to develop an optimization methodology to produce an optimum vertical highway profile for a pre-selected horizontal alignment. The aim of the program was to establish an initial vertical alignment according to discreet ground elevation of station. Considering the discreet characteristic of the ground elevation and the intersection point of grade line, a discrete model is presented. The automatic design problem is set to select the number, location and elevation of the intersection point of the grade line after considering several designing constraints. To solve the constrained nonlinear problem, an ant colony optimization algorithm is adopted to select the roadway grades that minimize the earthwork cost and satisfy the geometric specification. A numerical example is presented to illustrate the application of the program.

With the rapid development of highway construction in China, the importance of slope greening design is gradually increasing. This paper applied Analytic Hierarchy Process (AHP) into the design of slope greening and respective analyzed the weight of engineering effect, investment, ecologic function, aesthetics, visual safety for drivers and cultural connotation for a slope greening design. Through the analysis, this paper discussed the methods and principle for slope greening design using AHP. Finally, the paper obtained the result that the effectiveness and the reliability of engineering technology environments are the most key considered factors for slope greening design and also consider the act of protecting original ecological environment, hindering the noise and beautifying the environment for a slope greening design. The method and principle in this paper can provide theoretical method for slope greening design.

Early identification of voids under a roadway structure is critical on preventing major failures from occurring. In this study, a 400MHz Ground Coupled Penetrating Radar (GCPR) was utilized to characterize the subsurface conditions of two roadway pavements (US290 and 34^th Street). A huge (1.8m^*4.6m^*3.7 m=30.6 m³) void under US290's reinforced concrete pavement was successfully identified by GCPR. Video inspection indicated that a disjointed storm pipe had caused washout and void. Fortunately, the disjointed storm pipe was identified in time. Otherwise, the 30.6 m³ void would have continued to grow in size until the pavement collapsed, which may have caused human casualties and property loss. This study has successfully demonstrated that the GCPR is able to identify void locations. Despite leaking sand from a Mechanically Stabilized Earth (MSE) wall, no voids were detected by the GCPR surveys near the MSE wall on 34^th street. It is concluded that the erosion of the fill behind the MSE wall is in a very early stage, so that voids are not large enough to be detected by the GCPR. Therefore, it was recommended that regular inspections should be performed.

This paper addresses the needs for non-intrusively measuring 3-D internal soil deformation in geotechnical engineering. In this research transparent soil is used to measure internal soil deformation under a model footing. Transparent soil is made of either amorphous silica gel or powder with a pore fluid having the same refractive index to model either sand or clay. An optical system consisting of a laser light, a CCD camera, a frame grabber, and a computer was developed to optically slice a transparent soil model. A distinctive laser speckle pattern is generated by the interaction of the laser light and transparent soil. Digital image cross-correlation was used to calculate 2-D displacement fields between two speckle images captured consecutively during footing settlement. A 3-D displacement field was obtained in Matlab® by combining multiple slices of 2-D displacement fields. The results showed that the developed optical system and transparent soil are suitable for more advanced 3-D soil deformation measurements.

In the paper, for two cases of different ages and different depths, the speed of radar wave transmitted in the testing concrete lining is measured by using the ground penetrating radar (GPR), and corresponding data of permittivity of the concrete lining are therefore obtained. An abnormal phenomenon of the permittivity is observed which shows that the value of permittivity will increase linearly with the depth of the concrete lining. Combined with the characteristics of tunnel lining and taken the free water distribution into account, a new dielectric model of the concrete lining is put forward. Results show that this model can be used to explain the experimental results and provide correct reference for the GPR use in measuring the depth of the concrete lining with good accuracy.

In highway engineering, GPR is a nondestructive tool for measuring pavement layer thickness, moisture content of subgrade soils, and assessing other pavement conditions, such as moisture-related pavement damage. From the reflected GPR wave information, dielectric properties of the materials, which are highly dependent on soil or aggregate-water-air systems, can be estimated. An increase in dielectric constant may indicate an increase in water content of dielectric materials. However, the relationship between dielectric value and moisture content is complex and controlled by many factors. GPR studies, which consider both real and imaginary parts of dielectric value and its frequency-dependent behavior, have shown potentials for developing more robust model to predict moisture content. This paper presents an overview of GPR applications in estimating water content and assessing pavement condition. Further investigation of GPR is also discussed.

A non-nuclear, non-invasive instrument capable of measuring density and moisture content of soil using electromagnetic impedance spectroscopy (EIS) is currently being developed. During the development of the empirical soil model, it was found that the model was sensitive to the specific surface area of the material being measured. With the material's specific surface area being accounted for, in six test compactions a 119% increase in accuracy was seen by the soil density gauge's (SDG) wet density calculation when compared to the Nuclear Density Gauge's wet density calculation.

In this paper, results of a series of ultrasonic pulse velocity tests on compacted soil were presented and discussed. Ultrasonic pulse velocity tests provide compression and shear wave velocity information that can be used in calculating dynamic elastic moduli such as Young's modulus and shear modulus. From the test results, calculated Poisson's ratio shows a linear relation with the water content in compacted soil, which leads to a linear trend in both P and S wave velocity against water content. Furthermore, presenting plots in bulk density versus wave velocity gives a clearer trend than dry density versus wave velocity.

Seismic methods are useful tools to non-destructively assess the integrity of concrete. It has also been applied to characterize the behaviors of curing concrete to provide information for construction decision. This paper shows that freezing of concrete significantly affects the seismic properties of concrete. Attention needs to be paid when applying seismic method to concrete curing in cold weather. In the experimental program ultrasonic tests were conducted on curing concrete subjected to different freezing process. The results indicate while there exists linear correlation between small strain seismic wave velocity and concrete strength under normal curing conditions, such relationships do not hold if the concrete is subjected to freezing process. A correction accounting for the effects of ice on the bulk strength needs to be applied. This correction was found to have linear relationship with water content (or ice content if concrete is completely frozen). Procedures to correct the effects of freezing are proposed, which include the use of Time Domain Reflectometry to measure the water content. Fianally the strength of concrete in frozen status can be estimated. This information could be incorporated to determine the magnitude of Winter Load Increase in cold regions.

Time domain reflectometry (TDR) fails in soils with high electrical conductivities, because the attenuation of the signal eliminates the reflection from the end of the probe. This paper describes a new approach for determining dielectric constants in highly conductive soils using TDR measurements. It makes use of information contained in the reflection at the soil surface rather than the reflection at the end of the probe. A relationship between the reflection coefficients at the soil surface with the apparent dielectric constant of the soil was established theoretically. The apparent dielectric constant of the soil can be estimated from the surface reflection coefficient. Results indicate that the dielectric constant can be determined with reasonable accuracy by the proposed approach for soils with high electrical conductivities, where the conventional travel time analysis fails due to significant signal attenuation.

This paper discusses the comparison of the shear wave velocity results for the concrete, lime treated base and subgrade pavement layers obtained from two separate surface wave test methods at a concrete pavement site. The older Spectral Analysis of Surface Waves (SASW) and newer Multiple Impact of Surface Waves (MISW) test methods were performed at the same concrete pavement forensic investigation project for comparison purposes. Neither the SASW nor MISW test methods require the installation of boreholes to measure the shear wave velocity and layer thickness profiles of asphalt or concrete pavements, and the underlying base and subgrade layers, thus reducing the costs of the tests. The older SASW and newer MISW methods differ only slightly from one another in the equipment used, method of data collection, but involve significantly different data processing. This paper includes a comparison and discussion of the surface wave test results, as well as backgrounds of the MISW and SASW methods. The MISW method is able to provide much more accurate determinations of layer thicknesses (within 4–5 mm for the pavement surfaced layer) and layer thicknesses/moduli for the underlying less stiff base and subgrade layers than the SASW method which greatly overestimates moduli of less stiff base materials immediately below the stiffer asphalt or concrete pavement.

The Bangkok Area is underlain by 12 to 16 m deep soft compressible clay. Pavements on embankments 1.5 – 2.5 m high commonly undergo a total settlement of 500 – 1 000 mm in 10 years. This causes significant differential settlement problems between the bridge approach embankment and bridge structure founded on long piles with bases in the sand layers. Significant longitudinal or cross-sectional differential settlements of the roadway may also take place due to ground conditions. Stability and settlement are always associated problems on soft ground. Solutions that have been implemented in the past three decades include the use of preload embankments, light weight materials, concrete bearing units on precast piles, preloading with prefabricated vertical drains (PVD), and soil-cement columns. Case histories of investigation and analysis of the soil mechanics problems and design solutions by state-of-the-art methods are presented in this paper.

This paper shows for a loamy soil the benefits of lime treatment on the evolution of the geomechanical properties governing the slope stability and the resistance against erosion of embankments. The main results indicate that the effective internal friction angle (φ') is quite unchanged through time, while the effective cohesion (c') strongly increases. Furthermore, erosion tests using the LCPC erodimeter on slopes between 0 and 30 degrees, and for a curing time up to 112 days, have shown that the treated soil becomes insensitive to erosion after a few days. These results clearly establishe the benefits of lime treatment in safety and serviceability of embankments for highways and high speed trains and, consequently, have an important impact on the reduction of their life cycle costs.