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This study investigates the quasi-static bearing stress-settlement response of shallow foundations in monolithic tire derived aggregate (TDA) layers having a total thickness of 3 m using a large-scale container and loading system. Tests were performed on footings having a range of widths, embedment depths, shapes, and loading inclinations. In tests where tilting was restricted, a clear bearing capacity was not observed for settlements up to 1.2B, where B is the footing width, but in tests where tilting was permitted bearing capacity was observed between settlements of 0.2B to 0.7B. Surface settlements indicate a dragdown response of the TDA adjacent to the footing extending out to more than 3B from the footing center, while settlement plates beneath the footing indicate a zone of influence of induced settlements of 14% at a depth of 4B. While bearing capacity theories for frictional geomaterials provided a reasonable prediction of the bearing capacity of footings in TDA for most tests, the corresponding settlements may be excessive for engineering applications. Accordingly, a correlation was developed between the theoretical bearing capacity and bearing stress at a settlement of 0.1B. A test with sustained loading indicates slight creep settlements with some stress dependency with magnitudes consistent with past studies. [ABSTRACT FROM AUTHOR]

A promising energy storage option is to inject and store heat generated from renewable energy sources in geothermal borehole arrays to form soil-borehole thermal energy storage (SBTES) systems. Although it is widely recognized that the movement of water in liquid and vapor forms through unsaturated soils is closely coupled to heat transfer, these coupled processes have not been considered in modeling of SBTES systems located in the vadose zone. Instead, previous analyses have assumed that the soil is a purely conductive medium with constant hydraulic and thermal properties. Numerical modeling tools that are available to consider these coupled processes have not been applied to SBTES systems partly due to the scarcity of field or laboratory data needed for validation. The goal of this work is to test different conceptual and mathematical formulations that are used in heat and mass transfer theories and determine their importance in modeling SBTES systems. First, a non-isothermal numerical model that simulates coupled heat, water vapor and liquid water flux through soil and considers non-equilibrium liquid/gas phase change was adopted to simulate SBTES systems. Next, this model was used to investigate different coupled heat transfer and water flow using nonisothermal hydraulic and thermal constitutive models. Data collected from laboratory-scale tank tests involving heating of an unsaturated sand layer were used to validate the numerical simulations. Results demonstrate the need to include thermally induced water flow in modeling efforts as well as convective heat transfer, especially when modeling unsaturated flow systems. For the boundary conditions and soil types considered, convective heat flux arising from thermally induced water flow was greater than heat transfer due to conductive heat flux alone. Although this analysis needs to be applied to the geometry and site conditions for SBTES systems in the vadose zone, this observation indicates that thermally induced water flow can have significant effects on the efficiency of heat injection and extraction.

This paper presents an experimental study on the hydromechanical behavior of unsaturated sedimented soil to understand the impacts of suction on the apparent yield stress and gain insight into the differences in behavior from compacted soils. A large-strain oedometer was developed for use in a triaxial cell that permits initial sedimentation of soils from a slurry under backpressure, suction control using the axis translation technique, and mechanical loading to characterize the compression curve. A flow pump was used to control the pore water pressure at the base of the soil specimen and to track water flow during suction application and mechanical loading. After initial consolidation of saturated soil specimens from a slurry, the specimens were unloaded, different suction values were applied, and then the axial stress was increased to 11 MPa at a constant strain rate. An increase in apparent yield stress with suction was observed, and the compression curves for higher suctions diverged without reaching pressurized saturation in the applied stress range. When compared with compression curves for the same soil compacted dry of optimum presented in previous studies, the sedimented soil had a greater yield stress at saturated conditions but a similar increase in yield stress with suction. Sedimented soils also experienced smaller changes in void ratio with applied net stress and a higher air entry suction value compared to compacted soils, reflecting a more compact soil structure. Suction was found to have a greater impact on yield stress than suction stress for both sedimented and compacted soils. [ABSTRACT FROM AUTHOR]

This paper presents two-dimensional (2D) and three-dimensional (3D) numerical simulations of a half-scale geosynthetic reinforced soil (GRS) bridge abutment during construction and bridge load application. The backfill soil was characterized using a nonlinear elastoplastic model that incorporates a hyperbolic stress–strain relationship and the Mohr–Coulomb failure criterion. Geogrid reinforcements were characterized using linearly elastic elements with orthotropic behavior. Various interfaces were included to simulate the interaction between the abutment components. Results from the 2D and 3D simulations were compared with physical model test measurements from the longitudinal and transverse sections of a GRS bridge abutment. Facing displacements and bridge seat settlements for the 2D and 3D simulations agree well with measured values, with the 2D-simulated values larger than the 3D-simulated values due to boundary condition effects. Results from the 3D simulation are in reasonable agreement with measurements from the longitudinal and transverse sections. The 2D simulation can also reasonably capture the static response of GRS bridge abutments and is generally more conservative than the 3D simulation. [ABSTRACT FROM AUTHOR]

Unsaturated soils in engineered geostructures like embankments or retaining walls may experience seismic compression during earthquakes due to particle rearrangement associated with large-strain cyclic shearing. Although previous studies have investigated volume changes during drained cyclic shearing of unsaturated soils, undrained cyclic shearing presents a more complex situation. During undrained cyclic shearing, changes in total volume, matric suction, degree of saturation, effective stress, shear modulus, and damping ratio may occur that have complex coupling effects that affect seismic compression. To better understand these coupling effects, this study performed a series of undrained cyclic simple shear tests on unsaturated sand specimens. Contractile volumetric strain after 200 cycles in these tests was found to vary nonlinearly with degree of saturation. The largest volumetric contraction occurred at a degree of saturation of 0.4 and coincided with the largest decrease in mean effective stress. The sand specimens followed a wetting-path scanning curve during shearing, with small changes in matric suction. The decrease in mean effective stress during cyclic shearing for all specimens followed the same linear relation with the accumulation of volumetric strain. [ABSTRACT FROM AUTHOR]

Although tire-derived aggregate (TDA) has been used as an alternative backfill in geotechnical engineering applications, the interaction between TDA having large particle sizes (e.g. TDA with a maximum particle dimension of 300 mm) and reinforcing geosynthetics has not been studied. This paper presents results from pullout tests on uniaxial and biaxial geogrids embedded in Type B TDA using a new large-scale pullout device having internal areal dimensions that can accommodate TDA layers with a height up to 1470 mm. Normal stresses ranging from 10 to 60 kPa were applied to TDA layers using dead weights atop a rigid plate and the pullout force was applied via hydraulic actuators operated in displacement control to a bolted-epoxy sandwich-type grip mounted on slide bearings that permit pullout displacements of up to 810 mm. The maximum pullout force increased with normal stress, with a displacement at maximum pullout force ranging from 100 to 350 mm. Internal displacements measured using tell-tales indicate gradual mobilization with pullout force, and the TDA layers all contracted during geogrid pullout. Uniaxial and biaxial geogrids with square-shaped apertures showed higher pullout capacity than uniaxial geogrids with rectangular-shaped apertures, but they experienced combined tensile-pullout failure at higher normal stresses. [ABSTRACT FROM AUTHOR]

When tire derived aggregate (TDA) is used as a lightweight monolithic fill in civil engineering applications, such as embankments and retaining walls, the shearing behavior of TDA-interfaces with different materials should be carefully considered. This paper presents results from large-scale direct shear tests performed on interfaces between Type B TDA and layers of sand, aggregate, and clay for initial normal stress ranging from 19.0 to 76.7 kPa. To match field conditions, a separation nonwoven geotextile was used at the TDA-sand and TDA-clay interfaces, and a separation woven geotextile was used at the TDA-aggregate interface. Large shear displacements, typically between 200 and 350 mm, were required to fully mobilize the secant friction angle. Peak secant interface friction angles range from 26° to 32°, and peak strength envelopes are linear for the sand interface and nonlinear for the aggregate and clay interfaces. Failure envelopes for the TDA-soil interfaces are bounded above by the Type B TDA internal failure envelope and below by the Type B TDA-concrete interface failure envelope. A pair of replicate tests using woven and nonwoven geotextiles for the TDA-aggregate interface indicated that geotextile type had little effect on measured shear behavior as they only provide separation. [ABSTRACT FROM AUTHOR]

This study investigates the thermal soil-geosynthetic interaction mechanisms of reinforcing geotextiles confined in compacted silt that may be encountered when using mechanically-stabilized earth (MSE) walls as geothermal heat sinks. A thermo-mechanical geosynthetic pullout device was used that incorporates standard components for geosynthetic pullout or creep testing but also heating elements at the top and bottom of the soil box to apply boundary temperatures and dielectric sensors embedded in the soil layer to monitor distributions in temperature and volumetric water content. Two test series were performed: the first involves monotonic pullout of woven polypropylene geotextiles after reaching steady-state conditions under different boundary temperatures without a seating load, and the second involves monotonic pullout of woven polyethylene-terephthalate geotextiles after reaching steady-state conditions under different boundary temperatures with a seating pullout load. The results indicate that the pullout resistance of both geotextiles decreased with increasing temperature. Although heating led to drying of the unsaturated silt layers as expected, measurements from the second test series indicate accumulation of water at the silt-geotextile interface. An effective stress analysis considering thermal softening of soils indicates that the increase in effective saturation at the silt-geotextile interface was the cause of the decrease in pullout resistance with heating. [ABSTRACT FROM AUTHOR]

This study focuses on the load-deformation response of a heavily loaded rocking footing on geogrid-reinforced sand via centrifuge-model scale shake table tests. To mitigate issues observed with overturning failure and excessive settlement of shallow footings on unimproved ground, geogrid reinforcement can help control footing kinematics while maintaining the enhanced energy dissipation of a rocking footing. The scalemodel geogrid evaluated in this study was manufactured with 3D printing and placed at a depth equal to the footing width. Shake sequences induced controlled yielding, and the geogrid was observed to reduce settlement during rocking and preserved recentering under strong shaking.

The objective of this study is to compare two experimental approaches to characterize the ebullition pressure (or air-entry suction) of initially water-saturated organophilic clay blankets. The first is an indirect approach using the water-retention curve (WRC) and the second is a direct approach using ebullition experiments. The WRC along with the hydraulic conductivity of organophilic clay blankets in saturated and unsaturated conditions were measured using a flexible-wall permeameter with suction-saturation control. This device was also adapted to measure the ebullition pressure and the air permeability. The comparison of the experimental approaches was performed on organophilic clay blanket specimens in different initial conditions (unrinsed and rinsed to remove loose fines) under high and low effective confining stresses (20 and 5 kPa). The indirect estimates of air-entry suction from the WRC were similar to those obtained from the ebullition tests. This good agreement between the two approaches may add flexibility to the development of design specifications for capping systems. The hydraulic properties were found to be sensitive to rinsing and effective stress, with greater hydraulic conductivity and air permeability for the rinsed specimen due to the removal of fines, and greater air-entry suctions for specimens under higher effective stress. [ABSTRACT FROM AUTHOR]

Heat transfer in unsaturated soils occurs primarily due to conduction, convection of pore fluids in both liquid and vapor forms, and latent heat transfer. Due to the complexity involved in simulating this coupled problem, this paper investigates a simplified model for heat transfer in unsaturated soils using a conduction analysis with a nonisothermal thermal conductivity function. Specifically, a relationship between the apparent thermal conductivity and degree of saturation that indirectly incorporates the effects of heat transfer due to convection and water phase change through temperature effects was defined based on experimental observations, and the governing equation for conductive heat transfer was reconsidered to account for the variation in nonisothermal thermal conductivity with respect to space and time. An axisymmetric analysis for horizontal heat transfer in a soil layer from a line heat source was performed using the simplified heat transfer model, and results were compared with a conventional isothermal conduction analysis. Further, a comparison of simulated soil temperatures from the simplified heat transfer model with measured temperatures from an experimental study on heat transfer in unsaturated silt shows a good match, indicating that the simplified model may be used for preliminary analyses of problems involving monotonic heating. [ABSTRACT FROM AUTHOR]

The parametric approach to creating designs from a generalised model is discussed. The technique is extended to the manufacture of transfer port cores for two-stroke internal combustion engines. Bi-cubic patches representing each of the three-dimensional sides of the transfer port are constructed from a parametric model using the minimum amount of information. A postprocessor then creates a CNC program from the design data and enables the manufacture of cores for the casting of cylinder blocks containing the transfer ports. The complete process is illustrated by an example which takes a particular configuration through to final manufacture. [ABSTRACT FROM AUTHOR]