Faculty of Engineering, School of Civil Engineering

Among devices commonly used to measure the shearing behavior of sands, only the ring shear device can shear a soil to virtually unlimited displacements without creating substantial nonuniformities in stress and strain distributions. However, some limitations have precluded its widespread use.A new ring shear device was constructed at the University of Illinois that has large specimen dimensions to reduce stress and strain
nonuniformities, has auxiliary load and torque cells to measure any wall friction that develops along the confining rings, and utilizes quad-rings along the confining rings to prevent soil extrusion. Sample ring shear tests on a dry fine-grained, silty sand specimen demonstrate that the new ring shear device operates properly in both constant volume and drained conditions, providing identical effective stress friction angles at large displacements when shear and effective normal stresses on the shear plane are considered. Parallel drained and undrained triaxial compression tests on saturated specimens illustrate that the new ring shear device provides reasonable values of effective stress friction angle and show that the triaxial test does not shear specimens to sufficient displacement to reach critical state shear strengths for this sand, which was reached at displacements ranging from about 1 to 10 m.

The critical state (or critical void ratio) line is the locus of void ratio-effective stress conditions achieved after shearing a soil to large displacement and after all net void ratio changes and effective stress changes are complete. The triaxial compression test is commonly used to define the critical state line of sandy soils. In this study, we present drained and undrained triaxial compression and ring shear tests that are used to define the critical state line of a silty sand sampled  from the Mississippi River near Cape Girardeau, Missouri, USA. All specimens were prepared by pluviating the dry sand through air. The results show that both drained and undrained (or constant volume) triaxial and ring shear tests reach critical state at similar shear displacements prior to the onset of particle damage in the ring shear tests. A unique critical state line can be defined for these states. At larger shear displacements only possible in the ring shear tests, considerable particle crushing happens and dominates the sand behavior and only after very large shear displacements (>
750 cm) particle crushing ceases to continue and a complete particle rearrangement is reached. At this state, the stresses and volume of the sand become constant which corresponds to the critical state of the crushed sand. A unique line can also be drawn for this state. These unique critical state lines indicate that they are not influenced by the drainage conditions and shearing modes.

Modeling groundwater flow is a vital process to estimate the patterns of flow, salinity, and temperature distributions and the suitable regions for obtaining water for drinking, agriculture, industry, and electrical power generation can be found. In this study ground water flow in Illinois Basin from Christian County to Livingston County is modeled using the Basin2 numerical code developed at the University of Illinois. Input parameters include the profile, time of deposition, and composition of the rock formation column as well as the diffusion coefficients of these formations. In the Illinois Basin, salinity is produced by water interacting with the sandstone and limestone aquifers and therefore contains different minerals. The surface topography significantly affects the groundwater flow in this region. Through these analyses the effects of temperate of the groundwater on the density and thus hydraulic potential of groundwater and also salinity are discussed. The computations show that the salinity of the groundwater decreases towards the Christian County and the acceptable locations for potable water during different seasons of the year are identified according to their salinity and hydraulic pressures.

In this paper, particle damage of three test sands with different mineralogical compositions is studied using stress-displacement response measured in ring shear tests, particle size distributions of the original sand prior to shear and from the shear band after shear, and by examining particle shape changes determined by Scanning Electron Microscope (SEM). Particle damage during shear produced a wider particle size distribution, and damage typically continued until the normal stress was quite small (about 28 kPa) in constant volume ring shear tests and the internal stresses were distributed among sufficient particle contacts such that damage practically ceased. The dominant damage mechanism (typically either particle abrasion and shearing off asperities or particle splitting) depended strongly on the soil response (i.e., contraction or dilation), particle hardness, and particle size distribution, but both mechanisms produced particles that were more angular and rougher than the original sand particles. The magnitude of particle damage observed in the ring shear tests was influenced by the consolidation normal stress, shear displacement, particle mineralogy, particle size distribution, drainage conditions, and soil fabric (in constant volume tests). Lastly, the influence of particle damage on engineering properties including hydraulic conductivity, liquefaction resistance, stress-strain response, friction angle, and critical state are briefly discussed.

The excess pore water pressure developed in the Upper San Fernando Dam during the 1971 San Fernando Earthquake has been evaluated in several studies. Almost all of these studies indicate large excess pore pressure ratios developed only in the upstream and downstream shells which are not consistent with the limited deformation of the dam and the piezometer responses during the earthquake. In this paper, the construction and field observations of the behavior of the Upper San Fernando Dam are reviewed and a simple approach involving Newmark’s (1965) and Makdisi-Seed’s (1978) permanent deformation and limit equilibrium slope stability analyses are used to estimate the excess pore water pressures developed in the core and downstream shell areas during the earthquake for comparison with field measurements. The major differences of this analysis with previous studies lies in the assumptions regarding the selection of the failure plane, liquefiable zones, and mobilized shear strengths. The results explain the field piezometric observations and the limited displacement of the dam.

Shear band formation is an important factor in understanding failures in soil. In this paper, shear localization and shear band formation and evolution are examined using ring shear tests performed on three sands prepared by air pluviation. A transparent outer confining ring was used to visualize formation and evolution of the entire shear band. By comparing the ring shear stress paths with visual observations made during shearing, the authors show that the specimen shears uniformly over its entire height prior to shear localization. Bifurcation under constant volume and drained conditions occurs as the soil fully mobilizes its effective friction angle, and subsequent shear displacements occur only within the shear band. Consistent with previous studies, the final thickness of the observed shear band ranged from 10 to 14 times the median particle diameter. Substantial particle damage occurred within the shear band after large displacements, particularly for dilative specimens, causing additional strain-softening in contractive specimens and a second phase transformation and considerable strain-softening in dilative specimens.

The friction angle of sands is the most important parameter used for analyzing the response of sands to loading. However, its variation with stress level, fabric, and particle damage has been debated. This study examines the yield and critical state friction angles of three sands using triaxial compression and ring shear tests. Only contractive responses were used to define the yield friction angles and the critical state friction angles from the triaxial tests. However, both contractive and dilative (through particle damage) specimens reached a critical state in the ring shear tests, and therefore critical state friction angles were defined from both dense and loose specimens. The yield friction angle was affected by the initial sand fabric, decreasing as the pre-shear void ratio increased. However, the critical state friction angle from the ring shear tests was independent of stress paths analysed in this paper, initial sand fabric, and decreased only slightly with stress level, becoming essentially constant at stresses larger than about 200 kPa. Its value depended primarily on particle mineralogy and shape (angularity). Particle damage induced in the ring shear tests increased the critical state friction angle by a few degrees by producing a wider range of particle sizes and more angular particles.

In this study we performed 26 undrained triaxial compression and 32 constant volume ring shear tests on two clean sands and one silty sand. We then used these results to evaluate the critical states, and shear strength ratios mobilized at yield and at critical state. We obtained yield strength ratios that ranged from 0.16 – 0.32 and from 0.20 – 0.35 in triaxial compression and ring shear, respectively. Critical strength ratios mobilized prior to particle damage ranged from 0.01 – 0.26 in triaxial compression and from 0.04 – 0.22 in ring shear. However, particle damage and shear displacement increased the slopes of the critical state lines during ring shear testing, and consequently the critical strength ratios incorporating particle damage decreased to 0.02 – 0.12. In addition, specimen brittleness (before particle damage) increases with initial void ratio and state parameter and is affected by initial fabric and sand particle shape. However, particle damage and crushing considerably increases sand brittleness, making it essentially independent of initial void ratio. A unique relation is found between sand brittleness and critical strength ratio independent of sand type, mode of shear, fabric, and particle damage that indicates an upper bound critical strength ratio of about 0.3 for mildly contractive sands.

Cone penetration testing (CPT) has become the industry standard for in situ testing of cohesionless soils, and in particular, field liquefaction evaluation. The empirical methods for the interpretation of CPT data are either based on field data or the observation of CPT measurements in laboratory samples. In this study, a miniature cone penetrometer (with a diameter of 6 mm) is developed for understanding the response of loose to medium-dense sands. A modified triaxial cell is used for sample preparation and containment of the sample during cone penetration. The miniature cone can measure cone tip resistance, sleeve friction, and excess pore water pressure developed at the cone tip. While cone tip resistance is measured by a separate load cell, sleeve friction is obtained by subtracting cone tip resistance from a combined measurement of tip resistance and sleeve frictional force. Due to the free-draining nature of the sand tested in this study, no excess pore water pressure is developed during cone penetration. The measured data from the miniature cone are verified by comparison with CPT resistances measured in several other calibration chamber experiments on similar sands. Compared to a large calibration chamber with a standard size cone, the miniature cone allows quicker and less expensive CPT experiments in a more uniform sample.

The 1971 San Fernando earthquake led to the failure and large displacement of the Lower San Fernando Dam (LSFD) that was constructed by the hydraulic filling method. As such, hydraulic filling has been recognised as producing liquefiable sand deposits, while in situ relative densities as large as 60% have been reported in the LSFD. On the other hand, laboratory element

Reactive Powder Concrete (RPC) is an ultra-high-strength, high ductility and low porosity cementitious material. RPC properties are improved by pressing fresh RPC samples, which can increase its specific weight as high as 3000 kg/m3. However, high specific weight may be a ...

Very few studies have investigated soil shear modulus and damping characteristics at very shallow depths (< 3 m). In this study, average shear stress and strain histories are determined from reduced-scale shaking table model experiments at small confining stresses (< 20 kPa). Shear modulus reduction of sands becomes more non-linear at reduced confining stress levels, whereas sand damping ratio increases