Scott M. Olson

A New Ring Shear Device to Measure the Large Displacement Shearing Behavior of Sands

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.

Shear Band Formation Observed in Ring Shear Tests on Sandy Soils

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 writers 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.

Geotechnical Aspects of Failures at Port-au-Prince Seaport during the 12 January 2010 Haiti Earthquake

Presented herein are the results of geotechnical investigations and subsequent laboratory and data analyses of the Port-au-Prince seaport following the Mw7.0 2010 Haiti earthquake. The earthquake caused catastrophic ground failures in calcareous-sand artificial fills at the seaport, including liquefaction, lateral spreads, differential settlements, and collapse of the pile-supported wharf and pier. The site characterization entailed geotechnical borings, hand-auger borings, standard penetration tests, and dynamic cone penetration tests. The laboratory tests included grain size and carbonate content tests. The observations and results presented herein add valuable field performance data for calcareous sands, which are relatively lacking in liquefaction case history databases, and the overall response of the artificial fills are consistent with predictions made using semi-empirical relations developed primarily from field data of silica sands.

Shear Wave Velocity- and Geology-Based Seismic Microzonation of Port-au-Prince, Haiti

A seismic site classification microzonation for the city of Port-au-Prince is presented herein. The microzonation is based on 35 shear wave velocity (VS) profiles collected throughout the city and a new geologic map of the region. The VS profiles were obtained using the multichannel analysis of surface waves (MASW) method, while the geologic map was developed from a combination of field mapping and geomorphic interpretation of a digital elevation model (DEM). Relationships between mean shear wave velocity over the upper 30 m of the subsurface (VS30) and surficial geologic unit have been developed, permitting code-based seismic site classification throughout the city. A site classification map for the National Earthquake Hazards Reduction Program/International Building Code (NEHRP/IBC) classification scheme is provided herein. Much of the city is founded on deposits that classify as either NEHRP Site Class C or D, based on VS30. Areas of the city requiring additional subsurface information for accurate site classification are noted.

Behavior of Concrete-Faced Rockfill Dams during Initial Impoundment

Centrifuge tests to investigate the behavior during initial reservoir filling of a concrete faced rockfill dam (CFRD) with face slab stiffnesses that vary by a factor of about two are described. The two centrifuge models exhibited similar deformations at the crest and along the face slab, with crest settlements averaging 0.19H (%) and maximum face slab deformations averaging 0.88H (%). The centrifuge test results suggest that the face slab stiffness had little effect on deformations, at least for the range of stiffnesses examined here. A parametric study of transition (supporting) zone stiffness was performed using a numerical model calibrated using the centrifuge results. The numerical results indicated that face slab deformation is more influenced by transition zone stiffness than face slab stiffness, supporting the centrifuge results. Deformation measurements for 25 in-service CFRDs (including six Korean CFRDs—one of which was used as the basis for the centrifuge model dam) are presented and compared w...

Documenting Liquefaction and Lateral Spreading Triggered by the 12 January 2010 Haiti Earthquake

The 12 January 2010 Haiti earthquake (Mw 7.0) caused extensive damage to the Port-au-Prince region, including severe liquefaction failures along the Gulf of Gonâve coastline, along rivers north of Port-au-Prince draining into the Gulf, and a liquefaction-induced structural/bearing capacity failure of a three-story concrete hotel along the southern coast of the Gulf. During two reconnaissance missions, the authors documented ground conditions and performance at eight sites that liquefied and two sites that did not liquefy. Geotechnical characterization included surface mapping, dynamic cone penetration tests, hand auger borings, and laboratory index tests. The authors estimated median peak ground accelerations (PGAs) of approximately 0.17g to 0.48g at these sites using the Next Generation Attenuation (NGA) relations summarized by Power et. al. (2008). These case histories are documented here so that they can be used to augment databases of level-ground/near level-ground liquefaction, lateral spreading, liquefaction flow failure, and liquefaction-induced bearing capacity failure.

DIFFERENTIAL MOVEMENT AT EMBANKMENT-BRIDGE STRUCTURE INTERFACE IN ILLINOIS

Settlement of roadway pavement surfaces near highway bridge abutments often leads to abrupt grade differences at the abutments. These grade differences subject vehicles to a bump, which may lead to driver discomfort and potentially unsafe driving conditions. Furthermore, differential movement requires costly and repeated maintenance work that usually impedes the flow of traffic. The sources of differential movement in Illinois can be divided into six major categories: (a) compression or erosion of materials at the approach embankment-abutment interface, (b) a broken approach slab, (c) compression of foundation soils, (d) compression or internal erosion of embankment soils, (e) poor construction grade control, and (f) areal distortion of foundation soils. An approach gradient equal to or greater than 1/100 to 1/125 appears to cause rider discomfort and therefore is proposed as a criterion for initiating remedial measures.

Damage Patterns in Port-au-Prince during the 2010 Haiti Earthquake

The 2010 Haiti earthquake represents one of the most devastating earthquakes in history. Damage to structures was widespread across the city of Port-au-Prince, but its intensity varied considerably from neighborhood to neighborhood. This paper integrates damage statistics with geologic data, shear wave velocity measurements, and topographic information to investigate the influence of these conditions on the damage patterns in the city. The results indicate that the most heavily damaged areas in downtown Port-au-Prince are underlain by Holocene alluvium with shear wave velocities that average about 350 m/s over the top 30 m. The remainder of Port-au-Prince is underlain mostly by older geologic units with higher shear wave velocities. Damage was also concentrated on hillsides around Port-au-Prince. These pockets of damage appear to have been caused by a combination of factors, including topographic amplification, soil amplification, and failure of weakly cemented, steep hillsides.

Yield strength ratios, critical strength ratios, and brittleness of sandy soils from laboratory tests

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 to 0.32 and from 0.20 to 0.35 in triaxial compression and ring shear, respectively. Critical strength ratios mobilized prior to particle damage ranged from 0.01 to 0.26 in triaxial compression and from 0.04 to 0.22 in ring shear. 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 from 0.02 to 0.12. In addition, specimen brittleness (before particle damage) increases with initial void ratio and state parameter and is affected by initial fabric and particle shape. However, particle damage and crushing considerably increases sand brittleness,...

Seismic Performance of Earth Structures during the February 2010 Maule, Chile, Earthquake: Dams, Levees, Tailings Dams, and Retaining Walls

The 27 February 2010 Maule, Chile, earthquake occurred during the driest time of the year, which implied that most of the soils in the slopes were not saturated and that the dams had extra freeboard. This may explain the small number of slope failures caused by the earthquake. However, two important earth dams suffered seismically induced permanent ground movements, but no catastrophic damage was reported because the reservoirs levels were low. Five medium-sized mine tailings dams failed due to liquefaction; one of them tragically caused four casualties. Retaining structures of all types performed well and no failures were observed.