IN SITU GROUND FREEZING AND SAMPLING OF A PLEISTOCENE SAND DEPOSIT IN THE SOUTH CAROLINA COASTAL PLAIN

The procedures used to freeze and sample a Pleistocene sand deposit at the Coastal Research and Education Center near Charleston, South Carolina to preserve and study the effects of diagenesis are presented in this thesis. An initial feasibility study was conducted to target a layer of clean sand at the CREC site with little to no frost heave potential. To freeze the sand deposit, a ground freezing system with a central freezing pipe was installed to target a column of sand 1-m in radius and 2.3-m long. Liquid nitrogen was continuously supplied to the large steel freezing pipe, which was fabricated to isolate and radially freeze between depths of 1.8 m and 3.8 m below the ground surface, for 270 hours. Frozen sand cores taken from five locations 0.65 m to 0.7 m away from the central freeze pipe indicate the ground around the freeze pipe was frozen between depths of 1.8 m and 3.8 m below the ground surface at all but one location. A total length of core equal to 8 m with no indication of frost heave was retrieved from the site. Results of the ground freezing system including ground temperature measurements, growth of the frozen zone, and the amount of liquid nitrogen consumed are presented and compared with predicted values. Temperatures recorded during ground freezing indicate that the rate of freezing at CREC was influenced by the direction of groundwater flow, flow rate of liquid nitrogen, and the location and type of liquid nitrogen inlet. The frozen zone estimated with temperature measurements was shown to be tapered with the largest growth at the same elevation as the liquid nitrogen inlet. The frozen zone also appeared to extend in the direction of groundwater flow and contract in the upstream direction. To reduce the time required to freeze the soil surrounding the freeze pipe, the flow rate of liquid nitrogen was increased. While temperatures decreased as predicted when the liquid nitrogen flow rate was high, the volume of liquid nitrogen consumed was much higher than predicted. Frozen samples obtained from the CREC site were transported to Clemson University and the University of South Carolina following ground freezing. The samples will be used in high quality static and cyclic triaxial tests

Some Aspects of Liquefaction Assessment of Duncan Dam

A comprehensive program of field, laboratory and analytical investigations was carried out to assess the potential for liquefaction of the foundation soils and seismic stability of Duncan Dam. Duncan Oam is located on Duncan River in southeastern British Columbia, Canada. The 39 m high zoned earthfill dam is founded on a thick sequence of sands, silts and gravels. The liquefaction studies were carried out in two phases between 1988 and 1992 to characterize in detail the engineering properties of the foundation soils; and to assess its potential for triggering liquefaction, and the post liquefaction stability and deformation of the dam using parameters based on two approaches; one a site specific laboratory based direct method (Lab.method) and the other an indirect method (Seed\u27s method) which is based on field penetration data and field experience during past earthquakes. This paper describes some advanced aspects of the field and laboratory investigations including laboratory testing of undisturbed soil samples obtained after freezing the ground insitu. The influence of confining stress (K0) and initial static shear stress (K0) on liquefaction were investigated and site specific correlations for K0 and K. are presented. The laboratory investigations indicate that the residual strengths of the liquefied sand is a function of initial consolidation stress

General Report Session 3: Deformation and Liquefaction of Sands, Silt, Gravels and Clays

It has been almost 27 years since the damaging earthquakes of 1964 which occurred in Niigata, Japan and in Alaska, USA, focused the geotechnical engineers\u27 attention to liquefaction as a major problem in earthquake engineering. Considerable research and studies have been conducted on the subject of earthquake induced liquefaction since that time and these have included field observations, laboratory experiments and model tests, and theoretical studies. Progress in understanding the liquefaction phenomenon, in the assessment of liquefaction potential, and in the solutions to mitigate the liquefaction hazard has been made, yet the problem remains controversial in many respects, as reflected by the many stimulating papers presented in this session. The word liquefaction has been associated with many phenomena observed in the field during and after earthquakes such as sand boils, flow slides, lateral spreads, loss of bearing capacity and porewater pressure rise. In laboratory tests, liquefaction has been defined in several ways relating to pore pressure buildup under undrained cyclic straining or loading, or the development of a specified amount of shear strain in a fixed number of cycles of loading. Laboratory studies have also shown that the liquefaction phenomenon can be divided into three different behaviors, namely, true liquefaction, limited liquefaction and cyclic mobility. In theoretical studies, liquefaction occurs when the seismic-induced cyclic shear stress exceeds the cyclic shear resistance, or when the seismic porewater pressure increases to equal the effective stress. To compare the results from different papers, one must bear in mind the different definitions used by the various authors. Liquefaction-caused failure is really the result of excessive permanent deformation, e.g. tilting, settlement or heave of structures, excessive slumping or distortion, and sliding of slopes. Liquefaction-induced ground deformation is receiving more attention in the last decade. Soil failure due to liquefaction was the most dominant cause of damage in the recent M 7. 7 Luzon earthquake of July 16, 1990 in the Philippines. Remedial measures or ground improvement techniques to reduce the liquefaction hazards are becoming more common in recent years, not only for seismic rehabilitation of existing sites but also for newly developed sites. Refinements in equipment and techniques of existing methods are being developed. As well, new methods of ground improvements are being introduced. The M 7.1 Lorna Prieta earthquake of October 17, 1989 showed convincingly that liquefaction hazard can be avoided or effectively mitigated by soil densification prior to earthquake

Modeling the Static and Dynamic Properties of Uncemented, Natural Sands

Research to quantify the the influence of aging processes (or diagenesis) on the static peak shear strength, the dilatancy, and the small strain dynamic stiffness of uncemented predominatly quartz sands is presented in this dissertation. New equations are proposed to model the dilatancy and the static shear strength due to diagenesis in natural sands as functions of either age or measured to estimated velocity ratio (MEVR). New predictive relationships between small strain dynamic stiffness and age are also recommended based on laboratory and field test results in natural sands. A laboratory investigation was performed to quantify the influence of age (or diagenesis) on the peak shear strength and the dilatancy of an uncemented Pleistocene age sand deposit at the Coastal Research and Education Center (CREC) near Charleston, South Carolina. Drained triaxial compression tests were performed on high quality intact specimens retrieved using the in situ freezing and frozen core sampling method, and on remolded specimens prepared to match the densities of the intact specimens. The stress-strain behavior of intact specimens was accompanied by dilation and a maximum or peak shear value, whereas remolded specimens generally contracted throughout shearing. The peak friction angle of intact specimens was found to be 3.0-8.6° higher than the peak friction angle of remolded specimens. A diagenesis-dilatancy term was added to the dilatancy index equation proposed by Bolton (1986) to account for the difference between intact and remolded peak friction angle. The resulting equation suggests that dilatancy caused by diagenesis and by density are both suppressed with increasing confining pressure, which has important implications for the design strength of natural deposits under heavy surcharge loads. A profile of in situ peak friction angle with depth is established from the test results and compared with values estimated from empirical relationships. The diagenesis-dilatancy term was generalized as a function of age based on a dataset of triaxial compression test results for ten different uncemented, predominantly quartz sands. Stong evidence was shown that dilatancy due to diagenesis increases with age, and that a model including age and confining pressure terms significantly improved predictions over a model with no age term. Therefore an age-dilatancy model was proposed. It was also shown that other properties such as density have little influence on dilatancy due to age. Because age of natural deposits is often difficult to accurately determine, a MEVR-dilatancy model was also proposed based on the framework of the age-dilatancy model. The age-dilatancy and MEVR-dilatancy equations were recommened to estimate intact peak friction angle from remolded peak friction angle or for predicting loss of strength during a disturbance or under large surcharges provided reliable in situ peak fricting angle estimates are available. General models for estimating peak strength are implied by the age dilatancy and MEVR dilatancy equations and can be used once the model is validated with the data presented in this study and the data compiled by Bolton (1986). Relationships for predicting the change in small strain shear modulus max() G or shear wave velocity () SV with time are reviewed. The max G -time relationship proposed by Afifi and Richart (1973) and the MEVR-time relationship proposed by Andrus et al. iv (2009) are related using a term called velocity ratio VR, which is the ratio of SV at a given time relative to its value in a deposit of similar density at a selected reference age. VR datasets were established from laboratory tests conducted on remolded sands and from laboratory tests conducted on intact sands. The VR datasets were combined to propose a VR-time relationship intended for natural sands. The proposed VR-time relationship based on laboratory results was compared with the VR-time relationship based on in situ VS and penetration resistance measurements implied by MEVR. The laboratory based relationship suggested a 3% change in VR for each ten fold change in age, while the field test based relationship suggested a 8% change with each ten fold change in age. It is found that much of the difference in the slope of the laboratory and field based VR-time relationships can be explained by the difference in fines content of the VR laboratory cases and VR field cases, which provides strong evidence for an influence of fines content on diagenesis. Much closer agreement between the VR-time relationships of field and laboratory cases with clean sands only is observed. The results indicate that field and laboratory based VR-time relationships can be used as indices for degree of diagenesis, provided the influence of fines content is accounted for. The preliminary results of a numerical study to predict the response of a Pleistocene age natural sand deposit at the CREC site during an in situ liquefaction experiment involving one of the NEES@UTexas mobile field shakers are presented. A plasticity model intended for earthquake engineering applications, was used for the Pleistocene sand deposit. Calibration of the model required considerably adjusting one of three main model inputs, called the contraction rate parameter, using the procedure recommended by Boulanger and Ziotopoulou (2015) due to the relatively low density and high predicted cyclic strength of the CREC sand. The simulation predicted concentrations of cyclic shear strain, cyclic stress ratio, and excess pore pressure that were located near the corners of the mobile shaker base plate during loading, and tended to produce a biased accumulation of shear strain toward either side of the sensor area. Below the base plate and within the zone where liquefaction sensor were installed at CREC, the excess pores pressure ratio was predicted to reach a maximum value of 12% and 18% at respective depths of 2.7 m and 3.3 m in the Pleistocene deposit. The prediction of low excess pore pressure buildup agrees with the limited field observations that were available to the author at the writing of this dissertation

Mechanical Behavior of Non-Textbook Soils (Literature Review)

Traditionally, soil mechanics has focused on the behavior of two distinct types of geomaterials: clean sands and pure clays. Under the application of external loads, these two types of geomaterials represent and are conveniently associated with two extreme types of soil responses: drained and undrained behavior. The drained behavior of clean sands and the undrained behavior of pure clays have been covered extensively in most soil mechanics textbooks. In order to provide some insight into the mechanical response of additional materials, a literature review on the mechanical behavior of “non-textbook” soils (i.e. soils other than clean sands and pure clays) was carried out. The non-textbook soils investigated in this study were silty sands, clayey sands, silty clays, sandy clays, sandy silts, and cemented soils. The review focused on the following aspects of their mechanical behavior: (1) response to static loading; (2) response to cyclic loading; (3) compressibility, consolidation and creep behavior; (4) hydraulic conductivity; and (5) additional studies. Static response studies focused on both strength and stiffness properties of non-textbook soils. Investigations on the cyclic response emphasized the liquefaction resistance and, whenever available, the evolution of excess pore-pressure during cyclic loading. Whenever possible, an attempt was made to compile experimental protocols and theoretical frameworks used in the studies cited in the literature review. The literature review indicates that many aspects of the mechanical behavior of non-textbook soils have been studied in a somewhat superficial manner. A summary of the major observations regarding the mechanical behavior of non-textbook soils is presented. Topics meriting future research are identified

A new slurry-based method of preparation of specimens of sand containing fines

A new method of specimen reconstitution is presented that is appropriate for element testing of sands containing either plastic or nonplastic fines. The method allows reconstitution of homogeneous, saturated specimens of sands containing fines whose stress-strain response closely resembles the stress-strain response of natural soil deposits formed underwater (e.g., alluvial and offshore submarine deposits, hydraulic fills, and tailings dams). A procedure is described to evaluate the maximum void ratio (emax) of sands containing fines under conditions that more appropriately represent soil deposition at its loosest state in aquatic environments. For soils deposited in water, the data obtained with the procedure proposed in this paper suggest that ASTM D 4254 overestimates the emax of sands containing plastic fines and underestimates the emax of sands containing nonplastic fines. Copyright © 2008 by ASTM International