J. Antonio H. Carraro

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.

Shear Strength and Stiffness of Expansive Soil and Rubber (ESR) Mixtures in Undrained Axisymmetric Compression

The shear strength and stiffness of expansive soil and rubber (ESR) mixtures were evaluated systematically in this study in undrained axisymmetric compression. The materials tested included the Pierre shale residual soil from the Front Range of Colorado and granulated rubber with 6.7-mm nominal maximum particle size. The three mass-based rubber contents used were 0, 10 and 20%. All specimens subjected to element testing were consistently prepared at soil states defined for a single level of relative compaction equal to 95% and optimum water content, based on the standard Proctor compaction curves of each mixture. The effects of the rubber content and mean effective stress were systematically evaluated by performing isotropically consolidated undrained triaxial tests at mean effective stresses equal to 50, 100 and 200 kPa. Bender element tests were used to determine the small-strain stiffness of the Pierre shale residual soil and its ESR mixtures at mean effective stresses of 50, 100 and 200 kPa. The critical-state friction angle increased with increasing rubber content for specimens compacted to and tested at similar initial states. Conversely, the stiffness of the ESR mixtures decreased with increasing rubber content for all three levels of mean effective stress used in the tests. The drop in stiffness was more significant at low mean effective stresses.

Effects of compaction effort, inclusion stiffness, and rubber size on the shear strength and stiffness of expansive soil-rubber (ESR) mixtures

The effects of compaction effort, inclusion stiffness and rubber size on the shear strength and stiffness of expansive soil-rubber (ESR) mixtures was evaluated in this study in undrained axisymmetric compression. The materials tested included an expansive soil from Loveland, Colorado, two granulated rubber samples with 4.8- or 6.7-mm nominal maximum particle size and a 50/50 mix of broken auto glass and crushed bottle glass. The effect of compaction effort was investigated by preparing and testing identical ESR mixtures compacted to either 95 percent of the standard or modified Proctor maximum dry densities at optimum water content. The effect of granulated rubber size was investigated by preparing and testing specimens with either 4.8- or 6.7-mm granulated rubber. The effect of inclusion stiffness was investigated by replicating the gradation of the 6.7-mm granulated rubber with two types of glass and testing an expansive soil-glass (ESG) mixture compacted to 95 percent of the standard Proctor maximum dry density for the ESG mixture. Specimens were evaluated for strength and stiffness by performing isotropically consolidated undrained triaxial tests at a mean effective stress equal to 25 kPa. Peak and critical state friction angles increased with increasing compaction of the ESR specimens in addition to a slight increase in stiffness. The stress-strain response is shown to be similar for both sizes of granulated rubber but the 6.7-mm granulated rubber particle size resulted in slightly higher peak and critical state friction angles. The stiffness of the inclusions is shown to change the material stress-strain response and stiffness substantially.

Use of Recyclable Materials in Sustainable Civil Engineering Applications

1 Civil Engineering Department, Purdue University, West Lafayette, IN 47907, USA 2 Civil Engineering Department, New Mexico State University, Las Cruces, NM 88003-8001, USA 3 Centre for Offshore Foundation Systems M053, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia 4 Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA 94720, USA

Durability of reclaimed asphalt pavement–coal fly ash–carbide lime blends under severe environmental conditions

The sustainable use of industrial residue in enhancing the long-term performance of reclaimed asphalt pavement (RAP) has been proven to be effective under freeze–thaw and wet–dry conditions. This study focuses on coal fly ash (FA) and carbide lime (CL) as the enhancing agents. It evaluates how the durability and long-term performance of compacted RAP–FA–CL mixtures are impacted by dry unit weight and lime content. The tested mixture’s specimens were moulded in three layers through static compaction inside a cylindrical mould. Several single-level variables were used in the stabilisation process. Among these were: FA content of 25%, optimum water content of 9% (modified effort) and seven days of curing. Additionally, three target dry unit weights (17, 18 and 19 kN/m3 – the last of which was determined using the modified Proctor energy) and three percentages of lime content (3%, 5% and 7%) were used for a comparative analysis. The tested specimens’ accumulated loss of mass (after wetting–drying and freezing–thawing cycles) and splitting tensile strength were both evaluated as a function of the porosity/lime index. The experiments revealed that compacted RAP–coal FA–CL mixtures performed noticeably worse when subjected to freezing–thawing cycles than when subjected to wetting–drying cycles. These results indicate an increase in the breadth of the porosity/lime index, as it is shown to control the long-term performance of compacted RAP–coal FA–CL mixtures, in addition to controlling their mechanical response.

Analysis of simple shear tests with cell pressure confinement

ABSTRACT The high cost of offshore infrastructure provides continuous encouragement for optimisation of design practices. Development of a more rational method to interpret results from simple shear tests with cell pressure confinement can reduce costs and improve reliability of offshore infrastructure. This paper addresses a commonly overlooked issue affecting design parameter selection: specimen shape varies from right cylinder to oblique cylinder after loading along a single shearing direction. Thus, horizontal stresses are not always equal to the cell pressure and their magnitude varies throughout the specimen’s lateral surface. An analysis is proposed that accounts for changing specimen geometry and lateral surface area during shearing and for the actual effect of cell pressure during testing. The analysis also describes how the intermediate principal stress can be assessed. Test results for medium dense silica sand are interpreted following de Josselin de Jong’s alternative shearing mechanism hypothesis. Conventional interpretation methods yield conservative design parameters for this soil. Failure states develop when the intermediate principal effective stress is halfway between major and minor principal effective stresses. Typical results for the soil tested show equipment performance meets standard direct simple shear requirements for shear strain rate, vertical stress and specimen height control.

Mechanical response of two carbonate sediments from Australia's North West shelf

The carbonate sediments found offshore on the North West Shelf of Australia can generally be described as silts with varying proportions of clay-sized and sand-sized carbonate particles. This paper investigates the undrained shearing response (as measured under simple shear and triaxial conditions) of two sediments with different grading curves. The importance of the fines content in controlling the density and hence dilatancy and undrained strength of the materials is demonstrated. The paper discusses the importance of fabric to the behavior of these soils and provides guidance on how undrained strengths of soils of this nature may be assessed with a knowledge of a material’s in-situ water content (or void ratio) and composition.Copyright

Strain Accumulation Procedure During Staged Cyclic Loading of Carbonate Sediments

Design of offshore foundation systems requires assessment of the effects of cyclic loading on the soil strength. This paper investigates the applicability of the strain accumulation procedure, which is used to assess the effects of wave loading on the soil strength. Staged undrained cyclic simple shear tests were conducted on a carbonate sediment from the North West shelf of Australia, with varying shear stress amplitude in each stage. The shear strain mobilised at the end of the staged tests is compared with the value predicted by the strain accumulation procedure, using shear strain contours constructed from the results of single amplitude undrained cyclic simple shear tests. It was found that the strain accumulation procedure gives adequate prediction for normalised cyclic shear stress less or equal to 0.3, but largely underestimates the cyclic shear strain for normalised cyclic shear stress greater than 0.3 (the cyclic shear stress being normalised by the effective vertical stress at the end of consolidation).Copyright

A New Slurry-Based Method of Preparation of Hollow Cylinder Specimens of Clean and Silty Sands

Given that hollow cylinder testing of undisturbed sand samples is virtually impossible to carry out, a new slurry deposition method is described in this study that allows reconstitution of uniform, saturated hollow cylinder specimens of clean and silty sands deposited under water. A novel gradient density mold was designed to demonstrate the uniformity of hollow cylindrical specimens prepared with the proposed method. Based on the results of 40 hollow cylinder tests and six uniformity tests on clean and silty sand specimens, the proposed method is shown to yield uniform hollow cylinder specimens in terms of relative density and silt content that have a high initial degree of saturation and that can be easily saturated using conventional back-pressure saturation procedures. Specimens prepared with the proposed method present very repeatable stress–strain responses during anisotropic consolidation and drained principal stress rotation.