Silty Sand Specimens Research Articles

Estimation of liquefaction potential from dry and saturated sandy soils under drained constant volume cyclic simple shear loading

Understanding the liquefaction mechanism of sandy soils still remains as one of the challenges in geotechnical earthquake engineering, since clean sands, silty sands and clayey sands do not necessarily show identical reactions under seismic loading. This study investigates the cyclic simple shear responses of three sandy soils: clean sand (Sile Sand 20/55), silty sand (Sile Sand 20/55 with 10% IZ silt) and clayey sand (Sile Sand 20/55 with 10% kaolin) based on many dry and saturated specimens. Drained constant volume cyclic simple shear tests on clean and silty sand specimens have shown that liquefaction potential of those soils could also be determined via dry samples. This is an important observation, since dry specimens are much easier to prepare and less time consuming compared to their saturated counterparts, as the demanding saturation process is eliminated. However, cyclic responses of dry and saturated clayey sand specimens were shown to be quite different, and therefore saturation of these specimens is still a must for liquefaction assessment. For both silt and kaolin, adding 10% fines to the base sand increased the liquefaction potential of resulting sandy soils considerably compared to the clean sand at the same void ratio. But this difference relatively decreased as the specimens became looser.

Stiffness of intermediate unsaturated soil from simultaneous suction-controlled resonant column and bender element testing

Small-strain stiffness properties of unsaturated soils, particularly shear-wave velocity, shear modulus, and material damping, play a fundamental role in the analysis and design of geotechnical infrastructure resting on unsaturated ground, or made of compacted unsaturated soils, as they are subjected to static or dynamic loading. Most conventional soil testing devices, however, are not able to adequately capture this small-strain behavior and hence vastly underestimate the true soil stiffness. This paper introduces a suction-controlled, proximitor-based resonant column device also featuring an independent set of self-contained bender elements for simultaneous testing of soils using both techniques. The work is partly aimed at assessing the suitability of bender elements for soil testing under controlled suction states, as compared to more reliable and fully-standardized procedures such as resonant column or simple shear test methods. A series of resonant column and bender element tests were simultaneously conducted on statically compacted specimens of silty sand for suction states ranging from 50 to 400kPa attained via the axis-translation technique. Particular attention was devoted to the influence of suction over the frequency response curves, damped free-vibration cycles, and cyclic hysteretic stress–strain loops. Results show the critical influence of matric suction on small-strain stiffness properties of compacted silty sand, as well as reasonably good agreement between resonant column and bender element test results.

A mist pluviation method for reconstituting silty sand specimens

A mist pluviation (MP) technique was proposed in an effort to develop a practical method for reconstituting silty sand specimens without inducing severe particle segregation. The mist pluviation method includes both air and water pluviation processes, with the addition of a mist zone that mixes soil particles with water droplets while falling through air. The soil and water mixtures have similar particle sizes, thus resulting in significantly reduced particle segregation. A thin water layer on top of the deposited soil mimics the water deposition process, and saturates the soil with little chance for particle segregation. The performance of the MP method was evaluated with regard to homogeneity, repeatability, undrained monotonic compression, and cyclic strength of triaxial specimens with various fines contents. Results have indicated that the MP method can be a promising technique to prepare reconstituted silty sand specimens.

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.

Interfacial shear strength of silty sand–geogrid composite

This study has been carried out to investigate the interface shear strength of sand reinforced by high-density polyethylene cogged geogrid, with variation in fines content from 0 to 45%. To this end, a set of large direct shear tests (30 × 30 × 15 cm) was systematically conducted. The behaviour of sand and silty sand reinforced with a special type of cogged geogrid is studied in terms of interfacial shear strength of the soil. An analysis of test results indicates that the reinforcement improved the shearing behaviour of the sand and silty sand samples. Attaining the peak strength at greater shear strain due to reinforcement and lowering the post-peak loss of strength of specimens with higher silt content, compared to the specimens with lower silt content, are the indications implying that the reinforcement and increasing the silt content tend to transform the shearing behaviour of sand and silty sand specimens from a brittle to a ductile manner. The results also indicated that as the silt content increases up to 35%, the combined shear strength decreases. Further increase in the silt content made no significant change to the combined shear strength of the soil samples.

Field Evaluation of the Cyclic Strength versus Cone Tip Resistance Correlation in Silty Sands

ABSTRACT The liquefaction potential assessment under the framework of simplified procedure that involves the use of cone penetration tests (CPT) typically relies on empirical correlations between the soil cyclic resistance ratio, CRR and cone tip resistance qt. For sands that contain fines (particles passing #200 sieve), an adjustment based on fines content in the CRR-qt correlation is called for in currently available procedures. Earlier laboratory calibration tests in reconstituted silty sand specimens performed by the authors have indicated that partial drainage in CPT played an important role in the CRR-qt correlations. A series of laboratory tests on undisturbed samples and field piezocone penetration tests (CPTU) were carried out in an alluvial soil deposit at two test sites in Central and Southern Taiwan. The results indicated that unlike the uniformly mixed specimens reconstituted in laboratory, the tested natural alluvial silt/sand soils can be heterogeneous with closely spaced clean sand layers embedded in a matrix of silty material. This stratification can render the CPTU a drained test even at fines contents well in excess of 50%. The ignorance of free draining effects on CPTU due to stratification in alluvial soils may lead to overestimation of CRR. Because of these factors, calibration of the CRR-qt correlations by performing tests in local soil and field procedures to ascertain the drainage conditions in CPTU are important to the proper application of the CRR-qt correlations in the liquefaction potential assessment.

Cyclic strength of a natural liquefiable sand stabilized with colloidal silica grout

This paper summarizes the experimental results of a series of cyclic simple shear tests on liquefiable silty sand with and without sample improvement with colloidal silica grout. The objective of the paper is to evaluate the effectiveness of colloidal silica grouting in reducing the liquefaction potential of natural silty sand. Colloidal silica was selected as a stabilizing material due to its low viscosity, wide range of gel times, nontoxicity, and low cost. The soil tested in this experimental program is a poorly graded sand with 11.5% of nonplastic silt from the Port of Lázaro Cárdenas, México. Colloidal silica treated and untreated sand specimens show different pore pressure response and deformation behavior under cyclic loading in simple shear tests. The results indicate that, for a given initial relative density and initial effective vertical stress, liquefiable silty sand specimens stabilized with colloidal silica grout generally exhibit significant gain in liquefaction resistance compared with untreated specimens. It was also found that the colloidal silica grout reduces considerably the rates of pore pressure generation and shear strain of the silty sand specimens subjected to cyclic loading.

Implicit Algorithm for Modeling Unsaturated Soil Response in Three-Invariant Stress Space

An implicit integration algorithm has been refined to predict the stress–strain–strength response of unsaturated soil under suction-controlled, multiaxial stress paths that are not achievable in a conventional cylindrical cell. The algorithm supports numerical analyses in a deviatoric plane by using a mixed control constitutive driver, in conjunction with a generalized Cam-Clay model that also incorporates the influence of a third stress invariant, or Lode-angle θ , within a constant-suction scheme. True triaxial data from a previously accomplished series of suction-controlled triaxial compression, triaxial extension, and simple shear tests on 10-cm cubical specimens of silty sand, were used for the tuning and validation of the refined algorithm. The elliptical Willam–Warnke surface was adopted for simulation of unsaturated soil response in three-invariant stress space. Reasonably satisfactory agreement was observed between experimental and predicted deviatoric stress versus principal strain response for ...

Mathematical model for isotropic compression behaviour of cemented soil cured under stress

A mathematical model is proposed to simulate isotropic compression test results obtained for specimens of silty sand mixed with different cement contents and cured at different void ratios. The ability of the model to represent the isotropic test results of specimens with different cement contents cured at high and low void ratios under high confining stresses was successfully checked. The physical meanings of the parameters established by the model were also evaluated. Finally, the applicability of the model to other artificially cemented soils was demonstrated.

Constitutive modeling of unsaturated soil behavior under axisymmetric stress states using a stress/suction-controlled cubical test cell

Two elasto-plastic critical state-based formulations for modeling the constitutive behavior of an unsaturated soil are presented and briefly discussed. Computational constitutive drivers were implemented to allow for the numerical simulation of suction-controlled conventional triaxial tests. Simulations were obtained from explicit and implicit integration techniques. The algorithms support numerical analyses in a deviatoric stress plane by using a mixed control constitutive driver in conjunction with a generalized cam-clay model, within a constant-suction scheme. The results from a series of suction-controlled conventional triaxial tests conducted on several identically prepared, 10-cm side, cubical specimens of compacted silty sand, using a recently developed stress/suction-controlled cubical testing device, were used for validation of the models and the enhanced features proposed in the present work. Matric suction states in the specimens were induced and maintained constant during testing by using the axis-translation technique.

Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens

Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens

Closure to “Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens” by Kaare Ho̸eg, Rune Dyvik, and Geir Sandbækken

Closure to “Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens” by Kaare Ho̸eg, Rune Dyvik, and Geir Sandbækken

Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens

The differences in undrained stress-strain-strength behavior between undisturbed and reconstituted silt and silty sand specimens tested at the same void ratio and initial stress state may be dramat...

Engineering Behaviour of Fibre-Reinforced Pond Ash and Silty Sand

This note presents the results of laboratory investigations conducted on silty sand and pond ash specimens reinforced with randomly distributed polyester fibres. The test results reveal that the inclusion of fibres in soils increases the peak compressive strength, CBR value, peak friction angle, and ductility of the specimens. It is concluded that the optimum fibre content for both silty sand and pond ash is approximately 0.3 to 0.4% of the dry unit weight.

Fabrication of silty sand specimens for large- and small-scale tests : Brandon, T L; Clough, G W; Rahjardo, P P Geotech Test JV14, N1, March 1991, P46–55

Fabrication of silty sand specimens for large- and small-scale tests : Brandon, T L; Clough, G W; Rahjardo, P P Geotech Test JV14, N1, March 1991, P46–55

Fabrication of Silty Sand Specimens for Large- and Small-Scale Tests

Abstract In the course of research concerning the relation of cone penetration results and liquefaction resistance, it was necessary to develop a reliable method for preparation of silty sand specimens for laboratory triaxial testing (3.6 by 7.1 cm in diameter) and for a large-scale calibration chamber (1.5 by 1.5 m in diameter). The objective was to simulate the in situ soil fabric and to allow for creation of a range of densities. Four alternate procedures were studied, including kneading compaction, pluviation through air, pluviation through vacuum, and consolidation from a slurry. The primary conclusions from the research were: 1. Kneading compaction is effective in producing laboratory specimens with a range of densities, but it is not an effective procedure for placing these materials in the large-scale calibration chamber. 2. Pluviation through air and vacuum creates specimens with unrealistically high void ratios. Obtaining a range of densities was not possible. 3. Slurry consolidation proved to be successful in creating specimens with a range of densities and was the technique chosen for the calibration chamber. Only vertical drainage was used in the calibration chamber to avoid formation of a specimen with a soft core surrounded by stiff sides. Eighteen to twenty days were required for consolidation, and the density of the specimens along a vertical profile varied by no more than 6% from the average density. There was little evidence of segregation of fines.