Laboratory investigation of the stiffness and damping properties of binary and gap-graded mixtures of granular soils

Sandy and gravelly soils are encountered in many natural soil strata such as alluvial, fluvial, residual, and glacial deposits. These granular materials are used in the construction of many types of man-made geotechnical structures, fills, and ground improvements. A need exists to understand the dynamic behavior of these sandy and gravelly mixtures. A “binary packing model” has been proposed by some researchers to represent a simplified model for some sandy and gravelly soils that are composed of only a few, quite different, particle sizes (typically more than a factor of 20, and a factor of 34 used in this study) created during construction of geotechnical systems or in the natural environment. In other cases, gap-graded materials have been created. The packing condition and void distribution in the two types of gradations are complicated due to large variations in particle size and construction conditions. Up to now, no systematic studies have been conducted to evaluate key factors in the soil matrix (i.e., the parent materials in these mixtures) affecting the dynamic properties (i.e., shear modulus, G, and material damping ratio, D) of the binary and gap-graded mixtures considering the packing state of the matrix particles. In binary granular soils, estimating the critical packing condition, which represents the case when all void space between the large particles are completely filled with each group of small particles, is important. Additionally, the associated critical small-particle content (SPC*), which is the small-particle content (SPC) under the critical packing condition, can be calculated using the void ratios of the small-particle and large-particle materials. In this research, systematic variations of the parent materials in binary and gap-graded mixtures (i.e., the small and large particles in binary mixtures) were created, and the dynamic torsional resonant column (RC) testing was performed on a wide range of particle packing conditions. Some findings are: 1) the binary and gap-graded specimens for SPC ≥ 76% behaved very similarly to their parent poorly graded sand in both the small-strain and nonlinear dynamic properties; 2) the binary specimens for 15% ≤ SPC ≤ 100% showed a clear trend in the relationship of small-strain shear modulus at one atmosphere (A [subscript G]) and void ratio (e); 3) the binary specimens for 23% ≤ SPC ≤ 36%, which were in the range of SPC*, showed the highest stiffnesses and most nonlinearity; and 4) overall, the void ratio was a better parameter than the uniformity coefficient to estimate the nonlinear behavior of the specimens for 0% ≤ SPC ≤ 39%.Civil, Architectural, and Environmental Engineerin

Estimating Strength from Stiffness for Chemically Treated Soils

The central theme of this study is to identify strength-stiffness correlations for chemically treated subgrade soils in Indiana. This was done by conducting Unconfined Compression (UC) Tests and Resilient Modulus Tests for soils collected at three different sites—US-31, SR-37, and I-65. At each site, soil samples were obtained from 11 locations at 30 ft spacing. The soils were treated in the laboratory with cement, using the same proportions used for construction, and cured for 7 and 28 days before testing. Results from the UC tests were compared with the resilient modulus results that were available. No direct correlation was found between resilient modulus and UCS parameters for the soils investigated in this study. A brief statistical analysis of the results was conducted, and a simple linear regression model involving the soil characteristics (plasticity index, optimum moisture content and maximum dry density) along with UCS and resilient modulus parameters was proposed

Structural Evaluation of Full-Depth Flexible Pavement Using APT

The fundamentals of rutting behavior for thin full-depth flexible pavements (i.e., asphalt thickness less than 12 inches) are investigated in this study. The scope incorporates an experimental study using full-scale Accelerated Pavement Tests (APTs) to monitor the evolution of each pavement structural layer\u27s transverse profiles. The findings were then employed to verify the local rutting model coefficients used in the current pavement design method, the Mechanistic-Empirical Pavement Design Guide (MEPDG). Four APT sections were constructed using two thin typical pavement structures (seven-and ten-inches thick) and two types of surface course material (dense-graded and SMA). A mid-depth rut monitoring and automated laser profile systems were designed to reconstruct the transverse profiles at each pavement layer interface throughout the process of accelerated pavement deterioration that is produced during the APT. The contributions of each pavement structural layer to rutting and the evolution of layer deformation were derived. This study found that the permanent deformation within full-depth asphalt concrete significantly depends upon the pavement thickness. However, once the pavement reaches sufficient thickness (more than 12.5 inches), increasing the thickness does not significantly affect the permanent deformation. Additionally, for thin full-depth asphalt pavements with a dense-graded Hot Mix Asphalt (HMA) surface course, most pavement rutting is caused by the deformation of the asphalt concrete, with about half the rutting amount observed within the top four inches of the pavement layers. However, for thin full-depth asphalt pavements with an SMA surface course, most pavement rutting comes from the closet sublayer to the surface, i.e., the intermediate layer. The accuracy of the MEPDG’s prediction models for thin full-depth asphalt pavement was evaluated using some statistical parameters, including bias, the sum of squared error, and the standard error of estimates between the predicted and actual measurements. Based on the statistical analysis (at the 95% confidence level), no significant difference was found between the version 2.3-predicted and measured rutting of total asphalt concrete layer and subgrade for thick and thin pavements

Estimating Strength From Stiffness for Chemically Treated Soils

SPR-4420The central theme of this study is to identify strength-stiffness correlations for chemically treated subgrade soils in Indiana. This was done by conducting Unconfined Compression (UC) Tests and Resilient Modulus Tests for soils collected at three different sites\u2014US-31, SR-37, and I-65. At each site, soil samples were obtained from 11 locations at 30 ft spacing. The soils were treated in the laboratory with cement, using the same proportions used for construction, and cured for 7 and 28 days before testing. Results from the UC tests were compared with the resilient modulus results that were available. No direct correlation was found between resilient modulus and UCS parameters for the soils investigated in this study. A brief statistical analysis of the results was conducted, and a simple linear regression model involving the soil characteristics (plasticity index, optimum moisture content and maximum dry density) along with UCS and resilient modulus parameters was proposed

Effects of oversized particles on the dynamic properties of sand specimens evaluated by resonant column testing

textThis study was motivated by the fact that many times intact specimens with a number of oversized particles are dynamically tested in the laboratory and the impact of the particles on the dynamic properties is unknown. The effects of oversized particles represented by gravel particles on the shear modulus (G) and material damping ratio (D) of a uniform sand were evaluated in the linear (γ ≤ 0.001%) and nonlinear (γ > 0.001%) ranges of shear strain with combined resonant column and torsional shear (RCTS) equipment. The sand used in this investigation is a uniform sand as a reference, well-characterized material on the dynamic properties. Sand-gravel specimens were constructed using the undercompaction method. A variety of rounded gravel particles was used in building the specimens. Dynamic tests on the sand-gravel specimens were performed, and the tests results are presented. Among the findings of this investigation are that, compared to uniform sand: (1) oversized gravel particles symmetrically located along the longitudinal axis in uniform sand generally decreased slightly the small-strain shear modulus (Gmax), (2) oversized gravel particles asymmetrically located away from the longitudinal axis of rotation resulted in slight increases in Gmax and the small-strain material damping ratio (Dmin), (3) the G – log γ relationships of sand-gravel specimens with asymmetrically located gravel particles are generally above those with gravel particles symmetrically located along the longitudinal axis, and (4) the G/Gmax – log γ relationships of all specimens were reasonably close for the nonlinear ranges covered in these tests (γ 0.6). As long as the oversized particles were near the axis of rotation, the particles had little effect on the dynamic properties (Gmax, Dmin and G – log γ relationships) regardless of sizes and numbers of particles. However, once the oversized particles were located away from the axis of rotation and closer to the perimeter of the specimen, the oversized particles influenced the dynamic properties. Finally, the additions of oversized particles located both symmetrically and asymmetrically in the uniform sand specimens have little impact on the nonlinear dynamic properties (G/Gmax – log γ and D – log γ relationships) which compared well with uniform sand.Civil, Architectural, and Environmental Engineerin