Development of an Improved Test Setup for Measuring the Resilient Modulus of Stabilized Pavement Materials

2019 ◽  
Vol 2673 (2) ◽  
pp. 304-313 ◽  
Author(s):  
Stefan Louw ◽  
Rongzong Wu ◽  
Joseph Hammack ◽  
David Jones
Keyword(s):  
Strain Distribution ◽  
Resilient Modulus ◽  
Cyclic Stress ◽  
Triaxial Testing ◽  
Linear Strain ◽  
Test Setup ◽  
Full Depth Reclamation ◽  
State Highway ◽  
Triaxial Cell ◽  
Non Linear

In a recent study to develop mechanistic empirical relationships for full depth reclamation (FDR) in California, it was determined that the commonly used triaxial testing setup detailed in American Association of State Highway and Transportation Officials (AASHTO) T 307 was not suitable for testing stabilized materials. This paper investigates different testing setups, based on a comprehensive literature review, to determine an appropriate approach for measuring strains on both laboratory-compacted and field-cored specimens. Five different test setups were evaluated, ranging from measurements on the top cap of the triaxial cell, to third-point measurements on the specimen. This study also investigated methods of mounting transducer gauge points on the specimen in a repeatable and accurate manner, and for preparing the specimen ends to mitigate point loads. Two field cores, one sampled from an FDR project with cement stabilization (FDR-PC) and the other from an FDR project with foamed asphalt stabilization (FDR-FA), were subjected to unconfined, low stress cyclic triaxial testing using different deviatoric and seating stresses using each of the five test setups. The effects of non-linear strain distribution on the cyclic stress strain curves were compared. Based on these results, the recommended test setup for determining the resilient modulus of the stabilized material is the third point on-specimen setup for measuring strain. This approach was minimally influenced by the non-linear strain distribution, and provided resilient moduli that closely correlated with stiffnesses back calculated from the falling weight deflectometer deflections measured close to the core locations.

Post-liquefaction pore pressure dissipation in sand under cyclic stress triaxial testing

Géotechnique ◽  
2020 ◽  
Vol 70 (2) ◽  
pp. 95-107
Author(s):  
Saizhao Du ◽  
Siau Chen Chian ◽  
Changbing Qin
Keyword(s):  
Pore Pressure ◽  
Cyclic Stress ◽  
Triaxial Testing

Using Artificial Intelligence to Estimate Nonlinear Resilient Modulus Parameters from Common Index Properties

2021 ◽  
pp. 036119812110237
Author(s):  
Laura Camarena
Keyword(s):  
Machine Learning ◽  
Material Properties ◽  
Resilient Modulus ◽  
Nonlinear Behavior ◽  
Machine Learning Techniques ◽  
Design Parameters ◽  
Nonlinear Parameters ◽  
State Highway ◽  
Learning Techniques ◽  
State Highway Agencies

The Mechanistic–Empirical Pavement Design Guide (MEPDG) considers a hierarchical approach to determine the input values necessary for most design parameters. Level 1 requires site-specific measurement of the material properties from laboratory testing, whereas other levels make use of equations developed from regression models to estimate the material properties. Resilient modulus is a mechanical property that characterizes the unbound and subgrade materials under loading that is essential for the mechanistic design of pavements. The MEPDG resilient modulus model makes use of a three-parameter constitutive model to characterize the nonlinear behavior of the geomaterials. As the resilient modulus tests are complex, expensive, and require lengthy preparation time, most state highway agencies are unlikely to implement them as routine daily applications. Therefore, it is imperative to make use of models to calculate these nonlinear parameters. Existing models to determine these parameters are frequently based on linear regression. With the development of machine learning techniques, it is feasible to develop simpler equations that can be used to estimate the nonlinear parameters more accurately. This study makes use of the Long-Term Pavement Performance database and machine learning techniques to improve the equations utilized to determine the nonlinear parameters crucial to estimate the resilient modulus of unbound base and subgrade materials.

Non-Linear Dynamic Magneto Electric Effects in Ferromagnetic-Ferroelectric Layered Composites

2013 ◽  
Author(s):  
Satenik Harutyunyan ◽  
Davresh Hasanyan
Keyword(s):  
Vibration Frequency ◽  
Strain Distribution ◽  
Longitudinal Vibration ◽  
Three Dimensional ◽  
Low Frequency ◽  
Structure Design ◽  
Experimental Results ◽  
Physical Parameters ◽  
Wide Range ◽  
Non Linear

A non-linear theoretical model including bending and longitudinal vibration effects was developed for predicting the magneto electric (ME) effects in a laminate bar composite structure consisting of magnetostrictive and piezoelectric multi-layers. If the magnitude of the applied field increases, the deflection rapidly increases and the difference between experimental results and linear predictions becomes large. However, the nonlinear predictions based on the present model well agree with the experimental results within a wide range of applied electric field. The results of the analysis are believed to be useful for materials selection and actuator structure design of actuator in actuator fabrication. It is shown that the problem for bars of symmetrical structure is not divided into a plane problem and a bending problem. A way of simplifying the solution of the problem is found by an asymptotic method. After solving the problem for a laminated bar, formula that enable one to change from one-dimensional required quantities to three dimensional quantities are obtained. The derived analytical expression for ME coefficients depend on vibration frequency and other geometrical and physical parameters of laminated composites. Parametric studies are presented to evaluate the influences of material properties and geometries on strain distribution and the ME coefficient. Analytical expressions indicate that the vibration frequency strongly influences the strain distribution in the laminates, and that these effects strongly influence the ME coefficients. It is shown that for certain values of vibration frequency (resonance frequency), the ME coefficient becomes infinity; as a particular case, low frequency ME coefficient were derived as well.

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

2012 ◽  
Vol 504-506 ◽  
pp. 71-76 ◽  
Author(s):  
Alexandra Werber ◽  
Mathias Liewald ◽  
Winfried Nester ◽  
Martin Grünbaum ◽  
Klaus Wiegand ◽  
...  
Keyword(s):  
Plane Strain ◽  
Biaxial Loading ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Linear Strain ◽  
Forming Limits ◽  
Systematic Analysis ◽  
Measurement Systems ◽  
Non Linear ◽  
Strain Paths

In order to evaluate the formability of sheet materials forming limit diagrams (FLD) are recorded which represent the values of major and minor strain when necking occurs. FLDs are recorded based on the assumption that exclusively linear strain paths occur. In real forming parts, however, particularly in those with complex shapes, predominantly non-linear strain paths occur which reduce the accuracy of the failure prediction according to a conventional FLD. For this reason forming limits after loading with non-linear strain paths have to be investigated. In this contribution a systematic analysis of the forming limits of a conventional AA6014 alloy after loading with non-linear strain paths is presented. This material is pre-stretched in uniaxial, plane strain and biaxial direction up to several levels before performing Nakajima experiments in order to determine FLDs. During the pre-stretching process as well as during the Nakajima experiment the strain distribution can be measured online very precisely with the optical deformation measurement systems GOM Aramis or VIALUX. The gained curves are compared to the FLD of the as-received material. The results prove a significant influence of the pre-stretching condition on the forming limits of the used aluminum alloy. For a low pre-stretching in uniaxial as well as in biaxial direction the FLDs show a slightly reduced formability while after higher pre-stretching levels the forming limit can be improved such as for biaxial loading after uniaxial pre-stretching. The formability after pre-stretching in plane strain direction was changed. Also, a shift of the FLD depending on the direction of pre-stretching can be observed.

Investigation of Size Effects on Process Models for Plane Strain Microbending

2006 ◽  
Author(s):  
Richard M. Onyancha ◽  
Brad L. Kinsey
Keyword(s):  
Size Effects ◽  
Strain Distribution ◽  
Past Research ◽  
Peak Force ◽  
Process Models ◽  
Analytical Models ◽  
Linear Strain ◽  
Bending Force ◽  
Bending Process ◽  
Individual Grains

Accurate process models provide vital information in the design of manufacturing processes. To characterize bending operations, analytical models have been developed and shown to predict the peak bending forces fairly accurately for sheets in the macro or mesoscale (i.e. sheets with a large number of grains through the thickness). However, whether these models also accurately predict bending forces for sheets in the microscale (i.e. sheets with approximately ten grains or less through the thickness) has not been evaluated. The present study is aimed at investigating the use of two such models from previous work with microscale bending data. In addition, using these previous models as a foundation, additional bending force models were developed to predict the bending force specifically for microscale bending operations. Data analysis showed that the process models from past research, which provide accurate results for macroscale bending, over predict the peak force required for bending microscale sheets. These process models assume a non-linear strain distribution through the thickness and a curved formed wall. The two models developed in this research provide accurate results for the microscale bending tests, however, they under predict the peak force for the macroscale bending operation. These developed process models assume a linear strain distribution through the thickness and a straight formed wall. The linear strain distribution is more appropriate for the microscale bending process as there are few grains through the thickness and the strain in individual grains varies linearly across the grain. The straight formed wall is more appropriate for the microscale bending process as there is not sufficient distance to warrant a curved formed wall assumption. These differences represent size effects for assumptions in the process models. The material used for these investigations was Brass (CuZn15). The sheets had between 2 and 50 grains through the thickness with grain sizes of between 10 μm and 71 μm.

scholarly journals Experimental and Estimation Studies of Resilient Modulus of Marine Coral Sand under Cyclic Loading

2020 ◽  
Vol 8 (4) ◽  
pp. 287 ◽  
Author(s):  
Shao-Heng He ◽  
Qiong-Fang Zhang ◽  
Zhi Ding ◽  
Tang-Dai Xia ◽  
Xiao-Lu Gan
Keyword(s):  
Cyclic Loading ◽  
South China Sea ◽  
Effective Stress ◽  
South China ◽  
Stress Ratio ◽  
Resilient Modulus ◽  
Cyclic Stress ◽  
Marine Transportation ◽  
Cyclic Stress Ratio ◽  
Coral Sand

Coral sand is an important filler resource that can solve the shortage of terrestrial fillers in coastal areas. Recently, the foundations of many infrastructures in the South China Sea have been built with coral sand as fillers, which have been subjected to wave and traffic cyclic loads. Resilient modulus (Mr) is an important design parameter in marine engineering, but there are few studies on the resilient modulus response of coral sand under cyclic loading. A series of drained cyclic triaxial tests were carried out to investigate the effects of the initial mean effective stress (p0) and cyclic stress ratio (ζ) on the resilient modulus response of the coral sand from the South China Sea. The change of fractal dimension (αc) can reflect the rule of particle breakage evolution. The αc of coral sand shows a tendency of almost maintaining stable and then increasing rapidly with the increase of mean effective stress p0 under each cyclic stress ratio ζ. There is a threshold of p0, when the p0 exceeds this threshold, αc will increase significantly with the increase of p0. The increase of p0 has a beneficial effect on the improvement of the Mr, while the increase of ζ has both beneficial and detrimental effects on the improvement of the Mr. A new prediction model of the Mr considering particle breakage was established, which can better predict the Mr of coral sand in the whole stress interval. The research results can provide guidance for the design of marine transportation infrastructures, which can promote the development of marine transportation industry and energy utilization.

Photogrammetry-Based Method to Determine the Absolute Volume of Soil Specimen during Triaxial Testing

2020 ◽  
Vol 2674 (8) ◽  
pp. 206-218
Author(s):  
Sara Fayek ◽  
Xiaolong Xia ◽  
Lin Li ◽  
Xiong Zhang
Keyword(s):  
Unsaturated Soils ◽  
Optimization Techniques ◽  
Triaxial Tests ◽  
Triaxial Testing ◽  
Soil Specimen ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Absolute Volume ◽  
Triaxial Cell ◽  
The Absolute

Triaxial tests are used extensively to evaluate stress-strain behavior for both saturated and unsaturated soils. A literature review indicates that all conventional triaxial test methods measure the relative volume of soil; however, between the initial measurements and the start of the triaxial tests, there are unavoidably disturbances during installation that cause deviation of soil volume from that at the initial condition. Recently image-based methods have been developed to measure the absolute volume of soil specimens. However, these methods still have a major limitation in their inability to determine top and bottom boundaries between the soil specimen, and the top and bottom caps. This paper proposes a photogrammetry-based method to overcome this limitation by developing a mathematically rigorous technique to determine the upper and lower boundaries of soil specimens during triaxial testing. The photogrammetry technique was used to determine the orientations of the camera, and the shape and location of the acrylic cell. Multiple ray-tracings and least-square optimization techniques were also applied to obtain the coordinates of any point inside the triaxial cell, and thus back-calculate the upper and lower boundaries. With these boundaries and the side surface, a triangular surface mesh was constructed and the specimen volume was then calculated in both unconfined compression tests and triaxial tests. The calculation procedures are presented in detail with validation tests performed on a cylindrical specimen to evaluate the accuracy of the method. Results indicate that the accuracy of the proposed method is up to 0.023% in unconfined compression tests and 0.061% in triaxial tests.

scholarly journals Simplified Laboratory Assessment of Subgrade Performance Parameters for Mechanistic Design of Pavement Foundations

2005 ◽  
Vol 1913 (1) ◽  
pp. 77-85
Author(s):  
Matthew W. Frost ◽  
J. Paul Edwards ◽  
Paul R. Fleming ◽  
Stuart J. Arnold
Keyword(s):  
Resilient Modulus ◽  
Permanent Deformation ◽  
Design Parameters ◽  
Triaxial Testing ◽  
Performance Parameters ◽  
Laboratory Assessment ◽  
Foundation Design ◽  
Cyclic Triaxial ◽  
Analytical Design ◽  
Pavement Foundations

With the increasing agenda for sustainability, the United Kingdom is attempting to move away from the empirical design of pavement foundations to develop a performance specification approach that facilitates analytical design. The measurement of the subgrade performance parameters of resilient modulus and resistance to permanent deformation is required for analytical design. These parameters ideally should be assessed concurrently under loading and environmental conditions similar to those the materials will experience in the field. To date, measurement of these parameters is largely confined to research laboratories using cyclic triaxial testing with advanced on-sample strain measurement. This apparatus is considered too complicated for routine commercial use; hence, the implementation of laboratory performance evaluation for routine pavement foundation design is potentially limited. A previous program of cyclic triaxial testing on clay subgrades indicated a series of useful correlations between strength and permanent deformation behavior (via a threshold stress) and material resilient modulus at this threshold. The previous work is reviewed; with these correlations, data from tests performed on three different clay materials to develop simplified equipment and procedures for the routine measurement of the required design parameters are presented. Simple pseudostatic tests can measure a subgrade modulus for a simplified performance-based design. The previous data (in the light of the recent work) were reevaluated to show a boundary correlation that may allow a shear strength–based parameter to control (in design) the onset of permanent deformation, and the ways long-term subgrade water content changes can be accommodated are detailed.

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