Moeen Nazari

Numerical Study of Behavior of Anchor Plates in Clayey Soils

AbstractThis paper presents numerical models and mathematical formulations to predict the pullout capacity of anchor plates with different inclination angles embedded in clay. The models were developed based on the failure mechanism deduced from laboratory testing and utilize the Mohr-Coulomb yielding criteria. Expression was given to estimate the maximum pullout resistance of plates with different dimensions and inclination angles embedded in various clayey soils. A comparison between results of finite-element analyses has been performed to find out the effect of different parameters. New two-variable functions have been presented to show the relationship between pullout resistance and embedment ratio with different inclination angles. In addition, an interesting relationship among pullout capacities of anchor plates at different inclination angles was found, and a new concept, ellipse of pullout capacity, has been pronounced. Finally, a new theory has been introduced to predict the pullout capacity of a...

Influence of Tensile Strain at Failure on Flexural Properties of a Cementitiously Stabilized Subgrade Soil

AbstractFlexural properties of subgrade soils play an important role in the overall performance of pavements. In this study, a series of laboratory tests and finite-element analysis were conducted to evaluate the effect of the stress-strain behavior of cementitiously stabilized soil (CSS) on its flexural fatigue life. Three different amounts of cement kiln dust (CKD), namely 5, 10, and 15% (by weight), were mixed with soil, and beam specimens were prepared using these three mixes. Modulus of rupture (MoR) tests were conducted on the prepared specimens to measure flexural strength and tensile strain at failure. Four-point bending beam fatigue tests were conducted on CSS specimens to evaluate their flexural modulus and fatigue life of each mix. Also, finite-element models of the MoR tests were developed using a concrete damage plasticity model for the CSS material. The MoR test results showed that the flexural strength increases with an increase in the amount of CKD. However, the failure strain was not foun...

Flexural properties of chemically stabilised subgrade in designing semi-rigid pavements

Although flexural fatigue cracking of chemically-stabilised subgrade (CSS) layers is a major distress in semi-rigid pavements, the fatigue model of the CSS layer in the Mechanistic-Empirical Pavement Design Guide (M-EPDG) has not been calibrated. Design of semi-rigid pavements with regard to flexural fatigue life of the CSS layer was conducted using the M-EPDG method. Cylindrical and beam specimens of a lean clay, mixed with different types (cement kiln dust (CKD) and lime) and amounts of additives were prepared in the laboratory. Resilient modulus, modulus of rupture (MoR), flexural modulus and four-point flexural fatigue (FPFF) beam tests were conducted. Also, finite element (FE) models of different pavement sections having different thicknesses of hot mix asphalt (HMA) and different materials and thicknesses of CSS layer under traffic load were developed. The minimum required thickness of the HMA layer to avoid fatigue failure in the CSS layer was determined for different sections using the laboratory test results and the FE analyses. Finally, the effect of considering the flexural properties and fatigue life of the CSS layer on the designed HMA layer thickness was evaluated. The results showed that for the CSS materials with relatively low laboratory fatigue lives, the fatigue cracking of the CSS layer contained the most critical distress to be considered in designing the pavement structure. It was also found that by substituting the CSS resilient modulus with the properly-determined flexural modulus in the mechanistic-empirical design procedure, the designed HMA thickness, and, consequently, the construction cost could decrease significantly.

Use of Intelligent Compaction in Detecting and Remediating Under-Compacted Spots During Compaction of Asphalt Layers

Under-compaction of asphalt layers results in premature distresses like rutting, localized depressions and pot-holes. Over-compaction may crush the aggregates which can result in unstable asphalt mixes. It is therefore highly important to achieve the required air voids or relative density (6–8% air voids or 92–94% relative density). Real-time monitoring of the relative density can certainly be helpful in achieving the required relative density. The traditional quality control procedure, which involves collecting cores and conducting volumetric analysis on them, does not provide any measure of the air voids or relative density level during the compaction itself, thus under-compacted spots, if any, remain undetected. Intelligent compaction methods are able to continuously monitor the air voids or density of asphalt layers during the compaction process. The University of Oklahoma has developed an intelligent compaction analyzer (ICA). The ICA is based on the hypothesis that the vibratory roller and the underlying pavement form a coupled system whose response during compaction is influenced by the stiffness of the pavement layers. The ICA is capable of generating as-built maps providing information on coverage and quality of compaction of the compacted asphalt layers. This paper discusses the principle of ICA, and its application in measuring the density of asphalt layers. Results from one demonstration are included in this paper. The ICA measured densities were validated by comparing them with densities obtained from cores. It was found that the ICA measured densities and core densities correlated well with an R2 between 0.85 and 0.93. Also, t-test conducted with the ICA-estimated densities and core densities verified that the difference between the above-mentioned two types of densities are insignificant at 95% confidence level. ICA was able to detect several under-compacted spots which were then remediated with additional roller passes. The application of the ICA certainly helped in achieving higher and uniform density throughout the test section.

Quality control of subgrade soil using intelligent compaction

Intelligent Compaction (IC) of subgrade soil has been proposed to continuously monitor the stiffness of subgrade during its compaction. Modern IC rollers are vibratory compactors equipped with (1) an onboard measuring system capable of estimating the stiffness of the pavement material being compacted, (2) Global Positioning System (GPS) sensor to precisely locate the roller, and (3) an integrated mapping and reporting system. Using IC, the roller operator is able to evaluate the entire subgrade and address deficiencies encountered during compaction. Continuous monitoring of quality during construction can help build better quality and long-lasting pavements. However, most of the commercially available IC rollers report stiffness in terms of Original Equipment Manufacturer (OEM) specified indicator, known as Intelligent Compaction Measurement Value (ICMV). Although useful, additional tests are required to establish the correlation between these ICMV values and the resilient modulus of subgrade (Mr). Since the mechanistic design of the pavement is performed using Mr, it is important to know if the design Mr is achieved on the entire subgrade during compaction. This paper presents a systematic procedure for monitoring the level of compaction of subgrade in real time using intelligent compaction (IC). Specifically, the Intelligent Compaction Analyzer (ICA) developed at the University of Oklahoma was used for estimating the modulus of the subgrade. Results from two demonstration studies show that the ICA is able to estimate subgrade modulus with an accuracy that is acceptable for quality control activities during the construction of pavements.

Intelligent Compaction of Stabilized Subgrade of Flexible Pavement

The long-term performance of a flexible pavement largely depends on the compaction level achieved in different layers during construction. Traditionally, the compaction level of the subgrade is monitored through spot checking of moisture content and dry density at some discrete points. However, this type of quality control work does not cover the entire pavement and may leave under-compacted areas. These under-compacted areas could likely lead to early failure of the pavement structure. Therefore, it is necessary to develop a real-time compaction monitoring tool that can provide an accurate measurement of the compaction level of the entire pavement. Such measurements could be used to identify and remediate under- compacted areas and provide adequate support to asphalt layers constructed on top of the prepared subgrade. The application of the Intelligent Compaction Analyzer (ICA) for real-time monitoring of compaction of a stabilized subgrade is addressed in this paper. Four case studies demonstrating the successful application of the ICA are included. The compaction level of the stabilized subgrade was monitored in terms of ICA density and modulus. In each case study, it was found that ICA could estimate the compaction level with a reasonable accuracy. It was also found that the ICA modulus and nuclear density gauge (NDG) measured density exhibits a good correlation with R 2 equal to 0.73.