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"Expansive soils present significant engineering challenges, with annual costs associated with repairing structures constructed over expansive soils estimated to run into several billion dollars. Volume changes in expansive soil deposits induced by fluctuations in the moisture content can result in severe damage to overlying structures. A flexible pavement section near the Western Border of Idaho has experienced recurrent damage due to volume changes in the underlying expansive soil layer; traditional stabilization methods have provided partial success over the years. The main objective of this research effort was to characterize the problematic soil layer contributing to the recurrent pavement damage and propose suitable rehabilitation alternatives. An extensive laboratory test matrix was carried out to characterize soil samples collected from underneath the problematic pavement section. Laboratory tests showed that the problematic expansive soil deposit was often at depths greater than 6 ft. (183 cm) from the pavement surface. Potential Vertical Rise (PVR) values calculated for ten boreholes strategically placed along the problematic pavement section closely matched with the surface roughness profile observed in the field. Liquidity Index (LI) calculations indicated that the active-zone extended to a depth of least 11 ft. (335 cm) from the pavement surface, and therefore, most of the heaving likely originates from soil layers as deep as 11 ft. (335 cm) from the pavement surface. Clay mineralogy tests indicated the presence of high amounts of Montmorillonite that can lead to significant volume changes. Moreover, high sulfate contents were detected in soil samples obtained from several of the boreholes, indicating a potential for sulfate-induced heaving upon chemical stabilization using calcium-based stabilizers. Based on findings from the laboratory testing, it was concluded that chemical stabilization or shallow treatment alternatives are not likely to be successful in mitigating the recurrent differential heave problems. A mechanical stabilization approach using geocells was proposed as a likely rehabilitation alternative for this pavement section. By dissipating the heave-induced stresses over a wider area, this reinforcement configuration was hypothesized to significantly reduce the differential heave. Finite-element models of the pavement section comprising six alternative geocell-reinforced configurations were prepared using the commercially available package, ABAQUS. Moisture swelling and suction properties for the expansive soil deposit were established in the laboratory and were used in the numerical model to simulate the swelling behavior. Results from the numerical modeling effort established that placing two layers of geocell within the unbound granular base layer led to the highest reduction (~60%) in the differential heave. Placing a single layer of geocell, on the other hand, reduced the differential heave magnitude by approximately 50%. A single layer of geocell was therefore recommended for implementation to achieve the optimal balance between pavement performance and construction costs."--Boise State University ScholarWorks.
"The behavior of flexible pavements under traffic and environmental loading can be significantly affected by subsurface conditions. Inadequate support conditions under the surface can lead to excessive pavement deformations, often leading to structural and functional failure. This research effort focused on assessing the effects of base/subbase and subgrade layer conditions on flexible pavement behavior. The results of this study are presented in the form of two journal manuscripts. The first manuscript focuses on utilizing pavement structural and functional evaluation data in making pavement rehabilitation decisions. Visual distress surveys and Falling Weight Deflectometer (FWD) testing are often carried out by agencies as a part of their pavement preservation programs. Although back-calculation of individual layer moduli from FWD data is a common approach to assess the pavement's structural condition, the accuracy of this approach is largely dependent on exact estimates of individual layer thicknesses. Considering the lack of pavement layer thickness information for all locations, this study used Deflection Basin Parameters (DBPs) calculated from FWD test data to make inferences regarding the structural condition of individual pavement layers in conventional flexible pavements. The adequacy of DBPs to assess the structural condition of individual pavement layers was assessed through Finite-Element (FE) Modeling. Subsequently, four selected pavement sections in the state of Idaho were analyzed based on this method to recommend suitable rehabilitation strategies. The second manuscript focused on studying how improvements to subsurface layers can affect the flexible pavement behavior over expansive soil deposits. A recently completed research study at Boise State University investigated a particular section of US-95 near the Idaho-Oregon border that has experienced significant differential heave due to expansive soils. Laboratory characterization of soil samples indicated the presence of highly expansive soils up to depths of 7.6 m (26 ft.) from the pavement surface. Through subsequent numerical modeling efforts, a hybrid geosynthetic system comprising geocells and geogrids was recommended for implementation during pavement reconstruction. This research effort focused on evaluating the suitability of polyurethane grout injection as a potential remedial measure for this pavement section. Laboratory testing of unbound materials treated with a High-Density Polyurethane (HDP) demonstrated that resilient modulus and shear strength properties could be improved significantly. Finite Element modeling of the problematic US-95 pavement section indicated that depending on the treated layer thickness, the differential heave magnitude can be reduced significantly, presenting polyurethane injection as a potential nondestructive remedial measure. ."--Boise State University ScholarWorks.
Expansive soils, which have been reported as a worldwide problem, cover 25% of the United States. Due to the swelling and shrinkage behavior induced by moisture variations, expansive soil contributes to volumetric deformation, which in turn affects the stability and performance of structures. The Texas Department of Transportation (TxDOT) allocates 25% of its budget to pavement maintenance and repairs, much of which is triggered by expansive soil. In order to decrease the burden of this expense on maintenance authorities, it is necessary to have an accurate understanding of expansive subgrade behavior. Applying this knowledge to the pavement design and construction processes can significantly increase the pavement's service life. The specific objectives of this research were to (1) study the behavior of expansive soil with seasonal changes and climatic loading; (2) asses the real-time moisture and temperature variations in the expansive subgrade; (3) quantify the deformation pattern with time in response to environmental loading; (4) develop a realtime moisture, temperature, and deformation prediction model; (5) based on the investigation of the subgrade, provide solutions in order to combat the pavement deformation; and (6) evaluate the effectiveness of the proposed solution. In order to accomplish the objectives, one farm-to-market road and one state highway were selected for observation of the behavior of expansive subgrades in North Texas. Soil samples were collected and tested to determine the soil properties. Moisture, suction sensors, temperature sensors, and rain gauges were installed to record the variations of the variables over time. Moreover, geophysical testing was conducted to continually portray the subgrade over time. Deformation of the pavement was monitored through topographic surveying and a horizontal inclinometer. Collected data was analyzed in a statistical environment to develop real-time prediction models. The first attempt produced a moisture variation model that captured variations due to seasonal effects and temporary variations due to rainfall. The outputs of this model were within 90% of the values measured on-site. The second attempt produced a temperature prediction model that was dependent on depth and the day of the year. The squared correlation coefficient between the observed and predicted soil temperature was more than 0.90. Application of the developed models could allow for a non-invasive estimation of the response of soil strength and stiffness properties due to variations in moisture and temperature. While examining the deformation data, it was found that seasonal variations only capture a portion of the deformation, whereas the amount of precipitation plays a significant role in further modifying the model. Temperature and suction were also correlated with deformation to finalize the deformation model. Application of the developed model facilitates estimation of deformation at any time of the year, in response to precipitation. The study also attempted to focus, to a limited extent, on numerical modeling; however, the selection of unsaturated parameters was challenging. The selection of unsaturated permeability and flow parameters is usually laboratory-based, because a specific condition of the soil makes it impossible to capture them in real time in the field. This study attempted to determine the variations of unsaturated hydraulic conductivity based on rainfall response data. Rather than conducting the usual laboratory testing to determine the unsaturated flow parameters by curve fitting, a novel approach was undertaken to determine the flow parameters from field soil water characteristic curves. Finally, field-based values were used in the PLAXIS 2D environment for transient analysis. The validity of the estimated parameters was confirmed, as FE results corresponded with direct field measurements. The study results indicated that FE modeling can provide effective information about the subgrade matric suction variations. This research focused on finding a possible solution to the problem of pavement distress. It was found that controlling the moisture from the edge of the pavement can significantly improve the pavement performance. Consequently, a moisture barrier consisting of a geomembrane and a geocomposite (geonet sandwiched between two nonwoven geotextiles) was suggested. A combination of a 40-mil LLDPE geomembrane and an 8-oz. HDPE geocomposite was used to control the moisture from the edge of a 50 ft. section of FM 987. A control section along the same roadway was instrumented and monitored for comparison. Preliminary field monitoring results clearly indicated that the moisture barrier significantly reduced the water infiltration near the edge of the pavement. Moreover, the movement of the pavement was reduced by 80%, based upon previous recorded measurements of the control section.
Design related project level pavement management - Economic evaluation of alternative pavement design strategies - Reliability / - Pavement design procedures for new construction or reconstruction : Design requirements - Highway pavement structural design - Low-volume road design / - Pavement design procedures for rehabilitation of existing pavements : Rehabilitation concepts - Guides for field data collection - Rehabilitation methods other than overlay - Rehabilitation methods with overlays / - Mechanistic-empirical design procedures.
Functional Pavements is a collection of papers presented at the 6th Chinese-European Workshop (CEW) on Functional Pavement Design (Nanjing, China, October 18-21, 2020). The focus of the CEW series is on field tests, laboratory test methods and advanced analysis techniques, and cover analysis, material development and production, experimental characterization, design and construction of pavements. The main areas covered by the book include: • Asphalt binders for flexible pavements • Asphalt mixture evaluation and performance • Pavement construction and maintenance • Pavement Surface Properties and Vehicle Interaction • Cementitious materials for rigid pavements • Pavement geotechnics and environment Functional Pavements aims at contributing to the establishment of a new generation of pavement design methodologies in which rational mechanics principles, advanced constitutive models and advanced material characterization techniques shall constitute the backbone of the design process. The book will be much of interest to professionals, academics and practitioners in pavement engineering and related disciplines as it should assist them in providing improved road pavement infrastructure to their stakeholders.
At head of title: National Cooperative Highway Research Program.
Papers from a December 1997 symposium detail innovative and effective strategies for rehabilitation and maintenance of existing highways. Primary topics addressed include pavement evaluation for rehabilitation and management, cold in-place recycling techniques for pavement rehabilitation, effectiven