Pavana Vennapusa

Influence of Support Conditions on Roller-Integrated Machine Drive Power Measurements for Granular Base

A controlled field study was conducted to evaluate the influence of underlying layer support conditions on roller-integrated machine drive power (MDP) measurements. Multiple layers of granular base material were placed over a section of wet/soft subgrade and a section of concrete base for comparison. The material was compacted in layers using a 12-ton vibratory padfoot roller. MDP and in-situ spot test measurements were obtained on each layer and the results were statistically analyzed. Results indicate that compaction layer MDP measurements are strongly dependent on stiffness and heterogeneity of the supporting layer. If relatively stable and homogenous support conditions exist, the effect is not statistically detectable. Although the compaction layer properties (as measured by in-situ test measurements) are relatively uniform, the MDP measurements tend to capture the variability of the underlying layers. Post-construction tests by carefully excavating the compaction layers showed significant improvement in stiffness of the granular base layers compared to the initial compaction layer measurements. The reason is attributed to possible densification of underlying layers during compaction of the layers above and an increase in lateral stresses during compaction.

Rapid In Situ Measurement of Hydraulic Conductivity for Granular Pavement Foundations

This paper describes the application of a relatively new rapid in situ test device for measuring the hydraulic conductivity of granular pavement foundation materials. The test device uses air as the permeating fluid with compensations for fluid viscosity and unsaturated flow conditions. Because the test device allows for rapid measurement, many tests can be performed in a short time, which allows for statistical analysis of the results. Three different sections surfaced with crushed limestone subbase material were tested in this study. These test sections varied in support conditions beneath the subbase layer with cement-stabilized subgrade, geogrid at the subbase/subbase interface, and compacted subgrade (control section with no stabilization). Control section showed relatively high hydraulic conductivity on average and low amount of spatial variation. Cement-stabilized subgrade section showed relatively low hydraulic conductivity on average, and the geogrid reinforced section showed relatively high amount of spatial variation. The variations observed in hydraulic conductivity are directly related to the segregation and degradation of the base material, which occurred due to differences in the support conditions beneath the subbase layer and traffic loading.

Road Map for Implementation of Intelligent Compaction Technology

Over the past few years, intelligent compaction (IC) has been a focus of research, demonstration projects, and specification development in the United States. The Federal Highway Administration (FHWA) has recently moved IC to national level implementation. Equipment manufacturers, individual state departments of transportation (DOTs), and the Technology Transfer for Intelligent Compaction Consortium (TTICC), a Transportation Pooled Fund, TPF-5(233) initiative, are also focusing on implementation efforts. What this paper does is describe the results of a series of workshops attended by more than 400 attendees—representing several state DOTs, FHWA, equipment manufacturers, and researchers—that contributed to a detailed roadmap identifying implementation needs and action items. A key outcome of these workshops was the development of a prioritized list initially created in 2008 and updated annually through 2012. This paper describes in greater detail how this list was developed and prioritized and how it has changed since it was initiated in 2008. Accompanying this list is a set of action items to overcome the various barriers identified.

A Case Study of Geosynthetic-Reinforced Soil in a Low-Volume Bridge Abutment in Iowa

This paper presents findings from a case study conducted on a low-volume road bridge in Iowa, where geosynthetic-reinforced soil (GRS) was used as fill material in the reconstructed bridge abutments. The original steel bridge supported was on concrete abutments and was replaced with a longer railroad flat car bridge and spread footings founded on the GRS fill. The concrete abutments along with some of the existing fill were left in place to serve as GRS facing, and the soil under the new footing was excavated and replaced with GRS fill. The cost of constructing the bridge was about 60% lower than a conventional concrete bridge deck and abutments. Laboratory tests showed that samples reinforced with geosynthetic layers exhibit higher shear strength and lower permanent strain. When a static load was applied over the foundation with a loaded truck, horizontal stress increase was low along the excavation walls. Analysis indicated that the location of the water table and loading conditions influence the bearing capacity and global stability of the abutment system.

Interpretation of Dual Roller-Integrated Compaction Measurements on Layered Granular Fill

This paper presents findings from a field study conducted with a smooth drum vibratory roller equipped with machine drive power (MDP) and accelerometer based compaction meter value (CMV) technologies. Two test sections with layered granular materials were mapped using the roller and tested using light weight deflectometer (LWD) and dynamic cone penetrometer (DCP). One area consisted of a thin relatively stiff recycled asphalt material underlain by poorly graded fine sand and the other test area consisted of compacted layers of poorly graded sand. Results indicated that the thin stiff layer in one of the test areas influenced the MDP and LWD measurements more than the CMV measurements. CMV showed deeper influence depths (up to 1 m) compared to MDP (< 0.5 m). MDP measurements correlated well with LWD and DCP-California bearing ratio (CBR) measurements when data from the top 300 mm was used. CMV correlated well with CBR measurements when data from the full profile (up to 800 mm) was used. (161 words)