Development of Comprehensive Subgrade Deflection Acceptance Criteria - Phase 3 Report

This report has presented the findings of Phase III of research conducted to aid in the development of subgrade deflection acceptance criteria for WisDOT. The reconfigured rolling wheel deflectomter (RWD), portable truck-mounted deflection measurement systems, and automated dynamic cone penetrometer (DCP) were utilized on subgrade construction projects throughout the 2000 construction season. Laboratory analysis of soil properties, including Proctor, CBR and unconfined compression tests, were also conducted. The research findings have validated the concept of using deflection testing results to identify areas of poor in-place stability within constructed subgrades. It is recommended that pilot implementations of deflection acceptance testing be conducted in conjunction with subgrade penetration testing and moisture controls until more data has been collected, especially in moisture sensitive fine grained soil types. The use of deflection acceptance testing, in conjunction with in-situ penetration tests, should provide the data necessary to determine if the in-place support capacity for a given soil is sufficient to provide a stable construction platform for subsequent paving operations. However, it is important to note that both the RWD and DCP test results are related to the moisture-density conditions at the time of testing. Soils that show acceptable results (i.e., low deflections) may subsequently weaken due to changes in moisture content, freezing/thawing, etc. In instances where subgrade acceptance is well in advance of base course application, subgrade moisture changes may result in decreased soil support

Modelling vibratory roller–soil system dynamics using discrete element method

A simple yet useful implementation of lumped-parameter models using the discrete element method is discussed in this paper. Lumped-parameter models are often used in the modelling of vibratory roller-soil systems owing to their ability to capture the essential features observed during roller-soil vibrations. In order to investigate the system behaviour in the event of a decoupling (loss of contact between the drum and the soil), two conditions pertaining to the transition between the contact and non-contact phases are compared in the light of simulation results. The results demonstrate significant differences in the roller-soil system behaviour based on operating conditions. One particular case provides an unrealistic estimate of the contact force, and thus may lead to an incorrect prediction of the system dynamics. Another solution, however, provides a reasonable estimate of the system dynamics and is recommended herein

Mechanical and structural assessment of laboratory- and field-compacted asphalt mixtures

Compaction forms an integral part in the formation of the aggregate orientation and structure of an asphalt mixture and therefore has a profound influence on its final volumetric and mechanical performance. This article describes the influence of various forms of laboratory (gyratory, vibratory and slab-roller) and field compaction on the internal structure of asphalt specimens and subsequently on their mechanical properties, particularly stiffness and permanent deformation. A 2D image capturing and image analysis system has been used together with alternative specimen sizes and orientations to quantify the internal aggregate structure (orientation and segregation) for a range of typically used continuously graded asphalt mixtures. The results show that in terms of aggregate orientation, slab-compacted specimens tend to mimic field compaction better than gyratory and vibratory compaction. The mechanical properties of slab-compacted specimens also tend to be closer to that of field cores. However, the results also show that through careful selection of specimen size, specimen orientation and compaction variables, even mould-based compaction methods can be utilised with particular asphalt mixtures to represent field-compacted asphalt mixtures

Evaluation of Factors Affecting Earth Pressures on Buried Box Culverts

Factors affecting the earth pressures acting on buried box culverts under deep embankments were evaluated by field instrumentation and numerical analyses. Two instrumented cast-in-place concrete culverts were designed and constructed differently. Long term earth pressures under constant embankment height were observed after the completion of construction. Both observed earth pressures and those predicted by numerical analyses were compared with the current AASHTO earth pressure recommendations, as well as the AASHTO design pressures in effect at the time a failed box culvert was designed in the mid 1970s. Field measurements suggested that the previous AAHSTO design pressure (1977, 12th edition) significantly underestimated both vertical and horizontal earth pressures, whereas the current AASHTO (1996, 16th edition) provides more appropriate simplified earth pressures. Both measured and predicted earth pressures indicated that the level of compactive effort had a significant influence on the earth pressure distribution, especially the horizontal earth pressure acting on the culvert wall. A parametric finite element study suggested that the stiffness of the gravel backfill beside the culvert, which is dependent on the degree of compaction, had the greatest influence on the magnitude and distribution of earth pressure. An additional parametric study suggested that the modulus of the soil below the culvert also has a significant effect on the horizontal earth pressures. Dynamic horizontal earth pressures induced by different construction equipment operating close to the structure were also recorded. The measurements suggested that the dynamic strain in the structure in response to the maximum transient loading (about 70 kPa) was small and had negligible effect on the culvert. High residual compaction earth pressures measured after compaction were found to decrease rapidly with time to reach a steady value under constant embankment height. Analytical evaluation of the culvert orientation with respect to the embankment alignment suggested that the largest horizontal earth pressure acting on the culvert wall occurs when the culvert alignment is perpendicular to the alignment of embankment. The investigation of factors affecting the earth pressures on cast-in-place box culverts suggested that the design pressures are not only dependent upon the height of the embankment, but the relative stiffness of the surrounding materials is also important

Importance of controlling the degree of saturation in soil compaction

n the typical conventional fill compaction, the dry density ρd and the water content w are controlled in relation to (ρd)max and wopt determined by laboratory compaction tests using a representative sample at a certain compaction energy level CEL. Although CEL and actual soil type affect significantly the values of (ρd)max and wopt, they change inevitably in a given earthwork project while CEL in the field may not match the value used in the laboratory compaction tests. Compaction control based on the stiffness of compacted soil in the field has such a drawback that the stiffness drops upon wetting more largely as the degree of saturation, Sr, of compacted soil becomes lower than the optimum degree of saturation (Sr)opt defined as Sr when (ρd)max is obtained for a given CEL. In comparison, the value of (Sr)opt and the ρd/(ρd)max vs. Sr - (Sr)opt relation of compacted soil are rather insensitive to variations in CEL and soil type, while the strength and stiffness of unsoaked and soaked compacted soil is controlled by ρd and “Sr at the end of compaction”. It is proposed to control not only w and ρd but also Sr so that Sr becomes (Sr)opt and ρd becomes large enough to ensue soil properties required in design.Fundação para a Ciência e Tecnologia (FCT)info:eu-repo/semantics/publishedVersio

Dynamic Precompression Treatment - A Case History

An unusual case history of a condominium apartment building, originally designed for eleven storeys, to which four additional floors were added after the footings had already been constructed and was successfully completed to fifteen storeys in height . The use of rather high soil-bearing values, from 7 ksf ( 350 kPa) in the original design to over 12 ksf ( 600 kPa) . The project site , underlain by erratic soil profiles containing layers of soft fine-grained soils to about 20 ft (6 m) below the surface, had been effectively improved with an intense application of the Dynamic Precompression Treatment (OPT) . A historical background of the OPT and extensive general and specific details of the implementation of this technique are presented together with selection of design parameters, results of conventional in-situ testing and non-conventional stress-strain tests for determination of soil compressibility moduli. Stress settlement analyses and settlement records are also provided

RIDE VIBRATION AND COMPACTION DYNAMICS OF VIBRATORY SOIL COMPACTORS

This study explores the ride dynamics of typical North-American vibratory soil compactors via analytical and experimental methods. In-plane ride dynamic models of the vehicle are formulated to evaluate ride vibration responses of the vehicle in the transit mode on undeformable terrain surfaces with the roller vibrator off. An in-plane dynamic model is also formulated to study the compaction mode dynamics at lower speeds on elasto-plastic soil subject to roller induced vibration. Field measurements were conducted to characterize the ride vibration environments during the two modes of operations. The ride dynamic models of the soil compactor are thus analyzed to study its whole-body vibration environment while operating on undeformable random terrain surfaces. The modeling of the equipment in compaction mode of operation, however, gives insight over the efficiency of the compactor as a tool aimed to perform compaction of soil layers by plastic deformation (compression). The ride vibration environment of the vehicle and its compaction capability is subsequently assessed using the ISO-2631-1 (1997) guidelines and commonly accepted compaction criteria, respectively. The validity of the proposed model is demonstrated by comparing the model responses with the measured data. Comprehensive parametric analyses were subsequently performed to study the influences of variations in various design and operating parameters on the ride quality and the compaction efficiency of the mobile equipment. The results of the study are utilized to propose desirable design and operating parameters of the vibratory soil compactor for enhancement of its ride vibration environment and compaction performance