Bridge Approach Embankment Research Articles

Mass Stabilization for Environmentally Sensitive Projects in Florida

US-1 is a two-lane highway and the main route to and from the Florida Keys. A hurricane preparedness and public safety plan included the Florida Department of Transportation's replacement of the drawbridge over Jewfish Creek with a fixed bridge and widening of the roadway north of the bridge. Before construction, the widening program included mass stabilization to improve the soft underlying soils, which consisted of 5 ft of granular fill placed over 10 to 15 ft of soft organic silt overlying limestone. The bridge approach embankments reached up to 20 ft in height. Safety was critical because the work took place adjacent to an active highway. The entire project was environmentally sensitive and required attention to spoil controls because the work was performed adjacent to water and wildlife. In another environmentally sensitive area, a new two-lane bridge was planned for construction on driven piling over a waterway in Port Everglades, Florida. The subsurface consisted of 3 to 4 ft of sand followed by 8 to 10 ft of peat, then limestone. The peat layer was unsuitable to support the mechanically stabilized earth (MSE) walls planned for the abutments. A mass stabilization program was conducted to improve the bearing capacity and limit settlement and to ensure global stability of the MSE walls. Considerations included the existing condition of soils contaminated by petroleum hydrocarbon and environmentally sensitive adjacent properties, including a manatee mating area. The mass stabilization construction methods and procedures, design considerations, quality control, equipment, and performance monitoring of these two environmentally sensitive bridge projects are discussed.

Use of Lightweight ECS as a Fill Material to Control Approach Embankment Settlements

A research study was conducted to evaluate the use of light weight aggregate (LWA) material produced from the manufacturing of expanded clay and shale (ECS) for potential use as a roadway approach embankment material. The use of such LWAs is expected to reduce stresses on subgrade foundation, which in turn could lead to less or no approach settlements. The test site was constructed on the south end of a new bridge overpass on State Highway 360 in Arlington, Texas and a control section was constructed on the north end of the same bridge. In the control section, a low plastic borrow soil (normal fill) was used as an embankment fill material. This paper presents both laboratory and field evaluations of the utilization of both ECS material and conventional borrow soil as embankments fill material. Shear strength and consolidation tests were performed to evaluate strength and compressibility characteristics. The embankment section was instrumented with vertical inclinometers to monitor the fill movements due to field loading conditions. Pavement surface profiling of both ends of the bridge was also performed at regular time intervals. Numerical simulations of test sections were also attempted. Based on the data obtained from experimental, field monitoring and numerical studies, it can be mentioned that the utilization of ECS LWAs are efficient in minimizing the bridge approach embankment settlements and reduced bump problems at the entry and departure of the bridges.

3D coupled mechanical and hydraulic modeling of a geosynthetic-reinforced deep mixed column-supported embankment

Numerical studies were conducted to improve the understanding of the behavior of geosynthetic-reinforced column-supported embankments. Due to the complexity of the problem, so far, consolidation process and three-dimensional patterns of columns have not been well simulated in most published numerical studies. As a result, the time-dependant behavior and the serviceability of this system have not been well evaluated. In this study, a three-dimensional coupled mechanical and hydraulic modeling was conducted using FLAC3D to consider consolidation and three-dimensional arrangement of columns. This study was based on a well-documented bridge approach embankment reinforced by a layer of geotextile and supported by deep mixed (DM) columns. The foundation soils including soft clay and silt, the embankment fill, and the deep mixed columns were modeled as linearly elastic-perfectly plastic materials with Mohr–Coulomb failure criteria. The geotextile reinforcement was simulated by geogrid elements incorporated in the FLAC3D software, which can sustain in-plane tensile force only. The staged construction was simulated by building the embankment in lifts. The duration of each lift was the same as the actual construction time plus the lapse time between two consecutive stages. The development of settlement and tension in the geotextile with time is compared with the long-term monitoring data and yields good agreement. The generation and dissipation of excess pore water pressure during and after construction are presented and discussed.

Dynamic Analyses of a Skewed Short-Span, Box-Girder Overpass

A number of recent research studies have provided insight into the seismic response characteristics of short-span overpass bridge systems. Application of system identification techniques to measured earthquake response data for this class of bridges has indicated that the bridge superstructure, abutments and approach embankment soil constitute a strongly coupled system. The dynamical behavior of the foundation and embankment soil have a first order influence on the dynamic response of the bridge superstructure. Analysis of measured strong motion response data has also indicated that localized nonlinear behavior of the embankment soil can result in significant nonlinear global behavior of the entire system, even when the bridge superstructure remains linear. The current paper presents the results of detailed numerical simulation studies of the dynamic response of a short-span overpass bridge system. Two distinctly different modeling approaches are investigated. The first approach utilizes simple reduced order “stick” model idealizations of the bridge, and the second approach utilizes a detailed, large scale, three dimensional finite element model. The detailed model includes a discretization of the soil embankments and a simple nonlinear material model is used to represent the hysteretic soil behavior. The sensitivity of bridge response to various parameters, such as deck skew, embankment soil stiffness and soil mass, stick model modal damping values, and soil nonlinearity has been investigated. Earthquake response predictions are performed with both model types and the response computations are compared to earthquake response data measurements. The ability of the models to accurately represent the bridge seismic response is discussed, and the two modeling approaches are compared and contrasted.

Stress characteristics for shallow footings in cohesionless slopes

Footings placed at shallow depth in bridge approach embankments can be used to reduce the cost and to improve the performance of bridge supports. The embankments frequently terminate in slopes dropping to underpass level, and the footings therefore have lower capacity than that for footings on level ground. The needed design procedures have not been well validated.The paper describes a new solution using the method of stress characteristics for footing capacity in cohesionless slopes. The soil is assumed to have c = 0, [Formula: see text] = constant, γ > 0. Particular attention is paid to modelling the asymmetric nonfailing zone immediately beneath the footing. Solutions for various slope angles and friction angles have been obtained for footings placed at the crest of the slope with D/B = H/B = 0, and for H/B = 0.5, 1.0, and 2.0; D/B = 0.5 and 1.0. The theoretical bearing capacities are compared with experimental values from two series of laboratory tests. Key words: bearing capacity, footings, failure, bridge abutments, slopes, sand, cohesionless, stress characteristics.

Utilizing geotextiles in highway bridge approach embankments : Edgar, T V; Puckett, J A; Sherman, W F; Groom, J L Geotext GeomemV5, N1, 1987, P3–16

Utilizing geotextiles in highway bridge approach embankments : Edgar, T V; Puckett, J A; Sherman, W F; Groom, J L Geotext GeomemV5, N1, 1987, P3–16

Utilizing geotextiles in highway bridge approach embankments : Edgar, T V; Puckett, J A; Sherman, W F; Groom J L Geotext GeomemV5, N1, 1987, P3–16

Utilizing geotextiles in highway bridge approach embankments : Edgar, T V; Puckett, J A; Sherman, W F; Groom J L Geotext GeomemV5, N1, 1987, P3–16

Utilizing geotextiles in highway bridge approach embankments

Geotextiles have been employed to reduce lateral deformation of bridge approach embankments and to prevent closure of the expansion devices in the bridges. This unique application of geotextile materials has been successfully used by the Wyoming Highway Department for several years. The concept has recently been modified by eliminating the lateral pressure on the abutment wall. This is achieved by creating a free standing geotextile supported wall. This concept will be implemented in an existing bridge undergoing reconstruction. Problems concerning the retrofit design and construction are discussed. A laboratory testing program has been developed to obtain the deformational characteristics of the soil-geotextile composite. The significant findings are: 1. (1) Lateral deformations of 80–150 mm are required for the geotextile to totally support the soil. The range is dependent on the initial tension of the geotextile during forming. Once the free standing face has been developed, subsequent loading produces only minor additional lateral deformations. 2. (2) Preliminary testing indicates for a fixed lift height, the amount of deformation required to reduce the lateral stresses by specified amounts can be predicted. 3. (3) Common plastic foams do not appear to provide sufficient flexibility to reduce the lateral stress developed on abutment walls.

Geogrid reinforcement for cochrane bridge embankment

Construction of a 6·62 m (27·7 ft) high bridge approach embankment over weak marsh deposits in Mobile, Alabama was accomplished through the use of geogrid reinforcing and wick drains, resulting in estimated savings of US$600 000. Lightweight polypropylene geogrids and a nonwoven polyester geotextile were used in tandem to permit the construction of a 0·61 m (2 ft) sand blanket across the marsh. The sand blanket served as a working platform for the installation of wick drains which were used to reduce the time required for settlement of the embankment to less than two months. High density polyethylene geogrids were employed to reinforce the embankment so that full embankment height could be constructed without incurring the time delays of stage construction. The advantages of geogrid reinforcement and the construction procedure are discussed.

Two-Dimensional Analysis of Backwater at Bridges

A two-space dimensional mathematical model of computing steady flow distributions and water levels near contractions in natural waterways (e.g., highway bridges) is developed. The two-dimensional model provides a theoretical basis for such one-dimensional concepts as expansion losses by accounting for all losses by friction along properly located two-dimensional streamlines. The finite element solution algorithm locates these streamlines and integrates energy loss due to friction along them. Stagnation zones downstream from contractions can be predicted and located by the algorithm. A necessary condition for separation is that the velocity head at the point of separation exceeds head loss due to friction along some possible path for a free streamline. The absence of separation which is associated with scouring currents along the downstream side of bridge approach embankments can be predicted where the necessary condition is not satisfied.