<p><p><figure id='attachment_3371' style='max-width:640px' class='caption aligncenter'><img class="wp-image-3371 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of approach embankment over load transfer platform for approach to railroad bridge over Rancocas Creek between Camden and Trenton, New Jersey" width="640" height="480" /><figcaption class='caption-text'> Photo from FHWA (2004)</figcaption></figure></p><p><div><h2><strong>Project Summary/Scope:</strong></h2>An embankment for a light rail line was constructed on soft, compressible soils at a river crossing. This project called for expansion of an existing railway embankment resulting in a higher embankment with a wider footprint. The work site was 35 feet wide and over 1,000 feet long. It was determined that the peat/organic layer described below could not carry the additional load without unacceptable settlement and the potential for slope stability failure. The bridge foundation at the river crossing consisted of concrete-filled pipe piles driven through the compressible soils into the underlying dense sands and gravel. The CSE was used to minimize the “bump” at the end of the bridge, which is critical in railroad applications. Due to limited right-of-way, a hybrid wall consisting of pre-cast pieces in the shape of a “T” stacked to form a gravity/MSE structure (T-wall) was used in lieu of a conventional embankment.</p><p>Subsurface Conditions: A total of 29 borings were drilled with depths up to 105 feet. Drilling included SPT, undisturbed sampling, and placement of groundwater observation wells. The site consisted of 2 to 8 feet of fill and a silty-sand layer (possible fill) ranging in depth from 2 to 20 feet. Peat, organic silts, and silty clays were found at depths ranging from 8 to 28 feet. This layer had an N-value of 6 and design allowable bearing capacity of 1,500 psf. A dense, silty sand with a design allowable bearing capacity of 3,500 psf was found at depths ranging from 25 to 40 feet.</p><p>A 3-foot thick Load Transfer Platform (LTP) was used with three layers of biaxial geogrid. Vibro-Concrete Columns (VCCs) were installed on a 7- to 9-foot center-to-center triangular spacing. The diameter of the columns was 20 inches and the clear span between columns was 5 to 7 feet. Construction was completed in March 2001.<br><h2>Complementary Technologies Used:</h2>Vibro-Concrete Columns<br><h2>Alternate Technologies:</h2>The evaluation of soil improvement methods ruled out wick drains and surcharge due to the time required for stabilization and the amount of post construction settlement anticipated. Studies of retaining wall design and construction methods ruled out cast‑in-place concrete construction due to cost and schedule.</p><p><img class="aligncenter wp-image-3374 size-large" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Diagram of cross section of load transfer platform over vibro-concrete columns for approach to railroad bridge over Rancocas Creek between Camden and Trenton, New Jersey" width="1024" height="618" /><h2>Performance Monitoring:</h2>Four concrete cylinders were taken daily for the VCCs and tested. A load test in accordance with ASTM D1143 was conducted on one column to verify the design. A maximum settlement of ¼ inch was recorded three months after completion and backfill of the T-wall. Additional settlement surveys taken after a one-year period showed no additional deformation of the support systems.<br><h2>Project Technical Paper:</h2>Young, L.W., Minton, M.N., Collin, J.G, Drooff, E., (2004). “Vibro-concrete columns and geosynthetic reinforced load transfer platform solve difficult foundation problem.” 22^nd World Road Congress.</p><p>Young, L.M., Milton, M.N., Collin, J.G., and Drooff, E.R. (2008) “Vibro-Concrete Columns and Geosynthetic Load Transfer Platform Solve Difficult Foundation Problem”, Pan American Geosynthetic Conference, Cancun, Mexico, March 2008.<br><h2>Summary Source:</h2><em>Ground Improvement Methods</em>, FHWA NHI-06-019 (Vol. I) and FHWA NHI-06-020 (Vol. II), 2006.<br><h2>Date Case History Prepared:</h2><strong> </strong>November 2012</p><p></div></p></p>