Company:
GeoInsight Inc Manchester, NH

Project Details

Fabric 1

FX-800/100PET
Producer: Carthage Mills
Supplier: US Construction Fabrics, LLC


Engineer Name 1
Mike Penney, PE

Engineer Company 1
GeoInsight, Inc.

Design Name
Brian Nereson, PE

Design Company
GeoInsight, Inc.

Subcontractor Name
John Lopes

Subcontractor Company
Lawrence-Lynch Corp.

Project Manager Name
Erik Strand, PE

Project Manager Company
Gale Associates, Inc.

Installation Company
Lawrence-Lynch Corp.


Please describe the project specifications

The project involved significant expansion of airport runway and taxiway areas over existing wetlands. The new embankments fills ranged in thickness from 2 to 5.5 feet, with thick asphalt surfaces on top. The subsurface conditions included deep, soft organic deposits and a water table generally at the ground surface. Placement of new fill on top of the existing organic material would have resulted in very significant and variable settlement of the new embankments. After studying a number of alternatives to provide a stable base for the expansion areas, the use of a Load Transfer Platform (LTP) was identified as being the best solution due to its overall favorable cost, installation schedule, and expected performance. The key component in the LTP is a high strength geotextile, which carries the new embankment loads above the deep organic deposits and distributes the loads to foundation elements, which in turn transfer the loads to acceptable bearing soils located underneath the organic layer. The foundation elements included pre-cast concrete pile caps set on timber piles treated with preservatives. The geotextile spans between each pile cap in tension, keeping the new embankment fill loads from compressing the organic material.


What was the purpose of this project? What did the client request?

The client requested a cost-effective method of allowing the runway and taxiway expansion over very challenging soil conditions, while staying within very strict wetland work area boundaries, minimizing downtime of the airport use, and meeting strict Federal Aviation Administration requirements for essentially no settlement of the completed new embankment surfaces. The client was open to technically sound alternatives and accepted the design premise that the LTP would
confidently meet the performance requirements, even though the use of LTPs is not common in New England.


What is unique or complex about the project?

Unique and complex attributes of the project included the combined requirements of creating a finished airport pavement surface that would not settle (100% soil compaction density required), pursuing a rapid construction schedule, and staying within the defined zones of allowable wetland disturbance. The ability to use a high strength fabric (approx. 8,900 lbs/ft tensile strength) enabled a cost-effective support pile spacing. The airport improvement project was also challenged by limited access and staging, but the LTP method allowed work to be accomplished starting from ends of existing runway and taxiway surfaces and progressing outward. The project requirements favored a system that was relatively quick and straightforward to construct, and that would perform as designed within the tight limits of work. Special design details and installation specifications were needed to promote proper function of the geosynthetic fabric reinforcement because of these site conditions. Although the installation contractor had never completed a LTP previously, field training and oversight were sufficient to meet the requirements.


What were the results of the project?

Use of the fabric-reinforced layer in combination with the timber piles saved well over $1M compared to the other construction alternatives considered. The relative ease of installation of the LTP system using the geosynthetic fabric reinforcement allowed a high degree of confidence in the work during construction. Each phase of the LTP construction could be visibly observed and it was straightforward to correct deficiencies and make small field changes prior to installation of covering soil. Engineering observations made during construction and settlement monitoring performed during and after embankment.


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