Fiber-optic conduit seeks refuge under Fort Worth

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Fiber-optic conduit seeks refuge under Fort Worth



When American Communication Services of Fort Worth Inc. decided to build fiber-optic ring networks to serve business and government clients in downtown Fort Worth, TX, the company chose synchronous optical network technology. Sonet`s self-healing characteristics allow uninterrupted service in the event of a natural disaster, such as violent thunderstorms or a cable cut. Sonet`s capabilities for rerouting, electronic redundancy and power backup systems, as well as its built-in monitoring capabilities, convinced American Communications that it was the most secure system for its customers. Before determining that Fort Worth was a viable market for the installation of new fiber-optic ring networks, ACSI interviewed potential corporate users who wished to use alternative long-distance interconnect services.

For the heart of the backbone system in Fort Worth, ACSI installed an AT&T Fitel 96-strand, singlemode fiber-optic cable in 4-inch diameter, four-way multicell conduits. The fiber capacity is much greater than initially needed: Only one of four conduits is being activated, allowing substantial conduit reserves for expansion.

The fiber-optic rings consist of more than 180 fiber miles installed in the downtown business district. The network passes more than 30 buildings housing approximately 7 million square feet of office space, and it can provide service to hundreds of business and government customers.

Underground installation

To ensure maximum security and reliability of the system, ACSI selected a 100% underground installation strategy for the downtown network, even though aerial cabling is easier to install and less expensive.

Although routing through the city was preplanned and pre-approved, as work commenced, ACSI found an unexpectedly heavy concentration of utility conduit along the route. This existing cabling infrastructure often prohibited conduit placement where it had been originally planned. Furthermore, rock formations under city streets mandated open trenching instead of directional boring. The conduit-laying effort therefore required flexibility and cooperation between ACSI and the City of Fort Worth.

The company initially planned to use the latest installation technology--low-impact directional drilling or boring equipment--to tunnel for its new conduit, and keep excavation to a minimum. However, the unanticipated amount of rock and abundant utility conduit in place forced the company to use traditional trenching methods to complete the job. Four-person crews jackhammered the rock by hand or used a hoe-ram backhoe. Fortunately, blasting was not required.

ACSI acknowledged that conduit drilling becomes intricate when carried out in a downtown environment. The Fishel Co. in Columbus, OH, ACSI`s choice to handle construction, however, solved numerous installation challenges.

Some of the obstacles encountered included heavy, existing utility cabling, extensive rock formations, and the need to meet tight city standards for sidewalk and roadway replacement after each phase of the trenching work was completed. (Fort Worth has strict street-construction standards and enforces stringent specifications for the replacement of concrete and asphalt.)

The sidewalks and roads had steel reinforcements throughout. When they were removed during trenching, they had to be replaced according to uncompromising city ordinances. When trenching occurred in asphalt streets, an asphalt lane that was approximately 10-feet wide was replaced. During trenching, excavations were filled with flowable backfill.

Brick replacement

The most unusual replacement job, however, involved brickwork, which covered a portion of Main Street. ACSI found that digging up a portion of Main Street was essential in laying conduit. Consequently, ACSI had to punch three large holes in two areas at First and Seventh Streets, involving approximately 200 linear feet. The restrictive brick-relaying work cost nearly $100 per linear foot. Fishel hired local brickwork artisans to remove the bricks one-by-one, number them, map the removed brick area, and replace each brick in the same arrangement.

At frequent intervals, ACSI placed communication "hand holes." These 2-by-4 boxes were positioned in concrete along the conduit routed in the streets and allowed ACSI to serve customers from the backbone. The hand holes also serve to facilitate fiber-cable splicing.

The final link connected each building in the downtown area. The process consisted of obtaining a street coding permit, trenching up to the building foundation and coring into the building. Then, fiber cable was pulled into the building, and spliced onto the backbone of the network cable.

After the splicing operation was completed, the fiber-optic equipment in the building was installed. Next, service cables were strung to the customer premises locations on each floor of the building.

When installation of the fiber-optic system was completed, ACSI conducted a 72-hour test of the equipment before initiating service. From ACSI`s node--the main testing hub--a series of command signals were transmitted to the building. When the system proved error-free, ACSI turned up the building`s voice traffic.

Add services at any time

The Sonet system allowed seven buildings and the node to be connected on each Sonet ring, enabling all seven buildings to be tested, monitored and serviced simultaneously. The Sonet rings also make it possible for buildings to add ACSI services at any time. Once the customer service is online, ACSI will connect customers to their long-distance carrier of choice. Customers will use the system primarily for voice and data transmissions, but the network is capable of handling multimedia and advanced services.

ACSI intends to complete 20 fiber-optic ring networks by the end of 1996 and will use Sonet-ring technology in all of its target markets--mid-sized cities in the South and Southwest that have a solid corporate base. In addition to Fort Worth, locations will include Louisville, KY; Little Rock, AR; Greenville, SC; and Columbia, SC. q

Steve Ambrose is general manager at American Communication Services of Fort Worth Inc., TX. Th Lw32197 24

Workers trench under utility lines during American Communications Services Inc.`s Fort Worth, TX, downtown fiber-optic network construction. Rock formations under city streets mandated open trenching instead of directional boring.

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