San Antonio, Texas has been home to Tesoro Corporation since 1968. At some point, they were running out of space so they relocated their headquarters to the intersection of U.S. Highway 281 and Redland Road which is just north of Loop 1604 at Ridgewood Park. The property is owned by Patrinely Group, LLC and was under construction on 122 acres of space including 618,000 square feet reserved for leasing office space. It was set to be completed in the summer of 2009.
San Antonio's terrain includes rolling hills and some steep cliffs with exposed limestone rock. Ridgewood Park is no exception to the local terrain with significant elevation changes throughout the area. Approximately 300,000 cubic yards of mass grading was necessary for the building locations and two engineered bridges were included in the plan.
The developer needed access to the site from the south so it was decided to have an access road coming off Sonterra Blvd. The challenge with this location for an access road, there is a 75 feet elevation differential from the top of the street down to the existing grades on the property. Because there was limited space in this area, the constructed steepened slope was totally out of the question and a retaining wall would be necessary on the east side of the access road.
A Keystone engineered wall system using Miragrid® geogrid was considered the most economical and architecturally attractive choice.
The Design
The engineers on the project worked with the owner to figure out what type of MSE wall would meet their goal of constructing a pleasing, attractive structure capable of supporting loading conditions of the planned access road.
The Keystone engineered wall system was chosen for its creative appearance and its height-to-depth ratio would deliver a structurally sound, engineered wall system with superior stability, durability, and strength.
Geogrids are important for reinforcing components in the engineered wall system. Miragrid® 3XT, 5XT, and 8XT geogrids were brought into the design because of long-term durability and creep reduced design strengths and compatibility of the connection characteristics of the Miragrid® products to the Keystone wall blocks. Using Miragrid® for its high tensile strength in the Keystone wall system improved the wall design by creating a stable soil mass behind the wall. Using Miragrid® products in the wall system and getting the internal stability needed, the soil would be applied with less pressure on the back of the blocks which would greatly minimize bulging and other stability issues.
Construction
The terrain of the site offered many challenges for the construction of the wall system and the access road. Because of the elevation changes, the Keystone engineered wall system was constructed into a three-tiered system with the tallest part of the wall being 43 feet. The construction of the foundation of the wall system involved compacting a TXDOT type aggregate to a level grade. The contractor installed Miragrid® 3XT, 5XT, and 8XT at specific elevations for reinforcement of the soil structure. Because of Miragrid® XT geogrids’ flexible construction, the contractor was able to maneuver and connect the geogrid between the individual Keystone blocks more easily than with stiffer reinforcement grids. The Miragrid® XT geogrids’ strength helped compaction of the backfill material allowing the contractor to achieve a specific density requirement quite easily.
Performance
The project was a complete success and the contractor was able to complete the Keystone engineered wall system on time. The entire system gave the developer the goal of creating an aesthetically pleasing system by providing a solution to constructing an important access road into the property. Everyone involved with the design, construction, and the final results of the wall was rewarding.
