Permanent Earth Retention for Deep Excavation Installed Within Minimal Right of Way Limits-Paper

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The project involved constructing a mixed-use building with up to three levels of underground parking in State College, Pennsylvania. Excavations reached approximately 21–36 ft below street level, while tight right-of-way limits, busy streets, and existing and planned utilities ruled out a single conventional earth-retention solution. Subsurface conditions added difficulty: shallow overburden containing clay, cobbles, and boulders overlay highly variable karstic dolomite with weathered zones and open voids.<br /><br />The design combined soil nail walls with micropile soldier piles. Soil nails provided support across most of the site. Where utilities or right-of-way restrictions prevented their use—particularly in the upper excavation—micropiles acted as soldier piles, with soil nails supporting the lower wall. All areas received permanent shotcrete facings. To keep permanent nails within property limits, the design team coordinated with the building designers to use the garage floor slabs as lateral brace points. Temporary nails could extend into the right-of-way with municipal approval.<br /><br />Construction proceeded in staged excavation lifts, with shotcrete applied as initial and final facings. Irregular soil and broken rock made forming a smooth wall face challenging and increased shotcrete use. After heavy rain saturated the ground along Calder Way, soil-nailing work caused movement in the wall and sidewalk. The team stabilized the area with an earthen berm, installed micropile soldier piles, filled voids with flowable fill, and then completed the wall.<br /><br />The project demonstrated that a coordinated hybrid system can accommodate deep excavation, restricted space, utilities, and difficult geology while providing permanent retention. Close communication among the owner, designers, contractors, and municipality enabled timely responses to changing conditions and helped keep the work within project constraints.

Keywords

mixed-use building

underground parking

deep excavation

soil nail walls

micropile soldier piles

shotcrete facing

karstic dolomite

utility conflicts

right-of-way restrictions

retaining system