Kensey Nash

With the invention of the Angio-Seal™ Vascular Closure Device, Kensey Nash Corporation has established itself as a world leader in cardiovascular technology. Their recently completed facility in the Eagleview Corporate Center, Exton, Pennsylvania houses approximately 200,000 SF of state-of-the-art manufacturing space. Critical geologic factors identified and addressed by GeoStructures during design and construction included: 2 ft of wet surface clay; shallow perched groundwater; sublayers of loose sand (completely decomposed felsic gneiss); and 12-ft deep structural fills under the building foundations. Soil deficiencies were resolved through intensive subgrade preparation using a 15-ton roller in advance of filling, footing construction, and paving. Perimeter subsurface drainage was specified by GeoStructures to manage the perched groundwater and ensure a dry floor.

Eagleview’s “Trademark” Boulder Retaining Walls

Eagleview is unique in its widespread use of boulder retaining walls built of naturally occurring gneiss boulders exhumed from construction sites across the park. The largest walls are double-tier structures hundreds of feet long having a maximum height of 20 ft. In order to satisfy township codes, maximize the usefulness of such geologic materials, and ensure stability under critical conditions such as roadway and building surcharges, design drawings, typical details, specifications, and procedures for selecting and seating the boulders were standardized. Some of the boulders used in the base courses are the size of a small car.

While design of braced excavations is usually accomplished by empirical methods, such an approach raises questions about the deformation behavior of complicated systems under specific setups. Application of the finite element method (FEM) can bridge this gap and provide a calibration tool for detailed design optimization.

GeoStructures was retained by Schoor DePalma to analyze a 65-ft deep braced excavation along the Passaic River in Newark, New Jersey using finite element methods (FEM). The project involves installing two parallel rows of sheet piles—one driven along the riverside and the other 50 ft inland. The riverside sheet piles will be driven in the water along an existing bulkhead. Excavation to remove contaminated soil as well as the existing bulkhead is proposed between the two sheet pile walls to a maximum depth of 65 ft. As the excavation proceeds, internal bracings (waler and strut system) spaced at 25 ft are installed at various depths as shown in the finite element mesh. After removing contaminated soils, the excavation is backfilled to its original grade.

In order to remain competitive and to attract the best students, academic institutions across the United States are continually improving their facilities and infrastructure. Haverford College, a small but highly regarded liberal arts institution ten miles west of Philadelphia, is no exception. Founded in 1833 by the Quakers it is noted for its botanical setting and numerous historic structures. One of the latest campus improvements at Haverford College is an Integrated Athletic Facility—a 105,000-ft2, steel frame building having two stories above grade and two below grade.

The site’s bedrock geology belongs to the Wissahickon schist formation. During design, GeoStructures completed 22 test borings to explore the subsurface conditions. Our resulting characterization has identified a narrow zone of deeply weathered schist and relatively shallow groundwater under the center of site, suggesting an ancient tributary to Cobbs Creek. The original channel had been filled with granular soil.

The influence of the above factors and a maximum column load of 420 kips on shallow footing design was most pronounced at the transition between the squash courts and fitness room, which have a 23-ft difference in ground floor elevation. Our footing settlement predictions had to account for a bearing change from highly weathered rock in the basement to existing fill within the at-grade level. GeoStructures implemented a cost-effective but intensive densification operation to improve the fill for footing support through proofrolling with a 15-T roller, rather than undercutting and replacement. We were also responsible for inspecting footing construction, concrete and masonry.

In the middle to late 1800s the hills north of Palmerton, Pennsylvania were mined extensively for siderite, an iron carbonate mineral useful in the production of metallic paint. These underground “panel” mines were relatively shallow, steeply inclined features at a depth of 80 ft or less. The paint ore veins are associated with the weathered limestone of the Buttermilk Falls rock unit, which is sandwiched between the dramatic Stony Ridge cliff of resistant Palmerton sandstone to the south and Marcellus shale to the north. Due to relatively thin and highly weathered roof rock, the ground overlying the mines has been susceptible to sporadic subsidence, and any proposed building site in their vicinity must undergo a thorough geotechnical investigation and geologic risk assessment.

In their planning for a new middle school along Fireline Road north of Palmerton, architects and structural engineers of Quad Three Group hired GeoStructures to determine whether the site was geologically stable. Of particular concern less than 100 ft south of the site were signs of ground disturbance and boulder-filled shafts suggestive of historic exploration for economically viable paint ore deposits.

Our work began with research of USGS mineral publications for the Palmerton area, local records, photos, and historic mine maps. The mined out beds were noted to be 5 to 20 ft wide in the documents reviewed. Field mapping of Stony Ridge exposures by GeoStructures provided some understanding of local rock structure and the approximate location of the Palmerton-Buttermilk Falls geologic contact in advance of subsurface explorations. Core borings were used to check the identity and competency of the bedrock under the proposed school footprint, while 20-ft deep by 100-ft long test trenches were opened to determine the Palmerton-Buttermilk Falls contact as well as geologic structure.

For design of roadway improvements, GeoStructures conducted an existing condition survey of the roads using core borings, subgrade sampling, and laboratory testing of soil and asphalt. Conditions were found to be highly variable, with some of the roadways having a concrete base pavement and as many as nine separate overlays!

GeoStructures performed special borehole infiltration testing on site to assess potential groundwater recharge rates for existing soils. To accomplish this, four 8-in. diameter holes were drilled to depths of 10 to 14 ft then converted to test points using 4-in. diameter slotted casings, well sand, bentonite, and grout. Prior approval to use this method was obtained from Schuylkill Township through submission of a procedure and typical detail.

Swarthmore Rutledge Elementary School in Swarthmore, Pennsylvania is a stately, stone masonry building dating to the 1920s. Improvements and additions amounting to $9 million were recently completed by the Wallingford-Swarthmore School District. The work included a reconstructed front façade, new main lobby with elevator, and an elevator addition in the back of the building. Part of the existing façade was removed, as it was part of a 1950s reconstruction after a devastating fire and did not fit architecturally with the original style of the building. The new stone masonry façade restores its original classic appearance. The lobby and rear elevator additions are functional in nature.

To explore the subsurface and obtain as-built information on the existing foundations, GeoStructures conducted borings and test pits. Existing foundations were found to bear on dense silty sand or highly weathered schist rock of the Wissahickon formation. For structural design purposes, the dimensions and depths of the exposed footings were documented. Design options proposed by GeoStructures for supporting the new façade included widening the existing footings or constructing a new strip footing adjacent to the existing foundation. To optimize the design, different bearing pressures were provided for each option under varying soil and rock conditions. The primary issue associated with the lobby and rear additions turned out to be underpinning certain footings to accommodate the planned elevator pits.

GeoStructures was hired by Chestnut Hill College to design a retaining wall for a soccer field expansion project. Since the sports field is situated well inside the 100-year floodway of the Wissahickon Creek, we had to perform an impact study to demonstrate to the city of Philadelphia and the PADEP that its construction will not raise the level of the floodwaters. This was done according to FEMA’s equal conveyance replacement criteria, and as a result, certain improvements to the site’s surface and subsurface drainage were incorporated into the project. The retaining wall was designed and built as a geogrid-reinforced soil retaining wall.

Finite element analysis was utilized to model distressed pavement joints between concrete slabs and investigate the effects of mesh reinforcement on rehabilitation. Specifically, the contributing factors to pavement joint deterioration due to loss of support, aggregate interlock and dowel bars were studied and the effectiveness of steel mesh reinforcement in retarding reflective cracking through an asphalt overlay was evaluated.

Historic mining documents and old maps were obtained from the Office of Surface Mining (OSM) to study a dangerous collapsing shoulder problem along the Northeast Extension near Scranton. The records placed a vertical mineshaft in the area, and a deep core boring program verified the feature as a partially backfilled, 120-ft deep shaft. Careful consideration of various remedial options in terms of feasibility and disruption to traffic flow resulted in the selection of a compaction-grouting repair.

The cost of multi-story buildings can be greatly influenced by potential earthquake loads. This is especially true when loose fill or soft soils are present, as they are along navigable waterways of many cities. Under International Building Code (IBC) guidelines, the presence of as little as 10 ft of soft soil results in an ‘E’ or ‘F’ class even though more favorable soils may prevail in the upper 100 ft. Class ‘F’ automatically requires a seismic analysis to determine the magnification factors for structural design.

While classes ’A’ through ’E’ do not specifically require a seismic analysis, the determination of a site-specific response spectrum at the ground surface may justify upgrading to a better class. Ultimately, the use of site-specific magnification factors in place of standard values has the potential to reduce foundation size and optimize structural design.

On a project for Schoor DePalma across the Hudson from Manhattan, GeoStructures applied test borings, geophysical surveys, seismic cone soundings, resonant column testing, and dynamic seismic analysis using FEM and Quake/W to determine the site class. Our work enabled an upgrade in the site class from ‘E’ to ‘D’, resulting in significant savings in the building cost through optimization of the framing.

Program input requires that subsurface profiles and material properties be determined through a detailed test boring program, geophysical surveys, seismic cone soundings, and sometimes resonant column testing in the lab. These tools can account for interbedded soils, inclined strata, sloping bedrock, and other subsurface variations. Ground motion records from the field are scaled to the proper input motion at the bedrock, and dynamic analysis using time history is performed to develop a ground acceleration and response spectrum. The effects of structural features such as piles or caissons vs. shallow footings can also be accounted for in the analysis.

The cost of multi-story buildings can be greatly influenced by potential earthquake loads. This is especially true when loose fill or soft soils are present, as they are along navigable waterways of many cities. Under International Building Code (IBC) guidelines, the presence of as little as 10 ft of soft soil results in an ‘E’ or ‘F’ class even though more favorable soils may prevail in the upper 100 ft. Class ‘F’ automatically requires a seismic analysis to determine the magnification factors for structural design.

While classes ’A’ through ’E’ do not specifically require a seismic analysis, the determination of a site-specific response spectrum at the ground surface may justify upgrading to a better class. Ultimately, the use of site-specific magnification factors in place of standard values has the potential to reduce foundation size and optimize structural design.

On a project for Schoor DePalma across the Hudson from Manhattan, GeoStructures applied test borings, geophysical surveys, seismic cone soundings, resonant column testing, and dynamic seismic analysis using FEM and Quake/W to determine the site class. Our work enabled an upgrade in the site class from ‘E’ to ‘D’, resulting in significant savings in the building cost through optimization of the framing.

Program input requires that subsurface profiles and material properties be determined through a detailed test boring program, geophysical surveys, seismic cone soundings, and sometimes resonant column testing in the lab. These tools can account for interbedded soils, inclined strata, sloping bedrock, and other subsurface variations. Ground motion records from the field are scaled to the proper input motion at the bedrock, and dynamic analysis using time history is performed to develop a ground acceleration and response spectrum. The effects of structural features such as piles or caissons vs. shallow footings can also be accounted for in the analysis.

The city of Philadelphia is in the midst of a 21st century townhouse and condominium building boom as it rediscovers its historic and cultural heritage. Such projects present a common challenge with regard to protecting adjacent historic structures as new modern basements are extended below the old ones and there is a need for underpinning. On a recent project referred to as Olive Court, GeoStructures was hired by the developer, Taney Construction to design a safe and cost-effective underpinning system for an adjacent, historic, three-story stone masonry townhouse. Upon inspecting the foundation wall our engineers determined that it could sustain point loads from a helical pier type of support system, which is more economical than a conventional concrete pier option.

Our design called for thirteen, 12 to 15-ft long, 20-ton capacity, helical steel pier elements connected to the base of the wall using heavy duty steel brackets. No other connections were necessary, as the helical piers were spaced about every 32 in., the wall was capable of bridging between the brackets. GeoStructures prepared design drawings, specifications, and details for the project, and oversaw settlement monitoring by the project civil engineer. We were also on-site during construction to inspect pre-augering, installation of helical piers, grouting, and jacking of the brackets to load the piers. The contractor installed the piers into the ground using a terminal torque of 8,000 ft-lb to achieve their design capacity of 20 tons. Even with the close pier spacing, this system ended up being about half the cost of conventional concrete underpinning piers.

A case study of this foundation rehabilitation project was published in the ASCE Geotechnical Special Publication No. 81 – Soil Improvement for Big Digs.

Loose soil fill was responsible for a progressive foundation settlement problem under the garage adjacent to a 60 year-old stone masonry dwelling in Wynnewood, Pennsylvania. The maximum recorded subsidence was about 3 ¼ in., with a corresponding angular distortion of 1/100, resulting in distorted window and door frames.

Field explorations by the project geotechnical engineer showed that underpinning was necessary to stabilize the wall and prevent future settlement. Due to deterioration along the bottom of the wall, widely used discrete supporting elements such as helical piers or mini piles were not feasible without an expensive grade beam retrofit to distribute the point loads. Intermittent conventional underpinning by hand excavation and shoring from inside the garage was actually determined to be the least expensive option. Piers were excavated and constructed using the approach pit method with lintels in between. The depth of the underpinning piers was 8 to 11 ft below the bottom of the wall.

Contrary to common practice, this project demonstrates that under certain circumstances traditional, labor-intensive methods can still be preferred over the latest innovations.

A fill slope behind a 10-year old single-family dwelling was showing signs of distress in the form of slip scarps and rotational bulging features. GeoStructures explored the ground using a mini-trackhoe and found that the soil fill had not been compacted. Comparison of as-built plans to original plans indicated that a last-minute change must have been made that increased the setback of the house by about 15 ft, which placed it on the back edge of the prepared fill pad. Fortunately, the house footings were securely founded on well compacted fill, although the slope directly behind it was unstable and prone to slippage after heavy rains. Hence, there was concern on the part of the homeowner that the foundation soils would be undermined by erosion if the slippage were to continue. Erosion control mats did nothing to correct the situation.

The distressed slope was 28 ft high and overly steepened at 1.6H:1V without reinforcement. A detailed slope stability analysis was performed by GeoStructures to optimize the repair. In lieu of costly specialty systems such as helical screw anchors to stabilize the ground, we developed a carefully sequenced slope reconstruction operation from the ground up that could be done by any excavating contractor. Proper benching was critical to maintaining stability of the building pad while allowing for the installation of geogrid reinforcement and drainage measures.

As part of a 5-year open-end geotechnical contract with a large environmental consulting firm, GeoStructures has been providing shoring and underpinning design services in connection with the removal of soil contamination adjacent to and below existing residential structures. One interesting project affected an historic residence near Philadelphia, Pennsylvania, where GeoStructures was responsible for protecting the existing stone foundation walls of the house while an environmental contractor removed as much as 2 ft of fuel oil-contaminated soil from the basement. This work was sequenced and handled similar to conventional underpinning in that alternate sections were excavated to remove contamination next to the walls and concrete was poured incrementally to maintain lateral support of the foundation soil at all times.

I-95 through Wilmington, Delaware is part of the heavily traveled mid-Atlantic corridor which connects New York, Philadelphia, and Washington, D.C. A 2.7-mile segment of I-95 between the Wilmington Viaduct and U. S. Route 202 is slated for reconstruction by the Delaware Department of Transportation (DelDOT) in the near future. This 40-year old roadway was built as a 10-in. thick, jointed, reinforced Portland cement (JRPC) pavement over 3 to 4 in. of soil cement subbase. Performance problems include mid-slab cracking and joint deterioration. Maintenance teams have responded with full-depth and spot patching where needed, and “emergency” asphalt overlay within the city limits in 1996. Since then, reflective cracks have propagated through the overlay and conditions are deteriorating.

GeoStructures conducted a pavement condition survey and field exploration to assess the remaining life of the roadway. Initial falling weight deflectometer (FWD) testing at 189 points showed fair to good joint efficiency and a normalized deflection of 2 to 7 mils, indicating negligible loss of support from the underlying dense silty sand subgrade. DelDOT provided trailer-mounted core drills for sampling the pavement layers and subgrade. Laboratory strengths of concrete and soil cement specimens were 6,000 psi and 2,000 psi, respectively. Petrographic analyses showed only minor alkali-silica-reaction (ASR).

Our analysis revealed that the remaining service life of the roadway could be extended 8 years with a 6-in. overlay, although overhead clearance would not permit a 6-in. overlay. To provide an alternative to total reconstruction, a reduced overlay with steel mesh reinforcement to retard reflective cracking was proposed. Pavement stresses were modeled using the finite element method (FEM). We found that the mesh decreases tensile stresses and strains by 60 %.

In order to minimize drilling overruns on one hand and reinforcement waste on the other, the general contractor, Daniel J. Keating, Inc., sought accurate rock mass characterization beforehand. This was accomplished by GeoStructures by drilling a test hole at all 110 caisson locations (30 core borings and 80 percussion probes). Because it is a rapid but destructive drilling technique, percussion probing demanded careful calibration to core boring data before it could be relied on for design purposes. Deliberate timing of the percussion drilling in known conditions yielded category-assigned rates that were applied by our field engineers to characterize the rock mass and calculate socket lengths. On this site three general rock categories—soft, medium and hard—captured the variations in weathering, fracturing, hardness and unconfined compressive strength.

The original pile driving records as well as subsurface explorations carried out in the 1980s indicated that some of the piles terminated above design tip elevations on large slabs of old slate dumped before the approach fills were constructed, while others driven deeper than design tip elevations may have deflected off buried obstructions. Supplemental explorations conducted by GeoStructures in 2005 identified a 30 sloping rock surface below the South Abutment as a likely contributor to the erratic pile lengths under that particular substructure unit. Further complicating the subsurface picture at the south end of the existing bridge is the presence of a 60-ft high, 700-ft long, overly steep, distressed fill embankment.

 Design Challenges

GeoStructures is responsible for the geotechnical design aspects of a much wider replacement for the existing bridge that also includes improvements to a half mile of approach roadway at each end. Like most projects in mountainous terrain, this one transitions from deep rock cuts at each end to high benched fills toward the middle. Added to this are unusual challenges of stabilizing a distressed slope and understanding enough about the existing bridge instability to design a new foundation that will remain stable over the long-term. GeoStructures is also responsible for designing five 1H:1V geogrid-reinforced fill slopes in areas where right of way will not accommodate standard 1.5H:1V slopes.

GeoStructures considered many different geomembranes (HDPE, LDPE, PVC, Hypalon, etc.), each with advantages and limitations. An HDPE liner was determined to be both cost-effective and durable. Principal construction and quality assurance/quality control items checked by our engineers included: subgrade preparation and proofrolling; rapid response sinkhole remediation; embankment fill compaction; field and laboratory conformance testing of the geosynthetic materials; seaming; destructive and non-destructive seam testing; patching and repair of damaged spots; as-built liner panel layout; and compaction of the soil cover.

In conjunction with QA/QC, GeoStructures provided rapid response sinkhole consulting during initial massive earthwork, when two small collapses and depressions appeared. Those were excavated and stabilized to a depth of 20 ft by bridging methods using geogrid-reinforced plugs.

Since the USDS would be installed quite close to the toe of the 200-ft high landfill, the critical issues for the project were:

• Large lateral earth pressures on the USDS tanks from the retaining walls and slopes which could exceed the strength of the tanks.
• Potentially reduced slope stability factors of safety.
• Potentially reduced retaining wall factors of safety (bearing capacity, sliding, and overturning)
• Potentially reduced factors of safety against liquefaction of the hydraulically deposited fill in the recharge basin.

GeoStructures performed finite element analyses (FEM) to develop an accurate determination of the lateral earth pressures on the sides of the USDS tank. By running the FEM analysis, GeoStructures was able to optimize the design by revising the tank geometry and recommending minimum design strengths for the tanks which were then verified through material testing. GeoStructures also performed slope stability, retaining wall analyses, and liquefaction hazard analyses for the project. The liquefaction hazard analyses were performed using traditional semi-empirical methods, as well as 2-D dynamic finite element analysis. In the dynamic FEM analysis, selected ground motions were run to the model to study the effects, and the resulting dynamic stresses and strains were then utilized as inputs for a dynamic FEM slope stability analysis. The factor of safety could be analyzed at each time step in an earthquake record to study the resulting deformation of the slope above the zone of liquefaction.

A foundation block is proposed to support the machine based on the subsurface conditions and the magnitude of loading. Dynamic soil-structure interaction analysis is performed by using the powerful 3-D finite element program – Abaqus. The entire building and surrounding area including the machine pit and foundation are meshed in Abaqus/CAE. Transient/rotational loading from the machine is realistically simulated in the model.

The analysis provides real time ground vibration level at various distances from the machine. The results indicate that the ground vibrations are well below the threshold level and the proposed foundation block is adequate. The analysis also provides stress and strain in the foundation system, which can be used for the structural design of the foundation.