Updates from GNCB

GNCB Attends CSCE Spring 2017 Geotech Workshop on CT Varved Clay

  • By GNCB
  • 27 Apr, 2017

New Haven, CT

David Freed , GNCB Geotechnical department head, recently attended an informative one-day geotechnical workshop on the Connecticut Valley Varved Clay (CVVC). About 60 geotechnical professionals attended the workshop, sponsored by the Connecticut Society of Civil Engineers , which was held at the University of New Haven. Dr. Stanley Bemben - consultant, former UMASS professor, workshop organizer, and primary speaker - put together a team of seven speakers from the university and design professional environment to address topics on geologic aspects, characteristics and behavior, the “cementation” phenomenon, construction aspects. Several case studies were presented as well.

The CVVC deposit, which ranges up to about 100 ft. thick, is a direct result of the yearly deposition of alternating thin layers of silt and clay within the former Lake Hitchcock. This glacial lake, which is reduced in size and now approximately aligns with the Connecticut River, extends from about Hartford CT to the northern USA/Canada border.  A clay and silt layer represent one year’s cycle of time; the number  of cycles, much like the rings of a tree, are studied to provide a realistic estimate of the age of the deposit. The surface of the clay is stiff (desiccated crust), a result of exposure to drying once the lake was drained, however the majority of the deposit is very soft which exhibits large settlements when stressed above its maximum past pressure. In his presentation, Dr. Bemben states that “the silt/clay deposit has an inherent “cementing” due to precipitation of cementing agents and an ongoing time dependent aging process”. One net effect of the cementation process results in an under estimation of compressibility properties when interpreting one-dimensional consolidation tests using classical Terzaghi analysis.  

The CVVC deposit is well-studied, however its compressibility and strength characteristics vary considerable between locations.   One and two story structures can often be supported on shallow spread footing foundations, provided there is an upper alluvium sand or the surface of the CVVC has a desiccated crust. However taller structures often requires improvement of the CVVC by preloading that is aided by wick/sand drains, or by driving deep piles to the underlying dense glacial till or rock.   Due to the variable despite characteristics, tall structures supported on top of the CVVC requires a program of laboratory index, compressibility, and strength testing to document conditions at a specific site.

Working within the CVVC deposit can also be challenging. The soils are generally sensitive, requiring careful field procedures to preserve its intact condition, bearing capacity and strength. Workmen can easily disturb soils to the extent that they can no longer support the specified soil bearing.  

David Freed can be contacted at freed@gncbenigneers.com .

By GNCB 18 Aug, 2017

GNCB believes that it is important to foster students’ interest in the fields of structural engineering, geotechnical engineering, and historic preservation. The firm is proud of its internship program which supports students at both the high school and college levels. This summer, Ms. Eleanor Phetteplace of Roger Williams University (RWU) joined GNCB as an intern. Ms. Phetteplace is an Engineering major, with a specialization in civil engineering, and is minoring in both Historic Preservation and in Mathematics. She began her internship in May ( GNCB Welcomes Eleanor Phetteplace ).

While working at GNCB, Ms. Phetteplace was given the opportunity to work with our engineers is all three departments. She was tasked with a wide range of assignments both in and out of the office. As her education and interests lean towards historic preservation, Ms. Phetteplace worked mostly on existing and historic structures where she was responsible for site surveys, condition assessments, structural calculations, writing reports, and drafting. Some of her historic projects included unreinforced masonry mill buildings, timber churches, a caisson foundation lighthouse and several academic buildings.

In addition to working with existing buildings, Ms. Phetteplace worked on new construction projects where she helped create 3D Revit models and determined dead and live loads on bearing walls for the design of spread footings. Additionally, she conducted research on Fall Protection standards in order to participate in the assessment of fall protection systems for a Massachusetts college.

With our geotechnical engineering department, Ms. Phetteplace participated in the soil investigation of a new hotel site in central Massachusetts. As she has not yet taken any soils-related classes, she found this assignment particularly interesting and looks forward to incorporating geotechnical courses into her curriculum as her education continues.

Ms. Phetteplace’s favorite aspects of this internship included gaining knowledge and experience with structures in the field during site surveys and construction administration. She believes that her new skills with Autodesk Revit and Risa-3D will be incredibly beneficial in her future as a structural engineer. She also enjoyed learning about the interaction between design team and construction team members at different project stages.

By GNCB 08 Aug, 2017

The Church of St. Michael the Archangel reached its next milestone this July with the installation of its new steeple. The steeple is a reconstruction of the original steeple based on archival photos of the civil-war era Church. The original steeple blew off the Church shortly after it was built, making its reconstruction an integral component of this Project.

The steeple is anchored to the structure with a series of bolts fastened through the octagonal base of the steeple and an octagonal angle frame designed by GNCB. The steeple is braced with chevron braces within its square base which is constructed with structural steel designed to accommodate the replicated tapering of the original steeple.

Phase 1 of the reconstruction of St. Michael Church will soon be completed. In addition to the installation of the steeple, the cold-formed steel shear walls are close to completion as the exterior cladding and stained glass windows are being installed. The east and west entrances and rear additions are in progress. Phase 2 of the project will include the interior fit-out and finishing of the Church.

This marks the second major milestone in the reconstruction of St. Michael. The first milestone, the raising of the first timber truss , was celebrated by the Parish with a truss-raising ceremony during which Bishop Michael Cote of the Diocese of Norwich blessed the first truss before its installation.

Architect: Geddis Architects

Construction Manager: Petra Construction

Steeple Fabricator: Campbellsville Industries, Inc.

Watch the videos of the steeple and cross installation.

Steeple Installation Video

Cross Installation Video

By GNCB 07 Aug, 2017

GNCB recently provided geotechnical engineering and construction administration services for the recent renovation to Putnam High School located off of Woodstock Avenue in Putnam, CT. The project included classroom and library renovations and the addition of an expanded gym along the southeast side of the 1950s building. Other site improvements included expanding the parking areas, redirecting traffic and bus flow, and constructing retaining walls. The $36.6 million project was led by O&G Industries, of Torrington, CT, as construction manager.

GNCB’s services included a test boring program which revealed site conditions that consisted of thick sand and gravel. Previous site utility work resulted in deposits of man-placed fill at some areas. The man-placed fill required removal and replacement with compacted structural fill. The full extent of the fill was uncovered during construction, during GNCB’s field monitoring of building footing preparation. The deep cuts at the south end of the site for the new parking area enabled the on-site reuse of the excavated sand and gravel as structural fill.

Architect: Drummey Rosane Anderson (DRA Architets)

Construction Manager: O&G Industries

By GNCB 24 Jul, 2017

The Connecticut Cancer Foundation Headquarters in Old Saybrook, CT is close to completion. The Headquarters is GNCB’s latest “hometown” project. Throughout our 52 years in Old Saybrook, our structural engineers, geotechnical engineers, and historic preservationists have been involved in numerous Town projects including the elementary, middle, and high schools, the Katharine Hepburn Cultural Arts Center, the stabilization of the Town Dock, and various residential projects.

The CT Cancer Foundation Headquarters consists of a 4,400 square foot addition to the Sanford House, an early 19th-century, timber-framed home. The addition consists of reinforced concrete foundations supporting a steel-framed first floor and a wood-framed superstructure.

GNCB designed a strong-back system for the perimeter of the Sanford House to allow removal of the first floor framing and increased headroom for the new Headquarters. The original House’s chimney was removed at the interior of the building and is supported and stabilized with a new engineered wood framing system.

GNCB served as Structural Engineer of Record for the Headquarters. Additionally, our firm provided historic preservation and special inspection services for this project.

Architect: Point One Architects

Construction Manager: Enterprise Builders, Inc

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