Monitoring Structural Cracks

Home , Castillo de San Marcos

Castillo de San Marcos National Monument, St. Augustine, Florida. Taken in 1995, this view looks across the moat toward the southwest bastion, where several major cracks are visible.

APPLICATION Monitoring AT A GLANCE

Application type: structural cracks Geotechnical Monitoring

Campbell Scientific equipment helps to Project area: preserve and restore an historic monument Castillo de San Marcos National Monument, St. Augustine, Florida, USA he Castillo de San Marcos National Monument, St. Augustine, Florida, is a Author: 17th Century historic, cultural, structur- T David Wright, architect al, and civil engineering landmark. The Park Superintendent, Gordie Wilson, together with Grieves Worrall Wright & O’Hatnick the Southeast Region of the National Park Service, has commenced a long-range monitor- Contracting agency: ing effort at the fort. The goal is to better National Park Service understand the causes of movement—and the resulting cracks—that have plagued areas of the Datalogger(s): fort walls for two hundred years. The fort’s bastions are earthen-filled, mason- Campbell Scientific CR10Xs ry ramparts, constructed on shallow founda- tions. Two of the four bastions have evidenced Communication links: cracks since the early 1800s. The fort’s founda- Phone line tions ought to be structurally sound according to an extensive investigation of both the founda- Measured parameters: tions and the soil bearing capacity. An emerg- x-y-z movement along cracks, tilt, ing theory postulates that the wall construction is near its structural limit in retaining the earth soil moisture, meteorological fill. Rainwater infiltration may increase the conditions internal load on the walls, causing the structure Sensors are installed across a crack in the southwest bastion. Continued on back NE NW Campbell Scientific provided the datalogger, multiplexers, weather stations, and soil moisture probes. The equipment was integrated with crack and tilt sensors.

Sensor emplacements are denoted by squares (tilt meters/inclinometers), circles (x-y-z crack gauges), and triangles (soil core/moisture sensors).

Continued from front The equipment was integrated with crack and tilt sensors manu- to move. A design team was factured and installed by Geokon formed to investigate this theory. (Lebanon, NH). AMJ Equipment Headed by architects Grieves (Lakeland, FL) and PSI Worrall Wright & O’Hatnick, the Engineering (Jacksonville, FL) team proposed that the park moni- provided technical and installation tor: assistance. To reduce the installa- • existing cracks in three- tion’s aesthetic impact on the dimensions park, cables were concealed in • tilt of the large segments custom conduit with the help of between the major cracks the park’s maintenance staff. • change of soil moisture with in the bastion at two levels, The sensors are measured and one near the surface and one the data are stored by the CR10X 16 feet deep at 5 a.m. and 5 p.m. On a quarter- • weather conditions at the site ly basis, the data stored in the to assess their impact on CR10X is downloaded via phone geotechnical activity modem to computers located in Monitoring equipment was the offices of the engineers and assembled from several vendors. architects for analysis and inter- Campbell Scientific provided the pretation. The project is sched- datalogger, multiplexers, weather uled to collect data for five to ten Sensors straddle cracks to directly measure displacement in each stations, and soil moisture probes. years. of three axes.