岩土工程监测

Campbell Scientific equipment helpsto preserve and restore an historic monument
Monitoring structural cracks

 The Castillo de San Marcos National Monument, St.Augustine, Florida, is a17th Century historic, cultural,structural, and civil engineering landmark.  The ParkSuperintendent, Gordie Wilson, together with the Southeast Regionof the National Park Service, has commenced a long-range monitoringeffort at the fort.  The goal is to better understand thecauses of movement—and the resulting cracks—that have plagued areasof the fort walls for two hundred years.

The fort’s bastions are earthen-filled, masonry ramparts,constructed on shallow foundations.  Two of the four bastionshave evidenced cracks since the early 1800s.  The fort’sfoundations ought to be structurally sound according to anextensive investigation of both the foundations and the soilbearing capacity.  An emerging theory postulates that the wallconstruction is near its structural limit in retaining the earthfill.  Rainwater infiltration may increase the internal loadon the walls, causing the structure to move.  A design teamwas formed to investigate this theory. Headed by architects GrievesWorrall Wright & O’Hatnick, the team proposed that the parkmonitor:

•existing cracks in three-dimensions

•tilt of the large segments between the major cracks

•change of soil moisture within the bastion at two levels, onenear the surface and one 16 feet deep

•weather conditions at the site to assess their impact ongeotechnical activity

Sensors are installed across a crack in the southwest bastion.

Monitoring equipment was assembled from several vendors.Campbell Scientific provided the datalogger, multiplexers, weatherstations, and soil moisture probes. The equipment was integratedwith crack and tilt sensors manufactured and installed by Geokon(Lebanon, NH).  AMJ Equipment(Lakeland, FL) and PSIEngineering (Jacksonville, FL)provided technical and installationassistance.  To reduce the installation’s aesthetic impact onthe park, cables were concealed in custom conduit with the help ofthe park’s maintenance staff.

The sensors are measured and the data are stored by the CR10Xat5 a.m. and 5 p.m.  On a quarterly basis, the data stored intheCR10X is downloaded via phone modem to computers located in theoffices of the engineers and architects for analysis andinterpretation.  The project is scheduled to collect data forfive to ten years. 

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

Sensors straddle cracks to directly measuredisplacement in each of three axes.