Civil Engineering Reference
In-Depth Information
placed in the cleaned hole. The horizontal anchor was then adjusted to form a
90-degree angle with the face of the wall and to ensure vertical and horizontal
levelness of the ballpoint hardware mounted on the exposed end of the anchor.
After setting and hardening of the epoxy inside the hole, the tilt sensor was affixed
to the ballpoint and adjusted for vertical levelness and a zero initial reading (±5°).
Finally, the tilt sensor was connected to the datalogger installed on site.
4.2.2.3 Data Collection and Management
Data collection from the sensors was performed using two data-acquisition
systems. A datalogger was installed on the fourth level of the building and
mounted on the northern retaining wall 23 m from the northwestern corner, and
was connected to 8 VW displacement transducers and 12 tilt sensors all of which
were installed on the retaining wall. The datalogger was programmed to read the
sensor data at 15 second intervals and store one reading at 1 minute after the hour
in the memory. The data was then accessed and downloaded through a personal
computer via a remote modem installed on site and connected to the datalogger.
Twelve additional tilt sensors were read manually at weekly intervals, for a period
of one year, using a multi-purpose readout unit capable of displaying and
recording the sensors inclination and temperature data. The manual data were then
downloaded into a personal computer. A brief description of the data acquisition
systems is provided below for completeness.
4.2.2.3.1 Automatic Data Acquisition
The automatic dataacquisition system was comprised of eight VW displacement
transducers and twelve tilt sensors connected to two AM416 relay multiplexers
(by Campbell Scientific, Inc.) used to increase the datalogger capability of
scanning a larger number of sensors. The datalogger is capable of controlling
several multiplexers positioned between the sensors and the datalogger.
Mechanical relays are used to switch four wires simultaneously to each of the 16
channels that can be scanned.
The multiplexers were then connected to a CR10X datalogger (by Campbell
Scientific, Inc.) with non-volatile memory used to scan the sensors every 15
seconds and store their displacement or inclination and temperature every minute
after the hour. An AVW100 vibrating wire interface employing an amplifier and
filter circuit is placed between the datalogger and the multiplexer connected to
VW displacement transducers. The datalogger and the vibrating wire interface
were powered using a PS12LA lead-acid battery connected to a main AC power
supply available on site through an AC adapter. Communication with the
datalogger was established via telephone lines and a 9600-baud modem,
employing the Hayes AT command set, installed on site and connected to the
datalogger. A computer program was written to automate data retrieval and
