urrently underway in one of London’s wealthiest areas,
the De Vere Gardens development is located on the site
of two recently demolished hotels in Kensington and
Chelsea, next to Hyde Park. The project will provide two new
seven-story buildings and one five-story block incorporating
retained façades. In the middle of the site, encompassed on
three sides by extensive building work (including the enlarge-
ment of the existing basement to two levels), is a block of 15
privately owned flats. Sir Robert McAlpine, Ltd., a leading UK
building and civil engineering company, is the main contractor
on the De Vere project. In this pricey and historical area, moni-
toring the buildings and the retained facades for structural
damage is a critical part of the contract.
Having realized inadequate results from a monitoring subcon-
tractor, McAlpine decided to perform the monitoring itself.
The monitoring system had several requirements: It had to be
managed in-house; it had to be automated, real-time, reliable
and easy to use; and above all, it had to be in place before piling
began—a tight timeframe.
“The tight time schedule was significant for us,” explains Senior
Land Surveyor Vince Bridle, the manager tasked with installing
and overseeing the system. “Understandably, residents were
concerned about structural damage to their property. We felt
that a comprehensive monitoring program would help alleviate
their fears.” The team looked at several systems, ultimately
selecting a real-time solution of two Trimble S8 robotic total
stations with Trimble 4D Control software.
“We were already familiar with the hardware and software, which
cut down the learning curve,” says Bridle. “And having seen the
system demonstrated on a small-scale project, we knew that we
could manipulate it for our specific requirements. Strong vendor
support to get us up and running was also a factor.”
A control network of 13 base targets was established on
site, and 98 25mm prisms were fixed on the structures to be
monitored. The total stations were positioned at opposite
ends of the site, one on the McAlpine site building and the
other on the highest point of a retained façade wall, where
there was sufficient room to power it with three solar panels.
A 2.4-GHz wireless radio link connects the total stations to
an office PC running the Trimble 4D Control software, where
email and text alerts are generated automatically.
Trimble 4D Control software post-processes the monitoring
data collected by the total stations. It computes rounds of
angles measured in the field as individual sessions and reveals
any movement of targets over time. The terrestrial engine in
Trimble 4D Control processes each session, validates the data,
then stores the point information together with the raw data.
Other modules of the software use this data to create warnings
and alarms, as well as graphs and reports.
Monitoring London’s Upper Crust