Building on a Stable Platform
On the outskirts of Saint Petersburg, Lakhta Center offers an innovative model for urban development. The 400,000 square meters project includes commercial, retail, recreation and cultural spaces. The centerpiece is the Lakhta Center tower, which will stand 462 m tall. Development of Lakhta Center incorporates advanced methods for safety, environmental protection, energy management and efficient construction methods.
The city of Saint Petersburg is Russia’s cultural capital and key port on the Baltic Sea. With heritage extending from the 15th century, Saint Petersburg blends historic architecture with the energy of a modern commercial and transportation hub.
The Lakhta Center project is a mixed-use public and commercial complex featuring office space, theaters, a hotel, scientific and educational facilities as well as large outdoor spaces for concerts and recreation. The project also includes a health center with diagnostic and treatment facilities. Transportation facilities including a new metro station will provide easy access to Lakhta Center for work, shopping and entertainment.
Construction of the Lakhta Center began in 2012. The project contractor, Renaissance Construction, specializes in construction of commercial projects and high-rise structures.
Trimble Zephyr Geodetic GNSS antenna mounted on the Lakhta Center structure. A prism target is directly beneath the antenna.
During the construction of tall buildings, surveyors and engineers provide positioning data to support construction crews, optimize workflows and improve safety. As the structure rises, surveyors establish and maintain networks of precise control points that move up with the building to provide the reference frame for placement of concrete and structural components. Even a small positioning error might introduce problems as the construction moves higher.
Surveying methods for high-rise construction typically include optical measurement and marking plumb lines to connect points on the building with project control on the ground. As the building height increases, precise optical measurement becomes more difficult. Viewpoints for optical instruments must be far enough from the structure to measure high on the building, yet near enough to reduce uncertainties associated with high-angle measurements. Optical plumbing requires holes in floors and can disrupt construction activities.
Additional challenges may stem from the structure itself. Settlement or subsidence can produce tilting. Wind and thermal expansion can twist or warp the structure during the day. As a result, precise control requires frequent measurement. Lakhta Center surveyors needed to provide precise positioning at all times for workers atop the structure—without disrupting the busy site.
Renaissance Construction turned to proven GNSS technologies to handle the project’s demanding needs. Working with experts from Trimble, Renaissance implemented a solution that combines advanced GNSS receivers with monitoring and analysis software to provide high levels of precision and confidence.
According to Renaissance surveying engineer Huyesin Ozaslan, the positioning system at Lakhta Center includes multiple networks of GNSS receivers. The approach provides redundancy to ensure integrity of the control networks and precise positioning on the tower.
The measurement solution consists of five Trimble NetR9 Ti-M GNSS receivers with Trimble Zephyr™ Geodetic 2 GNSS antennas installed on permanent control points around the construction site. The receivers stream data to Trimble 4D Control software (T4D Control) at the project office. Five more NetR9 receivers with antennas are placed on mounts atop the building’s concrete core. As the building core grows upward, the mounts and receivers are repositioned to new, higher locations. The on-building mounts include small prism targets located directly below the GNSS antenna phase center to allow for optical positioning. The GNSS receivers connect to the T4D Control server through a dedicated Wi-Fi network.
The system operates three RTK engines simultaneously within the Trimble 4D Control software. The five ground-based receivers form a real-time network on the site. An RTK engine connects each receiver to a single geodetic control point in Saint Petersburg, approximately 9 km away. A second RTK engine monitors the relative location of the on-site receivers.
The software provides data on relative positions of the receivers and produces regular updates on the performance and changes in the receiver network.
A third RTK engine handles the network of five receivers on the ground plus the receivers on the tower. The coordinates of the ground receivers provide the basis for computing positions on the tower. In addition to generating GNSS measurements, Renaissance installed a network of tilt sensors into the tower. Data from these sensors flows to the Trimble 4D Control software, which uses the tilt sensor readings to adjust the GNSS-derived positions.
To produce coordinates for the prism targets on the building, the T4D Control software applies a vertical offset from the antenna down to the prism. The results are transferred to the Trimble TSC3™ field controllers running Trimble Access software. Surveyors working on the tower use Trimble S-Series total stations to orient the total stations into the project coordinate system. They can then perform layout and checking tower construction accuracy.
With completion scheduled for 2018, the Renaissance team has no room for error. The Trimble monitoring solution provides precise information and delivers it directly to the surveyors on top of the tower. The solution delivers several real-time key benefits:
- Rigorous Checking and Quality Assurance
Incorporating multiple receivers and three independent RTK calculation loops, the system assures strong internal integrity and high confidence in computed coordinates. Any motion of the control points on the ground can be quickly identified. Solutions for the on-building receivers are updated continuously. Customized messaging alerts designated personnel to movement or changes in the system status
- Immediate Updates
Project surveyors gain confidence by knowing they are working with current information. The T4D Control RTK computations produce coordinates for receivers on the ground and tower and automatically updates coordinates of the prism targets.
- Single Source Solution for Sensors and Software
The Trimble system delivers close integration between GNSS receivers, total stations and software. Information flows seamlessly between office and field systems and is readily available for detailed analyses. The single-source approach ensures comprehensive training and support from Trimble and its distribution partners.
The RTK network connecting the ground coordinates to five GNSS receivers on the tower. Data from tilt sensors in the tower provides additional information used in computations and analyses.
“Vertical construction requires accurate, up-to-the minute measurement information on the structure. The ground based monitoring system and control software helps us perform efficiently and with high confidence.”
Surveying Engineer – Renaissance Corporation