LanXin Railway Uses Trimble Intelligent Compaction System to Monitor Compactor Pass Count, Layer Thickness, and Project Status for High-Quality Base Layer Construction

With some sections as high as 3,859 meters (2.4 miles) above sea level, the LanXin Second Railway will be the world's highest - and one of the fastest - trains in operation in the world when complete. The 1,776km (1,103 mile) long line will run across China's Gansu and Qinghai provinces to the Xinjiang region. The build-out of the second line of the LanXin Railway is expected to take five years, with a completion date set for 2015 and an estimated cost of $140 billion yuan (or $21.4 billion US Dollars). The project, designed as a passenger route, will make way for the existing LanXin Railway to be used exclusively for freight.

Adding to the complexity of this considerable infrastructure build are environmental factors and the geographic location of the rail line. The line will traverse through the Gobi Desert, which covers parts of northern and north-western China as well as Mongolia. The Gobi Desert is characterized by extreme temperatures that can fluctuate between minus 40 degrees Fahrenheit in the winter and 122 degrees Fahrenheit in the summer. This region is also wind ravaged and known for its mountainous terrain that reaches altitudes of over 3,658 meters (12,000 feet). The LanXin Railway track must be designed to handle these punishing environmental factors while also accommodating the high-speed trains, which can reach speeds of 350 kilometers (217 miles) per hour.

According to Jacky Li, a member of the Trimble team that worked closely with LanXin Railway GanQing Limited Company, one of the contractors selected Trimble for intelligent compaction capabilities. Specifically, the leaders were looking for assistance to lay the sub grade for a 522.9km base bed layer that covers LXS-8 to LXS-17 rail sections. This stretch of track travels through the GanSu and QiangHai provinces.

Controlling the base quality for this section of the line requires that the sub-surface material is compacted to a specified target density which achieved Standard requirement. The Trimble® CCS900 Compaction Control System uses corrections from the SPS852 to get accurate position. The CCS900 system has a compaction sensor and on machine software to provide continuous control over compaction and depths.

More than 200 Trimble CCS900 systems were installed on vibrating rollers and used during base layer construction of this 500-plus km section. Working with the local Trimble dealer SITECH, engineers and operators were trained on how to use the Trimble system. On-site training visits ensured that the compaction point person for each section was thoroughly prepared and their questions were answered quickly.

For earthworks projects such as this, detailed documentation is required by the China Ministry of Railway to demonstrate that target compaction levels are in fact being met. To accurately measure the compaction of the material under the drum, a CM310 sensor is mounted on the side of the drum. This measures the stiffness of the soil and reports this back to the CCS900 software as a CMV (Compaction Meter Value) number. This CMV is correlated to the position of the drum and mapped in real time and recorded for documentation and review.

With the Trimble system, grade accuracy is checked and recorded continuously during the compaction process. Using a mobile printer connected to the Trimble CCS900, Compaction Meter Values (CMV) reports are immediately available to operators and engineers. This helped GanQing teams reach acceptable compacted soil states more quickly and consistently. This also reduced the need for traditional soil sampling methods, which are manually intensive and produce somewhat inconsistent and unreliable test results.

Documentation information of compaction results was collected and displayed directly on the in cab control box allowing the operator to understand the current real-time three-dimensional position of the rollers and compaction progress. This gave the contractors advanced compaction measurements for the entire roadbed and the ability to view mapping of compaction measurements as work was being done.

"GanQing initially had some concerns about base quality, particularly for this section of rail," said Li. "The customers, from the operators to the site managers and supervisors, were all very happy with CCS900 system functionality, accuracy and quality of the equipment. Pass counts were recorded, layer thickness monitored, and real time CMV values and reports were available as expected."

Li believes the ability to detect sub-surface material anomalies early in the construction process was very beneficial and enabled the project to keep on track. Weak areas in the sub grade were immediately identified in the field and geo-reference information was recorded automatically with the Trimble system. Using the in cab display, operators could identify soft spots and make decisions about adding fill, excavating or performing additional compaction before more costly re-construction work was needed. Ultimately, this helped to improve the quality and uniformity of sub grade compaction.

In terms of improving the quality and uniformity of the base layer, initial reports estimate that the intelligent compaction process increased the rate of compaction on average by over 4% from just over 94% to almost 99%, compared to the traditional method of rolling. This new process greatly exceeded compaction specifications.

And, because Trimble CCS900 successfully monitored compactor pass count, layer thickness and compaction status, the team was able to increase productivity with the more efficient placement of layers. Automatic and consistent documentation meant fewer density tests were required, fewer change orders were issued, and material usage decreased.

Under China's current economic plan, the country will continue to expand its high-speed rail line, with plans to have more than 16,000 kilometers of railway by 2015. Currently, more than 8,000 kilometers of line are in operation, already the most in the world. This infrastructure is expected to facilitate the transport of energy resources from the less populated areas of the country, specifically in the northwest, to other regions. With ambitious expansion plans set for the future, China's Ministry of Railway (MOR) continues to look for ways to utilize intelligent compaction technology as part of its expansive earthworks projects.

"Every operator, engineer, and manager agreed and was pleased with the results of the CCS900," said Li. "By using the Trimble system, the contractor was able to ensure the compaction work consistently met the tight specifications of the project as well as provided the necessary CMV reports and proper documentation. They know it will be a popular method in China and the Ministry of Railway is researching plans to make it part of the base construction standard."