China Railway No.3 Engineering Group Co., Ltd. has a strong development momentum in the field of subgrade engineering technology, with its scientific research capabilities continuously improved. In particular, researches carried out on the improvement of expansive soil of railway subgrade, the improvement of collapsible loess, the strengthening technology of deep soft soil base & the control of asphalt mixture on highway pavements are recognized by the industry. Also, research results have reached the leading domestic & above level.

In terms of expansive soil subgrade improvement & filling technology, China Railway No.3 Engineering Group Co., Ltd., relying on the improvement of the typical expansive soil in the test section of Hefei-Nanjing Railway, undertook the scientific research project "Research on Improvement Measures & Filling Test of Expansive Soil Subgrade in Hefei-Nanjing Railway" of the Ministry of Railways. Based on the complete set of optimal mixing quantity & construction techniques put forward by the technicians of the test section of this railway, it firstly worked out the mixing method for centrally premixed road of lime-improved expansive soil, which solved the problem of adverse effects on subgrade stability due to expansion & contraction of expansive soil, over consolidation & multiple fractures. Appraised by the Technology Department of the Ministry of Railways, the technology has reached the domestic leading level.

In terms of collapsible loess subgrade improvement & filling technology, China Railway No.3 Engineering Group Co., Ltd., relying on the Project of Zhengzhou-Xi'an High-speed Railway, undertook the scientific research project "Study on Key Technology of Improvement & Compaction of Collapsible Loess Subgrade of Zhengzhou-Xi'an High-speed Railway" of the Ministry of Railways. In response to the technical difficulties in subgrade filling & compaction in the collapsible loess area of Zhengzhou-Xi'an High-speed Railway, it put forward that the maximum dry density of cement-improved loess was time-based & such density index of cement-improved loess was dynamic. It used the maximum dry density of the 3-hour time-delayed compaction test as the control index of on-site inspection compaction, successfully solved the problem that the compaction degree of cement-improved loess was less than 95% of the designed figure. Besides, it came up with the collapsible loess improvement technology, control indexes & compaction technology suitable for Zhengzhou-Xi'an High-speed Railway, overcoming the engineering problem that inferior collapsible loess fillers cannot be used for filling the subgrade of passenger dedicated lines. The comprehensive technology reached the international advanced level & won the third prize of China Railway Group Limited for Scientific & Technological progress in 2009. Based on Huozhou-Yongheguan Expressway Project, it carried out a study on the subject of "High-fill Collapsible Loess Subgrade Treatment & Key Construction Technology of Expressway", in which it acquired the research & analysis of such measured data as number of impact, spacing between tamping points, number of tamping, pass of tamping & settlement volume via impact roller compaction, heavy tamping, strong tamping, dynamic compaction replacement, high-fill(impact rollers & dynamic ram compaction reinforcement) & V-groove construction on the original ground construction site of collapsible loess, determined rational construction methods & improved the working efficiency of construction equipment & quality control during the construction. Therefore, the compaction & integral strength of the subgrade was improved, while the settlement after the high-fill subgrade & differential settlement of V-groove was reduced, which ensured the integral construction quality of the subgrade, developing 1 enterprise construction method & 3 patents. The complete set of construction technology passed the appraisal of scientific & technological achievements organized by Shanxi Province & reached the international advanced level. Also, it won the second prize of China Association of Construction Enterprise Management for Science & Technology in 2013.

In term of the treatment of soft soil base, China Railway No.3 Engineering Group Co., Ltd., relying on the Project of Yongcheng North Station of Zhengzhou-Xuzhou High-speed Railway, conducted the "Research on Reinforcing Technology & Force Deformation Characteristics of Thick Soft Soil Base of Yongcheng North Station of Zhengzhou-Xuzhou High-speed Railway", in which it, according to the geological condition of thick soft soil mixing with thin hard layer, developed a drill rod limit system for drilling rig as well as a fast & precise assembly system for prestressed concrete tubular pile driver (support tooling for continuous flight auger), & solved such problems as severe broaching & slow pile alignment. By comparing & analyzing the seven pile construction techniques, machinery, personnel, quality as well as effectiveness on the construction site, it worked out the optimal pile type to be used under specific conditions. Moreover, based on the theoretical analysis of field measured data, it came up with the correction coefficient of the calculation formula of the composite foundation bearing capacity considering the stiffness influence of the superstructure. Currently, 4 construction methods & 4 patents are developed (including 1 patent for invention). The complete set of construction technology is regarded by the scientific & technical appraisal of China Railway Group Limited to have reached the international advanced level.

In terms of controlling the asphalt mixture for highway pavement, China Railway No.3 Engineering Group Co., Ltd. has started the subject research on the "Batch Mixer Production Process & Asphalt Mixture Construction Control Technology Controlled by Material Balance Method " on the basis of Huaide Highway, Jike Highway & Shangzhou-Manchuanguan Expressway since 2002. It also deepened the research & application exploration of such projects as Ethiopia Wukro-Adigrat-Zalambessa Highway Upgrade Project, Jilin-Caoshi Expressway B19 Contract Section, Jilin-Caoshi Expressway C05 Contract Section & Road Reconstruction Project of Luming Center Forest Farm. Through subject researches, it developed the theoretical research on the relationship between the production mix ratio & the target mix ratio of batch mixers, specified & quantified such relationship, filled the gaps in the existing technologies, created material balance method to control the construction production process, & proposed the control technology standard, calculation formula & key parameters through research. This fundamentally solved such phenomena as unstable mixture, hot aggregate bin overflow & equal materials in the process of producing hot mixed asphalt mixture by a batch mixer, tackled the technical problem of the longitudinal cold joints of asphalt pavement, improved the equipment according to the existing shortages of batch mixers, effectively solved the problem of insufficient material storage sites, provided a wide-spaced feeding hot-mixed asphalt batch mixer that could improve the screening capacity, reduce energy consumption, increase stand-alone production & production efficiency, summarized the key points of construction control steps for optimization for pavement longitudinal cold joint treatment, & proposed influencing factors as well as the basic points that should be taken into account in aggregate production & specification determination. Therefore, the amount of recycled powder was improved & the secondary investment of the raw material was saved. The complete set of construction technologies reached the international advanced level through the appraisal of China Railway Group Limited, winning the first prize of China Railway Engineering Corporation for Science & Technology in 2012 & the first prize of China Association of Construction Enterprise Management for Science & Technology in 2012.

These achievements reflected the strong scientific research capability of China Railway No.3 Engineering Group Co., Ltd. in subgrade engineering. It is able to independently assume projects & carry out construction technical consulting & services. The scientific research capability of subgrade engineering is a strong technical guarantee for its subgrade engineering construction.