As one of the important directions for the construction by China Railway No.3 Engineering Group Co., Ltd., tunneling has developed towards multi-professionals & multi-fields.The traditional tunnel construction records have been refreshed again & again with great success. Continuous breakthroughs have been made in the field of tunnel construction technology, with innovations of tunnel construction technology repeatedly appearing in collapsible loess, water-rich tertiary silty fine sands, karst area & other complicated geological conditions. In the field of long tunnel construction technology, the records have been constantly refreshed.New breakthroughs have been made in the field of tunnel mechanization construction & support field. The research, development & application of new technologies, new processes, new equipment & new materials have effectively increased construction efficiency & ensured construction quality as well as safety. A large number of construction technologies with core competitiveness have been formed to provide strong support for the construction safety, product quality, new technology as well as new process R&D.The research & application of core technologies of the company has ensured production safety & also brought significant comprehensive benefits to the company. In the field of tunnel engineering, a total of 20 scientific & technological achievements have been formed, of which 10 have reached the international leading & advanced level, 13 obtained the science & technology awards at  above the provincial & ministerial level, 58 construction methods were developed (including 2 national methods), & 38 patents were authorized (including 14 patents for invention).

(1) Major Achievements in Highway Tunnel Construction
During the construction of Qingdao Kiaochow Bay Submarine Tunnel, China Railway No.3 Engineering Group Co., Ltd. studied & adopted the combined technology of advance division excavation of small pilot heading & triplicate cut blasting, tackling the construction control difficulty that three-lane large cross-section shallow-buried highway tunnels go underneath city buildings in densely populated areas, which was first case at home & abroad back then. A record of monthly excavating 120m highway large cross-section (122㎡) tunnel in prosperous downtown area was made, developing 1 highway construction method. As the second submarine tunnel in China, Qingdao Kiaochow Bay Submarine Tunnel is the core project of Qingdao that runs through the east-west traffic artery. The application of this technology has played an important role in ensuring the safety of the submarine tunnel project & promoting the local economic & urban development.

During the construction of Hangzhou's Zizhi Tunnel (with the second largest cross-section in Asia, China Railway No.3 Engineering Group Co., Ltd. took the lead in studying such tunnel excavation techniques as the small pilot heading & step inverse expansion-excavation method, which set a precedent for the construction of the same type of tunnels, with the overall level of technology leading domestically as well as the development of 2 provincial construction methods & 3 patents. This technology tackled such difficulties as quick construction of urban tunnel (tunnel group) with super-large cross-section in building-intensive areas as well as blasting control of important buildings above the tunnels, hence it ensured the on-time completion of Zizhi Tunnel & obvious economic & social benefits. It also raised the company's technology level in the construction field of super-large cross-sections, super-close tunnels & highway tunnels with variable cross-sections.

The core technological achievements accumulated in tunnel projects have enabled the company to achieve ice-breaking in the emerging markets. China Railway No.3 Engineering Group Co., Lted had been participated in construction of the submarine tunnel of Qingdao Metro Line 1 in 2016. It is China's longest metro tunnel in the sea as well as the one that firstly used drilling & blasting methods domestically. The tunnel is 8.1km long in total, including about 3.49km sea section (passing through 14 fault fracture zones) & about 4.61km land section. Drilling & blasting methods are used for the whole tunnel. To properly solve smooth blasting problems of the tunnel & to prevent such geological disasters as collapse & flooding of the fault fracture zone, the project team, together with Shandong University & Shandong University of Science & Technology, overcame technical difficulties. They also carried out industry-university-research cooperation in the preparation of blasting plans, assessment of blasting effect, mechanization support, rational grouting plan & development of new grouting materials to ensure the construction period, safety as well as the quality of the submarine tunnel is controllable. As of February 2017, more than half of the submarine tunnel had been excavated. All indicators had met requirements.

(2) Major Achievements in Railway Tunnel Construction

Construction technology for large cross-section collapsible loess tunnel. In 2005, China Railway No.3 Engineering Group Co., Ltd. took the lead in studying the three-bench & seven-step method as well as other excavation technologies. It overcame the technical problems of the world's longest (7,851m) & largest (164m22) collapsible loess tunneling, effectively solving such unfavorable geology difficulties as collapse & collapsibility in soft loess area. It also created a record of maximally excavating 83.5m per month (72m averagely). The comprehensive construction technology used for the large cross-section loess tunnel reached the international leading level, with 3 provincial construction methods developed. Rich construction experience was accumulated for the enterprise in the selection of loess tunnel excavation method, matching of auxiliary processes & construction methods as well as settlement & deformation control of the tunnel, which raised the technology level of the enterprise in loess tunneling. This technology was successfully applied to Hanguguan Tunnel, Wenxiang Tunnel & other tunnels of Zhengzhou-Xi'an High-speed Railway, ensuring the safety & fast construction & generating good economic as well as social benefits.

A great breakthrough was made in the construction of tunnels with water-rich silt stratum. In 2012, the tunnel excavation, support, dewatering as well as other complete sets of key technologies, developed by China Railway No.3 Engineering Group Co., Ltd., managed to solve worldwide construction problems, including poor diagenesis of surrounding rocks, severe water & sand gushing, tunnels deeply buried in water-rich tertiary silty fine sand stratum, etc. The developed key technologies (complete sets of tunnel excavation & support technologies based on water inflow change, advance deep-hole dewatering with vacuum negative-pressure inside tunnel together with gravity dewatering well inside the tunnel) have great significance to improve stratum stability & to ensure the safe construction of the tunnel. The research achievement has reached the international advanced level, forming 3 provincial construction methods & 8 patents. Accumulating experience in the construction of tunnels with water-rich silt stratum for the enterprise, this research achievement was applied to the construction of Cheng'er Mountain Tunnel in Ningxia, effectively ensuring safe construction of the tunnel. The economic benefits brought by using new technologies amounted to RMB 6.62 million.

The construction records of long & large mountain tunnels have been constantly refreshed. In 2006, China Railway No.3 Engineering Group Co., Ltd. undertook the construction of the 20.7km long Lvliang Mountain Tunnel of Taiyuan-Zhongwei (Yinchuan) Railway, solving such difficult problems as long-distance single-headed ventilation, simultaneous ventilation of multiple working surfaces, as well as the construction of high-pressure stranded fissure water plugging. In 2010, it undertook the construction of the 16.9km long Taiyue Mountain Tunnel of Watang-Rizhao Railway. In 2013, it undertook the construction of the 28.4km long Ping'an Tunnel of Chengdu-Lanzhou Railway, which had "four extremes & three highs" features. With frequent earthquake, faults, rock bursts, gushing water, coal seam gas as well as other unfavorable geology problems, the tunnel was called a "geological museum". The developed full-cross-section excavation technology for weak surrounding rock tunnels" filled the gap in the construction technology for super long tunnels in strong seismic zone & under extreme geological conditions in China.

The construction technology of tunnels crossing large-scale karst caves in karst areas has reached international advanced level. Chongqing-Huaihua Railway, Yichang-Wanzhou Railway, Shanghai-Kunming Railway, Qianzhangchang Railway & other projects, participated by China Railway No.3 Engineering Group Co., Ltd., are distributed with different types of karst geology. In 2005, it undertook the construction of Wuzhuaguan Tunnel of Yichang-Wanzhou Railway which was located in karst mountainous area where karst, bedding, underground river, fault fracture zone, collapse & other unfavorable geological phenomena appeared frequently. With underground river over 1,000m, it's one of the 13 high-risk tunnels of the whole line. The "comprehensive tunnel treatment technology in complicated environment with underground rivers & karst caves" adopted for research achieved the international advanced level. In 2013, it undertook the construction of Zhushabao No. 2 Tunnel of Shanghai-Kunming Railway, which was located in karst development area where there were 2 karst cavities (volume of 290,000m³ & 310,000m³, respectively). There were also underground rivers on the bottom of the karst caves, so the tunnel must go through the top of them. The combination of "active protection network + bailey frame + passive protection network" was used for reinforcing the cave top, while "integrated filling & pouring" was used for reinforcing invisible beaded caves on the bottom. The developed high-drop concreting & S-type slowdown device solved the concreting problem for ultra-deep karst caves. The overall construction technology level of the tunnel has reached the international advanced level, filling the construction technology gap for the industry's high-speed rail tunnel through large-scale karst caves & winning the Special Prize for Scientific & Technological Progress Award of the China Railway Engineering Corporation. It has also been reported by many media such as CCTV, generating significant economic & social benefits.