Experimental Study and Engineering Application of Polypropylene Fiber Shotcrete for Bored Tunnels in Water-Rich Strata
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RESEARCH ARTICLE-CIVIL ENGINEERING
Experimental Study and Engineering Application of Polypropylene Fiber Shotcrete for Bored Tunnels in Water‑Rich Strata Ping wei Jiang1,2 · Jiang hua Fang1,3 · Jian yong Pang1,2 · Qiang Su1,2 · Xing Xia1,3 Received: 17 February 2020 / Accepted: 21 July 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract During the construction of water-rich bored tunnels, it is important to improve the impermeability of the primary support shotcrete to ensure construction safety. This work considers the underground excavation of water-rich strata in the section between the Baisheng Shaft and Xiba River Station of the Beijing Metro Line 12. A polypropylene fiber-reinforced shotcrete (PFRS) was designed using an orthogonal experimental method. The fiber size and content, cement content, sand rate, and water–cement ratio were the key factors in the PFRS performance. Based on the analysis of the experimental data along with numerical simulations and other research methods, a new mix proportion of PFRS is proposed and successfully applied to engineering sites. It is shown that compared with ordinary shotcrete, the impermeability of PFRS is greatly improved as the maximum can be increased by 42.5%. After the application of PFRS on-site, the problems of water seepage and excessive deformation of the tunnel supporting structure in the water-rich strata were alleviated. This fully ensures the overall stability of the tunnel and provides a guarantee for a safe construction site. Keywords Polypropylene fiber · Shotcrete · Bored tunnel · Orthogonal experiment · Numerical simulation
1 Introduction The shallow buried-tunneling method is applied to construct mountain tunnel openings, urban underground railways, and other suitable construction projects in weak rocks. This approach applies primarily to shallow buried underground caverns with a thickness span ratio greater than 0.2 in quaternary period strata for soils or weak and non-cemented sands, cobbles, and other unsuitable excavations [1, 2]. For strata with abundant groundwater, although measures such as water stop, precipitation, and drainage can be considered, if the impermeability of the shotcrete in the primary support is low, several problems will exist, such as severe water * Jian yong Pang [email protected] 1
School of Civil Engineering and Architecture, Anhui University of Science and Technology, Huainan 232001, China
2
State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine, Anhui University of Science and Technology, Huainan 232001, China
3
BeiJing Uni-Construction Group CO., LTD, Beijing 100101, China
seepage and excessive land subsidence. In the presence of severe cracks, there is the potential for collapse and the risk of gushing water to the soil of the tunnel face [3, 4]. Therefore, the impermeability of the shotcrete needs to be high for the primary support of the bored tunnels during construction in water-rich strata [5]. Polypropylene fiber is relatively stable in the
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