# Field Study on the Waterstop of the Rodin Jet Pile Method in a Water-Rich Sandy Gravel Stratum
## 1 Introduction  
High-pressure rotary jet grouting technology originated in Japan in the early 1970s. The technology is based on the single-tube method invented by Dr. [PERSON] in Japan and gradually has become the foundation reinforcement technology of various processes, such as the double-tube method and the triple-tube method [1; 2; 3]. The technology is guided by the jet theory, and it cuts soil with a high-pressure jet flow (20-40 MPa) and mixes the cement slurry with soil to form cement solidification. Rotary solidification has suitable quality and low permeability, can improve the shear strength and compressive modulus of the soil, and can form a closed waterstop curtain. Therefore, the technology is widely used as a foundation reinforcement and waterstop treatment, and is currently widely used in silty soils, silts, sands, silty clays and other strata [4; 5; 6]. However, conventional high-pressure rotary jet grouting technology is limited by the process conditions of the equipment and the swirling depth, which is generally within 30 m when the pile diameter is in the range from 0.8 to 1.0 m, and the technology mainly relies on the airlift principle to discharge the waste mud from the gap between the drill pipe and the undisturbed soil. As the construction depth increases, the airlift effect increasingly weakens. When the gap is blocked, the pressure in the surrounding layer of the high-pressure nozzle increases, which reduces the efficiency of the jet spray, affects the reinforcement and reliability, and in severe cases, leads to large deformations of the surrounding formation and surface uplift [7].  
With the acceleration of construction related to urbanization, urban underground spaces have been constructed at gradually increasing depths, and the surrounding construction, underground pipelines, hydrogeological conditions, etc., have become increasingly complex. Conventional high-pressure rotary jet grouting has been unable to meet engineering requirements due to small pile diameters, shallow construction depths, large disturbances to the surrounding environment, and insufficient flows of the high-pressure pumps [7; 8]. To meet the needs of an increasingly complex engineering construction environment and deep underground space development, improve construction efficiency and reduce construction costs, scholars have developed a series of ultra-high-pressure rotary jet grouting technologies based on conventional high-pressure rotary jet [9; 10; 11; 12], such as the Rodin jet pile (RJP) method, which has been widely used in soft soil areas such as Shanghai, Tianjin, Hangzhou, Xiamen, Fuzhou and Wuhan; however, there have been no successful cases in gravel strata similar to those in the Beijing area. According to the literature, the RJP method was tested in the superficial strata (within 4 m below the surface) of Tongxian County, Beijing, in May 1996 [13]. Since then, there has been no relevant experimental research. Therefore, this paper used the ventilating shaft in a section of the Beijing Metro as the construction background to carry out a field test of RJP ultra-high-pressure rotary jet grouting, and a series of tests were conducted, such as the ratio of grouting materials, grouting pressure, grouting pump flow, construction monitoring, solidification compressive strength and permeability, to provide references for design and construction in water-rich sandy gravel stratum.