## 7 Conclusions  
This study introduced a solution to the severe cement flurry losses of jet grouting in the water-rich sand stratum from grouting fluids and information-based construction. Three grouting additives, including high-polymer additive, red mud and phosphogypsum and metakaolin, were screened with a series of laboratory tests on solidification time and permeability. Based on the monitoring system-equipped double fluid jet grouting system, the mix proportions of grouting fluids in laboratory tests were verified with site tests of jet grouting and laboratory tests of drilling core samples to find reasonable operation specifications of jet grouting in the water-rich sand stratum. Some main conclusions are obtained as follows:  
1. The optimal ratio of HPCG is: A:B = 2:1, high-polymer additive:water > 1:3, water:cement ratio of 0.8. The solidification time of HPCG can be controlled in the range of 10 min to 20 min, which is more than 20 min shorter than the solidification time of OPC (40 min); the solidification time of RPCG and MKCG are similar to the solidification time of OPC.
2. Information-based construction of double liquid jet grouting can effectively monitor the key construction control parameters in real-time. The construction specifications of jet grouting are a drill rotational velocity of 10 r/min, a drill lifting speed of 0.2 m/min, an injection pressure of 20 MPa and a grouting flow rate of 40 L/min, which can effectively and stably control the quality of jet grouting. The pumping stability order of the three cement grouting material additives is: HPCG > RPCG > MKCG.
3. The permeability coefficients of cement-stabilized silt by three grouting additives in laboratory tests can all reach an order of 10\({}^{-7}\), while only the permeability coefficient of HPCG in situ core samples reached an order of 10\({}^{-7}\); these are similar to the laboratory results, which verifies the reasonableness of the optimal ratio of high-polymer composite cement (HPCG). The permeability coefficients of RPCG and MKCG in situ core samples could not reach the experimental results.
4. SEM images of HPCG show that the cluster blocks are connected by a dense network, and the particle units and flocs are closely arranged. It can be found that HPCG has significant performance advantages and good engineering applicability, and is a better grouting material for reinforcing underground engineering in the water-rich sand stratum.  
Figure 21: Comparison of permeability coefficients of in situ tests with laboratory tests at 28 days.  
**Author Contributions:** Conceptualization, P.Z.; methodology, P.Z. and S.W.; software, X.Q.; validation, S.W. and P.Z.; formal analysis, X.Q.; investigation, S.W.; resources, S.G.; data curation, S.G.; writing--original draft preparation, X.Q.; writing--review and editing, S.G. and P.Z.; visualization, S.G.; supervision, X.H.; project administration, P.Z.; funding acquisition, S.W. and X.Q. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was funded by the National Natural Science Foundation of China (Grant No. 41902282), Science and Technology Planning Project of Jiangsu Province (Grant No. BE2022605), and the Scientific research planning project of Jiangsu Open University (The City Vocational College of Jiangsu) in 2022 during the \"14 th Five Year Plan\" (Grant No. 2022 XK013).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.