Research On Key Technologies For Grouting Reinforcement And Repair Of Terraces In The Landslide-debris Flow Area Of Laohuzui, Yuanyan

This paper uses the restoration and management project of the Lao Huizui Terraces,a World Heritage Site,after being damaged by landslides and mudslides as a background,and uses an indoor physical model grouting test to explore the techniques for maintaining the original appearance of the terraces during the restoration and management process.Through the selfmade physical model test device,the grouting tests under different grouting pressure and watercement ratio under 9 conditions were carried out.Combined with the numerical simulation analysis and verification,the permeation and diffusion process of grout in terraced soil was studied.The grouting pressure and water-cement ratio of grout required for the appropriate grout diffusion distance under the fixed ridge width were found out,and the law of their influence on grout diffusion radius was analyzed.Finally,the durability and impermeability of the terraces were evaluated correctly by relevant experiments.Through this research,the main achievements are as follows:(1)The cement grout is mainly permeated and diffused in the soil,and there is partial splitting diffusion.The lower the water-cement ratio,the more obvious the profile of the split veins,and the weaker the permeability effect on both sides of the veins.Based on numerical simulation,it is concluded that the slurry mainly diffuses in ellipsoidal shape.(2)The grout diffusion radius is 10.6cm ～ 22.9cm under 9 working conditions,and the grout diffusion radius is positively correlated with grouting pressure and water-cement ratio.When the water-cement ratio of grout is large,increasing the water-cement ratio has no strong effect on the increase of diffusion radius.(3)The mathematical regression equations between the grouting pressure,water-cement ratio,permeability coefficient of the injected soil and the grout diffusion radius were obtained.The main and secondary influencing factors on the diffusion radius of terrace grouting in the disaster area are as follows: grouting pressure > grout water-cement ratio > soil permeability coefficient;(4)The internal pressure of soil decreases with the increase of distance from grouting hole.The closer to the grout hole,the greater the rate of pressure decay.The lower the grouting pressure,the greater the rate of pressure decay.The smaller the water cement ratio,the greater the pressure attenuation rate along the grout;(5)Under the conditions of this grouting,the compressive strength of the grouting consolidated body after curing for 7 days is roughly within the range of 0.72 MPa ～ 2.73 MPa,the softening coefficient is roughly within the range of 0.71-0.93,and the disintegration rate is1.47%-46.26%.After curing for 14 days,the compressive strength of grouting consolidated body is roughly in the range of 0.67 MPa ～ 3.16 MPa,the softening coefficient is roughly in the range of 0.70 ～ 0.94,and the disintegration rate is roughly in the range of 0.63% ～ 51.45%.The maximum seepage resistance pressure of the grouting consolidated body after curing for 28 days is within the range of 0.05 MPa ～ 0.4MPa,that is,the consolidated body with a height of 15 cm can withstand the static pressure of 5m ～ 40 m water depth to maintain no seepage water.The influence degree of water on the terraced grouting consolidation body in Lao Huzui disaster area of Yuanyang was evaluated as medium and slightly affected by water;(6)Grouting pressure and curing time are positively correlated with compressive strength,while water-cement ratio of grout is negatively correlated with compressive strength.The main and secondary effects of various factors on the compressive strength of consolidated body are as follows: grout water-cement ratio > grouting pressure > curing time;The water-cement ratio of grout is negatively correlated with the softening coefficient,while the grouting pressure and curing time are positively correlated with the softening coefficient.The main and secondary effects of various factors on the softening coefficient of consolidated body are as follows: grout water-cement ratio > grouting pressure > curing time.The grouting pressure is negatively correlated with the disintegration rate,while the disintegration frequency is positively correlated with the disintegration rate.There is a critical water-cement ratio between 0.8 and 1.0.When the water-cement ratio is smaller than the critical water-cement ratio,the disintegration rate decreases with the in crease of the water-cement ratio.When the water-cement ratio is bigger than the critical water-cement ratio,the disintegration rate increases with the increase of the water-cement ratio.The main and secondary effects of various factors on the disintegration rate of consolidated body are as follows: Disintegrating times > grout water cement ratio > grouting pressure > curing time;The grouting pressure is positively correlated with the maximum seepage resistance pressure,while the grout water-cement ratio is negatively correlated with the maximum seepage resistance pressure;(7)The grouting pressure of 0.45 MPa and the grout water-cement ratio of 0.8 are the most suitable grouting parameters among those selected for this occasion.