Developent and Application of Hybrid Method to Inhomogeneous Geology for Curtain Grouting -Case Study in Sedimentary Rock with Fold Movement for Nam Ngiep 1 Hydropower Project in Lao PDR-

Curtain grouting for dam foundation treatment is one of the most crucial work items in dam construction to secure the impermeability of the foundation rock. Some decades ago, the Grouting Intensity Number (GIN) Method developed in Europe has been frequently applied to relatively simple geotechnical structures. On the other hand, the Conventional Method, which requires phased mix proportion and water pressure tests through a sequence of the works, is as yet reliable for inhomogeneous geology. This paper presents the development of a modified curtain grouting method and its application to the Nam Ngiep 1 Hydropower Project in Lao PDR, which has an inhomogeneous geology of sedimentary rock with weak layers affected by fold movement. The method has been dubbed as “hybrid” because it garners both the economical superiority of the GIN Method in that it enables the use of a single mix proportion, and the technical superiority of the Conventional Method in that the individual design pressure in each stage is based on water pressure tests.

Seepage in Water-Rich Loess Tunnel Excavating Process and Grouting Control Effect

The tunnel passing through the loess stratum with high moisture content can easily lead to the seepage and mud burst accident and the instability and collapse of the tunnel face. Under the condition of high groundwater level, the seepage situation is more complicated, it is difficult to control the groundwater seepage, and the excavation progress is very slow. In order to solve the various disasters when the tunnel passes through the water-rich loess stratum, taking a water-rich loess tunnel in Gansu Province as an example, the method of comprehensive prevention and control of seepage and mud inrushing disaster by basement grouting and curtain grouting was introduced. Firstly, the basic situation of the Yulinzi tunnel is introduced, including site conditions, seepage collapse accident, and its cause analysis. On this basis, the design and construction methods of basement grouting and curtain grouting are introduced, and the effect of grouting reinforcement is evaluated in detail through on-site monitoring. The results show that the basement grouting and curtain grouting can effectively control the deformation of surrounding rock and the surface settlement, the decrease of the deformation of surrounding rock can reach 36%-71%, and the decrease of the surface settlement can reach 55%. After grouting, the deformation of the surface and surrounding rock can be controlled within the allowable value in the code. Grouting plus solid can effectively block the seepage of groundwater and prevent the surface cracks, water gushing, mud gushing, collapse, and other disasters in the process of tunnel excavation. It can be seen that the basement grouting combined with curtain grouting technology has a good reinforcement effect, which has significant engineering value for quickly and efficiently passing through high moisture content loess strata.

Groundwater Inrush Control and Parameters Optimization of Curtain Grouting Reinforcement for the Jingzhai Tunnel

Based on the systematic study on the characteristics of water and mud inrush during the excavation of Jingzhai tunnel, the mechanism of water inrush seepage transformation caused by excavation disturbance is analyzed. By means of electromagnetic geophysical prospecting, the potential water bearing area of the tunnel was analyzed. The constitutive model of rock mass and grouting parameters are considered in the numerical simulation. The law of tunnel crack initiation and expansion under different curtain grouting parameters is proposed. The characteristics of seepage water inrush caused by excavation are described. It is considered that there are three stages in the seepage characteristics of tunnel: incubation, sudden, and stable. Numerical simulation was used to analyze the crack propagation track and water inflow characteristics under the grouting thickness of 3 m, 5 m, and 7 m. When the curtain grouting thickness was 3 m, the fracture field penetrated the curtain grouting area. The dominant seepage channel is formed, which greatly increases the probability of water inrush. When the curtain thickness is 5~7 m, the expansion of the crack zone can be controlled basically, so that the fracture and water bearing rock layer cannot form a seepage channel. At last, the grouting scheme of 6 m thick grouting and 20 m advanced grouting was selected, and the water seepage was reduced by 83%.

Application and Analysis of Curtain Grouting in Seepage Prevention and Reinforcement of Masonry Dam

At present, the number of masonry dam in China is still relatively large. Due to various reasons, many of the dam body appears aging, degradation and other phenomena, and leakage is one of the common problems. Now grouting technology is the main technical means of anti-seepage treatment. Curtain grouting technology has wide adaptability to strata. With the gradual improvement of grouting technology, it has been widely applied in engineering and water conservancy projects. In order to ensure the safety of the dam and improve the grouting effect, this paper summarizes the rules of anti-seepage treatment based on the actual grouting treatment methods, and provides technical guidance for the anti-seepage treatment of other similar masonry dams.

Grouting Treatment of Water and Mud Inrush in Fully Weathered Granite Tunnel: A Case Study

When mountain tunnel passes through completely weathered granite strata, water and mud inrush is easy to occur, causing casualties and economic losses. Grouting is a common and effective treatment method for water and mud inrush disaster. The current existing researches focus on theoretical analysis, numerical simulation, and laboratory test, and the researches based on the field of engineering application are few. Based on the fully weathered granite tunnel of Junchang tunnel in Guangxi, this paper studies the grouting treatment of water and mud disaster in the fully weathered granite tunnel. This paper first introduces the geological and hydrological conditions of Junchang tunnel in order to understand the causes of water inrush and mud inrush. Then, the treatment method of full-section curtain grouting is introduced. During the grouting, the combination of exploration and injection is adopted. According to different hydrological conditions, different kinds of grouting materials are adopted. After grouting is completed, Transient Electromagnetic Methods, water inflow analysis, borehole investigation, and P-Q-T method are used to evaluate the grouting effect. According to the reaction of the detection results, the weak part of grouting can be supplemented to improve the grouting quality. The results show that the curtain grouting is effective for the treatment of water-mud inrush disaster in the fully weathered granite tunnel. This study provides a reference for the treatment of water and mud inrush in other similar tunnels.

An Intelligent Prediction Method of the Karst Curtain Grouting Volume Based on Support Vector Machine

The prediction of the grouting volume is a very important task in the grouting quality control. Because of the concealment and complexity of the karst curtain grouting engineering, there is little research on the prediction of the karst curtain grouting volume (KCGV), and the prediction is hindered by the practical problems of small samples, high dimensions, and nonlinearity. In the study, based on the basic idea of support vector machine (SVM), a multiparameter comprehensive intelligent prediction method of the KCGV is proposed, which overcomes the limitation of few sample data in practical engineering. This method takes the grouting construction conditions and the slurry conditions which control the slurry diffusion as the input parameters, which are the basic data which can be easily obtained in the field grouting process. This feature greatly improves the prediction accuracy and generalization performance of the method. The intelligent prediction method of the KCGV based on SVM is applied to a typical karst curtain grouting project. The mean absolute error of the prediction results is 3.47 L/m, and the mean absolute percentage error of the prediction results is 5.97%. The results show that the proposed prediction method has an excellent prediction effect on the KCGV and can provide practical and beneficial help for the field karst curtain grouting project.