###### Abstract  
Karst geology is common in China, and buried karst formations are widely distributed in Guangdong province. In the process of shield tunneling, the abundant water resources present in karst caverns could lead to the potential for high water ingress, and a subsequent in situ stress change-induced stratum collapse. The development and distribution of karst caverns should therefore be identified and investigated prior to shield tunnel construction. Grouting is an efficient measure to stabilize karst caverns. The total volume of karst caverns along the shield tunneling alignment, and its relationship with the required volume of grouts, should be evaluated in the preliminary design phase. Conventionally, the total volume of karst caverns is empirically estimated based on limited geological drilling hole data; however, accurate results are rarely obtained. This study investigates the hydrogeology and engineering geology of Guangzhou, the capital of Guangdong province, and determines the fractal characteristics of the karst caverns along the tunnel section of Guangzhou metro line no. 9. The karst grouting coefficients (\(V_{R}\)) were found to vary from 0.11 in the case of inadequate drilling holes to 1.1 in the case where adequate drilling holes are provided. A grouting design guideline was furthermore developed in this study for future projects in karst areas. karst Caverns; shield tunneling; fractal theory; ground treatment 1  
[PERSON], [PERSON], J.  
a karst system can be of hundreds of kilometers in length. A recent case history of a metro system's construction in Nanjing, China, indicated that excessive volumes of grout injected during construction resulted in side effects on the urban environment [8]. Due to limited studies on the treatment methods of karst geological formations, there is an urgent need to carry out in-depth research to better understand critical uncertainties during the grouting process (e.g., the grouting parameters and the injected volume of grouts) in grouting and jet grouting construction [22; 23; 24; 25; 26; 27]. Karst caverns that contain abundant fissure water and have high collapse potential need to be treated prior to tunnel construction. [PERSON] et al. [28] reported that the construction procedure for the treatment of karst caverns included site geological investigation, decision making, the treatment of karst caverns, and an effectiveness verification. Firstly, a preliminary geological investigation is carried out to identify the karst caverns. Secondly, the quantity, location, and filling of the karst caverns is detected to determine whether the karst caverns require treatment. Finally, an unconfined compression test (UCT) or a standard penetration test (SPT) is carried out to verify the effectiveness of the treatment. The factors largely affecting the unconfined compressive strength (UCS) of treated materials have been extensively investigated in previous studies [29; 30; 31]. Using the empirical formula proposed by [PERSON] et al. [29; 30], the UCS value of treated materials can be well predicted, and used as an indicator of quality control (QC) and quality assurance (QA) for the treatment of karst caverns. As a karst cavern is irregularly distributed and has various shapes, it is difficult to evaluate the total volume of karst caverns in the way of shield tunneling. Additionally, there are also fill materials with groundwater in caverns, so that there is no reliable measure to calculate the injected volume of grouts [32; 33]. A project's budget can be further reduced or well managed if the injected volume of grouts can be predicted during the preliminary design stage. To tackle these problems, there is a need to develop a measure to predict the total volume of karst caverns, and establish its relationship with the required volume of grouts. [PERSON] (1983) [34] developed the fractal theory, which can be utilized to describe the distribution of geotechnical objects that are neither random nor homogeneous. [PERSON] et al.