Fractal Prediction of Grouting Volume for Treating Karst Caverns along a Shield Tunneling Alignment

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.

Analytical approach for time‐dependent groundwater inflow into shield tunnel face in confined aquifer

“…Equation 24 shows that the total groundwater inflow Q n (t) is divided into uniform flow and non-uniform flow. The former is not relevant to length but the latter is, which illustrates the seepage interaction along the direction of tunnel excavation.…”

“…Meanwhile, the curves of S y along the y-axis and drawdown S γ (t) can also be derived on the basis of the solution to 24. Similarly, Equation 24 can be rewritten considering an isotropic confined aquifer, to give…”

“…The construction risks will increase rapidly when large‐scale groundwater inflow penetrates a tunnel or excavation . To reduce the risk related to groundwater inflow, prediction of time‐dependent groundwater inflow to tunnel is an essential and indispensable task so that groundwater control measures can be implemented, eg, drainage pumping, installing barriers, increase of stickness of grouting materials with high viscocity, or sealing using grouting or jet‐grouting …”

“…3,[9][10][11][12][13] To reduce the risk related to groundwater inflow, prediction of time-dependent groundwater inflow to tunnel is an essential and indispensable task 14 so that groundwater control measures can be implemented, eg, drainage pumping, [15][16][17] installing barriers, 4,11,13,18,19 increase of stickness of grouting materials with high viscocity, [20][21][22][23] or sealing using grouting or jet-grouting. 7,24,25 The mathematical models used for predicting groundwater inflow can be classified as deterministic, non-deterministic, or stochastic models. [26][27][28][29] The deterministic models can be sub-divided into analytical and numerical approaches, of which the former derived by a series of mathematical means could be used at the design stages with incomplete geological information and the latter used as a finite element, finite difference, and even discrete element scheme to analyse tunnel inflow in more complicated geological conditions.…”

Simple Method to Predict Ground Displacements Caused by Installing Horizontal Jet-Grouting Columns

“…Jet grouting is frequently used for the launching of shield machines or tunnel construction in complex geological conditions. Jet grouting technology is based on the injection of high velocity fluids through smalldiameter nozzles to erode the soil and mix it with injected grout to form a soil-cement column [16][17][18][19][20][21]. Based on the different methods of fluid injection, jet-grouting technology can be classified as (a) single fluid system (grout only), (b) double fluid system (grout + air), or (c) triple fluid system (water + grout + air) [22][23][24][25].…”