Abstract
There existed ever-increasing structural diseases in the Dugongling tunnel after the completion of the construction. Systematic research was carried out based on the information of tunnel engineering geology, disease development, mineral composition of surrounding rock and concrete, and laboratory tests. Results showed that (1) the concrete structure from the Dugongling tunnel suffered from a typical thaumasite sulfate attack (TSA); (2) tunnel diseases developed under the influence of multiple geological factors such as groundwater, karst, gypsum bearing stratum, and geological tectonics. Groundwater aggravated the appearance of engineering defects of various geological factors and accelerated the softening and swelling of surrounding rock. Moreover, the additional load of supporting structure increased, and the concrete structure was prone to sulfate attack; (3) the development of tunnel diseases showed long-cycle and large-scale characteristics, and the types of diseases are heterogeneous. The tunnel diseases develop rapidly in the third year after the construction. The structure collapse disease, one of the most serious diseases of tunnel lining, occurred in the fifth year after construction; and (4) according to the conditions of TSA, technical treatment measures were proposed. These measures included blocking the flow of CO 3 2 − , improving the impermeability of concrete structures, and decreasing the diffusion of external ions and groundwater. This work provides a solution for the treatment of similar tunnel disease and mechanism analysis.
Highlights
Project Overview e Dugongling tunnel [21] is a separated two-way four-lane highway tunnel. e starting and ending pile number of left line is from ZK33 + 226 to ZK35 + 700 with a length of 2474 m and that of right line is from YK33 + 227 to YK35 + 742 with a length of 2515 m; the overall direction of Advances in Civil Engineering tunnel axis is 264°, and the maximum depth of tunnel is 231 m. e construction clearance of the tunnel has a net width of 10.25 m and a height limit of 5 m
As of 2016, the total length of the tunnel structure that needed to be demolished and replaced due to diseases is 1,515 m. e main range of tunnel diseases occurred in sections from K34 + 500 to K34 + 800
In the supplementary survey of tunnel diseases in 2016, 223 samples from 119 cross-sectional primary support concrete were picked. e mineral compositions of the concrete were mainly calcite, dolomite, quartz, potash feldspar, plagioclase, ettringite, gypsum, and thaumasite. 60 sections of the 119 sections were detected with thaumasite sulfate attack (TSA), accounting for 50.4% of total samples; 84 of 223 samples of primary supporting concrete were detected with thaumasite (Figure 3), accounting for 37.7% of total samples
Summary
E disease scale of the tunnel reached 2321 m at the beginning of 2017, which accounted for 47% of the length of the tunnel (iii) e number of tunnel sections with Level 5 diseases has gradually increased in the 3 years, with an increasing rate of 86% and a length of 215 m, of which the fastest development occurred in 2014 to 2015 and 2015 to 2016. E results showed that the surrounding rock was gypsum rock with gypsum content of 97%– 98% (Figure 11 and Table 2); the thaumasite content in the primary supporting concrete was 19.3%, and the contents of gypsum and ettringite were 17.1% and 3.8%, respectively. Low Temperature. e tunnel sites in a temperate semiarid continental climate area. e temperature of this area is between −5.9°C and 23°C, and the average temperature of this area is 9.2°C. e temperature in the five months from November to March of the following year is below 10°C; the temperature inside the tunnel ranges from −5°C to 20°C throughout the year, with an average temperature of 8.8°C. erefore, the environment of the tunnel lining concrete structure provides low-temperature conditions for TSA
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