Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

The Freeze-Sealing Pipe-Roof(FSPR)method,which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge,is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions.When the FSPR method is used to construct shallow burial submerged tunnels,the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel,and its waterproof performance needs to be further investigated.In this paper,a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation.The results show that excavation has a weakening effect on both sides of the frozen wall,with a greater effect on the inner side,and a positive temperature appears in the local area inside the jacked pipe.The concrete fill in the jacked pipe obviously improves the freezing efficiency,and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m,i.e.,the design requirement.In practice,the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel.The study serves as a technical reference for the design and implementation of similar projects.

Classification and quantification of excavated soil and construction sludge:A case study in Wenzhou,China

With rapid urbanization in China,a large amount of excavated soil and construction sludge is being generated from geotechnical and underground engineering.For sustainable management of these construction wastes,it is essential to quantify their production first.The present study has attempted to classify the excavated soil and construction sludge according to their composition and geotechnical properties(particle size,water content,plasticity index).Based on these classifications,a new approach was proposed to quantify the production.The said approach was based on multi-source information,such as the urban topographic map,geological survey reports,urban master plan,and remote sensing images.A case study in Wenzhou city of China was also pursued to illustrate the validity of the newly developed approach.The research showed that in 2021–2025,the total excavated soils and construction sludge production in Wenzhou would reach 107.5×10^(6) and 81.7×10^(6) m^(3),respectively.Furthermore,the excavated soil was classified into the miscellaneous fill,crust clay,muddy clay and mud with silty sand.Likewise,the construction sludge was classified as liquid sludge and paste-like sludge.The classification and quantification can serve as guidance for disposal and recycling,thereby leading to high-level management of waste disposal.