Research on Surface Subsidence of Long-Span Underground Tunnel

Table 1

Underground excavation station main Earth and rock excavation classification and tunnel surrounding rock classification.

Soil (rock) layer number	Geotechnical name	Main engineering geological features	Stable condition after excavation	Dredge classification of Earth and stone	Surrounding rock classification	Saturated uniaxial ultimate compressive strength (MPa)
①, ①1	Artificial fill	The low compactness of plain and mixed filled soil has poor uniformity of soil quality and uneven water permeability, and the local sandy components have higher water permeability.	In the case of water, the excavation is prone to collapse and deformation, and the surface subsidence is usually large.	I	VI	—
⑪, ⑮1	Silty clay; completely weathered lamprophyre	Basically in plastic or hard plastic state, generally poor permeability, good self-stability.	It has good self-stability under the condition of no water, but it is easy to collapse when there is water, and it can collapse to the ground when it is shallow buried.	II	VI	—
⑫, ⑯top, ⑯middle, ⑯2, ⑯4	Sandy cohesive soil, highly weathered granite, mesozone, highly weathered granite porphyry, and sandy soil-like cataclastic rock	Generally in the hard plastic state, water permeability is better; the highly weathered rock has the characteristics of water-disintegrating, which is greatly disturbed by blasting construction and has a short self-stabilizing time under the condition of no support.	The surrounding rock is prone to collapse and deformation and needs timely support in case of water.	III	V	—
⑯bottom, ⑰4	Subzone of highly weathered granite; massive cataclastic rock	The rock material is soft and red in color. The weathering fissures are developed seriously. The water is poor, but the water permeable is good.	The surrounding rock is easy to collapse and deformation. When the support is not in place or there is a big collapse, the vault often falls.	IV	IV	—
⑰, ⑰2	Moderately weathered granite; moderately weathered granite porphyry	Light red, local structural joints and weathered fissures are well developed and contain groundwater. With the development degree of fissures, there is a great difference in water abundance and permeability.	Good self-stability and small collapse may occur when there is no support, which requires higher control of blasting construction.	V	III	15–20
⑱, ⑱1, ⑱2, ⑱6	Breezy granite, breezy lamprophyre, breezy granite porphyry, and granite porphyry	Light red, hard rock, a few joints, and fissures are not rich in groundwater.	Strong self-stability can be exposed for a long time; the probability of collapse is low, but the roof with poor combination between rock strata is prone to collapse.	VI	II	40–61