During the construction of largediameter
shield tunnels in waterrich sandy pebble strata, the
following difficulties are often encountered: collapsing tunnel faces, water
gushing, rock falls, and jamming of screw cutters. Meanwhile, due to the high
shield torque, high muck temperatures, and large volumes of slag, soil
conditioning becomes essential. Accordingly,
many laboratory experiments are conducted to explore the optimal mixing
proportion of bentonite and foaming agent, and according to analysis,
proportion and evaluation indices for soil conditioning are proposed. The following conclusions are
drawn: (1) The viscosity of bentonite increases with increasing sodium
bentonite ratios. (2) The foaming multiples and halflife
period of the foam solution increases with increasing foaming agent
concentration. (3) The fluidity of the conditioned soil significantly increases
with increasing proportions of bentonite and foaming agent; the permeability of
the conditioned soil decreases with increasing proportions of bentonite and
increases with increasing foaming agent proportion. Finally, it is recommended
that the bentonite viscosity should not be less than 35 s, bentonite volume
should be 10%~12% of the soil volume, foaming multiple of the foaming agent
should be less than 15, and volume of foam should be limited to approximately
20% of the soil volume. The soil conditioning effect is verified by actual soil
sampling and excavation parameter analysis.
XI Zhendong
,
HU Linhao
,
ZHANG Shuxiang
,
ZHANG Bo
. Soil Conditioning for Large-diameter
Shield Boring in Water-rich
Sandy Pebble Strata: a Case Study on a Shield-Bored Section of Chengdu Metro[J]. Tunnel Construction, 2021
, 41(1)
: 37
-43
.
DOI: 10.3973/j.issn.2096-4498.2021.01.004
