792
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
5.4 Edge to edge distance of building (L)
The figure6 shows that the increase of L decreases the influence
of the structure on lining loads. Also, it can be seen that with
reduction of building load the influence of L on induced loads
decreases. The obtained results show that in the case of building
existence in both sides of tunnel, maximum bending moment
occurs in lining invert. This is in converse of case that building
loads apply above the tunnel center that the maximum bending
moment occurs in lining crown.
Figure 8. Assessment of building weight –Building located centrally
The increase in lining forces due to building loads
disappears as Z
0
increase. For example percentage of increase in
maximum axial force and bending moment due to building
loads summarized in table 4 for various tunnel depth and
building loads compared to green-field condition. As a general
rule, building weight effect is higher for shallow tunnels
whereas, the decrease of building width and increase of distance
to tunnel center reduces the weight effect.
Table 4. Increase percentage of structural forces
C=1D
C=1.5D
C=2D
building
N(kN) M(kN.m) N(kN) M(kN.m) N(kN) M(kN.m)
10 story 70
112
35
79
20
55
8 story
58
92
27
63
16
44
5 story
35
60
17
40
10
28
3 story
20
36
10
24
6
17
Figure 6. Assessment of edge to edge distance of buildings - Building
located symmetrically on both sides, 10 and 5 stories.
5.5 Soil stratification
In this study the effects of soil stratification were considered in
two parts. At first part based on mentioned geotechnical section
of study region of Tabriz metro line 2 corridor, a two layer soil
include sand overlying by silty soil (ML) modeled. The
thickness of silt layer that locate above water table adopted
equal to 9m. In second part a homogeneous silty soil is modeled
and the effects of soil properties are studied. Figure 7 shows the
effect of soil stratification and tunnel surrounding soil types on
the lining loads for various tunnel depths.
6 CONCLUSIONS
In both green-field condition and building existing state,
presence of silt layer increase lining loads slightly and with
increase of tunnel depth the effect of silty layer reduces .A
considerable growth in lining structural forces occurs when
excavation of tunnel done in silty soil and for deep tunnels this
effect is greater. It seems that because of approximately equal
unit weight of two soil types, the greater lateral pressure
coefficient (K
0
) of silt layer causes more ground pressure on
lining and greater structural forces induced in lining.
Using characteristics of the Tabriz metro line 2 and code of
ABAQUS software, 240 two dimensional numerical models
were analyzed and According to the results of parametric
studies conducted in this research:
As a general rule, the existence of surface buildings in 2D
plane strain analysis will cause the lining loads increase
compared to the green-field condition. However, the influence
value depends on the combination of geometrical and
mechanical parameters of the tunnels, buildings and
surrounding soil.
According to characteristics of study region of the Tabriz
metro line 2 corridor, the buildings with 5 and more story has a
considerable effects on lining loads. For shallow tunnels these
effects is greater and with increase of tunnel depth building
effects decrease.
Based on obtained results in this study, existence of silty
layer above the sandy soil has not considerable effects on lining
loads, but when tunnel excavated in silty soil lining loads
increase intensively compared to tunnels excavated in sand.
7 REFRENCES
Figure 7. Assessment of soil layers types, centrally located 10 story
building
In 2-layer ground the effect of silt layer is small and
decrease with increase of tunnel depth .Conversely, in silty soil,
growth of axial force and bending moment increases as tunnel
depth increase.
Official Report of the International Tunnelling Association. 2000.
Guidelines for the Design of Shield Tunnel Lining.
Tunnelling and
Underground Space Technology
(15) , 303-331.
Hashimoto T. Nagaya J. Konda T. Tamura T. 2002. Observation of
lining pressure due to shield tunneling.
Geotechnical aspects of
underground construction in soft ground
, IS-Toulouse, Kanster et
al. (eds), Specifique, 119–124.
5.6 Building weight
The effects of building weight on the lining loads for tunnel
depth (Z0) of 18.4m have been illustrated in figure 8. As it is
shown, increasing the building weight in numerical simulations
will result in increase of lining loads in comparison with green-
field; however the exact influence of building weight depends
on tunnel depth, soil type and building’s parameters.
Mashimo H. and Ishimura T. 2003.Evaluation of the load on shield
tunnel lining in gravel,
Tunnelling and Underground Space
Technology
(18), 233–241.
Nunes M.A. and Meguid M.A. 2009. A study on the effects of
overlying soil strata on the stresses developing in a tunnel lining,
Tunnelling and Underground Space Technology
(24), 716–722.
Karakus M. 2007. Appraising the methods accounting for 3D tunneling
effects in 2D plane strain FE analysis.
Tunnelling and Underground
Space Technology
(22) ,47–56.
