1757
Technical Committee 204 /
Comité technique 204
beyond 20 m from the centerline of the tunnel. In the region
between the centerline of the tunnel and 20 m from centerline of the
tunnel, the surface displacements calculated by the FEA is the same
as those calculated by the SDE. The results obtained by the FEA
agree well with those obtained by the SDE.
Therefore, the finite element analysis gives a better estimation of
surface settlement as demonstrated with the comparison between
the calculated and the measured settlements in medium dense soils
involved in the case study. For the loose and medium sandy soils,
ignoring the appropriate soil characteristics in the surface
displacement equation (Eq. 2) probably leads to larger error and
further deviation from the actual values. The surface displacement
readings obtained by the FEA is more conservative than those
calculated by the SDE.
The difference between the two sets of computed settlements is
noticed in loose sand and in medium sand. The difference between
the two sets of computed settlements lies in the use of the width
parameter (i) as presented in Eq. (3). This (i) parameter is used for
cohesionless soils but it does not take into account the different
geotechnical parameters associated with different densities of
cohesionless soil. The proposed finite elements model takes into
account the effects of the stress and strength parameters of the
different sand soil densities. Therefore, the differences between
surface displacement profiles obtained by the FEA with those
obtained by the SDE may be due to the value of the shear strength
and stress parameters for the soil media around tunnel system
adopted in the 2-D nonlinear FEA.
7 CONCLUSIONS
Based on the proposed 2-D finite element model, the following
conclusions are presented due to tunneling through different sand
soil types.
- The 2-D nonlinear numerical model is applicable to analyze and
predict detailed performance of tunnel systems.
- The results calculated by the proposed 2-D nonlinear finite
element model have a good agreement with the field data.
- The predicated surface settlements due to tunneling underestimate
by up to 10 % from the field measurements. The discrepancy
between the calculated and the field readings may be due to the
stress-strain soil parameters and the strength soil parameters.
- Surface settlement profile computed by the surface displacement
equation (SDE) by Peck and Schmidt (1969) is in reasonable
agreement with surface settlement profile computed by the 2-D
finite element analysis in dense to very dense sand soil.
- Surface settlement profile calculated by the SDE does not agree
well with surface settlement profile calculated the 2-D FEA in loose
and medium sand soil.
- The surface displacement equation proposed by Peck and Schmidt
(1969) does not consider the impact of different sandy densities soil
types. However, the finite element analysis takes into account
strength and stress parameters of different sand densities.
- The surface settlement profiles calculated by the finite element
analysis are more conservative than those computed by the surface
displacement equation at different sand densities.
8 REFERENCES
- Ahmed, A.A. (1994). Analysis of deck road tunnels. Proceedings
of the international congress on tunneling and ground condition,
Abdel Salam (ed.), Cairo, Egypt. Published by Balkema,
Rotterdam.
- Abdel-Salam, M.E. (1998). Urban constraints on underground
works the Cairo metro-case histories. Egyptian society presentation,
Cairo.
- Attwell, P.B., Yeates, J., and Selby, A.R. 1986. Soil Movement
induced by tunneling and their effects on Pipelines and structures.
Blackie and son Ltd. Published in the USA by Chapman and Hall.
- Byrne, P.M., Cheung, H., and Yan, L. (1987). Soil parameters for
deformation analysis of sand masses. Canadian Geotechnical
Journal. 24, 366-376.
- Compo, D.W., and Richards, D.P. (1998). Geotechnical
challenges faced on line 2 of the Greater Cairo Metro System.
ASCE, Big dig around the world. USA.
- Duncan, J.M., and Chang, C.Y. (1970). Nonlinear Analysis of
Stress and Strain in Soils. Journal of the Soil Mechanics and
Foundation Div. ASCE, Vol. 96, No. SM5. September.
- Duncan, J.M., Byrne, P.M., Wong, K.S., and Mabry, P. (1980).
Strength, stress-strain and bulk modulus parameters for finite
element analysis of stresses and movements in soil masses.
University of California, Berkeley, CA. Report no. UCB/GT/80-01.
- Janbu, N. 1963. Soil compressibility as determined by oedometer
and triaxial tests. European conference on soil mechanics of
foundation engineering. Wiesbaden. Germany. Vol. 1, pp. 19-25.
- El-Nahhas, F. 1986. Spatial mode of ground subsidence above
advancing shielded tunnels. Proc. Of International. Congress on
Large underground Opening, Fireze, Italy, Vol. 1, pp. 720-725.
- El-Nahhass, F.M., Ahmed, A.A., El-Gammal, M.A., and Abdel
Rahman, A.H. (1994). Modeling Braced Excavation for Subway
station. Proceedings of the international congress on tunneling and
ground condition, Abdel Salam (ed.), Cairo, Egypt. Published by
Balkema.
- El-Nahhass, F. M. 1999. Soft ground tunneling in Egypt.
Geotechnical challenges and Expectations. Proc. of the Tunneling
and Underground Space Technology, Vol. 14, No. 3, pp. 245 – 256.
- Ezzeldine, O.Y. (1999). Estimation of the Surface Displacement
Field Due to Construction of Cairo Metro Line El-Khalafawy-
St.Thereses. Tunneling and underground space technology, Vol. 14,
No. 3, pp. 267-279. Published by Elsevier science Ltd.
- Mazek, S.A, and El-Tehawy, E.M. 2008. Impact of Tunneling
Running Side-by-Side to An Existing Tunnel on Tunnel
Performance using Non-linear Analysis. Proc of the 7
th
ICCAE. 27-
29 May, 2008. Cairo, Egypt.
- National Authority for Tunnels (NAT), 1993, Project Document.
- National Authority for Tunnels (NAT), 1999, Project Document.
- National Authority for Tunnels (NAT), 2010, Project Document.
- O'Reilly, M. P. and New, B. M. 1982. Settlement above tunnels in
the United Kingdom their magnitude and production. Tunneling
conference. London. pp. 173- 181.
- Peck, R. B. and Schmidt, B. 1969. Deep excavations and
tunneling in soft ground. Proc. Of the 17
th
International Conf. On
Soil Mechanics and Foundation Engineering, Mexico City, Mexico,
pp. 225-240.
Table 1: Geotechnical properties in Central Cairo City
Layer
Fill
Silty-clay
Silty sand
Sand
Bulkdensity γ
b
(t/m
3
)
1.8
1.9
1.85
2.0
Drained
Poisson’s
Ratio V
s
0.4
0.35
0.35
0.30
Effective Angle of
initial Friction(
ϕ
)
º
20
26
30
37
Effective Cohesion C
(KP
a
)
0
10
0
-
Standard penetration
(blows/0.3m)
4-20
13-15
-
35
Modulus Number(m)
300
325
400
400-700
Exponent Number(n)
0.74
0.6
0.6
0.5-0.6
Drained Modulus of
Elasticity E
s
(t/m
2
)
1000
1200
3000
7000
Over Consolidation
Ratio (OCR)
1
1.5
-
-
Coefficient of Lateral
Earth Pressure K
0
1
0.8
0.5
0.39
Table 2: Characteristics of the tunnel lining
Type
E
b
(t/m
2
)
(t)
cm
F
c
(t/m
2
)
W
(KN/m
2
)
V
Tunnel liner
2.1×10
6
40
4000
10.0
0.20
