Study on deformation prediction of metro running tunnel under building of soil and rock strata

Architectural Engineering May 2013, Volume 1, Issue 1, PP.6-11

Study on Deformation Prediction of MetroRunning Tunnel under Building of Soil and Rock Strata Xiaoyu Bai 1, Nan Yan #2, Hailei Kou 1, Mingyi Zhang 1 1. School of Civil Engineering, Qingdao Technological University, Qingdao, China, 266033 2. College of Environmental Science and Engineering, Ocean University of China, Qingdao, China, 266100 #

Email: yannan0527@163.com

Abstract This paper combines the first phase project of Qingdao Metro (No.3) that a shallow-buried subsurface excavated tunnel passed through existing buildings in the “combination of soil and rock” strata, and applied the MIDAS-GTS two-dimensional ElasticPlastic analysis of nonlinear methods in plane-strain, vault subsidence of the tunnel, surface settlement and building settlement were analyzed from the point of view of right line and left line interaction, it predicted the safety of the existing buildings above the tunnel in “combination of soil and rock” strata. The greatest difficulty of construction of the project was to ensure the normal operation of the existing buildings during the tunnel construction. Therefore, during the construction process, the tunnel should be timely carried out primary support, closed ring and promptly carried on backfill grouting behind primary support. The results can be a reference of the deformation analysis of the existing building caused by tunnel passing through it in “combination of soil and rock” strata. The results also have important reference values in latter construction of tunnel and the other similar project cases.

Keywords: Combination of Soil and Rock; Running Tunnel; Existing Building; Finite Element; Deformation

1 INTRODUCTION Construction of the Underground Railway is often in a compact district of buildings, roads and underground pipelines and other facilities, which has a potential threat to urban environment of existing building. Subway lines often emplaced along the city's main street, it cross a large number of buildings and underground pipelines inevitably, and have on the surrounding soil disturbance during construction, in turn, have an impact on adjacent buildings and underground pipelines, seriously, it might threaten the security of buildings and underground pipelines, and then lead to various environmental issues have become increasingly prominent in the construction of city tunnel [1-6]. In order to keep subway construction in buildings and underground pipelines working under the premise of safe and orderly manner, there is an urgent need to study the influence of metro construction on adjacent buildings and control issues, metro construction must ensure that the impact of the existing facilities within the allowable range. Study on the influence of metro construction on the surrounding buildings, it guarantee the safety and the normal use of existing facilities is of great significance [7-12].

This paper combines the project that a shallow-buried subsurface excavated tunnel under existing buildings of the first phase project of Qingdao Metro (No.3), and applied the MIDAS-GTS two-dimensional Elastic-Plastic analysis of nonlinear methods in plane-strain, it predicted the safety of the existing building above the tunnel in combination of soil and rock strata, which for the later construction of Qingdao Metro and similar building safety control of Metro Construction provide an important reference and reference value.

2 CONSTRUCTION SURVEY Qingdao is located in southwest Shandong Peninsula, low topography of the city is East and West, North - South ridges on either side, intermediate sag. Late Yanshanian solid granite mass in the form of the base distribution in -6http://www.ivypub.org/ae

surface or underground within a certain depth, and with the long-term weathering a certain thickness weathering zone, which deposited the different thickness quaternary unconsolidated sediment, is a typical " upper soft and lower hard" type of Geology type.

Wan Nian Quan Road Station to Li Cun Station running tunnels used underground excavation method, section form of horseshoe, composite lining dark-excavation structure, the running tunnels into Jing Kou Road along the Wan Nian Quan Road, the ground was commercial, business office, residential land, the running tunnels thickness of the soil around 11~21m. Due to the tunnels through more buildings, this paper only selected representative Li Cun branch of Bank of China, as shown in figure 1. The building was located in Li Cun River alluvial plain, the highest elevation of the ground was 18.03m, and minimum elevation of Li Cun River is 12.01m.

FIG.1 CURRENT SITUATION OF LI CUN BRANCH OF BANK OF CHINA

Li Cun branch of the Bank of China that the tunnel through the building is the ground 6 layer local 7 layers of brick masonry structure, built in 1990, no basement, was located the Xia Zhuang Road, was away from Li Cun Station 22m, the basis was reinforced concrete strip foundation independent column base, vertical distance of the tunnel and the building is 10.87m. The tunnel is located half sand and half rock strata, the upper half of the tunnel is located saturated sand layers, overlying strata of the tunnel is plain fill (2.2 m), silt clay (5.4 m), coarse sand (7.4 m), sand permeability coefficient for forty m/d, permeability of sand layer is 40 m/d, the lower portion of the tunnel located the medium-weathered layer, the special strata of “upper soft and lower hard� bring great difficulties to the construction, the construction risk is great. Li Cun branch of the Bank of China is a typical representative, so this paper selects it for calculation and analysis. The position between running tunnel and Li Cun branch of Bank of China as shown in Fig.2 and Fig.3.

FIG.2 RUNNING TUNNEL UNDER THE BANK OF CHINA STRUCTURED FLOOR PLAN -7http://www.ivypub.org/ae

FIG.3 TUNNEL UNDER THE BANK OF CHINA STRUCTURE PROFILE

3 DEFORMATION ANALYSES 3.1 Calculation model and calculating sketch This paper used MIDAS-GTS two-dimensional Elastic-Plastic Analysis of nonlinear methods in plane- strain, the model was two-dimensional model, and used stratum structure model. Plane elements simulated the strata materials and plane beam element simulated primary support in calculation models. Considering the influence of boundary effect, the computation model size took for 72 m×45 m. In the boundary conditions, the side and the bottom was the normal constraint, the upside was the free surface. Step Method was used the tunnel excavation; this paper only considered tunnel excavation and primary support stage during calculation. At the same time, this paper considered small duct and complete cross section grouting entirety stabilization effect of Soil surrounding, strengthening regional of the small duct and deep hole grouting area would improve the level of surrounding rock grade (according to the Ⅴ class value of surrounding rock in reinforcement area), ground building load each layer took 20 kN/m uniform load, total 7×20 kN/m =140 kN/m.

The main purpose of calculation was to analyze the mechanical effects of the construction process, therefore, not to the secondary lining analyzed, the mechanics parameters of the supporting structure such as table 1 and table 2, the finite element model as shown in figure 4.

TABLE1 CALCULATION PARAMETERS OF SOIL LAYER DENSITY OF

COHESIVE

INTERNAL FRICTION

ELASTIC

POISSON'S

NATURAL

STRENGTH

ANGLE

MODULUS

RATIO

ρ(g/cm3)

c(kPa)

φ(°)

E(MPa)

υ

plain fill

1.80

20

15

10

0.35

silt clay

2.00

17.6

12.2

10

0.35

coarse gravel sand

2.05

20

35

60

0.26

2.44

2000

30

15000

0.22

slightly weathered granite

2.54

8000

40

36000

0.2

reinforcing ring

2.1

100

35

500

0.3

GEOTECHNICAL NAME

medium-weathered coarse grained granite

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TABLE2 MECHANICS PARAMETERS OF SUPPORT STRUCTURE PRIMARY SUPPORT

SURROUNDING LINING TYPE ROCK GRADE

ADVANCED SUPPORT

STEEL MESH

STEEL ARCH

SHOTCRETE

deep boring grouting technology applied in early strength the tunnel, sand layer of excavation section concrete with primary

3.0 m range were strengthened, advanced

arch wall

small pipe was used in the arch of the

φ8@150×150

VI grade support

Spacing 0.5m

C25, the thickness with

tunnel, the length with 3.0 m, ring distance 250mm and longitudinal distance were 0.3 m.

FIG.4 FINITE ELEMENT MODEL

3.2 Calculation model and calculating sketch The tunnel under Bank of China, to ensure the normal operations of the Bank, to prevent settlement deformation of the building due to the tunnel excavation, where focused on analyzing vertical deformation of the building, the surface settlement and the vault crown settlement of the tunnel during the tunnel excavation process, the calculation results as shown in figure 5 and figure 6.

FIG.5 DISPLACEMENT IMAGES OF LEFT LANE AFTER THE EXCAVATION FIG.6 DISPLACEMENT IMAGES OF RIGHT LANE AFTER THE EXCAVATION

Through the figure 5, it is known that the tunnel vault sink 5.2 mm after the left line of the tunnel completed, surface subsidence caused by 2.2 mm, after the left line of the tunnel completed, vault subsidence caused by 8.0 mm, Li Cun branch of the Bank of China subsidence was 4.1 mm, it was less than the control standard of existing buildings. But -9http://www.ivypub.org/ae

considering the complexity of soil structure, the monitoring survey of the tunnel was strengthened during construction process, grouting pressure was adjusted in real time, to ensure the safety of the structure of existing buildings.

According to the analysis of the causes of the settlement, it should be divided into three parts: (1) No excavation phase of the settlement, the subsidence mainly caused pre-settlement of the front of strata by deformation of the working face; (2) The settlement of excavation phase, because redistribution process of the formation stress caused the settlement by tunnel excavation; (3) Consolidation settlement after the excavation, due to previous construction activities to the disturbance of the formation, which caused the non-uniform deformation of soil, and achieved a new balance after consolidation again.

From the analysis, the 2nd settlement was the main factors influencing of the strata, therefore in terms of the technical measures, means we have taken, the key was how to shorten the time of stress redistribution of the strata, that is, strata was quickly and effectively provided a constraint with stiffness requirements through the primary support structure (take short footage - footage 50cm of each circulation, steel support.) Secondly, to reduce the settlement factors of the advance excavation, we adopted measures such as advanced small duct grouting and closed working face as much as possible to achieve. Finally, to reduce the influence of after-settlement, it should be taken such as the backfill grouting behind primary support, increased steel lock foot bolt and timely closed primary support measures etc.

Through the above analysis, we can show that, through grouting can be very good to improve tunnel excavation process to the surface settlement and buildings settlement influence, through the effective reinforcement measures of grouting, it can minimize the influence of the upper buildings in the maximum limit because of the tunnel excavation.

4 CONCLUSIONS (1) In the “combination of soil and rock” strata, the mining tunnel under the building was relatively rare in domestic projects. The biggest difficulty of construction of the project was to ensure the normal operation of the existing buildings during the tunnel construction. Therefore, in the construction process, deep boring grouting technology applied in the tunnel, sand layer of excavation section 3.0 m range were strengthened, advanced small pipe was used in the arch of the tunnel, the length with 3.0 m, ring distance and longitudinal distance were 0.3 m, meanwhile, the steel arch of 0.5m interval was used, that is, the settlement factors of pre – excavation was reduced.

(2) Along with the tunnel excavation, cycle time of excavation increased, leading to support time delay, which was one of the main reasons of the surface settlement. In addition, surrounding rock of the tunnel arch was weak, disturbance and destruction of rock strata was another reason for surface settlement caused by too large because of construction of drilling and blasting method. So the key was how to shorten the time of stress redistribution of the strata, that is, strata was quickly and effectively provided a constraint with stiffness requirements through the primary support structure.

(3) This paper applied MIDAS-GTS two-dimensional Elastic-Plastic analysis of nonlinear methods in plane-strain, vault subsidence of the tunnel, surface settlement and building settlement were analyzed from the point of view of right line and left line interaction, the analysis results met the control index of buildings.

(4) Reinforcement measures of grouting can be very good to improve tunnel excavation process to the surface settlement and existing buildings settlement influence; it can minimize the influence of the upper buildings in the maximum limit because of the tunnel excavation. To reduce the influence of after-settlement, it should be taken such as the backfill grouting behind primary support, increased steel lock foot bolt and timely closed primary support measures etc.

(5) Reinforcement scheme of buildings and tunnel, advanced support measures, and measures of tunnel excavation and supporting that this paper proposed had important reference value for the domestic similar construction of underground engineering under existing buildings.

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REFERENCES [1] E J Cording, W. H. Hansmire. Displacements around soft ground tunnels[A]. 5th Pan American Conference on Soil Mechanics and Foundation Engineering, Argentina, 1975, (4): 571-633 [2] LIU Tao, ZHANG Jin, YAN Nan. Pilot Study of Retaining Structure Design of Subway Station of Undercutting with Shallow Overburden in Rock Strata[J]. Chinese Journal of Rock Mechanics and Engineering, 2010(Supp.2): 347-350 (in Chinese) [3] LIU Zao, Yu Caigao, Zhou Zhenqiang. Design and Construction of Metro Engineering [M]. Beijing: China Communications Press, 1993 (in Chinese) [4] F. Martos. Concerning an approximate equation of subsidence trough and its time factors[A]//Proc. of the International Strata Control Congress[C]. Leipzig: Leipzig University Press, 1958 [5] R. B. Peck Deep excavations and tunneling in soft ground[J]. State of the Art Report.Prvc.7thInt, conf. on Soil Mechanics and Foundation, Mexico city, 1969, 225-290 [6] J Litwiniszyn. Fundamental principles of the mechanics of stochastic medium[A]//Proc of 3rd Conf Theo Appl. Mech[C].

Bongalore: Bongalore University, 1957 [7] Shi Zhongheng. The Design and Construction for Metro[M].Xi'an: Shanxi Science and Technology Press, 2002 (in Chinese) [8] The National Standard Compilation Group of People's Republic of China. (GB50517-2003). Code for Design of Metro[S]. Beijing: China Planning Press, 2003 (in Chinese) [9] WANG Mengshu. Theory of Technology of Method of Undercutting with Shallow Overburden in Underground Engineering[M].

Hefei: Anhui Education Press, 2004 (in Chinese) [10] WU Bo. Study on land subsidence induced by urban subway tunneling on complicated conditions [Ph. D. Thesis][D]. Chengduďźš Southwest Jiaotong University, 2003 (in Chinese) [11] YAO Xuande, WANG Mengshu. Statistic analysis of guideposts for ground settlement induced by shallow tunnel construction[J].

Chinese Journal of Rock Mechanics and Engineering, 2006, 25(10): 2030-2035 (in Chinese) [12] Chi S. Y, Chen J. C, Lin C. C. Optimized back-analysis for tunneling-induced ground movement using equivalent ground loss model[J]. Tunneling and Underground Space Technology, 2001, 16(3): 159-165

AUTHORS The First Author: Xiaoyu Bai (1984-),

The Third Author: Hailei Kou (1984-), male, the Han

male,

Master,

nationality, Master, Doctoral candidate, mainly engaged in the

Doctoral candidate, mainly engaged in

the

Han

nationality,

field of soil mechanics and pile foundation, in 2007, graduated

the field of foundation and underground

from

engineering, in 2007, graduated from

engineering, acquired Master Degree.

Qingdao Technological University in

Email: kou123321@126.com

geotechnical

The Fourth Author: Mingyi Zhang (1958-), male, the Hui

engineering,

acquired

Qingdao

Technological

University

in

geotechnical

Master Degree. Email: baixiaoyu538@163.com

nationality, Ph.D., Professor, Doctoral supervisor, mainly

The Second Author: Nan Yan (1982-), female, the Han

engaged in testing, teaching and research of soil mechanics and

nationality, Master, Doctoral candidate, mainly engaged in the

foundation, in 2001, graduated from Chongqing University in

field of rock and soil mechanics and engineering, in 2007,

geotechnical engineering, acquired PhD.

graduated

Email: zmy58@163.com

from

Qingdao

Technological

University

in

geotechnical engineering, acquired Master Degree.

Email: yannan0527@163.com

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