1785
Subsoil Settlement Feature of Immersed Tube Tunnel in Deep Soft Subsoil with
Heavy Siltation in Open Sea
Caractérisation du tassement sur sol mou de grande épaisseur d’un tunnel tube immergé soumis à
un envasement important en condition de mer ouverte
Xie Y., Zhang S., Zhang H., Liu B.
School of Highway, Chang’an University, Xi’an, China
ABSTRACT: Hong Kong-Zhuhai-Macao Link that crosses the Pearl River Estuary is a connection bridge between Hong Kong,
Macao and Zhuhai, which will improve the communication of these three places in China. The bridge is an oversized cross-sea project
over the east and west coasts of the Pearl River. Relied on the undersea immeresed tube tunnel (IMT) for Hong Kong-Zhuhai-Macao
Link project and focused on the consolidation settlement feature of the subsoil for IMT on deep soft subsoil under the conditions of
large excavation, backfilling and siltation in open sea, a full stress path of subsoil was simulated for the process of compression in
consolidation, unloading in excavation and re-compression in backfilling, by using of Geotechnical Digital Systems with on-site
CPTU test results and the in-situ bored soil sample. Based on these results, the process of subsoil consolidation – excavation – tube
location – backfilling – siltation as well as the re-excavation of channel was simulated by using gotechnical centrifuge, to find out the
settlement feature of the subsoil during and after tunnel construction. The settlement and consolidation feature of the deep soft subsoil
with heavy siltation in open sea was presented.
RÉSUMÉ : La construction de la liaison routière entre Hong-Kong, Macao et Zhuhai est un projet national en Chine, qui concerne
particulièrement de grands ponts au-dessus et d’un tunnel au-dessous de la mer. Dans cet article, à partir de résultats d’essais CPTU
in-situ et d’essais GDS en laboratoire, dans le but de préciser les caractéristiques de tassement et de consolidation de sols mous sous-
marins de grande épaisseur soumis à de grandes excavations et à la mise en place d’un tunnel, la procédure complète du chemin de
contraintes “compression de consolidation – décharge par excavation – recharge due aux remblais et au tunnel” appliquées
effectivement pendant les travaux de fondation du tunnel immergé a été simulée. Un essai en centrifugeuse a aussi été effectué afin
d’étudier les caractéristiques de tassement et de consolidation pendant et après les travaux. Les résultats nous permettent de mieux
connaître le comportement de ce type de tassement dans la condition de mise en place d’un tunnel immergé avec un envasement
important.
KEYWORDS: IMT; Settlement; Stress Path; Centrifugal Model
1 INTRODUCTION
The oversized Hong Kong-Zhuhai-Macao bridge which crosses
the Pearl River Estuary, connects Hongkong, Macao and Zhuhai.
The IMT approach was selected to pass LingDing West channel
and TongGu West channel based on the aviation high limit of
Hong Kong International Airport, the proposed channel, and on
site investigation of Hong Kong-Zhuhai-Macao bridge.
The immersed tube tunnel has the characteristics of long
tube, deep water, large silting on tube surface, weak and uneven
foundation, difficult settlement control, stress concentration
near between the island and the tunnel joints and complex
construction process. Generally, Immersed tube tunnel is not
sensitive to soil settlement. But uneven settlement will occur
due to significant change in soil characteristics and load
distribution along the tunnel. The load redistribution will lead to
additional stresses. Thus it is important to estimate the
subsidence quantity for immersed tube tunnel which is made of
brittle concrete materials. Therefore, it is important to study the
soil settlement with resilience-recompression characteristics in
IMT under Hong Kong-Zhuhai-Macao bridge project.
2 THE DEFORMATION CHARACTERISTICS OF IMT
FOUNDATION SOIL BASED ON SIMULATION OF
STRESS PATH
2.
1 Soil engineering property and its simulated conditions
In order to study the resilience-recompression characteristics of
IMT foundation soil caused by different load condtions, the
complete stress path of trench soil was simulated by numerical
method and GDS triaxial test with standard stress path to
understand the complete stress path, consolistaion and
compression, and resilience-recompression characteristics.
Through suveries and CPTU data, it was found that the tunnel
foundation has 5 distinctive cross sections. Three sections are
studied in this paper, as shown in Table 1 The distribution
profile of the cross-sectional test points is shown in Figure 1.
The basic engineering properties of the soil are presented in
Table 2.
The whole research process was based on detailed
engineering survey and the CPTU data. Using numerical
simulation of the actual conditions, different characteristics of
foundation soil stress is obtained, and then stress path
simulation test is carried out. Saturated specimen was prepared
based on dry density, which is 39.1mm in diameter and 80mm
in height. First consolidation module K
0
was selected, and then
K
0
consolidation test was performed. Through the back pressure
volume measurement volume change, the target value of K
0
consolidation was stress value from the numerical simulation of
the original stress state. Then take the stress path test module,
simulation consolidation - excavation unloading - backfill
reload - navigation path excavation and unloading. According to
the numerical calculation results, set the stress path module of
each phase of the set target value, then finish stress path
simulation test with these methods. Through the test to obtain
different stress paths condition of modulus of compression
、
modulus of resilience and recompression modulus, then the
numerical calculation is carried out again by using these test
modulus. Get new stress characteristics of different foundation
soil. And compare with the original calculation results until the
test results and calculation results are close enough to the
acceptable level.
