Large-scale Underground Structures Research Articles

Construction geological logging of the Thames Tideway Tunnel beneath central London: unearthing the ground truth

Large-scale underground structures excavated during the construction of the Thames Tideway Tunnel have facilitated observations of the in situ geology and revealed sedimentary characteristics that were not fully evident in disturbed samples from ground investigation boreholes or laboratory tests. These have led to significant improvements in the understanding of groundmass behaviour of several strata within the London Basin geological sequence that are not easily studied by intrusive ground investigations, especially those involving sand channels and the ‘Pebble Bed’ within the Lambeth Group deposits. Further validation of the ground model and geology projected over the scheme during the preconstruction design has been gained from logging the geology within deep shafts, open-face connection tunnels and the main 8.8 m-outer-diameter tunnel from behind the tunnel-boring machine cutterhead. It is recommended that an archive of field logs, as obtained during construction, be established to augment archives of borehole logs. Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

Seismic Responses of a Large Unequal-span Underground Subway Station in Liquefiable Soil Using Shaking Table Test

ABSTRACT Sand liquefaction is considered to be one of the main causes of severe earthquake damage. The seismic response of large-scale underground structures is mainly controlled by the deformation of surrounding soils, and the large liquefaction-induced lateral displacement poses a serious threat to large underground structures. In this paper, a large-scale shaking table test is performed to simulate the dynamic interaction between liquefiable foundation, diaphragm wall and underground subway station. The results indicate that the interaction mode between soil and underground structure changes significantly with the different liquefaction states of surrounding soil. The underground structure improves the liquefaction resistance of adjacent lateral soils, but significantly reduces the liquefaction resistance of soils located directly below the structure. The development of dynamic pore pressure is related to the seismic intensity, and a significant dissipation of dynamic pore pressure usually occurs after the end of a strong seismic excitation. Moreover, the acceleration response law along the vertical direction has changed significantly within the buried depth of the underground structure. Specifically, the acceleration response of the lateral foundation is inhibited in the absence of liquefaction, but is enhanced in the complete liquefaction. In addition, the liquefaction states of model site also affect the spatial strain response of the underground structure.

Hybrid Simulation of Seismic Responses of a Typical Station with a Reinforced Concrete Column

During the 1995 Kobe earthquake, damages were observed in the Daikai subway station and adjacent tunnels. It was the first large-scale underground structure that failed under the earthquake excitation. Numerical and experimental analyses have been conducted to study the failure process of the Daikai station. However, the issue of the scale ratio still exists in the shaking table tests of underground structures. In order to tackle this issue, a hybrid simulation technique is developed here to study the seismic performance of a typical subway station. Based on the previous research, it is found that the central column is the critical component of the structure. Therefore, a reinforced concrete central column is physically tested in the hybrid simulation process. On the other hand, the remaining parts of the structure and soil domain are numerically modeled at the same time. Four hybrid simulation cases are conducted with peak ground accelerations of 0.01 g, 0.1 g, 0.22 g, and 0.58 g. The test results of displacement and shear force are compared with the analytical results. Moreover, the good agreement between the test results and numerical results validate the accuracy of the proposed hybrid test method. After the hybrid simulation process, a quasi-static test is conducted to illustrate the mechanical properties of the central column after the earthquake excitation.

Experimental Study on Structural Form and Excavation Model of Urban Metro Cross Transfer Station with Super Large Cross Section and Shallow Excavation

The construction of urban underground cross‐interchange transfer subway stations often encounters the difficulties of shallow‐buried, different surrounding rock, large spans and heights, congested road traffic, and surrounding buildings sensitive to the construction sequence. Therefore, there is a need for an underground project that controls the stability of underground space and ground subsidence. Based on the construction difficulties of a certain station (the maximum excavation area over 760 m2), this paper conducts a comprehensive selection design of the structure, construction mechanics response, and control technology of this type of interchange station structure and construction excavation. First of all, based on the design experience of large‐scale underground transfer transportation engineering and taking full consideration of the stratum conditions, an “arch‐wall” cross transfer structure method is proposed. The refined numerical analysis shows that the structure can fully utilize the stratum conditions to reduce the ground surface settlement. Then, in view of the stability of surrounding rock during the construction of a large section, based on the traditional large section excavation method, a construction method of “cross rock beam + heading method” was proposed. In order to verify the effect of the construction method, the three‐dimensional detailed numerical model was used to simulate the construction conditions, and the mechanical response characteristics and displacement changes of surrounding rock under each excavation step are explored. Simultaneous interpreting with the traditional large section excavation method, the results show that the new method has advantages in controlling the stability of the surrounding rock. Meanwhile, in order to ensure the safe construction of the project, the self‐developed multifunctional engineering test system for traffic tunnels is used to carry out a large‐scale physical model experiment to simulate the entire process of the “arch‐wall” cross transfer structure construction response characteristics. By analyzing the data of measuring points, the results show that the structure form and the excavation method cause the ground surface settlement, stress, and structural forces meet the requirements for safe construction. Finally, the station can be safely constructed under the new structure form and construction method. Therefore, the structure form and method proposed in this paper can be adapted to the large‐scale underground structure under construction in complex environments.

Three-dimensional dynamic response analysis of a single-ring structure in a prefabricated subway station

Traditional subway construction technology still mainly involves on-site poured concrete construction, which causes many social and environmental problems and at the same time is not compatible with the modern concept of resilient city construction and sustainable development. A new prefabricated subway station construction technology can effectively solve many of the problems caused by traditional cast-in-situ technology and provide for the sustainable development of subway construction programmes. As an important part of an urban lifeline system, the seismic performance of subway stations has always attracted much attention. This paper focuses on the dynamic response of the single-ring structure of a prefabricated subway station under horizontal earthquake shaking. Using the commercial finite element software ABAQUS, numerical analysis models of two large-scale underground structures have been developed: the single-ring structure of a prefabricated subway station and the traditional cast-in-situ subway station. Under the same earthquake action, there are obvious differences between the prefabricated structure and the traditional cast-in-place structure. Compared to the seismic response of traditional cast-in-situ structures, the ground acceleration response of the prefabricated structure is slightly reduced, the overall deformation is slightly increased, the maximum internal force and stresses are significantly reduced, the internal force transmission path is changed, and the area of influence in the surrounding soil is significantly reduced. Comprehensive comparative analysis shows that the single-ring structure of the prefabricated subway station has good deformation resistance and excellent mechanical properties under horizontal earthquake shaking and the overall seismic performance meets the design requirements. Finally, the seismic response characteristics and energy dissipation advantages of the prefabricated single-ring structure are discussed. The research conclusions will provide useful references for resilient city construction and sustainable urban development.

Seismic responses of a subway station and tunnel in a slightly inclined liquefiable ground through shaking table test

A lateral displacement of a soil layer caused by sand liquefaction in a slightly inclined ground may pose a serious threat to the seismic safety of subway stations and other large-scale underground structures. Owing to the sharp stiffness variation of the subway station–tunnel connection (STC), the seismic response of a subway station and tunnel near the connection differs from that of the normal part. Thus, this study presents an extensive shaking table test that focuses on the seismic response of the connecting part between a subway station and a running tunnel located under a slightly inclined (dip angle = 6°) liquefiable ground. Results demonstrate apparent asymmetric liquefaction distribution characteristics in the surrounding soil on both sides of the subway station. The asymmetric settlement of the ground surface and horizontal displacement of the slope was also analyzed. The non-uniform elevating of the subway station was also observed in the test. The STC could also aggravate the strain responses of a nearby tunnel structure in the longitudinal direction and those of a nearby column of a subway station. In comparison with the results obtained in the horizontally stratified ground, the distribution law of the strain responses of the subway station was also changed by the lateral liquefaction deformation of the slightly inclined ground.

Comparative numerical analysis on dynamic effects of underground large scale frame structures under seismic waves

In this paper, dynamic effects of the underground large scale frame structure (ULSFS) with large scales along both two horizontal directions are investigated by 3-D numerical analyses. To guarantee the accuracy of seismic inputs, seismic waves are transformed into equivalent forces adding on the truncated boundary nodes based on the viscous-spring artificial boundary. 3-D finite element models of 4-span, 8-span, and 20-span underground frame structures with surrounding foundation are proposed to simulate small, middle and large scale underground structures. For a comprehensive study of results, another two analyses of the ULSFS are proposed to evaluate the two dynamic effects of structures: structural inertial effects on inner structures, and effects of structural vibration on the whole soil-structure system, respectively. Furthermore, several soil conditions are employed to study influences of the relative stiffness between the structure and soil on the two mentioned dynamic effects of the ULSFS. The results demonstrate that dynamic effects of the ULSFS are much more significant compared with small scale underground structures which make the structural deformations and internal forces to be larger; and dynamic effects of the ULSFS would decrease with increasing elastic moduli of surrounding soils due to great soil constraints.

Seismic damage assessment and mechanism analysis of underground powerhouse of the Yingxiuwan Hydropower Station under the Wenchuan earthquake

The Yingxiuwan underground powerhouse is one of the closest large-scale underground structures from the epicenter of the Wenchuan earthquake and suffered significant damage during this earthquake. What makes this case even more interesting is that the seismic damage is mainly distributed in the upper part of the concrete structure in the underground powerhouse. A full three-dimensional dynamic finite element model of the underground structure and rock system is adopted to make a reasonable assessment for the seismic damage observed in the field and to study the damage characteristics and mechanisms of the underground powerhouse. Additionally, to approximate actual field conditions, the oblique incidence of seismic waves and the rock-structure interaction (RSI) are both considered in this study, and their effects on the seismic response are evaluated. The numerical results indicate that the oblique incidence of the seismic wave and the RSI both contribute to a larger seismic response, and the results compare well with the field observations when the two are considered. The damage distribution of the concrete structure is mainly dominated by the structure feature itself. The main cause of the severe damage in the upper structure is due to the lack of sufficient constraints on it, which leads to a large deformation in the upper structure.

Dynamic Response of Underground Structures in Sand: Experimental Data

A densely instrumented system of large-scale underground structures consisting of two vertical shafts connected through a cut-and-cover tunnel and two independent shield tunnels was installed in an 8 m-diameter laminar soil box at the E-Defense shake table in Miki, Japan. The system was subjected to step-sine sweeps and scaled ground motion records of the Kobe (1995) earthquake. The underground structures were embedded in Albany Silica Sand with an average relative density of 54%. System instrumentation consisted of over 800 sensors, including strain gauges, accelerometers, displacement transducers, bender elements and pressure sensors. A U.S.-Japanese research collaboration was established to instrument the vertical shaft elements and record seismic soil pressures. Data records are archived at the NHERI DesignSafe Data Depot_and can be used to analyze the structural response, soil-structure interaction and other response parameters of individual subsurface components as well as the entire system. The DOI for the data set is 10.17603/DS21C78.

外環自動車道 京葉 JCT トンネル防災計画

Keiyo JCT intersecting Tokyo Outer Ring Road and the Keiyo road, all of the Ramps comprise a complex tunnel structure.This is a large-scale underground structure unprecedented in Japan. And if a fire accident in the tunnel occurs, disaster prevention measures to ensure the evacuation environment has become an issue. We introduce the disaster prevention plan in Keiyo JCT.

국내 지하공간 개발 및 대책

우리나라는 99,274 <TEX>$km^2$</TEX>의 협소한 면적에 산지가 약 70%을 차지하고 있다. 게다가 인구밀도는 세계 3위의 조밀한 국가이다. 따라서 우리나라는 지하공간을 새로이 활용해야 할 국토로 간주하고 적극적으로 개발할 필요가 있다. 우리에게는 지하공간개발이 선택이 아니라 필수이다. 국내에서는 1970년 이후로 가스 원유비축기지, 지하 양수발전소가 건설되었고 주로 대도시에서 지하철, 상가, 보도, 공동구, 주차장 등의 형태로 지하공간이 활용되어 왔다. 여수 지하석유 비축기지와 지하철은 세계적인 규모이다. 최근에는 지하공간의 개발이 더욱 다양화 되고 또한 대규모화 되고 있는 추세이다. 국내 지하공간 개발현황과 문제점 및 대책에 대하여 소개하였다. Approximately 70% of the Korean peninsula is composed of mountains, around 99,274 <TEX>$km^2$</TEX>. Even worse, population rate of Korea is the No.3 in the world now. Accordingly, it is necessary to develop the potential underground space actively with the concept of another territory to be utilized. The development of underground space should be considered not a choice but an indispensable issue. Since 1970s, many large-scale underground structures have been constructed like as crude-oil storage bins, liquefied petroleum gas storage caverns, and underground pumped storage powerplants. Also, In urban area, the underground facilities such as subway networks, underground shopping mall, underground pedestrian network, electric power tunnels, and car parking lots have been used extensively. The scale of Yeosu oil and gas underground storage facility and Seoul subway systems are one of the massive scale in the world. Recently, the trend of the development of underground space becomes more diverse and larger scale. The current status of Korean underground space developments and strategy are described in this paper.

다층 지하 구조물로의 고고도 전자기파(HEMP) 커플링 현상에 대한 전자기적 모델링

본 논문에서는 다층 지하 구조물로의 고고도 전자기파(high altitude electromagnetic pulse: HEMP)의 커플링 현상을 분석하였다. 이를 위하여, 고고도 전자기파에 대한 모델링을 통하여, 고고도 전자기파의 스펙트럼이 100 MHz 이상의 대역에서 -30 dB 이하로 급격히 감소함을 확인하였다. 또한, 고고도 전자기파의 커플링 영역인 다층 지하 구조물은 지구의 표면과 내부를 구성하는 5층 구조물로 가정하여, 본 구조물을 구성하는 물질의 전파 상수(propagation constant)를 바탕으로 투과 현상을 분석하였다. 그 결과, 50 kV/m의 평면파를 입사시켰을 때, 지상에서 100 m 깊이에 위치한 지하 터널에서 0.1 MHz와 1 MHz의 평면파에 대하여 각각 약 10 kV/m와 5 kV/m의 투과 현상이 발생함을 확인하였다. 투과된 전기장의 효과적인 차폐 효과 확보를 위하여 토양층의 감쇠 상수(attenuation constant)를 이용한 자연 차폐 방법과 금속 격자 구조물의 필터링(filtering) 현상을 이용한 차폐 방법을 통하여 각각 최대 20 dB와 90 dB의 차폐 효과를 얻을 수 있음을 분석하였다. This paper gives a electromagnetic coupling mechanism of the high altitude electromagnetic pulse (HEMP) into large- scale underground multilayer structures using analytic and numerical methods. The modeling methods are firstly addressed to the HEMP source which can be generated by intentional nuclear explosion. The instantaneous and intense electromagnetic pulse of the HEMP source is concerned from DC to 100 MHz band, because the power spectrum of the HEMP is rapidly decreased under -30 dB over the 100 MHz band. Through this range, a penetrated electric field distribution is computed within the large-scale underground multilayer structures. As a result, the penetrated electric field intensities at 0.1 and 1 MHz are about 10 and 5 kV/m, respectively. Therefore, additional shielding techniques are introduced to protect buried structures within the large-scale underground structures such as high-lossy material and filtering structures (wire screen).

Experimental investigations of the law governing longitudinal interaction between elongated underground structures and the soil

Studies of the interaction between seismic blast waves and underground structures are conducted to select boundary conditions on the contact surface between these structures and the soil. In relation to this, a law governing longitudinal interaction between an elongated underground structure and the soil which, among other things, combines condition with Coulomb's dry-friction law, permitting slippage of underground structure relative to the soil, is proposed in this paper. The present study is devoted to experimental determination of the adaptability of conditions (expressed here as equations) at the contact boundary between elongated underground structures and the soil under dynamic (seismic, blast) effects along the axis of the structure. Experiments with large-scale underground structures (tunnels, subways, etc.) were conducted under difficult conditions to ascertain the law governing their interaction with the soil under dynamic or static effects. Values of the tangential stresses on the contact surface between the steel pipe and soil were determined from longitudinal-force recordings.

Stressed state of the rock mass during excavation of the underground machine gallery for the Inguri hydroelectric plant

These field studies and computations provide the basis for us to draw the following conclusions. 1. The development of deformations over an entire chamber periphery is undesirable, even in cases where its surface is rigidly braced, as has taken place in the underground machine gallery of the Inguri hydroelectric plant. The most vigorous process of strain development (≈80–90% of the total) is observed just during the period when the chamber is being opened. Active strain development with time does not exceed 4–5 months on the average, after which the deformations are stabilized prior to the start of excavation on the next stage of the compartment. The outer face of the softened zone reaches ≈ 1/2 the span of the chamber under favorable geological conditions; beyond the limits of this zone, the rock mass may be considered virtually nondeforming. 2. In avoiding the development of high stresses in the mass surrounding the chamber and, consequently, significant peripheral deformations, the use of any rigid support, or type of reinforced-concrete crown, is not promising. It is expedient to use the bearing capacity of the rock itself by including it in the working scheme by the creation of a semielastic lining with deep-seated stressed anchors whose length exceeds the zone of active deformations. 3. Use of the results of field observations as initial data to determine the stress-strain state of the rock mass surrounding a chamber in computations performed by the finite-element method make it possible to obtain good convergence between the computation results and real deformations of the chamber periphery. This demonstrates the expediency of the broad use of complex studies in designing large-scale underground structures.