Key protection techniques adopted and analysis of influence on adjacent buildings due to the Bund Tunnel construction

The Bund Tunnel is 14.27 m in diameter. It is the first application of super diameter earth pressure balanced shield (EPBS) in China. There are many historical buildings along the construction line, and the minimum horizontal distance from the building to the tunnel side varies from 1.7 m to 30 m. Considering the importance of these historical buildings and the complicated construction processes, it is essential to adopt effective protection techniques to ensure safety during the tunnel construction. Three kinds of protection techniques are presented in this paper. Firstly, underground cut-off wall built by bored piles is used to separate the buildings and tunnel when the minimum horizontal distance from the building to the tunnel side is less than 5 m. Secondly, the grouting reinforcement technique is adopted when the minimum clear distance is between 5 m and 10 m. Finally, if the minimum clear distance is larger than 10 m, the optimized construction parameters are selected to reduce the influence induced by the EPBS excavation. The deformations of some typical buildings are monitored. The results of this project will be a useful reference for similar future projects.     

Characteristics of diaphragm wall lateral deformations and ground surface settlements: Case study in Iran-Ahwaz metro

The effect of deep excavation on lateral deformation of diaphragm walls and on the ground surface settlement adjacent to the excavation in five metro stations in the southwestern section of the Ahwaz metro was evaluated. In one of these stations (Kargar Square Station) the ground surface settlement around the station and the lateral deformation of the top of the diaphragm wall were measured in three stages during excavation to a depth of 5 m. After construction work was suspended in this section of the metro, numerical methods were used to predict the ground surface settlement and the lateral wall deformation that would be caused by excavation at depths between 5 m and 17.2 m. The measured data were used to back calculate soil parameters required for this analysis. The ground surface settlement and the lateral deformation of the wall in all these stations that would result from excavation to a final depth of 17.2 m below ground were predicted using the back calculated parameters. The relationship between the maximum ground surface settlement and the distance to the wall for all five stations of the Ahwaz metro was predicted. The predictions were found to fall in zones I and II of the Peck chart. The surface settlement and the lateral wall deformation and their influence on adjacent buildings were predicted and compared with similar projects around the world. The effect of settlement on adjacent buildings in one of these stations was predicted to cause at most superficial damage, unlikely to have structural significance.     

Challenges and strategies involved in designing and constructing a 6 km immersed tunnel: A case study of the Hong Kong–Zhuhai–Macao Bridge

A 6 km immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge (HZMB) has been designed and funded. Once completed in 2016, the HZMB Tunnel will break the record of the 5.8 km BART Tunnel in the United States, although it will soon be overtaken by the ∼20 km Fehmarn Tunnel between Denmark and Germany that is to be completed in 2020. Construction of the HZMB Tunnel was started in 2011 and more than ten elements thus far have been installed on the site. This paper presents details about the challenges and solutions for the design and construction of the HZMB Tunnel on a strategic level. Special features of the HZMB Tunnel include a long length of 6 km, a deep water depth of almost 45 m, and a thick backfill of 23 m. Challenges include severe marine environment, strict requirements for waterproofing, construction of sections connecting the tunnel with artificial islands, and tunnel stability after future excavation of fairway trenches. Moreover, the HZMB Tunnel is challenged by possible sand liquefaction in seismic events, conservation of white Chinese dolphin, and waterway dispersion during construction. Details about the strategies are given in order to improve the immersed tunnel design and construction methods.     

Design and construction of river crossing tunnel beneath Tachia River,Taiwan

Due to the impact of the 1999 Chi-Chi earthquake (ML = 7.3) and the following typhoon induced heavy rainfalls and floods, the tailrace tunnel of the Kukuan Hydropower Plant was severely blocked and must be realigned and rebuilt. The new tailrace tunnel is 1991 m long with a 140 m section passing underneath the Tachia River, where the shallowest rock cover is 3.5 m. In view of the common phenomenon that weak zone developed along river channel and debris accumulated on river bed, the ground improvement from the surface to the tunnel is difficult. Therefore, a construction shaft, a water sealing pre-grouting plan and a special supporting system were designed to prevent the potential water inflow when tunneling underneath the Tachia River. In the construction phase, adequate excavation cross sections, support elements, auxiliary treatments, and water sealing grouting methods were selected to overcome the difficult ground condition encountered. The experience learned from this successful case can be a valuable reference for the design and construction of similar river crossing tunnels in the future.     

Experiences of TBM operation in gas bearing water condition – A case study in Iran

The Nowsud tunnel (Lot 2B) project is a 25.7 km length water conveyance tunnel which was bored with a 6.73 m diameter double shield TBM. The tunnel consisting of 6.0 m inside diameter which lined with 25 cm thick, 4 pieces honeycomb precast segments. The geology is consisted of limestone, limy shale, black shale and Shally limestone of Cretaceous Garu and Pliocene Gurpi formations. During heading of tunnel, it was encountered with CH₄ gas emission and H₂S bearing water inrushes, up to 890 l/s. A source which could not be plugged with grouting and the heading had to be stopped for several days and months. As far as the author is aware, this condition has not been seen in double shield TBM tunneling.This case study attempts to discuss firstly the quality and origin of poison gases and water ingress into the excavations. Then, the destructive effects of the poison gases and water ingress on different parts of TBM, concrete corrosion, considerable delay in tunnel progresses and negative impact on tunnel personals productivity have been evaluated.Finally, with respect to restricted space in TBM and back up, a executable solution methods have been pursued to abatement and prevention of the poison gases and water ingress into the excavations, while the construction is in progress by double shield TBM.     

Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel

Deformations and stress distributions in tunnel intersection areas are more complicated than those in common tunnels. The literature on deformations and stress distributions in tunnel intersections, in which the intersecting tunnel is in a different section, is limited. The Shangxinjie subway station in Chongqing, China, was selected to investigate the deformation, stress and plastic zone responses of a tunnel intersection using numerical simulations. Based on the numerical results, the scopes of influence with respect to the deformation, stresses and possible failure modes of the tunnel lining were further studied. The numerical results show that the deformation in a section close to the tunnel intersection was larger than the deformations in distant sections. Compared with the common section, the crown settlement reached the maximum value at the tunnel intersection, and the maximum rate of increase was approximately 28%. The range of the plastic zone at the tunnel intersection was much larger than that in the other areas, and it was mainly located in the side wall and tunnel crown. In the longitudinal direction, the lengths of the scopes of influence were 2.4 B and 1.6 B with respect to the deformation and stress, respectively. The magnitudes of the internal forces in the longitudinal and circumferential directions were almost equal. The bending moments of the tunnel lining within 135° and 225° significantly changed, but the axial force decreased dramatically. Tensile and compressive failures may occur at the tunnel intersection and in a section 5 m away. Locally thickening the supporting structures is suggested to improve the stability of the tunnel.     

Artificial Ground Freezing to excavate a tunnel in sandy soil. Measurements and back analysis

The paper is dedicated to the case history of a 13 m wide, 17 m high and 40 m long service tunnel at Toledo Station, previously constructed in a deep open shaft and belonging to the Line 1 of the Napoli underground network. The existing Line 1 has been recently extended with a new stretch consisting of five new stations connected by twin rail tunnels for a total length of about 5 km. Toledo Station main shaft is located by a side of the line and it is connected to the pedestrian platforms by the above mentioned large size service tunnel. The station is situated in the historical center of the city of Napoli, under a deeply urbanized area. In Fig. 1 a longitudinal section of the main shaft of the station and of the large service tunnel with the above and surrounding buildings is sketched. The focus of this paper is on the settlement caused by the tunnel excavation and on the use of the Artificial Ground Freezing (AGF) technique to allow the safe excavation of the large crown of the service tunnel, located about one half in a silty sand layer and one half in yellow tuff, well below the groundwater table.     

Key techniques for the largest curved pipe jacking roof to date: A case study of Gongbei tunnel

The Gongbei tunnel, as a part of the Zhuhai Connection highway and Hongkong-Zhuhai-Macao Bridge project, is currently being constructed in Zhuhai, China. To guarantee the tunnel traversing under the Gongbei Port, a combination technology of curved pipe jacking roof for ground support and ground freezing for waterproof is applied. This jacked pipe roof, comprised 36 steel pipe strings of 1620 mm diameter with 355–358 mm gap between adjacent strings, has been faced with various challenges for design and construction due to the site conditions of multiple soft soil and high underground water pressure. These challenges include risks of excessive soil deformation, possibility of path deviation, excessive jacking force, leaking of pipe joint and failure of jacking machine gasketed launch and reception devices. This paper provides an overview of this project, summarizes the most challenging aspects they faced and introduces the relevant techniques applied during construction.     

Bidirectional construction process mechanics for tunnels in dipping layered formation

The geological conditions surrounding the Tianpingshan Tunnel of the Gui-Guang railway in Guizhou Province are very complex. To study the mechanical regularity of the Tianpingshan Tunnel during construction process, a 3-D physical model was carried out based on the conditions of the section located between 372.335 km and 372.435 km (DK372 + 335 ∼ DK372 + 435) of the tunnel. The 3-D physical model was conducted to clarify the effect of the dipping formation and bidirectional excavation on the tunnel deformation. The results of the crown settlements, floor heave and radial displacement of the equivalent sections in the physical model were analyzed. In the physical model the results of the model test show that in the section located at 25 cm the crown settlements are much smaller than those in the section of 175 cm. And the floor heave in the section located at 25 cm is larger than that located at 175 cm. Furthermore, the radial displacement in horizontal direction is found to be much larger than that in vertical direction in the section located at 25 cm. However, the variation characteristics of radial displacement in the section located at 175 cm are reverse to that in the section located at 25 cm. The numerical study and the field measurements were compared with the model test to demonstrate the effectiveness and accuracy of the results of the numerical study.     

Modeling with ANN and effect of pumice aggregate and air entrainment on the freeze–thaw durabilities of HSC

The objective of this work is to calculate the compressive strength, ultrasound pulse velocity (UPV), relative dynamic modulus of elasticity (RDME) and porosity induced into concrete during freezing and thawing. Freeze–thaw durability of concrete is of great importance to hydraulic structures in cold areas. In this paper, freezing of pore solution in concrete exposed to a freeze–thaw cycle is studied by following the change of concrete some mechanical and physical properties with freezing temperatures. The effects of pumice aggregate (PA) ratios on the high strength concrete (HSC) properties were studied at 28 days. PA replacements of fine aggregate (0–2 mm) were used: 10%, 20%, and 30%. The properties examined included compressive strength, UPV and RDME properties of HSC. Results showed that compressive strength, UPV and RDME of samples were decreased with increase in PA ratios. Test results revealed that HSC was still durable after 100, 200 and 300 cycles of freezing and thawing in accordance with ASTM C666. After 300 cycles, HSC showed a reduction in compressive strength between 6% and 21%, and reduction in RDME up to 16%. For 300 cycles, the porosity was increased up to 12% for HSC with PA. In this paper, feed-forward artificial neural networks (ANNs) techniques are used to model the relative change in compressive strength and relative change in UPV in cyclic thermal loading. Then genetic algorithms are applied in order to determine optimum mix proportions subjected to 300 thermal cycling.     

Evaluation of common TBM performance prediction models based on field data from the second lot of Zagros water conveyance tunnel (ZWCT2)

Zagros water conveyance tunnel (ZWCT) is a 49 km tunnel designed for conveying 70 m³/s water from Sirvan River southward to Dashte Zahab plain in western Iran. This long tunnel has been divided in 3 Lots namely 1A, 1B, 2. By November 2014, about 22 km of the Lot 2 (with a total length of 26 km) has been excavated by two double shield TBMs from two southern and northern portals. The bored section of tunnel passed through different geological units of 3 main formations of Zagros mountain ranges which mainly consist of weak to moderately strong argillaceous-carbonate sedimentary rocks. In this paper, the operating and as-built geological data collected during construction phase of the Lot 2 of ZWCT project was used to compare the calculated machine performance by empirical methods such as the Hassanpour et al. (2011), Q_TBM, NTNU, Palmstrom, and theoretical model of Colorado School of Mines or CSM. The predicted penetration rates were then compared with the observed field performance of the machine and the variations of predicted rates were examined by statistical analysis. The results showed that the site-specific model, which was based on TBM performance in similar formations can provide estimates closer to actual machine performance.     

Frost attack resistance and steel bar corrosion of antiwashout underwater concrete containing mineral admixtures

This study aims to evaluate frost durability and steel-bar corrosion in antiwashout-underwater concrete, which has been neglected to date. To achieve this goal, repeated freezing and thawing and accelerated steel-bar corrosion tests have been performed for three types of antiwashout-underwater concrete specimens.The results of repeated freezing and thawing test reveal that adding mineral admixtures has little effects on frost durability because of the large and uneven entrapped-air imprisoned by the cellulose-type antiwashout-underwater admixture. Slight improvement of frost durability was observed through the action of air-entrained (AE) agent in the case of SG50 which presented an air content of 6 ± 0.5%.Measurement results using the half-cell potential showed that, among the entire specimens, steel-bar in Control specimen manufactured under artificial seawater was the first one that exceeded the threshold value, −350 mV proposed by ASTM C 876, at 14 cycles, where the corresponding corrosion current density and concentration of water soluble chloride were measured as 0.3 μA/cm² and 0.258%, respectively. For the other specimens, potential values became below −350 mV later than 18 cycles.     

Influence of thermal insulation position in building envelope on the space cooling of high-rise residential buildings in Hong Kong

At the present time, thermal insulation is almost not used in fabric of tall residential buildings in Hong Kong, as their fabric slabs usually comprise concrete layer covered on each side by plaster layers. This study investigates into the influence of an existence of the thermal insulation layer in the outside walls on the yearly cooling load and yearly maximum cooling demand in two typical residential flats in a high-rise residential building by employing HTB2, detailed building heat transfer simulation software. During the investigations, the thermal insulation layer up to 15 cm thick was placed either at the inside, or at the outside, or at the middle part of the outside wall structure. Then, the concrete layer was up to 40 cm thick. The simulation predictions indicate that the highest decrease in the yearly cooling load of up to 6.8% is obtained when a 5 cm thick thermal insulation layer faces the inside of the residential flat. The highest decrease in the yearly maximum cooling demand of 7.3% is recorded when a 5 cm thermal insulation layer faces either the outside or the inside of the flat; this depends on the flat orientation. However, much weaker reductions in the yearly cooling load and yearly maximum cooling demand are found when the thickness of thermal insulation is increased above 5 cm and the thickness of concrete is increased above 10 cm.     

Ground response of closely spaced twin tunnels constructed in heavily overconsolidated soils

As part of the City of Edmonton’s light rail transit expansion, twin 6.5 m diameter oval shaped tunnels were constructed using conventional tunnelling methods. The geology of the site consists predominately of a hard, fissured cohesive till unit. The tunnel face construction was sequenced as top header, bench and invert excavations. At its narrowest, the pillar separating the twin tunnels was less than 1.5 m across or 0.23 tunnel diameters. Typically, the minimum pillar spacing required to reduce the interaction between twin, side by side tunnels is one tunnel diameter. Because the tunnel construction was within an urban environment, there was considerable concern with ground loss and excessive surface settlements. This study demonstrates that within similar materials, a pillar width of 0.5 tunnel diameters sufficiently reduces the tunnel interactions and minimize the risk of damage to nearby structures.     

The effects of air entrainment and pozzolans on frost resistance of 50–60 MPa grade concrete

An experimental investigation was conducted using an air-entraining agent and pozzolans such as silica fume and fly ash, to meet the design strengths 50 and 60 MPa, as well as frost resistance to 300 cycles of freezing and thawing. Among a series of concretes of grade 50 or 60 MPa, only a small part could resist 300 cycles of freezing and thawing. It was demonstrated that frost resistance might be independent on strength of concrete. By means of mercury intrusion porosimeter, the pore structure characteristics of six concretes were identified. Air entrainment, no matter whether the pozzolans were used, caused an increase in cumulative pore volume, and also an increase in the mean pore size. It is revealed that, as to concrete at a 0.32 water/binder ratio, air entrainment should be a main approach to enhance frost resistance, although the pozzolans could be used to increase long-term strength of concrete.     

The effect of principal stress orientation on tunnel stability

In order to investigate the effect of principal stress orientation on the stability of regular tunnels and cracked tunnels, experiments by using square specimens with a centralized small tunnel were conducted, and the corresponding numerical study as well as photoelastic study were implemented. Two kinds of materials, cement mortar and sandstone, were used to make tunnel models, and three types of tunnel models were studied, i.e. (1) regular tunnel models loaded by different orientation’s principal stresses, (2) tunnel models with various orientation’s radial cracks in the spandrel under compression, and (3) tunnel models with a fixed radial crack loaded by various orientation’s principal stresses. In the numerical study, the stress intensity factors of the radial cracks were calculated, and the results agree well with the test results. For regular tunnels, when the angle θ between the major principal stress and the tunnel symmetrical axis is 45°, the corresponding tunnel is the most unfavorable; for tunnels with a radial crack in the spandrel, when the angle β between the crack and the tunnel wall is 135°, the corresponding tunnel is the most unfavorable; for tunnels with a β = 130° radial crack, when θ = 0° or θ = 70°, the compressive strengths of the tunnel models are comparatively low, whereas when θ = 90°, it is the highest.     

The characteristics of air void and frost resistance of RCC with fly ash and expansive agent

In order to assure the outer concrete of Longtan dam in China possesses excellent of frost resistance, the losses of strength, mass and air void characteristics of roller compacted concrete (RCC) containing fly ash, superplasticizer and a novel MgO-bearing expansive agent (HNM) were studied using the freezing–thawing method ASTM C666. The results show that there is a linear correlation between strength and mass losses in RCC subjected to cycles of freezing and thawing.There is a relationship between the air void spacing factor and the frost resistance of RCC. However, for RCC containing fly ash and superplasticizer a spacing factor of 0.25 mm is not necessary. Using a water:binder ratio of 0.48 in RCC containing 50% fly ash and 8% HNM a durability factor of over D₃₀₀ can be achieved provided the spacing factor is less than 0.4 mm.     

Review and perspective of expressway tunnels in Taiwan,China

Since the construction of the first expressway in the 1970s, the total length of expressways in Taiwan has increased to over 1 000 km, of which 40 km are aligned with tunnels. These twin-tube tunnels, which have two or three lanes in each tube, are characterized by large cross-sections. Due to the complicated topography and heterogeneous geological conditions of Taiwan, tunnel construction has encountered many difficulties. Thus, many advanced excavation methods were developed during tunnel construction. To satisfy the concurrent requirements of safety, economy and efficiency, new construction methods and techniques should be developed or introduced. Moreover, environmental protection and ecological conservation must be paid increasing attention to the goal of substantial development.     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

Estimation of deformation and stiffness of fractures close to tunnels using data from single-hole hydraulic testing and grouting

Sealing of tunnels in fractured rocks is commonly performed by pre- or post-excavation grouting. The grouting boreholes are frequently drilled close to the tunnel wall, an area where rock stresses can be low and fractures can more easily open up during grout pressurization. In this paper we suggest that data from hydraulic testing and grouting can be used to identify grout-induced fracture opening, to estimate fracture stiffness of such fractures, and to evaluate its impact on the grout performance. A conceptual model and a method are presented for estimating fracture stiffness. The method is demonstrated using grouting data from four pre-excavation grouting boreholes at a shallow tunnel (50 m) in Nygård, Sweden, and two post-excavation grouting boreholes at a deep tunnel (450 m) in Äspö HRL, Sweden. The estimated stiffness of intersecting fractures for the boreholes at the shallow Nygård tunnel are low (2–5 GPa/m) and in agreement with literature data from field experiments at other fractured rock sites. Higher stiffness was obtained for the deeper tunnel boreholes at Äspö which is reasonable considering that generally higher rock stresses are expected at greater depths. Our method of identifying and evaluating the properties and impact of deforming fractures might be most applicable when grouting takes place in boreholes adjacent to the tunnel wall, where local stresses might be low and where deforming (opening) fractures may take most of the grout.