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With urban space becoming much more crowded, the construction of underground spaces continues to expand to deeper, and the requirements for the large depth and minor deformation in urban engineering construction are getting more urgent. A new kind of in-situ assembling caisson technology (called VSM) is a vertical shaft method (VSM), which excavates the stratum under water with a mechanical arm and assembles the prefabricated caisson segments at the same time. This paper takes the Shanghai Zhuyuan Bailonggang Sewage Connecting Pipe Project as an example, which is the first construction project in the soft soil area, such as Shanghai, and makes a technical analysis of the VSM by comparing the field measurement and numerical simulation. Ground settlements and layered deep displacements were monitored in the field measurement during the VSM construction. It shows that the maximum ground settlement caused by the VSM is 15.2 mm and the maximum horizontal displacement is 3.74 mm. The influence range of the shaft excavation on the ground settlement is about 30 m away from the shaft center. The results demonstrate that the VSM construction has great applicability in the soft soil area. A finite element simulation model of the VSM shaft is established and verified by field measurement. There is a certain error between the traditional theoretical calculation by analogy to the common retaining walls of the deep foundation pit and the measured results, while the simulation results are relatively consistent with field measurements. The reasons for the difference are well-analyzed. Finally, the effects of the VSM construction method on the engineering environment are analyzed, and the suggestions for deformation control in the future are put forward. [ABSTRACT FROM AUTHOR]

Simultaneous construction of adjacent projects may lead to emergencies in a foundation pit group, which significantly affects the deformation and safety of foundation pits. In this study, the deformation characteristics of a deep foundation pit group and the mutual interactions among the adjacent foundation pits were observed by a monitoring system during excavation. Field data of the foundation pit group, including the lateral deflections of the enclosure pile, the ground subsidence, as well as the vertical column movements, were analyzed and compared with individual excavations in Shanghai. The field data showed that the excavation of the adjacent foundation pit reduced the lateral deformation of the enclosure structure, caused by the reduction of active earth pressure acting on the retaining pile. Furthermore, the foundation pit excavated later caused upward movements of the soil between them. However, the foundation pit excavated earlier had a negligible influence on the vertical column movements of the foundation pit excavated later. Due to the optimized excavation sequence of the deep foundation pit group, the deformation of this special excavation was well controlled. [ABSTRACT FROM AUTHOR]

Summary: Though the dynamic performance of high‐rise buildings under wind has been widely investigated, there have been relatively limited studies focusing on the wind effects on 600 m+ super high‐rise buildings based on real measured data during typhoons. This paper presents the field measurement results of structural dynamic characteristics and wind‐induced responses of the Shanghai Tower with a height of 632 m during two successive typhoons, from August 12 to 18, 2018. Additionally, based on the analytical mode decomposition method, a modified discrete‐time Fourier transformation method combined with moving window technology in time domain is developed to analyze the time‐varying characteristics of natural frequencies. The relationship between the mean wind speed and acceleration amplitudes is investigated as well. A numerical experiment is carried out to verify the effectiveness of the random decrement technique, by using which the time‐varying average damping ratios of the first mode associated with the Shanghai Tower are identified. In addition, the damping ratios do not exhibit an increasing trend with the increase of vibration amplitudes without the contribution of the tuned mass damper. It recommends that the critical damping ratios under high vibration amplitude are 2.5%–3.0% when the damper is active and 0.5%–1.0% when the damper is inactive. The analytical results can provide useful information for the dynamic characteristics as well as the wind‐resistant design for 600 m+ super high‐rise buildings. [ABSTRACT FROM AUTHOR]

An 18.4-m-deep triangular foundation pit with in-plane excavation area of approximately 10,000 m2 was constructed in soft clay. The excavation located at Hongqiao comprehensive transportation hub center in Shanghai, in which an energy gallery, many underground pipelines, and viaduct piers exist. Deformation characteristics of the foundation pit and the impact on the adjacent buildings and structures were observed by a monitoring system during excavation. Field data including wall deflections, vertical wall movements, ground subsidence, as well as vertical column movements were analyzed and compared with other excavations of metro stations or rectangular excavations in Shanghai. This excavation exhibited different deformation characteristics from other excavations because of its triangular shape with acute corners. The deformation law of this special excavation was beneficial for the design and construction of special-shaped foundation pit in complex environment. [ABSTRACT FROM AUTHOR]

• The interaction effects between socketed pipes during jacking were revealed. • The closure error evolution law of the large-scale pipe-roof was investigated. • A numerical pipe-roof jacking model considering constraint effect was developed. • The impacts of the interaction effects on the surface settlement were concluded. Pipe-roof Pre-construction Method (PPM) usually acts as an auxiliary trenchless technology for large underground excavation to assure construction safety and protect surrounding facilities. During the construction process of PPM, complex interaction would take place between inner-connected pipes (socketed pipes), which could affect the closure of the pipe-roof and ground settlement. Nevertheless, scarce research was carried out to explore these interaction effects and their impacts. In this paper, a comprehensive field measurement for a large undercrossing project in Shanghai soft ground by means of roof-box jacking (RBJ) was conducted on the postures of a group of socketed pipes and surface settlements. Based on the observations, several conclusions could be drawn: 1) Notable constraint effect between sockets (especially in the direction perpendicular to the pipe row) and jacking distance effect of pipe were observed via the statistical analysis of the relative deviations. 2) Closure quality of the pipe-roof was well maintained when launching and jacking in the reinforced zone, but closure errors soared in the zones beyond owing to the jacking distance effect, which could cause clearance invasion and even block the latter jacking of box culvert. 3) The surface settlement was successfully controlled within 25 mm without interruption on the traffic above. The shielding effect, repeated disturbance effect and constraint effect had a non-negligible impact on the magnitude and distribution of surface settlement. The case serves as a valued example for engineers to understand the origin and effect of group-jacking deviations and better control the jacking precision and ground disturbance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Coupling numerical simulation with systematic view was efficient for optimization. [•] A robust anti-upheaval system was effective and decisive in the deconstruction. [•] Dividing large unloading into small ones could achieve small overall displacement. [•] Optimized reconstruction sequence can control the final disturbance to a minimum. [Copyright &y& Elsevier]

The support system stiffness is crucial to designing the excavation support system by displacement control, but the current methods of estimating the system stiffness are inapplicable to narrow excavations. The field data from narrow excavations in the same site in Shanghai soft clay were analyzed and it was found that the deformations of these excavations were significantly affected by the width-depth ratio (B/H). 111 numerical simulations were carried out to study the contributions of wall bending stiffness (EI), average vertical support spacing (S v) and width-depth ratio (B/H) to the support system stiffness. A parameter was proposed to quantify the support system stiffness for narrow excavations. It can consider the coupled effects of EI , S v and B/H. An equation for the maximum wall deflection was presented based on the parameter and it was applicable to the cases with B/H less than 1.5. The proposed method was verified against the measured data from several narrow excavations in clay and the overall agreement was satisfactory. [ABSTRACT FROM AUTHOR]