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This paper establishes an intelligent framework for real-time prediction of trajectory deviations in the process of earth pressure balance (EPB) tunnelling. A hybrid model was developed which integrates principal component analysis (PCA) and a gated recurrent unit (GRU). PCA was adopted to mine the interrelated input parameters and reduce the accompanying data noise. A scroll window mode was implemented in the GRU to predict the shield movement in real time. The proposed PCA–GRU model was implemented and validated through a case study of the Guang-Fo intercity railway in Guangzhou, China. Another three machine learning models were also used for comparison. The results revealed that the proposed model predicted the shield moving trajectory with higher precision than other models. The implications for trajectory regulation were discussed using field data. The proposed prediction framework represents a promising solution for real-time prediction of the shield moving trajectory in EPB tunnelling.

The performance of neural networks with quadratic cost function (MSE cost function) is analyzed in terms of the adjustment rate of weights and its performance in multi-magnitude data processing using a qualitative mathematical method based on mean squared error. However, neural networks using quadratic cost functions exhibit low-weight updating rates and variations in performances in multi-magnitude data processing. This paper investigates the performance of neural networks using a quadratic relative error cost function (REMSE cost function). Two-node-to-one-node models are built to investigate the performance of the REMSE and MSE cost functions in adjustment rate of weights and multi-magnitude data processing. A three-layer neural network is employed to compare the training and prediction performances of the REMSE cost function and MSE cost function. Three LSTM networks are used to evaluate the differences between REMSE, MSE, and Logcosh in actual applications by learning stress and strain of soil. The results indicate that the REMSE cost function can notably accelerate the adjustment rate of weights and improve the performance of the neural network in small magnitude data regression. The applications of the REMSE cost function are also discussed.

Foundation dewatering combined with a waterproof curtain is widely applied to ensure the safety of the foundation pit in areas with multi-aquifer–aquitard alternative strata. The buried depth of the diaphragm wall can influence the environmental effect due to dewatering obviously. This paper investigates the impact of the buried depth of the diaphragm wall on the groundwater drawdown considering the anisotropic permeability of the dewatering aquifer. Numerical simulation is conducted based on an engineering case. The ratio of penetrating depth of diaphragm wall to thickness of dewatering aquifer (RW) and the ratio of horizontal and vertical hydraulic conductivity of dewatering aquifer (RC) are varied. The relationship between approximate hydraulic gradient (Δi) and RW (or RC) can be fitted by Boltzmann curve (or logarithmic curve). Effective, suggested and control values of RW (or RC) are proposed, of which the suggested value is recommended in practical engineering. The effective, suggested and control value of RW can be calculated by logarithmical equation considering the value of RC.

The degradation mechanism of ethylene–propylene–diene monomer (EPDM), when used as a sealant material for shield tunnels, must be known to assess of the service life of sealant gaskets. Thi...

Shenzhen has abundant river systems, intense tectonic activity and complex geological conditions. The depth of Quaternary deposits is thin and uneven, and the primary bedrock comprises granite with various degrees of weathering, which covers more than 50% of the area of Shenzhen. Karst strata have developed in the eastern part of Shenzhen, and there are five groups of fracture zones in the area. Shenzhen also has some problematic soils, including granite residual soil, and muddy clay and silt. Metro tunnels are constructed using the shield tunnelling method. In Shenzhen, different strata are encountered during metro shield tunnelling, including upper-soft and lower-hard strata, hard rock strata, soft–hard alternating strata, under-crossing river or reservoir strata, muddy clay and silt strata and granite residual soil strata. The various strata encountered during shield tunnelling may result in a series of problems with the geological environment. Environmental geological problems during tunnelling are different for different strata, among which the major issues include serious cutter wear, difficulty in controlling the trajectory of the shield machine, shield machine jam, roof fall and slurry spewing. Different countermeasures should be implemented according to the characteristics of the strata to ensure the safe construction of metro tunnels. In this study, a case study of the Shenzhen Metro Line 10 is introduced, where tunnels pass through three specific strata: hard rock strata, boulder strata and under-crossing reservoir strata. In the future, more engineering cases that pass through different strata can be summarized according to the tunnel construction project in Shenzhen.

This paper presents a case study on an ancient drainage system in the Hetao old urban center, Ganzhou, China, which is playing a key role in the prevention of urban flooding. The system includes ancient city walls, a Fushou ditch, and ponds. The ancient city walls were constructed to defend the river water intrusion. The Fushou ditch and ponds primarily served for the drainage and storage of the rainwater, respectively. The process of rainwater management in the Ganzhou ancient drainage system, including the guidance, storage, infiltration, purification and utilization, and drainage of rainwater, confirms the feasibility of the design concept of modern sponge city. Based on the lessons learnt from this ancient drainage system, the guideline for the rainwater management and design of sponge city is proposed. It is suggested that the sponge city should be planned before the new urban development. During the construction of sponge city, the dispersed ponds and the ditches made of durable and permeable materials in Ganzhou ancient drainage system are recommended to increase the amount of infiltration, storage and utilization of rainwater.

This study presents a non-linear spring model for modelling the backfill grout consolidation behind shield tunnel lining. Two important parameters, i.e. the time-dependent grout pressure decay induced by consolidation and the grout-cake thickness, were derived through a non-linear spring model and continuity equation. The proposed non-linear spring model for backfill grout consolidation was validated based on vertical pressure and strain relationships determined from an oedometer test. The derived equations were applied to the Groene Hart Tunnel (GHT) project. The results show that the calculated grout pressures agree well with the measured values. The calculated grout-cake thicknesses are in good agreement with the measured values. Two key factors influencing the grout consolidation are discussed: grout diffusion into the soil, and the initial distribution of the grout injection pressure. It is found that grout diffusion into the soil can dissipate the grout pressure quicker than grout consolidation. The distribution of the initial grout injection pressure dominates the final distributions of the grout pressure/grout cake around the tunnel lining.

Shallow organic free-phase biogas is distributed in the Quaternary deposit along the coastal region of Shanghai, particularly in the Yangtze River Estuary and Hangzhou Bay. This biogas exerts a significant effect on the environment because of the existence of gas reservoir pressure. Some offshore engineering works, e.g., drainage pipelines, cross-river bridges, and tunnels, have been constructed in the gassy soils around Shanghai. Once the gas cap layer and reserve layer are disturbed during construction, biogas may be released, which will influence the characteristics of the surrounding soils, endanger the engineering safety, and create a harmful environment for the workforce on such projects. Exploration and construction technologies are adopted to control the effects of this hazardous biogas during underground construction. Pre-exhausting technology is frequently used to release the shallow free-phase gas to the ground through pre-exhausted borehole(s) before starting construction. Three case histories constructed in such gassy soils, e.g. Shanghai Sewerage Project, Hangzhou Metro Line No. 1, and Hangzhou Bay Bridge, are introduced to avoid failure. Since the characteristics of shallow gas in practical engineering operations differs from those encountered at smaller scales, field tests were undertaken before pre-exhausting to predict the gas-exhausting effect in these cases.

Construction accidents are a significant hazard to the community, affecting sustainable development. This paper summarizes the safety situation of the construction industry in China over the past ten years. Detailed analysis is performed on fatal accidents that occurred in 2018 to reveal the spatiotemporal distribution pattern and characters of construction safety accidents. The construction failures are mainly attributed to management aspects rather than technical aspects. A case involving a major accident during shield tunnel construction in Foshan, Guangdong, in 2018 is investigated in detail. Strategic environmental assessment (SEA) is used to analyze the management issues of the Foshan metro project during planning, geological investigation, design, and implementation of construction works. The SEA result shows that the safety risk was very high with a low total SEA score. Based on the analysis, a guideline for safety construction management for sustainability is proposed.

To promote sustainable development, the Chinese government launched a new municipal solid waste (MSW) classification strategy in 2017. Shanghai was selected as one of the first pilot cities for MSW classification. The Shanghai municipal government first established the new MSW classification policy in 2017. The Shanghai Municipal Solid Waste Management Regulation was published in 2019 and came into effect on 1 July 2019. This short communication reports on Shanghai’s new MSW classification policy and its implementation. The main content and measures adopted by Shanghai’s government to ensure the effective implementation of the new MSW classification policy are introduced. Besides, a SWOT (i.e., strengths, weaknesses, opportunities, and threats) analysis on the present policy and measures is conducted, and based on the results, some discussions and suggestions regarding the implementation of MSW classification in Shanghai and the whole of China are presented.

Land subsidence was once a major geo-hazard in the city of Shanghai, China. From 1921 to 1965, the maximum cumulative land subsidence in the urban areas of China reached 2.6 m. This large subsidence has resulted in high economic losses for Shanghai. The Regulation of Prevention and Control of Land Subsidence of Shanghai Municipality was published in 2013 (simply cited as the 2013-regulation in the following context). The characteristics of the 2013-regulation included the combination of the subsidence monitoring network and the groundwater detection network due to both the effects of groundwater withdrawal and construction. In addition, the setting up of a supervision system was also incorporated in the 2013-regulation. To control the land subsidence, Shanghai demarcated three land subsidence control zones, where special measures have been implemented. From a strategic environmental assessment (SEA) point of view, the 2013-regulation attains a high total score, indicating that the control of groundwater withdrawal and recharge is effective. The observed land subsidence over the past six years also confirms the effectiveness of the 2013-regulation with the most consideration of SEA for sustainable environment protection in Shanghai. However, more effort should be made in the implementation of SEA in land subsidence control in the future.

The prediction of earth pressure balance (EPB) shield performance is an essential part of project scheduling and cost estimation of tunneling projects. This paper establishes an efficient multi-objective optimization model to predict the shield performance during the tunneling process. This model integrates the adaptive neuro-fuzzy inference system (ANFIS) with the genetic algorithm (GA). The hybrid model uses shield operational parameters as inputs and computes the advance rate as output. GA enhances the accuracy of ANFIS for runtime parameters tuning by multi-objective fitness function. Prior to modeling, datasets were established, and critical operating parameters were identified through principal component analysis. Then, the tunneling case for Guangzhou metro line number 9 was adopted to verify the applicability of the proposed model. Results were then compared with those of the ANFIS model. The comparison showed that the multi-objective ANFIS-GA model is more successful than the ANFIS model in predicting the advance rate with a high accuracy, which can be used to guide the tunnel performance in the field.

This study proposes a novel fuzzy model for identifying high-risk factors during excavations in urban karst geological environments. The proposed model incorporates the interval analytic hierarchy process (I-AHP) into the technique for order preference by similarity to an ideal solution (TOPSIS). The developed model considers the complex geological conditions, monitoring data, management quality, and surrounding environment. I-AHP is employed to assign the weights of the criteria, while TOPSIS is applied to identify high-risk factors. An expert confidence index is introduced to increase the reliability of the evaluated results. A case study of karst excavation at Ma'anshan Park Station on Guangzhou Metro Line 9 is analysed to validate the proposed model. The results indicate that high-risk factors can be identified in different excavation stages. The evaluated results concerning variations in risk factors can provide a guide for adopting construction measures to mitigate risk and reduce accident occurrence.

Land subsidence is a severe geo-hazard in coastal regions and represents a great threat to infrastructure. Based on long-term measurement data, including that for deep compaction from vertical multipoint extensometers, land subsidence and infrastructural settlement from leveling surveys, groundwater levels in multiple confined aquifers, and hydrogeological conditions, this study investigates the effects of groundwater exploitation and recharge on land subsidence and the settlement of infrastructure in Shanghai, China. Further, groundwater exploitation and the consequent responses of piezometric heads in the multiple confined aquifers of Shanghai soft deposits are discussed. Subsequently, regional land subsidence, local deep-soil deformation, and infrastructural settlement are analyzed in terms of groundwater exploitation. It is found that the subsidence pattern is related to the trend of groundwater exploitation and the variation of piezometric heads in the aquifers, which can be roughly divided into three phases. Subsidence funnels could occur, and could be interpreted according to the differences in groundwater exploitation intensity and the spatial variability of lithology. Since the towers of Nanpu Bridge are located within the area of the subsidence funnel, this could be the main reason for the differential settlement of the bridge.

This paper presents a brief review on major accidents and conducts bibliometric analysis of risk assessment methods for excavation system in recent year. The summarization of potential risks during excavation provides an important index for establishing an early warning system. The applications of fuzzy set theory and machine learning methods in risk assessment during excavation are presented. A case study of excavation in Guangzhou metro station is used to demonstrate the application of a machine learning method for risk evaluation. The large amount of data collected by 3S techniques (RS, GIS and GPS) and sensors increases accuracy of risk assessment levels in excavation. These procedures, integrated into building information modelling (BIM) management platform, can manipulate dynamic safety risk monitoring, control, and management. Finally, the processing and analysis of big data obtained from 3S techniques and sensors provide promising perspectives for establishing integrated technology system for excavation.

This paper presents a case history where the hydraulic parameters of a weathered mylonite fault located in the way of shield tunneling for the Xie-Zhong section on Metro Line No. 7 in Guangzhou City were determined using a series of field pumping tests. The weathered mylonite fault contains fissure groundwater, which would result in a high potential of water ingress during shield tunneling within the weathered mylonite strata. Therefore, the first stage of pumping tests involving five pumping wells was initially carried out. To verify the validity of the hydraulic parameters derived, the second stage of pumping tests involving four pumping wells was carried out. In addition, both an analytical method that involves a well-flow calculation for a fissure-confined aquifer for non-orthogonal anisotropic rock mass and a numerical simulation based on the theory of the equivalent continuum porous media were used to derive the hydraulic parameters based on the field pumping test data. The analytical method can provide the values of hydraulic conductivity only in the horizontal plane and is not able to capture the hydraulic characteristics of standalone stratum of the multi-aquifer system. In the numerical model, the weathered mylonite fault due to the nature of non-uniform mylonite strata distribution is further divided into four sub-regions with different hydraulic conductivities, according to the calculated influence radius of groundwater drawdown or geological formation. This leads to estimates of hydraulic parameters that are closer to real values, and enhances our understanding of non-uniform fissure development.

Flooding hazards caused by heavy rainfall in Shanghai have been reported extensively in the last 15 years. Geologically, Shanghai is sensitive to flooding hazards due to low-lying ground caused by land subsidence. Climatically, Shanghai is in the East Asia monsoon area and frequently experiences torrential rains. In this study, data from fifty-four pluvial flooding events between 2001 and 2015 were collected and analysed. The influence factors contributing to pluvial flooding are evaluated, and recommendations for protective measures are presented. The pluvial flooding prevention capacity in Shanghai is controlled by rain water storage and discharge capacity, which is associated with the sewer network, pumping stations and its sluice and pumping gates. Within the last three decades, the number of local torrential rainfall events and short-duration torrential rains has increased annually. However, the rain water storage capacity has decreased dramatically and the rain water discharge capacity has become limited during this period. In an extreme case, the discharge function of the sewer network was even temporarily lost because of flooding of the distributaries of the Huangpu River. Thus, in order to prevent flooding hazards caused by heavy rain, it is suggested that a large sluice and pumping station between the Huangpu River and the Yangtze River estuary is constructed in the near future, considering the continuous subsidence of the city and the ongoing rising sea levels.

This study presents an approach for eutrophication evaluation based on the technique for order preference by similarity to an ideal solution (TOPSIS) method and Monte Carlo simulation (MCS). The MCS is employed to produce a normally distributed dataset based on the observed data while the TOPSIS method and membership function are used to evaluate the level of eutrophication. Herein, a eutrophication problem in Lake Erhai is evaluated to check the performance of the proposed approach. The evaluation results were consistent with the real situation when the coefficient P in the membership function is equal to 1. Moreover, the developed approach is able to (i) deal with evaluation items with inherent fuzziness and uncertainties, (ii) improve the reliability of evaluation results via MCS, and (iii) raise the tolerance to errors in measured data. A global sensitivity analysis indicated that the potassium permanganate index (CODMn) and Secchi disc (SD) are the most sensitive factors in the developed approach. Finally, a range for the coefficient P value in the membership function was recommended.

This paper summarized the shallow geothermal resources within a depth of 200 m in China. This geothermal resource is divided into five regions based on the geological structures, geomorphology, geology, and hydrogeology. The recoverable amount of shallow geothermal energy (SGE) is equivalent to 7 × 1012 kg of standard coal in a survey area of 1.69 × 105 km2, 60% of which is distributed in the mid-eastern region of China. SGE is mainly used for building heating and cooling via ground source heat pump (GSHP) technology since 1990s. The coefficient of performance (COPs) of the GSHP system exhibits large regional differences, and the energy utilizing efficiencies of GSHP systems are not high. The utilization rate of SGE is still low compared with those of other forms of renewable energy. Some measures, including a standardized and simplified management system, a feasible evaluation and utilization plan, modified technology and standards, an intelligence environmental impact assessment, and intelligence monitoring, can be considered to enhance the utilization efficiency of SGE.

This paper presents a comprehensive review on subsea jet trenching technology via a critical analysis of its principle, mechanism, devices, modeling approaches, as well as properties of subsea sediments. This review shows that the success of jet trenching operations is closely related to some key factors including the soil conditions, trencher specifications, and characteristics of pipelines or cables. Three case histories are presented to demonstrate the importance of these key factors and their interrelationships. This paper also points out a number of challenges pertaining to the implementation of the jet trenching method in carbonate sediments, as well as some limitations and gaps in the existing modeling approaches. Future perspective researches that are recommended to develop: (1) promising theories, like turbulent submerged flow, and (2) robust numerical approaches, such as the smoothed particle hydrodynamics (SPH) and material point method (MPM) to substantiate the experimental experience and reveal possible hidden mechanisms.

The urban area of Hangzhou is located in the northeast region of the Hangzhou Bay, beside the estuary of the Qiantang River. Three main ancient rivers are present in the case study area. The ancient rivers, together with the influence of three transgressions, influence the geological and hydrogeological formations of the urban area of Hangzhou. Soft clay is widely deposited in the study area and the Quaternary strata are rich in pore water, karst water, and bedrock fissure water. Confined aquifers located in the case study area have high pressure, high permeability, and rich water, and their levels fluctuate with tide. Karst strata, soft clay, ancient confined aquifer, and shallow gas deposits are potential geological features, which may threaten underground construction in the urban area of Hangzhou. As such, corresponding pre-treatments should be adopted to control the potential geohazards. Karst caves are proposed be infilled or reinforced before the commencement of underground construction works. Ground improvement methods can be adopted to enhance the strength of soft soil. Foundation dewatering in foundation pits with pensile curtains can be adopted to control ancient confined aquifers. Pre-exhaustion of shallow gas prior to commencement of construction works is an effective measure to control shallow gas with high pressure. Moreover, the impacts of the Qiantang River tide on the groundwater level and the deformation of underground structures should be considered.

Pipe-jacking is a construction method widely used in pipeline constructions. Prediction of ground deformation induced by pipe-jacking, is important for safety and scheduling purposes. This paper presents an approach to predict ground deformation during pipe-jacking considering following factors: (i) bulkhead additive thrust, (ii) friction on jacking machine, (iii) grouting pressure, and (iv) ground loss. Mindlin&rsquo, s solution was used to calculate the ground deformation induced by bulkhead additive thrust and friction on the jacking machine. The shearing disturbance coefficient was adopted to evaluate the mitigation effect of shearing behavior on ground deformation. Verruijt&rsquo, s solution was used to simulate the effect of grouting pressure. Sagaseta&rsquo, s method was adopted to consider the ground loss induced by over-excavation. Subsequently, a three-dimensional analytical solution for ground deformation induced by pipe-jacking was obtained. A case study based on a pipe-jacking project undertaken in Jiangsu, China was analyzed to validate the proposed approach. The results indicated that the proposed approach was robust and could be implemented for future pipe-jacking projects.

The Yangtze River Basin and Huaihe River Basin in Southern China experienced severe floods 1998 and 2016. The reasons for the flooding hazards include the following two factors: hazardous weather conditions and degradation of the hydrological environment due to anthropogenic activities. This review work investigated the weather conditions based on recorded data, which showed that both 1998 and 2016 were in El Nino periods. Human activities include the degradations of rivers and lakes and the effects caused by the building of the Three Gorges Dam. In addition, the flooding in 2016 had a lower hazard scale than that in 1998 but resulted in larger economic losses than that of 1998. To mitigate urban waterlogging caused by flooding hazards, China proposed a new strategy named Spongy City (SPC) in 2014. SPC promotes sustainable city development so that a city has the resilience to adapt to climate change, to mitigate the impacts of waterlogging caused by extreme rainfall events. The countermeasures used to tackle the SPC construction-related problems, such as local inundation, water resource shortage, storm water usage, and water pollution control, are proposed for city management to improve the environment.

This paper reports on a massive landslide event, in which 8 million cubic meters of earth and rocks slid down from the top of a mountain in the village of Xinmo, located in the county of Maoxian, in the province of Sichuan, China, on 24 June 2017. This landslide resulted in 10 fatalities and 73 people were reported as missing. This paper details the preliminary investigation, the joint-force rescue activity, and the analysis of the nearby topography, rainfall, and seismic fracture zone. The combined effects of large amounts of rainwater, steep topography, deep-seated sliding interface, and significant altitude difference between the highest point of the mountain and the Xinmo villagers’ houses are considered as the main influencing factor that triggered this landslide event. To develop geological disaster-prone areas in the future, four main recommendations to reduce casualties and environmental impacts are provided in this paper.

In order to rapidly determine the hydraulic conductivity for both marine and deltaic deposits in field, an approach is proposed to evaluate the hydraulic conductivity of soil using cone penetration tests with pore water pressure measurement, known as piezocone testing. This approach is based on the test results from a series of laboratory penetration tests investigating the expansion shape of soil using a model cone tip with different tip angles and considering the influence of the soil characteristics. To derive the calculation method, two assumptions are made: i ) the flow surface of pore water is assumed to be a half ellipsoid shape, covering the whole tip of the cone, and ii ) the initial state of induced excess pore pressure is assumed to be have a negative exponential distribution and to dissipate from the half ellipsoid surface. The proposed approach is compared with the existing approach based on piezocone data and laboratory testing. All of the three methods were applied to analyze three field cases, in which two cases is marine deposit and one is deltaic deposit. The results show that the proposed approach can predict hydraulic conductivity of both marine and on-land deposit, which extends the range of the application of the existing approaches as proposed by Chai et al.

This paper presents a case history on the performance of a coastal embankment reinforced by a layer of geotextile at the bottom of the embankment on soft marine deposits. The coastal embankment is the sea wall of the Qinshan nuclear power station on the northern side of Hangzhou bay near Shanghai, China. Monitoring of settlement and excess pore water pressure were carried out during and after embankment construction. The finite element method (FEM) was used to analyse the performance of the geotextile reinforcement and its effect on soil behaviour under the embankment loading, based on the field monitored results. Stability analyses were conducted using two approaches: c-ϕ reduction in FEM, and limit equilibrium analysis. Both field and simulation results indicate that the geotextile has an effect on reducing the vertical displacements of subsoil. However, the results show basal reinforcement cannot increase the overall factor of safety, but the factor of safety at the local position, under reinforcement, can be increased during the construction procedure, and this is due to the confinement of the soil element by the reinforcing fabric. Thus, in these circumstances, one layer of basal geotextile reinforcement can prevent sudden failure of subsoil during embankment construction.

This paper presents a laboratory evaluation on the strength behavior of cement–clay admixture improved by polypropylene fiber. Waste polymer textile bags are harmful to the environment and sustainable means to reuse them are urgently being sought. A novel method to recycle these waste polymer textile bags is applying them in soft soil improvement projects, such as compacted-pavement base/subbases. In order to verify the effectiveness of fiber bundles used in soil mixing, a series of laboratory investigation are conducted on fiber-reinforced cement-improved soft Shanghai clay. In the tests, two types of polymer fibers were employed; the first one is monofilament polypropylene fiber and the other is fiber bundles split from polymer textile bags. The tests were conducted using unconfined compressive strength (UCS) test after the specimen of fiber–soil–cement admixture were cured for some period. The results show that fiber additive can significantly improve the strength and ductility of the cement treated Shanghai clay. The UCS of fiber–soil–cement admixture is related to both content and length of fiber. Both two kinds of fiber-reinforced cement clay reached their peak strength at fiber content of 0.5%. UCS will slowly reverse if the fiber content continues to increase. Even though the polypropylene fiber works better than the fiber bundles, the difference is less than 5%. These results indicate that the fiber bundles split from polymer bags can be used as the reinforcement in soil mixing, thus providing a novel approach to treat waste polymer textile bags.

Based on a simplified mechanical model, the stress distribution pattern in subsoils around tunnels due to train movement is investigated. In this model, the effects of rails, connection bolts, ballast, lining and foundation are taken into account. The initial stress state and the dynamic stress state of the subsoils induced by train loading are obtained from a two-dimensional finite-element calculation. After combining the above results with the empirical equation proposed by Chai and Miura in 2002, the cumulative plastic strain of subsoils and the long-term settlement of tunnels are obtained. The results show that the cumulative train-load-induced tunnel settlement increased, but at a decreasing rate. The cumulative settlement was 15·5 mm after 8 years, 60% of which occurred within the initial 6 months.

This paper presents a numerical investigation into the leakage behavior of cut-off walls in gravel strata due to dewatering in a deep excavation pit. The calculated values of the groundwater head and surface settlement using a model agree well with the measured values. Values of the hydraulic conductivity (k) and storage coefficient (Ss) of each soil layer are obtained from the test results when the cut-off wall is 43 m deep. The leakage through the cut-off wall in gravel is analyzed by considering a variation in hydraulic conductivity in different sections of the cut-off wall. The simulated results show that a significant leakage occurred in the 54 m deep cut-off wall. Although leakage did occur in the full cut-off wall in the confined aquifer, the full cut-off wall is still more efficient in preventing groundwater seepage than the partial cut-off wall. The relative depths of the cut-off wall and of the wells have a significant effect on ground surface settlement during the withdrawal of groundwater. Therefore, the appropriate selection of relative depth of both cut-off wall and pumping well is an effective way of controlling surface settlement outside the pit.

This paper presents a case history of the leakage behavior during dewatering tests in the gravel strata of an excavation pit of a metro station in Hangzhou, China. The groundwater system at the test site is composed of a phreatic aquifer underlain by an aquitard and a confined aquifer with coarse sand and gravel. The sandy gravel stratum has very high hydraulic conductivity. The maximum depth of the excavation is 24 m below the ground surface, which reaches the middle of the aquitard strata, where the thickness of the clayey soil is insufficient to maintain the safety of the base of the excavation. To understand the hydrological characteristics of gravel strata, single- and double-well pumping tests were conducted, where a cut-off wall was installed 43 m deep with its base penetrating 2 to 3 m into the aquifer. Test results show that this partial cut-off of the aquifer cannot effectively protect the base of the excavation from the upward seepage force of the groundwater during excavation. Therefore, a new cut-off wall (second phase) was constructed to a depth of 54 m to cut off the confined aquifer. A second pumping test was conducted after the construction of the second phase cut-off wall, and test results show that this full cut-off combined with dewatering can control groundwater effectively during excavation. This finding indicates that when a deep excavation is conducted in a confined aquifer with high hydraulic conductivity, determination of the depth of the retaining wall should be based on three factors: the stability of the base, the upward seepage stability, and settlement control.

Karst landscapes are widely distributed and different characteristics are displayed in different regions due to the effect of various natural environmental factors which occur throughout China. Buried karst cavern systems covered by sandy strata, which are widely distributed in Guangdong Province, possess the following features: high fissure water content, high rock permeability, susceptibility to collapse, variability in shape and an irregular distribution. Socket diaphragm walls are usually adopted to retain soil and to cut-off groundwater during deep excavations in Guangdong Province, for the safety of the excavation and to reduce the impact on the surroundings. However, geohazards often occur during the construction of diaphragm walls in karst regions, causing problems such as diaphragm wall collapse, water or mud ingress, ground collapse and long-term instability. An eight-step treatment technique is proposed, which involves filling the karst caverns before the construction of diaphragm walls. A case study using the treatment technique in Maanshan Park Station on Guangdong Metro Line 9 is also presented. Leakage of the diaphragm wall was observed during the excavation, and grouting failed to seal the leakage. The mechanism of the leakage process was analysed and countermeasures were undertaken.

This paper presents an innovative technology referred to as Dual Function Well (DFW), which has been developed in order to reduce the construction costs of dewatering when excavation is conducted in an aquitard over a confined aquifer. DFW technology is a method to lower both shallow groundwater and deep groundwater, either separately or simultaneously, using one well. The DFW includes two or more independent screens corresponding to each aquifer, and a valve is located between the screens inside a steel pipe. When the valve is closed, groundwater is pumped from the upper screen in the shallow aquifer. When the valve is open, groundwater is pumped from the screens in both the shallow and deep aquifers. DFW technology is used to replace the traditional method involving two sets of wells, in which the first set of wells pumps groundwater from the shallow aquifer, and a second set pumps groundwater from the deep aquifer. To investigate the effectiveness of DFW, field pumping tests using a DFW were conducted, and both groundwater head and settlement were monitored. Numerical simulation was adopted to simulate the results of the pumping tests. Comparison between the results from the DFW and from an ordinary mixing well indicates that the use of a DFW with the valve closed can reduce the pumping time from a deep aquifer and can reduce the ground settlement caused by dewatering. The results indicate the DFW technology is feasible and effective.

This paper presents a case history of behaviour during a series of pumping tests in an alternated multi-aquifer-aquitard system in a foundation pit in Tianjin, China. The test site is located at Tianjin Railway Station, which is in the downtown area and is surrounded by many buildings. The groundwater system at the test site is composed of a phreatic aquifer and three confined aquifers. Four groups of single well pumping tests were conducted in each aquifer to obtain the hydrogeological parameters of the aquifers and investigate the hydraulic connection among the aquifers. Test results show that there is hydraulic connection among the upper 3 aquifers. Moreover, both analytical and numerical methods were employed to analyse the hydrogeological parameters. The analytical solution was obtained for the phreatic aquifer using the Dupuit equation, and the Cooper–Jacob method was conducted for the confined aquifers. The numerical simulation was performed using a finite element method (FEM). The results illustrate that the numerical method gives more reliable results than the analytical method does. The numerical simulation considers the anisotropic characteristic of soils, and the hydrogeological parameters of all of the soils can be calculated. The analytical solution, however, may be influenced by wellbore storage or by the leakage effect of the aquitards, and it only gives the parameters of the aquifer where the pumping tests were performed.

Although many field investigations into pipe-jacking installation have been reported within the literature, there are few reports on the rebar stress in jacking pipes. This paper presents the field performance of concrete pipes during the jacking carried out under the Guan River in Jiangsu, China. Rebar stresses at two wings (the left and right side), the top crest, and the base in the longitudinal and circumferential directions for four different pipes were monitored. The maximum rebar stresses during the jacking were 37.1 MPa in the longitudinal direction and 36.6 MPa in the circumferential direction. However, the maximum rebar stresses after construction were only 18.5 MPa in the longitudinal direction and 20.3 MPa in the circumferential direction. A normalized jacking force “ α ” is proposed to evaluate the additional rebar stress in jacking pipes. The range of α is from 0.04 to 0.25. The relationship between the rebar stress and the construction procedure is presented and discussed. An excessive jacking force, an alignment deviation or an increased penetration rate would generate a large incremental rebar stress.

This article presents a case history of determination of effective depth of prefabricated vertical drains (PVDs) under embankment loading on a very soft clay deposit in central China, near Jiujiang, Jiangxi Province. The height of the embankment was 5.3 m and construction time was about one year. The PVDs were installed to a depth of 8.5 m at a spacing of 1.5 m in a triangular pattern. Field observations and the finite element method (FEM) were employed to analyze the performance of the soft deposit during embankment construction. The influential depth of the embankment loading was evaluated based on settlement, excess pore pressure, and stress increase in subsoil, both from the observed data and FEM analysis. The effective PVD depth was determined in the following ways: (1) the depth of 5% subsoil settlement of surface settlement; (2) vertical stress increase in subsoil of 25% in-situ stress; and (3) consolidation time/PVD depth relation by FEM. Based on the analysis, the effective depth of PVDs was dete...

In Shenzhen, a complex series of folds and fractures, and intensive metamorphism took place during the pre-Caledonian, Caledonian, and Hercynian to Indosinian orogenies. Then, Yanshanian orogeny, with the most tectonic movement, occurred. Strong invasive activity of granitic magma, a massive blowout of acidic volcanic rock, and magmatism-related mineralisation are the features of Yanshanian orogeny. Moreover, deep faults were also developed and wide folds were formed. A large amount of granite rock was formed from the Yanshanian orogeny in Shenzhen. The outcrop area of the granite in Shenzhen reaches 760 km2, almost covers 50 % of Shenzhen land area. Granite is primarily susceptible to chemical weathering. Though weathered, granite and solitary granite boulders are of high uniaxial compressive strength (UCS). The weathered granite may be covered by Quaternary soil with low shear strength, such as backfill, sand, silty clay, and clay. The thickness of the Quaternary soil ranges from 0 to 40 m. Socket diaphragm walls are usually adopted during deep excavation construction in Shenzhen for their safety and low impact on the surrounding environment. When the excavation depth is increased, the socket diaphragm walls are embedded in weathered granite to a depth of between 3 and 10 m. However, the traditional socket diaphragm wall construction is only viable in soft ground, as it is not practical to penetrate hard weathered granite. As a consequence, difficulties arise during construction in the Shenzhen region, such as difficulty in breaking down the rock, socket diaphragm wall collapse and leakage. To solve these construction problems, countermeasures, such as monitoring, heavy hammer dropping, smooth blasting and a modified slurry, are proposed in this study. It can be concluded that the heavy hammer dropping method should be chosen to deal with weathered granite with a UCS of less than 50 MPa and the smooth blasting method should be adopted to deal with weathered granite with a UCS of more than 50 MPa. A case study of a metro station excavation using the smooth blasting method in Shenzhen is also introduced. The successful construction of the socket diaphragm walls demonstrates the applicability of the smooth blasting method.