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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.

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.

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.

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.

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 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.

This paper presents an investigation into increased deformation of Aquifer II caused by groundwater pumping from the aquifer in Changzhou, China. As groundwater levels of aquifers have been decreasing in recent decades due to uncontrolled water pumping, land subsidence is becoming a serious geohazard in Changzhou. Based on recently reported field data, the compression of aquitards has not increased compared to that of aquifers with the same scale of layer thickness. The Cosserat continuum model was adopted to analyse the observed phenomenon in this study. A classic Cauchy continuum model is also used for comparison. The comparison between these two models indicates that the proposed approach can interpret the increased deformation well, and the classic Cauchy continuum model underestimates the aquifer deformation as it does not consider shear displacement and macro-rotation. A discussion on the relationship between the groundwater level in the aquifer and subsidence is then undertaken. The results show that the severity of the annual subsidence is correlated with the variation in groundwater level in Aquifer II. To mitigate the subsidence hazards, countermeasures should be adopted to avoid the shear stress in aquifers which results from the high hydraulic gradient, by the appropriate allocation of pumping wells and by restricting groundwater withdrawal volume from each pumping operation.

Karst landscapes are widely distributed in China, and buried karst is widespread in Guangdong. This study mainly focuses on buried karst or karst caves which are underground at depths of up to 50 m and can significantly affect engineering construction activity. The karst caves, which are widely distributed in Guangdong Province, have the following features: high fissure water content, high rock permeability, prone to collapse, variable shapes, and irregular distribution. When a shield tunnel is constructed in this kind of environment, hazards, such as sink holes, the ingress of water or stones, and damage to the constructed tunnels may occur. Thus, karst caves need to be treated before tunnel construction. This paper presents a procedure for karst cave treatment to mitigate possible hazards during shield tunnelling in karst regions. The construction procedure includes field investigation, judgment, treatment, and effectiveness check. The treatment criteria, grouting material, construction steps, and effectiveness check for the karst cave treatment are introduced in detail. A field test on shield tunnelling excavation was conducted using the karst cave treatment in the karst region of Guangzhou, China. Field investigations include testing the unconfined compressive strength (UCS) of borehole samples of grouting materials, standard penetration test (SPT), core recovery (CR), ground surface settlement and building settlement. All of the UCS values of the borehole samples are greater than 0.2 MPa, the modified SPT values are more than ten, and the CR values are greater than 90 %. The measured values of ground surface settlement and building settlement are all within the allowable ranges. All of the test results demonstrate the applicability of this treatment process in karst regions.

Foundation dewatering has become a major cause of land subsidence in Shanghai. The burial depth of foundations in relation to geotechnical construction works is less than 75 m, and the corresponding groundwater includes phreatic, low-pressure artesian, and the first confined aquifers. Based on the geological and hydrogeological conditions beneath Shanghai, methods of dewatering may be divided into three modes and further five patterns according to the insertion depth of the dewatering-retaining system. The most common dewatering mode aims to reduce the water pressure in the confined aquifer by setting the dewatering wells inside the pit, whilst the retaining walls are buried in the confined aquifer and partially cut off the confined aquifer layer. To predict the settlement due to foundation dewatering, numerical models are generally adopted, which are similar to those used to predict land subsidence induced by regional groundwater withdrawal; however, since foundation dewatering is conducted along with the setting of retaining walls and foundation pit excavation, which differs from regional groundwater withdrawal, interactions between the retaining wall-dewatering well, the dewatering-excavation, and dewatering-recharge are important factors affecting the analytical model. Since the grading of the shallow soil layers is different, stratified settlement characteristics of the shallow soil strata and seepage erosion, which results in additional deformation, need to be given particular consideration.

In the design of a deep retaining wall, it is necessary to consider the blocking effect on groundwater seepage of retaining walls in aquifers. In this study, both laboratory tests and numerical simulation with finite element method (FEM) were adopted to investigate the blocking effect on groundwater seepage under different insertion depths of retaining wall in aquifer. Laboratory tests were conducted to analyze this blocking effect in an unconfined aquifer. The test results indicate that the effective insertion depth ratio ( J ) of a retaining wall in Shanghai aquifer sand is about 70%. A three-dimensional numerical model (3D-FEM) was conducted to analyze the laboratory test results. The FEM results show that FEM is a reliable method to analyze the blocking effect on groundwater seepage in an aquifer. Based on the same aforementioned procedure, a 3D FEM model is established to investigate the blocking effect in the confined aquifer in Shanghai deposit. Both laboratory test and FEM results show that drawdown of groundwater level decreases with an increase of the insertion depth ratio, J , of retaining structures in an aquifer. The optimal value of J (approximately 70%) is achieved for retaining wall based on the synthetic results from laboratory test, FEM analysis, and the equation of Pujades et al. for either unconfined aquifers or confined aquifers of Shanghai.

This paper presents an investigation into the hardness and unconfined compressive strength (UCS) of cement-stabilized Shanghai clay. Various specimens with different cement content and curing time were made in order to conduct hardness tests and unconfined compression tests. The Shore-A durometer was used in a pioneer manner to measure the hardness of stabilized clay. Hardness tests suggest that the measured values of degree of hardness ranged from 1 to 87 DH, and the unconfined compression tests showed that the measured UCS varied from 56 to 1,061 kPa. Test results indicate that the average degree of hardness decreases dramatically with an increase in the clay-water/cement ratio. It is shown that the relationship between the degree of hardness and the curing time is approximately linear in the semi-logarithmic plot. An exponential equation is proposed to express the unique relationship between the UCS (q u ) and the ratio of degree of hardness (S/S r) by regression analysis. The expected prediction range of UCS using the Shore-A durometer was calculated to be between 0.04 and 1.79 MPa. The exponential equation proposed in this study may be used to produce a quick prediction of UCS by measuring the hardness of samples in the field.

Dewatering using a combination of waterproof curtain and pumping wells is commonly adopted to ensure the stability of foundation pits in multi-aquifer strata. However, dewatering is likely to result in environmental problems. This paper investigates the impact on surroundings owing to the interaction between the waterproof curtain and pumping wells by numerical simulation. The depth of the diaphragm wall penetrating the dewatering aquifer (D) and the filter length of pumping wells (L) are varied in the simulation. The relationship between approximate hydraulic gradient (Δi) or ground settlement outside the foundation pit (S) with curtain depth ratio RD (D over the thickness of the dewatering confined aquifer Ha) or filter length ratio RL (L/Ha) can be divided into three change parts, namely initial gradual, middle sharp and final gentle part. Three values of RD and RL, namely effective, suggested and control value, are proposed. RD and RL should vary between the effective and control value. The suggested value of RD and RL is recommended in actual engineering by comprehensive consideration. The effective, suggested and control value of RD can be calculated by a linear equation according to the value of RL.

Alternative subsidence mechanisms related to groundwater extration and surface loading of built infrastructure in Shanghai have been evaluated to explain continued subsidence despite the controlled reduction of groundwater extraction. The traditional theory of aquifer-system compaction embodied in the aquitard drainage model cannot fully explain this phenomenon. Two possible alternative mechanisms were studied previously: (i) surface loading attributed to urban construction; (ii) creep occuring in sandy deposits of aquifers. These mechanisms could not fully explain the observed subsidence. Two additional alternative mechanistic models are proposed that involve principles of load transfer considering the temporally and spatially redistributed stresses associated with groundwater extraction: (i) the Cosserat continuum mechanism, considering shear force on the permeable coarse-grained matrial in the aquifer due to hydraulic gradients in the aquifer; and (ii) internal erosion of fine-grained (clay and silt) particles within the aquifer. Initial results based on simulations incorporating Cosserat mechanics look promising.

Recent monitoring of land subsidence and soil deformation indicates a new phenomenon where excessive and continuous deformation occurs in the sandy aquifers in Shanghai and the Su-Xi-Chang region of China. It is hard to explain factors contributing to this phenomenon with traditional Cauchy continuum mechanics in which low normal stress in the ground could not cause such large deformation. Steep hydraulic gradient would be formed in the aquifer if groundwater is pumped from densely distributed wells, and shear stresses would develop then. Accumulated shear stress could then lead to deformation of the aquifer or even land subsidence. Accumulated shear stress due to the drawdown of groundwater level is one of the main factors that contribute to deformation within an aquifer. Traditional Cauchy continuum mechanics cannot consider this shear stress because of the hypothesis of equal shear stress in the aquifer unit. Cosserat continuum mechanics can be applied to analyse the mechanism of aquifer deformation controlled by accumulated shear stress by considering the scale effect and the asymmetric distribution of shear stress in the aquifer unit.

Distributed piles are often installed in the foundation pit in sandy soil before dewatering. Hydraulic conductivity should be estimated considering the block effect of piles on groundwater seepage. Research shows that the effective medium theory (EMT) could be used to calculate the equivalent hydraulic conductivity (k eq) of a heterogeneous medium with other material inclusions. In order to verify the applicability of EMT in an aquifer with piles, an experimental investigation is conducted. In this experiment, a sandy soil is considered as an aquifer and polyvinylchloride pipes are adopted as piles. Piles are distributed in rectangular and triangular layouts. The relationship between k eq of the aquifer and the volume replacement ratio is plotted for these two layouts. The results indicate that EMT could well predict k eq for the cases with the rectangular layout; however, for triangular layouts, the prediction becomes poor. To provide a better prediction of k eq of the aquifer with piles distributed in a triangular layout, a modified EMT (MEMT) is proposed, in which a correction factor is adopted considering different layouts of piles. The MEMT can provide better k eq predictions for an aquifer with piles in the triangular layout pattern than those obtained using the EMT.

Shanghai is a typical example of a region in China suffering from severe land subsidence. Previous investigations have shown that land subsidence is strongly related to groundwater pumping in both the temporal and spatial domains. A series of field investigations shows that the deformation rate of aquifer IV (AqIV) has increased, contributing significantly to the total subsidence in Shanghai. To predict the deformation behavior of AqIV in Shanghai due to groundwater pumping, four different models have been applied in this study: (i) a model based on groundwater flow theory, (ii) an elastic model based on Cauchy mechanics, (iii) a creep model incorporated into Cauchy mechanics, and (iv) a recently proposed land subsidence model by Budhu based on Cosserat mechanics. Based on a number of assumptions, Budhu’s concept was extended to consider the time-dependent behavior of groundwater potential in aquifers and the consolidation behavior of overburdened aquitards. The calculated results of AqIV’s deformation were compared with the field-measured data. The results show that when using groundwater flow theory and Cauchy mechanics, it is difficult to predict the increased deformation rate of the sandy layers in aquifers even when the creep behavior is incorporated into the calculation. However, Budhu’s method based on Cosserat mechanics can predict this increased deformation rate well. The predicted result indicates that increased deformation of aquifer IV is due to volumetric contraction caused by shear stress rather than the creep of aquifer sand. The phenomenon of deformation delay in aquifers can also be interpreted with the proposed model.

This article presents a new approach to estimate hydraulic conductivity of soil from cone penetration test with pore water pressure measurement (referred to as CPTU hereafter). The proposed approach is based on the test result of the spherical cavity expansion of the soil at the tip of a pile. During the piezocone penetration, the flow shape of pore water around the tip of the cone is assumed to be a spherical crown and induced excess pore water is assumed to dissipate from the crown surface. Based on this assumption, a bi-linear relation between the piezocone sounding metric (which is the product of the pore water pressure ratio Bq and the tip resistance Qt) and the hydraulic conductivity index KD is derived to estimate the hydraulic conductivity of the soil layer. The derived approach expands the applicable range of existing approaches in the literature. It is demonstrated that the proposed approach can cover the entire tip angles of the cone and the modified equation can fit the CPTU test data well.

To control land subsidence due to groundwater withdrawal, it is important to estimate allowable withdrawn volume of groundwater in a soft deposit. This technical note presents a simple approach for estimating the allowable withdrawn volume of a deposit. A regression analysis method was used based on measured land subsidence and recorded net withdrawn volume. This approach was proposed based on the principle of soil compression at different effective stresses, i.e. the soil compression is small when the consolidation stress is lower than the yield stress of the deposit, but large when the consolidation stress is higher than the yield stress. Two case studies are presented in this technical paper to demonstrate how to use the simple approach to estimate the allowable withdrawn volume.

This paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe-jacking. The microtunneling project is the construction of four parallel pipes under Guan River in Jiangsu, China. Four parallel tunnels with external diameter of 4,160 mm and horizontally spaced at 4.8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry-balance microtunnel boring machines (MTBM) at a depth of 4.6 m under the river bed. Since the overburden soil is very thin, proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed. In order to optimize the operation parameters prior to construction under the river bed, a field trial was conducted, which included measurement of ground surface settlement, subsurface settlement, and lateral displacement of the subsurface soils, as well as excess pore water pressure and earth pressure. The relationship between ground response and const...

Xi’an City is located at the central region of the Fenwei Plain, and there are 14 ground fissures (labelled GF1–GF14) which have been closely monitored in the urban area of Xi’an City. When a shield tunnel is constructed in a region with ground fissures, problems (such as cracking or failure of the tunnel lining, leakage of groundwater into the tunnel, damage to the completed tunnels and shield, and long-term instability) may be encountered due to the activity of ground fissure. To mitigate the adverse impact caused by the activity of ground fissure, a series of countermeasures are suggested in this paper, which include installation of movement joints, installation of a flexible layer for controlling deformation, foundation reinforcement with cement grouting, and improvement of existing water resistance. A case history regarding the metro tunnel (Xi’an Metro Line 1) which has been intersected the ground fissure 5 (GF5) obliquely was analyzed. The aforesaid countermeasures were applied to this case history. After improving the existing water resistance, the permeability of the surrounding soils was effectively reduced to about 4.0 × 10−8 cm/s and the groundwater leakage into the tunnel was minimal. Observations of the accumulative ground surface settlement near the fissure verified the effectiveness of the countermeasures applied to this case history.

The quaternary deposit of Shanghai is composed of an alternated multi-aquifer-aquitard system (MAAS) consisting of a sequence of aquitards laid over aquifers one by one. In the MAAS, any drawdown of groundwater head in an aquifer may cause consolidation of the overburden aquitard. When underground structures penetrate those aquifers, groundwater seepage path changes and drawdown occurs at the side characterized by the lower hydraulic potential along the flow direction (hereafter refers as to the lower side). This drawdown may cause additional subsidence at the lower side and unbalanced load between the two sides of the underground structure. In order to evaluate the cutoff effect of an underground structure on groundwater seepage in a MAAS representative of the underground of the city of Shanghai, a numerical analysis based on a groundwater flow model has been carried out. The simulated results have shown that underground structures which cut off groundwater flow locally change both magnitude and direction of the flow velocity field. The induced changes in the groundwater field are highly sensitive to the penetration depth and width of the underground structure. Design recommendations for underground structures in aquifers belonging to a MAAS are also presented, which has not yet been considered in the engineering practice of Shanghai.

This paper presents a case history of an earth pressure balance (EPB) shield tunneling constructed in a close distance near constructed underground structures in soft deposit of Shanghai. In order to protect existing underground structures, field observation was carried out, including reinforcement stress of interior structure and lateral displacement of the diaphragm wall. Throughout the shield tunneling construction, various countermeasures were adopted based on field observation feedback to minimize adverse environmental influences. The maximum cumulative lateral displacement of the diaphragm wall is about 11 mm. The maximum stress of reinforcement is 18.6 MPa, much less than the design value of steel tensile strength. These results and countermeasures are useful for engineers and technicians to select serviceable machine operation parameters and reduce environmental impacts during shield tunneling construction.

The lining of shield tunnel is usually composed of segments, in which the joints, cracks, and the grouting holes (hereafter called lining deficit) exist. During the long-term running, soils and groundwater may leak from these kinds of lining deficit. The leaking of soil and groundwater causes the long-term ground loss around tunnel and thus results in the settlement of ground surface. This paper aims to analyze the impact of the leakage of groundwater through segments on the long-term settlement of ground surface. The adopted analytical method is based on the theory of groundwater seepage by using numerical simulation. The analyzed results show that settlement of ground surface increases gradually with the increase of the leaked volume of tunnel segments. When the leaked volume was unevenly distributed, differential settlement occurred locally. Comparative analysis by changing the leaked volume was conducted. The results reveal that there is a linear relationship between settlement and leaked volume when the leaked volume was controlled within the allowable limit.

Pipe jacking is a microtunneling construction technique that is widely used as a trenchless technology in infrastructure and can be adopted in various geological conditions. Ground responses, such as displacements and soil fracturing, will occur during pipe jacking. In order to reduce disturbance to the surrounding soils, factors resulting in ground responses should be evaluated prior to construction. This article presents a series of laboratory tests to investigate the ground response that is due to shallow buried pipe jacking in sandy soil. Single and parallel pipe-jacked tunnel tests were conducted to simulate different construction conditions. Vertical soil displacements and corresponding jacking forces for various cases were observed and discussed. The results indicate that factors such as the existing pipes, the thickness of overburden soil, and the grouting slurry used have significant effects on the ground responses during pipe jacking. Slurry with a proper ratio is proposed for pipe jacking construction. Soil fracturing and grouting overflow can easily occur in the shallow buried tunnels when slurry injection points are opened at the upper side of the pipe. The jacking parameters should also be controlled within a range to reduce the risk of soil fracture and grouting overflow.

This paper presents a case history of an approach road remediation project on a low embankment over soft Ariake clay, located in the coastal Saga Plain of Japan. After the road had been opened to traffic for two-and-a-half years, large settlements were observed, and there was significant differential settlement between piled structures and approach road embankments on soft clay. This differential settlement had a significant impact on vehicle ride quality, and necessitated a remediation programme. In the remediation project, a new method called the column approach (CA) method was adopted to support a transitional zone at the interfaces of piled structures and road embankment. With the CA method a transitional zone was designed at these interfaces to be supported by soil-cement columns of varying lengths to smooth out the settlement profile within these zones. Field monitoring was conducted following completion of remediation. The CA method was also compared with two other Japanese code-designated methods: overlaying a new pavement on the existing pavement at a certain time interval, and constructing a concrete cushion slab under the road pavement. Both practical and economic aspects are examined in the case study presented. This study shows that, when the differential settlement is over 0·3 m, overlay remediation is not economic, and the approach cushion method does not perform well. The CA method not only reduces the differential settlement effectively, but also reduces the total construction cost, although the initial investment is relatively high.

The Quaternary deposits in coastal regions are multi-aquifer-aquitard system with characteristics of high compressibility, high sensitivity, and low shear strength. The metro tunnels have been widely constructed in coastal regions in recent years. The tunnel settles continuously since the metro tunnel operated. This paper gives a general introduction to influencing factors on the longitudinal deformation of metro tunnel in soft deposit in coastal regions of China: (i) regional land subsidence; (ii) shield tunnel construction; (iii) construction of nearby engineering, such as pit excavation, construction of pile, construction of bypass tunnels, etc; (iv) groundwater leakage; (v) dynamic loading of trains. Influence of land settlement, groundwater leakage and train loading is long-term and influence of tunnel construction and disturbance from the adjacent construction is short-term. Since all of these factors interact with each other, the longitudinal deformation of the tunnel is caused by the comprehensive action of the aforementioned factors.

This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. T...