Adjacent Excavation Research Articles

Prediction of the tunnel displacement induced by laterally adjacent excavations using multivariate adaptive regression splines

Excavations may cause excessive ground movements, resulting in potential damage to laterally adjacent tunnels. The aim of this investigation is to present a simple assessment technique using a multivariate adaptive regression splines (MARS) model, which can map the nonlinear interactions between the influencing factors and the maximum horizontal deformation of tunnels. A high-quality case history in Tianjin, China, is presented to illustrate the effect of excavation on the tunnel deformation and to validate the FEM. The hypothetical data produced by the FEM provide a basis for developing the proposed MARS model. Based on the proposed model, the independent and coupled effects of the input variables (i.e. the normalized buried depth of tunnels Ht/He, the normalized horizontal distance between tunnels and retaining structures Lt/He, and the maximum horizontal displacement of retaining structures, δRmax) on the tunnel response are analysed. The prediction precision and accuracy of the MARS model are validated via the artificial data and the collected case histories.

Hybrid Method for Predicting the Response of a Pile-Raft Foundation to Adjacent Braced Excavation

AbstractWith the increasing development of underground spaces in cities, a critical indicator for the design of excavation in urban areas is controlling the damage potential of adjacent buildings. ...

Collapse of a high-rise building with pretensioned high-strength concrete piles

On 27 June 2009, a 13-storey building founded on pretensioned spun high-strength concrete piles suddenly collapsed in Shanghai, China. Prior to the collapse, an underground garage was excavated to the south of the building while excavated soil was dumped to its north side and formed a 10 m high fill slope. A comprehensive field investigation was carried out to collect physical evidence relating to the sudden collapse, particularly damage to building piles. The ultimate bending moment and shear capacities of this type of pile were determined through a series of full-scale tests to assist in evaluating failure patterns. Likely factors that could have influenced the collapse – namely, geotechnical pile failure, adjacent excavation and excessive surcharge – were tested by carrying out calculations, three-dimensional centrifuge tests and finite-element analysis. This paper reports on the forensic investigation process, the findings of the investigation and the most likely collapse mechanism. Lessons learned from the accident and recommendations to avoid a similar collapse in the future are also presented.

Dynamic response of rock-soil dam to blasting-induced vibration with different distances

In order to assess the dynamic performance of a rock-soil damn Zhejiang, Eastern China and suggest a proper blasting scheme for the adjacent tunnel excavation, a three-dimensional finite difference model was established, and dynamic simulation analyses were carried out. Results show that close blasting will have severe impact on the stability of the dam. The different part of the dam has different response to the blasting shock. The velocity response at the side close to the blasting is far larger than that of the other side. Local damage may occur in the dam body near the blasting point. The vibration amplitude of the dam due to the blasting decreases with the distance of blasting point to the dam. The peak vibration velocity reduces to less than 0.4 cm/s and the maximum permanent displacement of the dam decreases to no more than 0.1cm when the distance between the blasting point and the dam reaches to 180m. It indicates that the blasting at this distance has little influence on the stability of the dam. So, a safe blasting distance of 180m is suggested in the project.

Experimental Study on the Transverse Effective Bending Rigidity of Segmental Lining Structures

The transverse effective rigidity ratio is a key parameter when the uniform rigidity ring model is adopted to design or numerically analyse segmental lining structures commonly used on a shield‐driven tunnel. Traditionally, the transverse effective rigidity ratio η is treated as a constant, which can be evaluated through theoretical analysis and model tests. In this study, scale models were designed and tested to investigate the variation of the transverse effective rigidity ratio in the segmental linings’ flattening deformation process. The test results suggested that in the elastic stage, the transverse effective rigidity ratio fluctuated between 0.667 and 0.734 for the stagger‐jointed rings and fluctuated between 0.503 and 0.642 for the straight‐jointed rings. When segmental linings were squashed and started to crack at the circumferential joints, the transverse effective rigidity ratio decreases sharply. Then, a regression equation was obtained to fit the variation trend of η with the increase of horizontal convergence to the outer‐diameter ratio (ΔD/Dout). Finally, in a case study, the regression equation was adapted to determine the value of η of an operated shield tunnel which was once surcharged accidentally and deformed severely so as to numerically predict the prospective deformation induced by the upcoming adjacent excavation. Numerical results indicated that as the value of η decreases, the horizontal convergences of shield tunnel induced by adjacent excavation increase significantly and even more than doubled in the case study. Comparatively, through taking account of the operating tunnels’ exiting transverse deformation, the predicted deformation tends to be unfavourable.

Parameter Study of Track Deformation Analysis by Adjacent Excavation Work on Urban Transit

Parameter Study of Track Deformation Analysis by Adjacent Excavation Work on Urban Transit

Research on Influnence Law of Existing pipe-jacking Tunnel affected by Adjacent Foundation Pit Excavation in Soft Clay Stratum

The problem that existing pipe-jacking tunnel was disturbed by adjacent foundation pit excavation had arose relative researcher’s attention, especially in soft clay stratum. Firstly, by means of numerical simulation, the deformation of diaphragm wall and settlement law of soil outside the pit during foundation pit construction were analyzed. Then deformation and stress characteristics of existing pipe-jacking tunnels were studied influenced by different spacing between foundation pit and pipe-jacking, different excavation depth of foundation pit and different buried depth of pipe-jacking. The main conclusions were as follows. (1) The maximum horizontal displacement of the diaphragm wall was located at 3/4 of the excavation depth of pit. (2) Due to the blocking or isolation effect of existing rigid pipe-jacking on the deformation of surrounding soil, the surface settlement became smaller.(3) Deformation, structural stress of pipe-jacking would gradually decreased under the conditions of increase of the spacing between foundation pit and pipe-jacking, decrease of excavation depth of pit and buried depth of pipe-jacking, (4) Due to the influence of pit excavation, deformation and stress of pipe-jacking near the end wall and middle of the foundation pit were relatively large. (5) When the buried depth of pipe-jacking was located at near 3/4 of excavation depth of pit and the spacing was less than 10m, excavation of the pit has a great impact on the existing pipe-jacking tunnel.

Long-term performance of metro tunnels induced by adjacent large deep excavation and protective measures in Nanjing silty clay

This paper presents the construction of a large-scale basement excavation adjacent to the two running metro tunnels in Nanjing silty clay. To investigate the influences of excavation on existing tunnels, a numerical modelling was carried out to predict the possible deformation of tunnels before construction. Then, referring to the obtained numerical results, a targeted monitoring program was proposed and comprehensive field monitoring was performed to monitor the deep excavation and tunnels response over four years. The monitoring items include the diaphragm wall lateral deflection, the tunnel crown settlement, the springline horizontal displacement, the diameter convergence and the opening width of the segment joint. Based on monitoring results, the evolution of tunnels deformation was analysed, and the safety of tunnel structures was evaluated. According to the evaluation results, micro-disturbance grouting was proposed and adopted to correct the deformed tunnel, and the treatment effectiveness was evaluated. The results indicate that the evolution of tunnel crown settlement, springline horizontal displacement and diameter convergence can be divided into slow growth, rapid growth and stable growth stages, and they correspond to the pre-excavation, main excavation and post-excavation stages of deep excavation respectively. Based on the simple beam principle, the settlement range of tunnel can be taken two times the distance between the monitoring section with the maximum settlement and the section with the settlement of 0. In the process of micro-disturbance grouting treatment, the deformed tunnel goes through a correction stage and a rebound stage respectively, and the additional deformation induced by adjacent excavation is well corrected by micro-disturbance grouting.

The failure mechanism of surrounding rock around an existing shield tunnel induced by an adjacent excavation

Foundation pit excavation may disturb the initial stress field and induce the deformation of the surrounding rock mass. Due to the excavation, the originally compact rock mass and lining structure may become loose with adverse impacts on the normal operation of the existing tunnel. A new failure mechanism is constructed on the basis of the deformation characteristics of the rock mass around an existing tunnel induced by an adjacent excavation. Using this failure mechanism, the upper bound solution of the slip surface equation for the rock mass around an existing tunnel is derived in the framework of the upper bound theorem in conjunction with a variational approach. The shape and range of the slip surface are plotted for different parameters. A three-dimensional numerical model is constructed to simulate the deformation of the rock mass around the existing tunnel induced by adjacent excavation. By comparing the analytical results for the slip surface with the failure surface provided by numerical simulation, it is found that the differences between the analytical results and the numerical results are small. This comparison shows that the proposed method is valid for investigating the deformation of the rock mass around the existing tunnel induced by adjacent excavation.

Stress transfer mechanisms and settlement of a floating pile due to adjacent multi-propped deep excavation in dry sand

Three-dimensional numerical parametric study is conducted to investigate stress transfer mechanisms and settlement of a floating pile due to multi-propped basement excavation by using hypoplastic sand model. Centrifuge test results are adopted to validate the soil model and model parameters. Effects of excavation depth, pile location with respect to basement, working load, sand density and support system stiffness are examined. Downward and upward load transfer mechanisms are observed at different excavation stages, depending on the ratio of excavation depth (He) to pile length (Lp). If excavation-induced reduction of shaft and base resistances are ignored, the pile settlement is underestimated by up to 39%. Negligible pile head settlements are observed when the pile is located at a distance exceeding 2.5 He (excavation depth) from the retaining wall. Basement excavation-induced pile settlement is doubled when the designed factor of safety of pile before excavation reduces from 3.0 to 1.5. By increasing the relative sand density 30–90%, the pile settlement decreases by up to 66%. Excavation-induced pile head settlement is almost insensitive to support system stiffness for shallow excavation (He/Lp < 0.4).

Numerical modelling of effects of different multipropped excavation depths on adjacent single piles: comparison between floating and end-bearing pile responses

Owing to a shortage of land, high-rise buildings are increasingly preferred to meet the development and economic growth of major cities in the world. The construction of high-rise buildings often requires deep foundations such as single piles or pile groups when the underlying soil and rock strata do not have sufficient bearing capacity. On the other hand, underground basements are constructed to facilitate inhabitants in the buildings for parking. Development of underground transportation systems consist of tunnels, excavations for basement construction and cut and cover tunnels. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This research presents three-dimensional coupled consolidation analyses (using clay hypoplastic constitutive model that takes account of small-strain stiffness) to investigate the responses of a floating and an end-bearing pile due to adjacent excavation at different depths in clay. It was revealed that the maximum induced bending moment in both types of piles after completion of excavation in all the cases is much less than the pile bending moment capacity (i.e. 800 kNm). Moreover, the end-bearing piles were subjected to significant dragload due to negative skin friction. In contrast, no significant changes in load distribution along floating piles were computed.

Predicting settlement along railway due to excavation using empirical method and neural networks

More and more excavation projects are being performed near existing buildings and structures due to large-scale urban construction, in which the excavation unavoidably causes settlement and potential danger to the surrounding construction and buildings. For linear traffic facilities parallel to the excavation, the settlement profile parallel to the excavation, namely, the settlement along the traffic line, should also be considered. Moreover, the precise control of the differential settlement along the traffic lines also plays a very important role. Thus, it is necessary to establish a quick prediction model, which is able to consider both vertical and parallel settlement profiles, using the basic information on the excavation. Based on the large amount of field data, the characteristics of the settlement profiles are analyzed. A simplified empirical method is proposed; it is established based on the Rayleigh and Gauss distribution functions for predicting the ground settlement along railways induced by an excavation. Meanwhile, back-propagation neural networks are also used to predict the settlement behavior. A comparison between the predicted results and the monitoring data is given to verify the feasibility of the proposed method. A good agreement indicates that the proposed method can be employed to predict the settlement along railways due to an adjacent excavation.

Effect of Soil Reinforcement on Tunnel Deformation as a Result of Stress Relief

Adjacent geotechnical engineering activities, such as deep excavation, may adversely affect or even damage adjacent tunnels. Ground reinforcement before excavation may be an effective approach to reduce tunnel heave as a result of stress relief. However, there are few quantitative studies on the effect of soil reinforcement on tunnel deformation. Moreover, the reinforcement mechanism of the reinforced soil and the reinforcement depth are not fully understood. In order to investigate the effect of reinforcing the ground on the tunnel response, a finite element analysis was conducted based on a previously reported centrifugal model test with no ground reinforcement. The effect of the Young’s modulus and depth of the reinforced soil on tunnel deformation was analyzed. Soil stresses around the tunnel were also considered to explain the tunnel response. The results revealed that the Young’s modulus of the reinforced soil and the reinforcement depth had a significant impact on tunnel deformation as a result of basement excavation. The tunnel heave in the longitudinal direction decreased by 18% and 27% for modulus of the reinforced soil, five times and ten times higher than that of the non-reinforced soil, respectively. The reinforcement depth was effective with regard to controlling the tunnel heave caused by stress relief. This is because the reinforced soil blocked the stress transfer and thus reduced the tunnel heave caused by excavation unloading. It is expected that this study will be useful with regard to taking effective measures and ensuring the safety and serviceability of existing metro tunnels during adjacent excavation.

The Responses of an End-Bearing Pile to Adjacent Multipropped Excavation: 3D Numerical Modelling

It is well recognised that superstructure load is transferred to surrounding soil through piled foundation. Consequently, the high stress regime (stress bulb) is generated surrounding of the pile. On the other hand, the excavation in the ground inevitably results in the ground movement due to induced-stress release. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This condition leads to a big challenge for engineers to assess and protect the integrity of piled foundation. This research presents three-dimensional coupled consolidation analyses (using clay hypoplastic constitutive model which takes account of small-strain stiffness) to investigate the responses of an end-bearing pile due to adjacent excavation at different depths in soft clay. The effects of excavation depths (i.e., formation level) relative to pile were investigated by simulating the excavation near the pile shaft (i.e., case S) and next to (case T). It was revealed that the maximum induced bending moment in the pile after completion of excavation in all the cases is much less than the pile bending moment capacity (i.e. 800 kNm). Comparing the induced deflection of the end-bearing pile in the case T, the pile deflection in case S is higher. Moreover the piles in cases of S and T were subjected to significant dragload due to negative skin friction.

Serving valid notices: Not as simple as it first appears

Serving valid notices is the essential first step in progressing a request to exercise rights granted by the Party Wall etc. Act 1996. It is an entirely sound assumption that if an initial party wall notice is invalid, then any resultant associated award served must also be invalid and any works progressed by way of that award could be found to be unlawful. Serving notices is often perceived as an inconvenient and generic exercise to which only limited attention and time is afforded. In these overly litigious times, a review of the common pitfalls and misconceptions related to the serving of party wall notices is essential. When considering ‘serving valid notices’, it is necessary to consider both the means of creating valid notices and the means by which such valid notices are served. The following key areas of party wall practice and associated case law are therefore explored in this paper: the sections of the Act which prescribe service requirements; types of notices — Line of Junction, Section 2, Adjacent Excavation and all other lesser used notices and how to ensure they are validly drafted; ensuring notices are served on the correct person and/or legal entity; validly noting owner details. Key findings are: a detailed description of proposed notifiable works is essential; the service provisions of Sections 15(1) and 15(2) must be taken in their literal sense; notices served on a ‘body corporate’ must be served on the ‘Secretary or Clerk’; Section 1 notices must accurately describe the intended wall and differentiate between Section 1(2) and 1(5) rights; Section 6 notices must include detailed drawings and elevations and full details of any strengthening or safeguarding works if proposed; notices must always list all owners in full; always record proof of service; building owners must be asked if it is intended to change the building owner entity; Section 12(1) notice must be served before any associated notifiable works commence.

Numerical Simulation of Impact Caused by Construction of High-Rise Building upon Adjacent Tunnels

In this study, stress deformation of Qingdao Jiaozhou Bay undersea tunnel terminal during high-rise building construction engineering was evaluated by real 3D numerical modeling using Midas software. The simulations were performed during high-rise building foundation pit blocks, stratified excavation unloading, and loading the whole building construction on adjacent existing tunnel. The influence of the whole process through tunnel convergence, tunnel vertical displacement and horizontal displacement, as well as deformation curvature changes of additional stress and lining were used to evaluate the tunnel safety. The results showed that excavation at depth of 6 m, the whole process of high-rise building construction on adjacent tunnel deformation was conform to requirements of control. As building load deformation reduced near tunnel ceiling, one side of foundation pit became bigger and far away from side of foundation pit but did not return to front of foundation pit excavation tunnel state. The construction load of adjacent tunnel excavation generated small additional stress with overall design no more than tunnel load values. Overall, the tunnel was in safe working conditions and the proposed research provide certain guidance and reference for similar projects.

Evaluation of lateral response of single piles to adjacent excavation using data from cone penetration tests

Excavation inevitably induces stress changes in the surrounding soil, which causes significant lateral movements, additional forces, and bending moments in the existing pile foundations. To prevent or minimize damage to adjacent piles, this paper presents an actual full-scale instrumented study to examine the lateral response of existing piles to an adjacent test pit excavation. Cone penetration tests (CPTs) near the test piles before and after excavation are conducted and compared. A simple p–y evolution model for lateral piles during excavation is proposed. The proposed model is defined by the pre-excavation and post-excavation p–y curves from CPT data, which can provide better predictions by comparison with the field measured results. Additionally, for analysis of the pile behaviour after excavation, the observed lateral bearing capacity of full-scale tests are compared with those computed by the pre-excavation and post-excavation p–y curves. The post-excavation p–y curve can generally give a satisfactory prediction of the residual pile bearing capacity after excavation. The calculated results from the free-field cone parameters have a serious overestimation and are detrimental to the service design of pile foundations.

A discussion of “a simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations” by Zheng et al. (2018)

In this short paper, the semi-empirical model introduced by Zheng et al. (2018) for evaluating the tunnel displacements induced by adjacent excavation was extended to a probabilistic model. To this end, the input parameters of the problem were defined as random variables with certain means and standard deviations. A reliability model was then established and solved by the Monte Carlo method. The results showed that the probability of exceedance fell sharply by increasing the tunnel displacement so that the probability of tunnel displacement of larger than 41 mm was less than 5%. Moreover, the reliability sensitivity analysis showed that the excavation depth and tunnel burial depth mostly affected the small range of tunnel displacements between 0.5 and 10 mm. However, the maximum impact of the retaining structure displacement and the horizontal distance of the tunnel from the excavation site were found to fall in medium and large (0.5 to larger than 21 mm) ranges of tunnel displacement. Having the exceedance probability curve presented in this paper, the exceedance probability for any desired value of the tunnel displacement is available, which can be used for safety evaluation and risk assessment of existing tunnels close to the surface excavations.

3D finite element analysis of pile responses to adjacent excavation in soft clay: Effects of different excavation depths systems relative to a floating pile

To gain new insights into single pile responses to adjacent excavations in soft ground, three dimensional numerical parametric studies are carried out. An advanced hypoplastic (clay) constitutive model which takes account of small-strain stiffness is adopted. The effects of excavation depths (He) relative to pile (Lp) were investigated by simulating the excavation near the pile shaft (i.e., He/Lp = 0.67), next to (He/Lp = 1.00) and below the pile toe (He/Lp = 1.33). In addition, the effect of pile head boundary conditions and different working loads with FOS = 3.0 and 1.5 were also studied. The model parameters are calibrated and validated against measured results in centrifuge reported in literature. It is found that the pile responses to excavation depend upon formation level of the excavation as well as the embedded depth of the wall. With different wall depth in each case, the induced settlement, lateral displacement and bending moment in the pile at the same stage of the excavation was different in the three cases. Among the three cases, the excavation in case of He/Lp = 1.33 resulted in the largest pile settlement (i.e., 7.6% pile diameter). On the other hand, the largest pile deflection was induced in case of He/Lp = 0.67. On contrary, insignificant bending moment and changes in axial load distribution induced in the pile on completion of the excavation in each case. However, significant bending moment (60% of pile BM capacity of 800 kNm) induced in the pile with fixed head condition. The different working loads (with FOS = 3.0 and 1.5) influence induced pile settlement but have relatively minor effect on induced bending moment.

Reply to the discussion on “A simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations” by Far et al.

Reply to the discussion on “A simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations” by Far et al.