Shaft Excavation Research Articles

Research and Application of Shaft Excavation by Deep Hole One-Time Blasting Technology

In the construction of subway, tunnel, mining and other underground projects, in order to speed up the construction progress, it is often necessary to excavate a shaft first and then dig at both ends of tunnel at the same time. The shaft excavation is a difficult problem in underground engineering. At present, the shaft excavation construction mainly adopts upward construction method and downward construction method, which are characterized by high labor intensity, high risk coefficient and slow construction speed. In order to realize the efficient excavation of vertical shafts, this paper presents a technology of deep hole one-time blasting into wells. Based on theoretical analysis and practical shaft engineering, the blasting parameters of the deep hole one-time blasting technology are given, such as hole diameter, spacing, layout, charge structure and blasting sequence of each hole, and the technical scheme is formed finally. The technology is applied in a shaft excavation construction in Changping District, Beijing of China and good results are obtained, which proves that the technique is feasible.

Mechanical Behavior of Supporting Structure of Rectangular Deep Ventilation Shaft in Rail Transit

In order to analyze the mechanical behavior of surrounding rock and initial support during shaft excavation and support process, reveal the law of stratum displacement, the stress characteristics of surrounding rock and the internal force of supporting structure during construction, this paper establishes a three-dimensional finite element numerical model relying on the construction process of a ventilation shaft in Chongqing Rail Transit. The results show that the stress of shotcrete, the bending moment of supporting structure, the axial force of bolt and the axial force of I-beam are all within the allowable range. The "S" shape bending occurs in the range of 60m~70m for the axial force of bolt and cross brace I-beam. According to the results of model test, there is inflection point in the pressure distribution of rectangular deep ventilation shaft in rail transit, which provides a basis for the support design of deep ventilation shaft.

Novel Excavation and Construction Method for a Deep Shaft Excavation in Ultrathick Aquifers

Dewatering using the dewatering systems composed of diaphragm walls and pumping wells is commonly adopted for deep excavations that are undertaken in deep aquifers. However, dewatering can sometimes induce environmental problems, especially when diaphragm walls cannot effectively cut off the aquifers. This paper mainly presents an innovative excavation technique combining dewatering excavation and underwater excavation without drainage, which is employed for a deep shaft excavation in ultrathick aquifers (up to 60–70 m thick aquifer) in Fuzhou, China. The shaft excavation with the depth of 41.6 m below the ground surface (BGS) is divided into two major phases, that is, (1) the first part of the excavation (the depth of 23.6 m BGS) is conducted by the way of conventional dewatering and braced excavation (Phase I) and (2) the second excavation with the depth of 23.6 m to 41.6 m BGS is carried out by the novel underwater excavation without drainage technique (Phase II). Field monitoring results show that the ratios of maximum ground surface settlement δvm to the excavation depth He in this case ranged from 0.03% to 0.1%. Most of the ratios of maximum lateral wall deflection δhm to excavation depth He are less than 0.1%. All these results are lesser than that predicted by empirical methods, which also confirmed the applicability of this innovative excavation. Thus, this innovative solution can be applicable to other deep excavations that are undertaken in ultrathick aquifers, especially for the excavation of coarse sediments with high permeability.

Design of initial support required for excavation of underground cavern and shaft from numerical analysis

Excavation of underground cavern and shaft was proposed for the construction of a ventilation facility in an urban area. A shaft connects the street-level air plenum to an underground cavern, which extends down approximately 46 m below the street surface. At the project site, the rock mass was relatively strong and well-defined joint sets were present. A kinematic block stability analysis was first performed to estimate the required reinforcement system. Then a 3-D discontinuum numerical analysis was conducted to evaluate the capacity of the initial support and the overall stability of the required excavation, followed by a 3-D continuum numerical analysis to complement the calculated result. This paper illustrates the application of detailed numerical analyses to the design of the required initial support system for the stability of underground hard rock mining at a relatively shallow depth.

Investigation of Deep Mine Shaft Stability in Alternating Hard and Soft Rock Strata Using Three-Dimensional Numerical Modeling

The problem of shaft instability has always been a major difficulty in deep mining practices. The shaft fracture has a high probability of being located near the aquifers and the soft–hard rock contact zone. This paper describes the deformation and stress characteristics of surrounding rock and the shaft lining under the interactive geological conditions under soft and hard rock strata in Anju coal mine, Shandong Province, China. Using the Method of Geological Strength Index (GSI ) and considering the rock-softening characteristics of water, the parameters of rock mass are calibrated. By means of the 3DEC-trigon method, the variation characteristics of surrounding rock and the shaft lining are simulated. After shaft excavation, under the condition of no support, shear failure and tensile failure occur in shallow surrounding rock shafts, and a pressure relief zone is formed. Shear failure is the main destruction mode in deep surrounding rock. Because of the different strengths of the surrounding rock, the deformation of the surrounding rock is significantly different. After the surrounding rock is softened by water absorption, the difference is magnified. The maximum shear stress and plastic zone appear near the interface between soft and hard rock. Under the condition of shaft lining support, uneven deformation of surrounding rock surely leads to nonlinear variation of pressure on the shaft lining. Under the action of an inhomogeneous pressure field, partial shear failure occurs in the shaft lining, and the shear failure area increases after the surrounding rock is softened by water. Because of the nonlinear deformation of the shaft lining, it is easy to produce stress concentration and bending moment near the interface between hard and soft strata. The control methods of advance grouting and pressure relief excavation are proposed to improve the stability of the shaft, and a good effect is gained.

Case studies of circular shaft construction in London

At present, there are few well-documented case studies of circular shaft construction, making it difficult for designers to estimate reliable ground movements arising from such construction. This paper describes field observations of ground surface settlement assembled during the construction of 27 circular shafts built for three major tunnelling projects in London: Crossrail, National Grid's London Power Tunnels project and Transport for London's Northern line extension. Two categories of shaft construction were identified: support before excavation (SBE) and excavation before support (EBS). For the SBE category, the shaft was first supported by pre-installed walls followed by excavation of the soil between the pre-installed walls. For the EBS category, the ground was progressively excavated in sections followed by construction of the shaft lining. Interpretation of the field observations showed the importance of the shaft construction method on ground movements. Settlements were much more significant for EBS shaft construction than for SBE shaft excavation, although settlement arising from the installation of pre-installed walls or dewatering operations should not be overlooked. Normalised charts are presented to help the industry make estimates of settlements due to circular shaft construction in London, with due consideration for different shaft geometries and construction methods.

Fracture characterization using hydrogeological approaches and measures taken for groundwater inrush mitigation in shaft excavation

Plentiful groundwater in fractured rock masses adjacent to a construction site of a shaft in a highway tunnel project has been notified, which might cause groundwater inrush during its excavation. Hydrogeological approaches were used before the construction of the shaft to investigate the hydraulic features of the site, and thus to characterize the site and propose corresponding measures for groundwater inrush mitigation. This study further determines the fractures and the Q-values of rock masses in the bare walls following excavation of the study shaft, and the hydraulic conductivity of surrounding rocks, based on the measured variations of groundwater level and pressure in four observational wells around the shaft, to check the predicted results using the hydrogeological approaches and conventional Q-logging. The applicability of the proposed mitigation measures to groundwater inrush is also assessed. The results of comparisons indicate that the spatial distributions of three preferential flow paths that were predicted using hydrogeological approaches based on fractures in rocks are consistent with those revealed after excavation of the shaft. The depths at which groundwater inflow is high and the direction of the source of the groundwater can be predicted more precisely from hydrogeological approaches than using Q-values. Mitigation of groundwater inrush involves a grouted curtain that is applied to the regolith stratum from the surface, grouting for sealing that is carried out in the shaft, and aspirating pumps within the shaft and by pumping wells around the shaft. These methods effectively reduce the impact of groundwater on shaft construction. However, the aspirating pump takes time to control the water level inside the shaft. Hydrogeological approaches predicted the hydraulic conductivity of regolith and fractured rock masses nearby the study shaft over four orders of magnitudes, yielding results that are consistent with those obtained by excavation of the shaft, also confirming their reliability in elucidating the hydrogeological characteristics and groundwater inrush potential at a shaft site in a fractured rock mass.

Development of new empirical models for performance estimation of a raise boring machine

Raise boring machines (RBMs) are used for drilling/excavation of shafts and other inclined structures in mining and construction fields. Proper selection and accurate performance estimation of RBMs are two main parameters that affect the cost estimation and planning of the mining and construction projects. This paper aimed to suggest new empirical models for estimation of performance and operational parameters of RBMs in reaming operation by using simple (linear and non-linear) and multiple (linear and non-linear) regression methods. Balya lead-zinc underground mine was visited to investigate excavation of the ventilation shaft with a RBM. Length and diameter of the excavated ventilation shaft are 331.36 m and 2.44 m, respectively. Core samples obtained from the closest borehole to the fifth ventilation shaft in Balya lead-zinc underground mine were tested for defining some of the basic physical-mechanical properties. In addition, operational and performance parameters of the RBM were recorded/calculated during field studies. The results of field and laboratory studies were used in a statistical analysis to develop new empirical models for estimation of performance and operational parameters of the RBM. The results indicated that the uniaxial compressive strength might be used for estimation of rotational speed and consumed reamerhead torque. Moreover, Brazilian tensile strength with static elasticity modulus could be good estimators for field specific energy. However, accuracy and reliability of the proposed models should be improved by additional rock types and RBMs with different sizes and capacities.

The influence of temperature and moisture content on sandstone thermal conductivity from a case using the artificial ground freezing(AGF) method

The thermal conductivity (TC) of rocks is influenced by a number of environmental factors including temperature, moisture content, and pressure. A series of experiments are presented in this work to address the influence of temperature both sides of the freezing point 0 °C as well as moisture content on sandstone TC values. All of the specimens discussed were collected from a coal mine shaft excavation using the artificial ground freezing (AGF) method. Thus, TC values of 32 pairs of medium grained sandstone and 21 pairs of coarse grained sandstone specimens were measured at temperatures ranging between −30 °C and 50 °C. The results show that TC values tend to increase as temperature decreases regardless of whether specimens are dry or water-saturated. It is also the case, however, that water-saturated specimens commonly have higher TC values than their dried counterparts at different target temperatures, especially at the range of between 5 °C and − 10 °C, while TC values of water-saturated specimens exhibited rapid increases. This phenomena also shows a good agreement with the deflection zone presented in Raman spectral peak values, clear evidence for the water-ice phase transition period.

Cutting parameter optimization for one-step shaft excavation technique based on parallel cutting method

Abstract The outcome of the cutting blasting in a one-step shaft excavation is heavily related to the cutting parameters used for parallel cutting method. In this study, the relationships between the cutting parameters (such as the hole spacing L and the empty hole diameter D) and damage zones were investigated by numerical simulation. A damage state index γ was introduced and used to characterize the crushing and crack damage zones through a user-defined subroutine. Two indices, i.e., η1 and η2 that can reflect the cutting performance, were also introduced. The simulation results indicate that an optimal value of L can be obtained so that the η1 and η2 can reach their optimal states for the best cutting performance. A larger D results in better cutting performance when the L value maintains its best. In addition, the influences of the loading rate and the in-situ stress on the cutting performance were investigated. It is found that an explosive with a high loading rate is suit for cutting blasting. The propagation direction and the length of the tensile cracks are affected by the direction and the magnitude of the maximum principal stress.

Geotechnical characterization of the Miocene formations at the location of Ivens shaft, Lisbon

The design of complex underground structures in an urban environment requires in the first instance an appropriate characterization and interpretation of the ground conditions and of the mechanical behaviour of soil formations in the ground profile. With such information it is then possible to select and calibrate appropriate soil constitutive models for application in advanced numerical analysis, with the objective of predicting the induced ground movements and the potential damage to existing structures and services. This paper provides an interpretation of the site investigation data collected for the numerical analysis and design of the Ivens shaft excavation in Lisbon, Portugal. For the first time a comprehensive set of interpreted data is obtained for two of the main formations in the Lisbon area, Argilas e Calcários dos Prazeres (AP) and Areolas da Estefânia (AE), improving the understanding of their mechanical behaviour and making the data available for application in most soil constitutive frameworks. It is evident from the results that even with careful testing procedures the data may appear to be inconsistent, requiring further assumptions when deriving soil parameters. Such assumptions are discussed and emphasis is placed on the need to combine data from laboratory and field investigations.

Lake Mead Intake No. 3

Abstract As a result of a sustained drought in the Southwestern United States, and in order to maintain existing water capacity in the Las Vegas Valley, the Southern Nevada Water Authority constructed a new deep-water intake (Intake No. 3) located in Lake Mead. The project included a 185 m deep shaft, 4.7 km tunnel under very difficult geological conditions, and marine works for a submerged intake. This paper presents the experience that was gained during the design and construction and the innovative solutions that were developed to handle the difficult conditions that were encountered during tunneling with a dual-mode slurry tunnel-boring machine (TBM) in up to 15 bar (1 bar = 105 Pa) pressure. Specific attention is given to the main challenges that were overcome during the TBM excavation, which included the mode of operation, face support pressures, pre-excavation grouting, and maintenance; to the construction of the intake, which involved deep underwater shaft excavation with blasting using shaped charges; to the construction of the innovative over 1200 t concrete-and-steel intake structure; to the placement of the intake structure in the underwater shaft; and to the docking and connection to an intake tunnel excavated by hybrid TBM.

Closed-form elastic solution for irregular frozen wall of inclined shaft considering the interaction with ground

An analytical solution is derived that provides a closed-form formulation for stresses and displacements of a deep inclined shaft with irregular frozen wall liner in an infinite elastic medium, subjected to a non-uniform stresses. This solution is based on: (i) the conformal mapping of a doubly connected domain of prescribed shape onto a circular ring by an appropriate numerical optimization scheme which is achieved by MATLAB program, (j) the complex variable method. For a particular case, the distributions of hoop stress and radial displacement inside frozen wall are presented with analytical solution. The accuracy of stress functions is verified by comparison of different number of coefficients in stress functions and it show that the number of coefficients k≥15 is advised. The validity of analytical solution is verified by a comparison between its result and that obtained from the finite element program ANSYS. Noting that the shaft excavation can be regarded as relaxation of initial ground stresses around shaft excavation boundary, this paper presents the mechanical problem as two separate problems: (i) initial stresses and displacements model where stresses keep constant and displacements equal zero around frozen wall and ground, (j) stresses relaxation model with relaxed normal and shear stresses acted on excavated boundary. The solution is worked out by the principle of superposition in elastic medium. The Young's modulus ratio (β) of the frozen wall to the ground reflects the influence of ground to frozen wall, and the influence decreases with the growth of β. The proposed solution can provide analytical basis for frozen wall design and be used as a quick-solver for back-analysis of in situ stresses and displacements.

A study of Triaxial creep test and yield criterion of artificial frozen soil under unloading stress paths

The triaxial shear test method with consolidation, low temperature freezing, and radial unloading was applied to simulate the mechanics process of the unloading process of deep artificial frozen clay during the excavation of a freezing mine shaft. The triaxial unloading creep test on artificial frozen clay showed that the first and second stages of the creep deformation occur only when the deviatoric stress is low and that creep deformation accounts for >70% of the total deformation. The third stage of creep deformation occurs only when the stress level exceeds a certain critical value, and is characterized by the frozen soil undergoing a large plastic flow, with breaking for 3 to 5h. The creep strength envelope at low confining pressure is linear, in compliance with the Mohr-Coulomb strength criterion, and the critical stress value in the third stage can be described with the improved Zienkiewicz-Pande parabolic yield criterion.

Fracture Characterization and Rock Mass Damage Induced by Different Excavation Methods in the Horonobe URL of Japan

We conducted detailed fracture mapping of the soft sedimentary rocks (uniaxial compressive strength of 10–20 MPa) in shaft walls at the Horonobe Underground Research Laboratory to characterize fractures and to understand the influence of different excavation methods on rock mass damage. The mapping indicates that the fractures are numerous and can be divided into shear fractures and extension fractures. On the basis of orientation and frequency, the shear fractures are inferred to be pre-existing fractures, and the extension fractures are considered to be newly formed fractures (EDZ fractures) induced by the shaft excavation. The frequencies of pre-existing and newly formed fractures have a negative correlation, and we infer that stress relief leads to the formation of excavation damaged zone by the generation of the newly formed fractures in the parts of shaft that have intact rock, and by the reactivation of pre-existing fractures where such fractures are numerous. Although more newly formed fractures are formed by blasting excavation than by mechanical excavation, there is little difference in the comparative excavation rates. These results indicate that rock mass damage is caused by the mode of excavation rather than excavation rate. Therefore, the mechanical excavation is preferred to blasting excavation from the viewpoint of minimizing rock mass damage.

Challenges of shaft excavation in Nepal Himalaya: case study from hydropower projects

The excavation of the long blind shaft is one of the most difficult and risky in Nepal Himalaya for hydropower development. Excavation of the shaft greater than 200 m length is a challenge due to vertical or inclined orientation, limited space, available technology and changing geological conditions. Amongst Alimak raise climber, shaft sinking and raise boring excavation methods, Alimak raise climber is most commonly used in Nepal. Selection of excavation method depends on geological conditions, size, length of shaft, access and of course the cost. Pressure shaft of Jhimruk, Khimti I, Chilime, Kaligandagi, Kulekhani, Khani Khola, Upper Tamakoshi and other hydroelectric projects were excavated with the help of conventional Alimak raise climber method. Severe overbreak problems were faced in Khimti I hydropower project during construction of upper inclined pressure shaft whereas recently 214 m vertical pressure shaft of Upper Tamakoshi and 280 m vertical pressure shaft of Khani Khola hydroelectric projects in Dolakha have been constructed successfully. Raise boring method was tried in Upper Tamakoshi Project but could not succeed due to deviation of pilot hole and hence shaft sinking and Alimak raise climber were used.

Considerations for monitoring of deep circular excavations

Understanding the magnitude and distribution of ground movements associated with deep shaft construction is a key factor in designing efficient damage prevention/mitigation measures. Therefore, a large-scale monitoring scheme was implemented at Thames Water's 68 m deep Abbey Mills Shaft F in East London, UK, constructed as part of the Lee Tunnel Project. The scheme comprised inclinometers and extensometers which were installed in the diaphragm walls and in boreholes around the shaft to measure deflections and ground movements. However, interpreting the measurements from inclinometers can be a challenging task, as it is often not feasible to extend the boreholes into ground unaffected by movements. The paper describes in detail how the data are corrected. The corrected data showed very small wall deflections of less than 4 mm at the final shaft excavation depth. Similarly, very small ground movements were measured around the shaft. Empirical ground settlement prediction methods derived from different shaft construction methods significantly overestimate settlements for a diaphragm wall shaft. The results of this study will help to inform future projects, such as the forthcoming 25 km long Thames Tideway Tunnel with its 18 deep shafts being constructed adjacent to existing infrastructure.

Why Excavation of a Small Air Shaft Caused Excessively Large Displacements: Forensic Investigation

AbstractAny deficiency in excavation design or construction could lead to excessively large retaining wall and ground displacements, usually accompanied by damage to adjacent structures or facilities. This paper documents a case history of a small air shaft excavation in Shanghai soft clay. Its maximum lateral wall displacement and ground settlement were twice and three times the local deformation control criteria and 3 and 14 times those of one adjacent air shaft excavation featuring similar subsurface conditions, geometric size, and supporting system. To identify probable causes pertaining to its poor performance, a comprehensive investigation was carried out in both design (propping element, supporting system stiffness, wall penetration ratio, and jet grouting of basal soils) and construction (excavation duration, excavation width, exposed wall length, and management of heavy-duty truck and stockpile of construction materials). The investigations show that there were several major contributory factors,...

San Pasquale Station of Line 6 in Naples: Measurements and Numerical Analyses

The paper reports some geotechnical aspects of the design and construction of the San Pasquale Station, intermediate along Line 6 and located close to the sea and at the same time within one of the most fascinating district of the city known as Chiaia borough. The station required an excavation deeper than 25 m, almost entirely located in pyroclastic sand below the groundwater table. The main shaft is 85.5 m long and 24.1 m large, containing also the whole length of the pedestrian platform while a single large section tunnel, built before the excavation of the station shaft, accommodates the two operating rail tracks. In the paper monitoring data will be presented and discussed. Settlements and horizontal displacements represent certainly very significant outcomes among the observed data. Their variations along with time and main construction steps are first of all presented in the paper. The monitoring data have also been submitted to a process of careful interpretation based on the use of numerical analyses to better understand the interaction of deep excavation with urban area. The FEM code Plaxis has been adopted for such a purpose adopting advanced constitutive soil models which are available in the code library.

Response of a drilled shaft foundation constructed in a redrilled shaft excavation following collapse

Two drilled shaft foundations (DSFs) of equal size (1.2 m diameter) were installed at the Turrell Arkansas Test Site (TATS). The soil stratigraphy at the TATS consisted of 6.1 m of clay underlain by 3.0 m of silt underlain by sand. After drilling the excavation for the North 1.2 m DSF, the silty soil collapsed from the sidewall of the excavation into the bottom of the excavation. Following the collapse, the excavation was redrilled and the construction of the DSF was completed. The measured capacity, unit side resistance, and end bearing resistance of the South 1.2 m diameter DSF were predicted by using software programs and mean values of soil data. The measured response of the North 1.2 m diameter DSF was backward modeled to determine the appropriate strength and stress reduction. Based on the measured data for this site, a 10 percent reduction in unit weight within the silt layer and a modification of the soil properties within the top 3.0 m of the sand layer produced predicted responses that matched t...