Excavation Walls Research Articles

Design of Initial Shotcrete Lining for a Mine Shaft Using Two-Dimensional Finite Element Models Considering Excavation Advance Rate

Shotcrete is widely used as a temporary support element in the construction of underground mine excavations, tunnels, and shafts. It is sprayed on the excavation walls to provide safe working conditions for mine personnel and equipment until the permanent support is installed. Therefore, the ability of the shotcrete liner to resists falls of ground is of paramount importance. In this paper, a two-dimensional finite element program is used to simulate a three-dimensional excavation advance and a shotcrete liner that is used as temporary support in a mine shaft. The mechanical properties of the shotcrete are determined based on existing empirical equations by considering the shaft advance rate. The study uses three methods to analyze the stability of the initial shotcrete liner. The first method pertains to the calculation of the load factor of safety based on the convergence confinement method. In the second method, the shotcrete liner is simulated using a structural element with elastic properties, and its stability is analyzed using support capacity diagrams. In the third method, a material model is used to explicitly simulate the shotcrete liner with elastic perfectly-plastic material behavior. This method allows for capturing the progressive yielding of the shotcrete liner during the excavation advance. The results of numerical simulations are then used to calculate a strain factor of safety for the shotcrete liner by dividing the lateral strain capacity of the shotcrete by the radial strain of the liner due to the shaft convergence. The study infers that the strain factor of safety for the 100 mm shotcrete liner is greater than unity although its load factor of safety is less than unity. Therefore, it is concluded that the 100 mm shotcrete liner can be used as temporary support until the installation of the final concrete liner.

Prediction of jet grouting diameter in Swedish soil conditions

Soil improvement by jet grouting has been used extensively in continental Europe and Japan, and its use has gradually increased in Scandinavia. The most frequent practical use of Jet Grouting in Sweden is water sealing of sheet pile wall excavations. In this application the diameter of the jet grouted columns governs the design, and the mechanical properties of the columns are of less importance. The existing methods for estimation of jet grouted column diameter have been developed in geological conditions in continental Europe and Japan, which are significantly different from the soil stratas normally encountered in Sweden. To assess the applicability of these methods for Jet Grouting in Swedish soil conditions, the current article provides a description of these methods as well as the Swedish geology in which jet grouting is commonly executed. The resulting predicted diameters from such methods are then examined for three different case studies in the Stockholm region in Eastern Sweden, and the design diameters of the columns are given. The applicability of the current methods is elaborated and the consequences for practical design is discussed. The work concludes that none of the two examined methods can be used by themselves in Swedish soil conditions but need to be supplemented with tests at site.

Damage Estimation in Masonry Buildings Based on Excavation-Induced Ground Movements

Excavation-induced ground movements and the resulting damages to adjacent structures and facilities is a source of concern for excavation projects in urban areas. The concern will be even higher if the adjacent structure is old or has low strength parameters like masonry building. Frame distortion and crack generation are predictors of building damage resulted from excavation-induced ground movements, which pose challenges to projects involving excavations. This study is aimed to investigate the relation between excavation-induced ground movements and damage probability of buildings in excavation affected distance. The main focus of this paper is on masonry buildings and excavations stabilized using soil nail wall method. To achieve this purpose, 21 masonry buildings adjacent to 12 excavation projects were studied. Parametric studies were performed by developing 3D FE models of brick walls and excavations stabilized using soil nail wall. Finally, probability evaluations were conducted to analyze the outputs obtained from case studies. Based on the obtained results, simple charts were established to estimate the damage of masonry structures in excavation affected distance with two key parameters including “Displacement Ratio” and “Normalized Distance”. The results also highlight the effects of building distance from excavation wall on its damage probability.

Seismic performance of deep excavation restrained by guardian truss structures system using quasi-static approach

The control of deformation and stability of the deep excavation walls under seismic and static loads is one of the most important issues in geotechnical engineering. Therefore, in the present study, using the finite element method and taking into account Hardening soil's behavioural model, the effect of different parameters affecting the performance of the deep excavation walls with the guardian truss structures using quasi-static analysis and its comparison with static analysis has been performed. According to the most important results, increasing in the geotechnical parameters of soil such as cohesion, friction angle and elastic modulus will reduce the maximum horizontal displacement in the vertical trench wall. Besides, the maximum settling in the adjacent ground and the maximum swelling in the bottom of the excavation will be reduced. In this way, the improvement in soil resistance parameters will increase the safety factor. Conversely, by increasing the horizontal distance between the trusses, the maximum horizontal displacement and the maximum settling in the adjacent ground and the maximum swelling in the bottom of the excavation will increase and the safety factor will be reduced. Also, the findings from this research show that by increasing the horizontal seismic acceleration coefficient (Kh) and as the construction stages progress, the maximum horizontal displacement of the wall, the maximum settling of the adjacent ground of the wall and the maximum swelling on the bottom of the trench increase and the safety factor will decrease. As well as, the results obtained from the quasi-static seismic analysis of the vertical trench restrained by the guardian truss structure such as the maximum horizontal displacement of the vertical trench wall and the maximum settling in the adjacent ground and the maximum swelling of the bottom of the excavation are much more than the static analysis.

Design of deep urban excavations using life cycle cost in comparison with acceptable risk and conventional method

This paper aims to investigate risk based design of deep urban excavations, considering three case reports. Random Sets (RS) reliability analysis combined with finite element methods are deployed to consider the variability of ground parameters and to obtain the envelopes of probability of deformation for excavation walls. These envelopes are used to estimate the probability of deformation in surrounding buildings and infrastructures. Then, loss estimation is performed based on deformation probability. Finally, different design approaches including (i) Life Cycle Cost (LCC), (ii) acceptable risk and (iii) conventional method are compared together for three projects. Results show that conventional methods may not lead to the best suited design and the transition from conventional to risk based design in the context of deep excavations is an important necessity. The LCC method is evaluated in some real projects and it is shown that LCC is an efficient tool for risk based design of deep urban excavations.

Soil movement mechanism associated with arching effect in a multi-strutted excavation in soft clay

Arching effect behind the wall in a multi-strutted excavation is a soil stress transfer process related to differences in stiffness between the well-braced soil and the underlying soil. This effect has been demonstrated by studies on soil stress transfer and lateral wall pressure in the literature. However, the soil movement mechanism associated with the arching effect is still unknown. In this study, a multi-strutted excavation in soft clay in Ningbo was closely monitored to determine the contours of the total soil movement and engineering shear strain, and these data were then used to produce a detailed interpretation of soil arching development and its influence on soil movement. It is found that plastic flow occurs behind the wall as soil arching develops to the ground surface, resulting in a large soil movement zone and a dramatic increase in ground surface settlement. The soil in the shear zone is also disturbed and verified by cone penetration tests. In addition, this study proposes that the ratio between soil volume loss due to ground surface settlement and soil volume gain due to wall deflection can be used to characterize soil arching development and its influence on soil movement. This study improves the understanding of the soil movement mechanism behind walls in multi-strutted excavations in soft clay, which is very important for protecting adjacent structures and facilities.

Step fixings of vertical trench walls to prevent ground failure

The most commonly used designs for securing vertical walls of trenches and excavations in the actual conditions of work in them do not allow for strict compliance with regulatory safety requirements. To prevent ground failure in trenches and excavations, you can develop ground with a slope angle smaller than the natural slope angle. Development of excavations with vertical walls without securing them is limited to their depth depending on the strength properties of the ground. When excavating to a depth of up to 2-3 m the vertical walls of trenches and excavations must be secured. In this case, the development and backfilling of such excavations should be carried out using constructive solutions (e.g. anchoring), which in original combinations with modern construction materials and technologies allow various construction works to be safely performed in them.

Evaluation of Excavation Stabilization by the Top-down Approach in the Control of Excavation Wall Deformation based on Numerical and Field Studies

Evaluation of Excavation Stabilization by the Top-down Approach in the Control of Excavation Wall Deformation based on Numerical and Field Studies

Численное моделирование процесса высокочастотного виброизвлечения шпунтовых свай в условиях водонасыщенных пылевато-песчаных и пылевато-глинистых грунтов

The most common excavation walls are sheet piles, which are often sunk by vibration machines. In conditions of big thickness of water-saturated dispersed soils, one of the regulated safety criteria for the use of dynamic technology is the magnitude of soil vibrations and the structures that come to be located in the influence zone. The article presents the measured vibrations of the soil near the pile space in the process of vibration extraction of sheet piles. A characteristic oscillogram of vibration velocity with the characteristic stages of work production is added. Spectral analysis of the impact was performed to assess the prevailing frequency of the impact. The description of the process of numerical simulation of vibration extraction of a pile is given. As for the simulation results, there were obtained calculated oscillograms of the sheet piles located at 1.4 and 2.8 m distance from the sheet pile, and the influence zone was estimated. The calculated data obtained were compared with the results of field experiments.

Из опыта мониторинга ограждения глубокого котлована

Приводятся результаты мониторинга горизонтальных перемещений стенки из свай трубобетонной конструкции, ограждающей котлован глубиной до 15,5 м. Сопоставлены расчетные и фактические значения горизонтальных перемещений ограждающей стенки. Отмечается существенное увеличение (более расчетных) фактических перемещений ограждающей стенки в сторону котлована при отклонениях от заданной проектом технологической последовательности выполнения работ по устройству котлована. Представлены соображения по интерпретации полученных результатов мониторинга применительно к ограждению котлована,сохранявшему при этом устойчивость, и предложения по их использованию при проектировании ограждений котлованов.

Numerical simulation of vertical shaft sinking using artificial ground freezing

Artificial ground freezing (AGF) is used worldwide for vertical shaft sinking in difficult hydrogeological conditions. The modern tendency is to determine the design parameters of the freezing technique based on numerical simulation. This work is devoted to the numerical simulation of the formation of an ice-soil wall in the soil stratum due to the AGF and shaft sinking under the protection of the wall. For this purpose, a fully coupled thermo-hydro-mechanical model of soil freezing has been developed on the basis of the theory of poromechanics. The developed model considers important features of the freezing process, such as the phase change, pore water migration due to cryogenic suction, frost heave, and consolidation of the soil. The results have shown that the model allows to predict the distribution of ice content, assess stress and strain in the ice-soil wall, and estimate displacement of the excavation wall.

Numerical Study of the Use of Tyre-Derived-Aggregate (TDA) as the Backfill Above Flexible PVC Pipeline

Tyre Derived Aggregates (TDA), produced by shredding scrap car tyres, show many interesting features, such as: durability, low bulk density, thermal insulation, good drainage properties or ability to damp vibrations, which makes them a useful material for civil engineering. One of the possible applications is the partial filling of excavations with TDA during the construction of underground pipelines in order to decrease the load applied on the pipe. The article presents results of a multivariate numerical study of 2D FEM models of a flexible PVC pipe - soil system, in which the presence of a mixture of sand and TDA (tyre chips - 40% by weight) (STCh) in the backfill was simulated. The models differed in the thickness of the STCh layer (t = 0 – 0.9 m) and inclination of the excavation walls (a trench with vertical walls or open excavations with 3:1 and 1:1 slopes). The main goal of the numerical analyses, performed by means of the Z_Soil.PC program, were to investigate the effect of the presence of the softer STCh layer in the backfill zone on the pipe deformation (relative deflection δ/D) and internal forces in the pipe wall. The soil was simulated with the use of either the Hardening Soil Small (HSS) or Coulomb-Mohr (CM) constitutive model with the parameters’ values estimated based on results of laboratory tests (published by researchers from Wollongong University). The PVC pipe was modelled as linear elastic. The results of the analyses show that, due to enhanced arching, STCh layer of the optimum thickness t = 0.55 m can effectively reduce δ/D when used in the backfill of the trench. It can also decrease the difference between the maximum and minimum bending moment in the pipe wall, leading to less ovalization of the pipe cross-section. This positive effect diminishes if the width of excavation is larger, as the model is gradually transforming towards the positive projecting conduit type. The CM model gives underestimated values of the pipe deformation and internal forces. Though, in the case of lack of all the HSS parameters’ values, it is better to use the CM model with E = E 50 than E = E ur as it gives a better approximation of pipe behaviour.

The stress-strain state of the soil body in the quarter plane subjected to the strip load

Introduction. The construction of high-rise buildings, having elaborated substructures located inside deep excavations, entails a quantitative evaluation of the stress-strain state (SSS) of soils beyond the excavation wall with regard for the interaction with the surrounding built-up area and conditions of the contact with the enclosure structure. The paper analyzes the effect of distributed load p = const over a horizontal area having width b = 2a at the distance of с < a from the edge of a rectangular profile wall, which causes a non-uniform stress-strain state in the soil body having the shape of a quarter plane. It is assumed that the vertical wall is fixed with sprung structures, although vertical displacement of soil is acceptable.
 Materials and methods. The analytical solution to the problem of the effect of the distributed load on the horizontal soil body having the shape of a quarter plane is based on a well-known solution to the plane elastic problem designated for the half-space subjected to load p = const distributed over a strip. MathCAD software (SW) was employed to obtain the analytical solution; PLAXIS 2D software was used to obtain the numerical solution.
 Results. Analytical and numerical methods were applied to solve the problem of exposure of a horizontal soil body, having the shape of a quarter plane, to a distributed load. A comparative assessment and analysis of the stress strain state values were performed.
 Conclusions. Analytical and numerical solutions demonstrate good convergence pursuant to the analysis of the results. Therefore, further development of new methods for the quantitative evaluation of the stress strain state of the soil body based on the existing theoretical solutions is one of the main challenges to be tackled in advanced design of beddings and foundations.

Earth Pressure on an Excavation Wall in Rock Mass

In this study, the earth pressure on an excavation wall in rock mass is investigated under various conditions (type of rock, angle of join inclination, shear strength of joint, groundwater, permeability of wall, and earth pressure coefficient at rest). Based on the results of a physical model test of an excavation wall in joined rock mass, extended parametric study is performed considering the rock-structure interaction based on the discrete element method. The study results suggest that the earth pressure is strongly influenced by the condition of groundwater as well as the condition of wall and rock mass. The effect of groundwater on the earth pressure in a jointed rock mass different depending on rock type, the earth pressure coefficient at rest, wall permeability, and joint inclination angle. The groundwater effect was greatest under an impermeable wall condition and a vertical joint acted as an impermeable wall. Under inclined joint and groundwater conditions, the earth pressure in a permeable wall increased when compared with no groundwater condition and the increase was more evident when the earth pressure coefficient was smaller. As the rock and joint conditions were deteriorated further, the earth pressure increased and the influence of groundwater decreased. The study results also showed that for hard rock and good joint conditions, the influence of groundwater was more significant as the earth pressure coefficient increased, but as rock and joint weathered, the influence of groundwater was more significant as the earth pressure coefficient decreased.

Rancangan Teknik Reklamasi Penambangan Pasir dan Batu Di Dusun Banaran, Desa Keningar, Kec. Dukun, Kab. Magelang, Jawa Tengah

The research was conducted in Banaran Hamlet, Keningar Village, Dukun Subdistrict, Magelang District, Central Java, which is a mining area for sand and rock, previously the area was a private forest. Mining system used in the form of open pit mining and traditional mining methods. The purpose of this research is to determine the level of land and the technical design of mine reclamation mining areas at the study site. The methods used in this research was field survey, mapping and descriptive analysis. The sampling technique used in this research was purposive sampling technique which is a part of non-probability sampling. Descriptive analysis was based on the Environment Ministerial Decree Number 43 of 1996 concerning Standards Criteria for Environmental Damage for Group C mining Businesses and Activities on Land and DIY Governor Decree Number 63 of 2003. Based on the research report, the mining area fulfills the damaged criteria because out of all the tested parameters, only 1 parameter fulfills the good criteria. No management of topsoil, the base relief excavation is more than 1 meter, the average wall slope is 55 o (142,81% ) , the height of the excavation wall with an average of ±5,6 meters and land cover/vegetation reaching 33,35%. The technical design will be used is making bench terraces and making drainage channels. The plants used as revegetation are sengon, jackfruit and vetiver grass as cover crop plants. Keyword s : Sand and Rock Mining, Land Degradation, Soil Fertility, Reclamation

Using numerical modeling method for design and constructive controlling of excavation wall in Madison Building, Ho Chi Minh city

The basement of a high-rise building is the optimal space for technical systems and parking. However, the construction in narrow urban areas usually has many unstable hazards. In this study, a numerical model has been established and calibrated using the finite element method on Plaxis 2D software that allowed well control of the design and construction processes of the Madison Building basement. The model covers all structural elements and complex engineering geology conditions. Displacements of the excavation wall and surrounding ground base subsidence were analyzed corresponding to the constructive phases of three basements. The analysis results of the numerical model were consistent with the actual construction process that is useful for design and constructive controlling of the excavation wall.

Precise multi-image pointing (MIP) applied on convergence close-range photogrammetry images

PurposeDisplacement measurement in large-scale structures (such as excavation walls) is one of the most important applications of close-range photogrammetry, in which achieving high precision requires extracting and accurately matching local features from convergent images. The purpose of this study is to introduce a new multi-image pointing (MIP) algorithm is introduced based on the characteristics of the geometric model generated from the initial matching. This self-adaptive algorithm is used to correct and improve the accuracy of the extracted positions from local features in the convergent images.Design/methodology/approachIn this paper, the new MIP algorithm based on the geometric characteristics of the model generated from the initial matching was introduced, which in a self-adaptive way corrected the extracted image coordinates. The unique characteristics of this proposed algorithm were that the position correction was accomplished with the help of continuous interaction between the 3D model coordinates and the image coordinates and that it had the least dependency on the geometric and radiometric nature of the images. After the initial feature extraction and implementation of the MIP algorithm, the image coordinates were ready for use in the displacement measurement process. The combined photogrammetry displacement adjustment (CPDA) algorithm was used for displacement measurement between two epochs. Micro-geodesy, target-based photogrammetry and the proposed MIP methods were used in a displacement measurement project for an excavation wall in the Velenjak area in Tehran, Iran, to evaluate the proposed algorithm performance. According to the results, the measurement accuracy of the point geo-coordinates of 8 mm and the displacement accuracy of 13 mm could be achieved using the MIP algorithm. In addition to the micro-geodesy method, the accuracy of the results was matched by the cracks created behind the project’s wall. Given the maximum allowable displacement limit of 4 cm in this project, the use of the MIP algorithm produced the required accuracy to determine the critical displacement in the project.FindingsEvaluation of the results demonstrated that the accuracy of 8 mm in determining the position of the points on the feature and the accuracy of 13 mm in the displacement measurement of the excavation walls could be achieved using precise positioning of local features on images using the MIP algorithm.The proposed algorithm can be used in all applications that need to achieve high accuracy in determining the 3D coordinates of local features in close-range photogrammetry.Originality/valueSome advantages of the proposed MIP photogrammetry algorithm, including the ease of obtaining observations and using local features on the structure in the images rather than installing the artificial targets, make it possible to effectively replace micro-geodesy and instrumentation methods. In addition, the proposed MIP method is superior to the target-based photogrammetric method because it does not need artificial target installation and protection. Moreover, in each photogrammetric application that needs to determine the exact point coordinates on the feature, the proposed algorithm can be very effective in providing the possibility to achieve the required accuracy according to the desired objectives.

Analysis of Deformation Characteristics of Foundation-Pit Excavation and Circular Wall

The surrounding ground settlement and displacement control of an underground diaphragm wall during the excavation of a foundation pit are the main challenges for engineering safety. These factors are also an obstacle to the controllable and sustainable development of foundation-pit projects. In this study, monitoring data were analyzed to identify the deformation law and other characteristics of the support structure. A three-dimensional numerical simulation of the foundation-pit excavation process was performed in Midas/GTS NX. To overcome the theoretical shortcomings of parameter selection for finite-element simulation, a key data self-verification method was used. Results showed that the settlement of the surface surrounding the circular underground continuous wall was mainly affected by the depth of the foundation-pit excavation. In addition, wall deformation for each working condition showed linearity with clear staged characteristics. In particular, the deformation curve had obvious inflection points, most of which were located deeper than 2/3 of the overall excavation depth. The characteristics of the cantilever pile were not obvious in Working Conditions 3–9, but the distribution of the wall body offset in a D-shaped curve was evident. Deviation between the monitoring value of the maximal wall offset and the simulated value was only 4.31 %. The appropriate physical and mechanical parameters for key data self-verification were proposed. The concept of the circular-wall offset inflection point is proposed to determine the distribution of inflection-point positions and offset curves. The method provides new opportunities for the safety control and sustainable research of foundation-pit excavations.

Empirical and Numerical Finite-Element-Based Model to Improve Narrow Vein Mine Design in Peruvian Mining

This paper proposes a numerical finite-element-based model aimed at optimizing narrow-vein stope stability. This model combines empirical and numerical methods to develop a sequence, which may determine an acceptable stope safety factor. A stope stability analysis was conducted through the Mathews stability graph method, which requires two factors: the hydraulic radius (HR) and stability number (N’). The Mathews stability graph method is used to assess the stability of an underground design. Variations in stope dimensions are estimated by changing the HR and Factor A within the N’, which is determined through numerical methods. The results of the numerical simulation indicate that the HR increases with an increase in stope dimensions, while Factor A maintains an inverse relationship with the maximum stress induced on the excavation walls. This document demonstrates the potential of combining empirical and numerical methods in stope design optimization, especially when developed in small narrow vein mines.

A Comprehensive Numerical Study on Building-Excavation Interaction

This paper presents results of a plane strain comprehensive numerical study on the interaction between a 31-meter-deep excavation and an adjacent 12-story building; the study emphasizes on parametric analyses with respect to the building characteristics, such as the building width in plan (B), i.e., the side perpendicular to the excavation wall, the embedment depth of the building foundation (D), as well as the building distance to the excavation edge (e). Through the parametric analyses and assuming different values for B, D, and e, settlements and rotations of the building and horizontal displacements of the excavation edge were computed and evaluated using the finite element method adopted in PLAXIS 3D software. Prior to the parametric study, the numerical modeling was verified by modeling a recorded case study, which is an anchored deep excavation adjacent to a 12-story building. The results of the parametric analyses suggest that for the given soil and excavation, (1) the position of the developing potential failure surface, PFS, in the soil behind the excavation is almost independent from the building location and (2) the position of the building with respect to the outcrop of the PFS in the excavation crest, i.e., if the building locates fully on the potential failure wedge or PFS intersect the building base, is the main factor affecting the induced displacements and rotations of the building.