Volumetric Block Research Articles

Failure mechanism of a tunnel in a soil–rock mixture based on a new combined finite–discrete element method

The mechanical properties and failure characteristics of soil–rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite–discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil–rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young’s modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil–rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Shear behavior and dilatancy of an artificial hard-matrix bimrock: An experimental study focusing on the role of blocky structure

Bimrocks are characterized by their geotechnically significant blocky structure, presenting complex shear behavior. This study investigates the shear behavior and dilatancy of bimrocks featuring a rock-like matrix, such as conglomerates. The study addresses a gap in current research, which has predominantly examined the shear behavior of soil-matrix bimrocks (bimsoils). Laboratory direct shear tests were performed on idealized models with varying volumetric block proportions (VBPs). The results highlight that blocks exert both positive and negative effects on shear strength, dilation, and block breakage factor (BF), depending on VBP. Results indicate 40% and 60% as critical VBPs, revealing distinct shear strength trends within this range, contrary to the dominant downward trend. Blocks positively impact dilation and BF between 20% and 50% VBP, while negatively affecting them beyond this range. Blocky skeleton inherently promotes stable dilatancy under normal stress increments and intensifies stress dependency of shear strength. Variations in dilation angle concerning normal stress and VBP suggest the potential for characterizing this factor using equivalent strength and roughness, akin to rockfill materials. Indirect assessments of equivalent strength revealed positive effects of blocks when VBP was between 30% and 70%. Lastly, the findings indicate that blocks notably impact pre- and post-peak behaviors by reducing shear stiffness and inducing local hardening phases. This study also discusses the similarities and distinctions in the function of blocks within soil-like and rock-like matrices. It offers new insights into the exact role of blocks in bimrock shear behavior beyond the traditional interpretation through the variation of friction and cohesion.

Finite-discrete element modelling of fracture development in bimrocks

Block-in-matrix rocks (bimrocks) are a complex geological feature composed of hard blocks in a weak matrix bonded together via a weak interface. The failure mechanism and deformation behavior of the bimrocks is quite complex due to the simultaneous existence of blocks with different shapes, strengths and proportions in a matrix. Therefore, it is of great importance to characterize the bimrocks under different situations. This study employs the combined finite-discrete element method (FDEM) to characterize the failure pattern and load carrying capacity of the bimrocks considering changes in various parameters, including block size, volumetric block proportion (VBP), the strength ratio of block-matrix interface to matrix, and the shape of the blocks (angular, circular, and elliptical shapes). First, the robustness and feasibility of the FDEM in modeling fracture development is verified against an analytical solution as well as a series of experimental tests accompanied with the digital image correlation (DIC) method. Then, the verified model is used to model disc specimens with various block shapes and properties. The results indicate the remarkable influence of VBP, block size and block-matrix interface characteristics on the bimrock mechanical behavior under the same VBP. The results are assessed based on macroscopic observations to investigate the influence of determinative physical properties of bimrocks. The results are also evaluated based on the mode of failure, mode I, II, or mixed mode, to qualitatively elucidate the influence of key factors on the formation of different cracks in different places, including the interface of matrix-blocks or intergrain or intragrain. The results show that since the loading is a quasi-static scheme, all the cracks are intergrain and no intragrain crack is observed for any VBP. The simulations outcomes shows that the block sizes determine the failure pattern, failure mode, and load–displacement behavior, where the larger blocks exhibiting the lowest load carrying capacity due to experiencing more interface breakage in shear. It is found that the VBP is a crucial parameter in the deformation of the bimrocks, showing that the strength of the bimrocks significantly increases with a decrease in the VBPs and the ones with greater VBPs experience more breakage and thus less resistance to loading. The block-interface strength is found to be the most critical factor in the deformation of the bimrocks (regardless of the value of the VBP). Finally, the effect of block shape is shown to have a considerable impact on bimrocks with the higher VBPs (more than 70%).

Modeling Volumetric Block Types in Residential Building Construction

The article focuses on the erection of residential buildings from large-sized volumetric blocks as a modern and progressive trend in housing construction. It is noted that one of the major tasks in the development of this promising area of construction is to justify the choice of type of volumetric blocks. The authors propose a method of type formation that, depending on the set objective, can either be composed of large-sized volumetric blocks only, or include combinations of large-sized and smaller-sized blocks. The article details the steps and procedure of modeling the type of volumetric blocks, which comprises three stages. At the first stage, the parameters of boundary blocks are determined, and then, by changing these parameters step by step, the parameters of blocks between the boundary blocks are set. The second stage involves developing options for the placement of blocks in accordance with the space and layout design solutions employed in the residential buildings to be erected. At the third stage, blocks are selected, and their actual type is approved. The stages of modeling of the volumetric blocks type are illustrated by practical examples, tables, and figures.

Electrical resistivity tomography for the evaluation of Areal Block Proportion (ABP) in bimunits: Modelling and preliminary field validation

The measurement and estimation of the Areal Block Proportion (APB) and of the Linear Block Proportion (LBP) are the basis for the estimation of the Volumetric Block Proportion (VBP), which is a fundamental parameter for the mechanical and technical characterization of bimunits. Existing approaches for ABP estimation are strongly conditioned by availability of accessible outcrops and/or borehole data. To address this problem, we propose a methodology based on non-invasive geoelectrical surveys. We realized numerous numerical simulations of the resistivity field on simplified geological sections across bimunits, characterized by different internal organizations of hard (high resistivity) blocks in a softer clay-rich (low resistivity) matrix, aiming at investigating the relationship between resistivity and ABP. We compared the results of the numerical simulations with real electrical resistivity tomographies (ERTs) acquired in two representative test sites in bimunits, providing a preliminary validation of modelled data. Our findings allowed us to define an equation relating the ABP with the electrical resistivity, which offers the possibility of estimating the ABP through non-destructive geo-electrical surveys, favoring their correlation with outcrop and/or borehole data and supporting their interpretation.

An Experimental Investigation of the Effects of Block Proportion on Bimrocks, Considering Different Block-to-Matrix Strength Ratios.

The rock block proportion is one of the most important factors affecting the mechanical properties of bimrocks. Under different block-to-matrix strength ratios, the influence of rock block proportion is different. To explore the influence of rock block proportion on the mechanical properties of specimens under different block-to-matrix strength ratios, a new indoor test method for making bimrocks was proposed. A uniaxial compression test and a direct shear test were carried out on specimens with different rock block proportions. The results show that this method can control the block-to-matrix strength ratio well, and the influence of rock block proportion is obviously different under different block-to-matrix strength ratios. The strong matrix sample will decrease significantly after reaching the peak compressive strength, while the weak matrix will decrease slowly after reaching the peak strength. The rock block proportion is negatively correlated with the uniaxial compressive strength of strong matrix samples (the reduction was 12.53%) and is positively correlated with the uniaxial compressive strength of weak matrix samples as a whole, but it changes when block proportion is more than 50%. With the increase in normal stress and rock block proportion increases from 30% to 60%, the shear failure zone of the weak matrix sample increases, and the cracks are inclined, while the strong matrix sample has more secondary cracks. The results of this study also show that the effect of volumetric block proportion (VBP) on the internal friction angle and cohesion of the sample is less related to the block-to-matrix strength ratio.

Experimental evaluation of the strength of the floor slab of a volume block

Modular construction is a new method that uses standardized blocks to construct buildings quickly and efficiently. This approach can significantly reduce construction time and costs, as well as improve the accuracy and quality of work. One of the key aspects of modular construction is careful design and material selection to ensure that structures are durable and safe. The study presents an experimental evaluation of the strength of the floor slab of a volumetric block. The research methodology includes the creation of laboratory conditions to recreate real operational situations, as well as the application of modern methods of measurement and data analysis. The results obtained allow conclusions to be drawn on the strength characteristics of the floor slab, which showed that the experimental failure load exceeded the control failure load by 11%. The vertical deflections of the slab before failure did not exceed 8 mm, which characterizes the floor slab as having high stiffness. The information obtained is an important basis for designing and constructing buildings where volume block is used. The work significantly contributes to the efficiency of construction processes and provides more reliable structural performance, which is critically important in the field of construction industry and engineering solutions.

Bearing capacity of a steel frame of a multi-storey modular building with consideration of the rigidity of quick-assembled connections

The article is devoted to the analysis of calculation and design problems and features that arise when designing multi-storey modular buildings with a steel frame. The article describes the main features of the classification and trends in the construction of volumetric block buildings in Russia and the world.
 The object of the study is quick-assembly connections of compressed-bent load-bearing elements of frame modular systems.
 The main purpose of the study is to obtain reliable analytical and theoretical data to determine the characteristics of the rotational stiffness of module connection nodes and assess its influence on the stress-strain state of the frame and its elements.
 Within the work, the concept of an experimental modular building was developed using I-beam columns as part of the frame, as well as inter-module joints for their connection. Flange connections with high-strength bolts without controlled tightening are considered as the main design solution for the inter-module connections. The designed connections include inspection windows to access the hardware.
 A numerical study was performed to evaluate the bearing capacity and stiffness of the connections. The influence of the stiffness on the behavior of the frame in relation to two groups of limit states was assessed using the finite element method.
 The paper substantiates the relevance of using I-beam profiles as columns of the frame of a modular building, which is not a common solution in modern practice.
 The developed concept of quick-assembly inter-module flange connections makes it possible to ensure the safety of the building while reducing the time and labor costs for its installation.

Collapsing Embedded Cell Complexes for Safer Hexahedral Meshing

We present a set of operators to perform modifications, in particular collapses and splits, in volumetric cell complexes which are discretely embedded in a background mesh. Topological integrity and geometric embedding validity are carefully maintained. We apply these operators strategically to volumetric block decompositions, so-called T-meshes or base complexes, in the context of hexahedral mesh generation. This allows circumventing the expensive and unreliable global volumetric remapping step in the versatile meshing pipeline based on 3D integer-grid maps. In essence, we reduce this step to simpler local cube mapping problems, for which reliable solutions are available. As a consequence, the robustness of the mesh generation process is increased, especially when targeting coarse or block-structured hexahedral meshes. We furthermore extend this pipeline to support feature alignment constraints, and systematically respect these throughout, enabling the generation of meshes that align to points, curves, and surfaces of special interest, whether on the boundary or in the interior of the domain.

Prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum

This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown. A series of numerical analyses is performed to examine the effects of cover depth ratio (C/D), tunnel volume loss rate (ηt) and volumetric block proportion (VBP) on the characteristics of subsurface settlement trough and soil volume loss. Considering the ground loss variation with depth, three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown. Then, analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory. The influences of C/D, ηt and VBP on the key parameters (i.e. B and N) in the analytical expressions are discussed to determine the fitting formulae of B and N. Finally, the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation. Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters. Besides, the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.

Numerical investigation on influence of dispersed rock particles on bimslope stability

Analysing the stability of bimslopes (i.e. slopes made of bimrock (block-in-matrix rock)) is challenging because bimrock has a complex internal structure. In the study reported here, a stochastic finite-element analysis with the shear-strength-reduction method was conducted to elaborate how dispersed oversized rock particles influence the stability of a vertical bimslope. Numerical models with different rock compositions were generated and analysed to characterise the definiteness and randomness. The factor of safety and the failure zone were used to establish the relationship between slope stability and fractal dimension (FD) of rock-size distribution and rock spatial variability. The numerical results show that the FD and spatial locations of the rock particles influence bimslope stability indirectly, with the key indicator for the skid resistance of a bimslope being the compactness of the rock composition crossing the sliding surface with given volumetric block proportion. This finding also highlights the validity and feasibility of stochastic analysis in outperforming deterministic analysis. Overall, the present findings offer a reference for further understanding of the collapse mechanism and reinforcement measures of existing bimslopes.

The Effect of Block-Matrix Interface of SRM with High Volumetric Block Proportion on Its Uniaxial Compressive Strength

The soil–rock mixture (SRM), as a heterogeneous and discrete geomaterial, can be widely found in nature and may present difficult design and construction issues for structures within or on top of them. Engineers face a difficult problem when determining the mechanical behavior of geomaterials with SRM, especially those with a high volumetric block proportion (VBP). As it is often very difficult to prepare undisturbed and representative samples of these materials. Thus, this paper proposes a novel method that can generate SRM models with a high VBP and produce a block-matrix interface (BMI) around the rock block, which can simulate unwelded SRM in nature. Then, the finite difference method (FDM) is applied to simulate uniaxial compression tests. The conformity of the numerical simulation results with the experimental results shows that the method is reasonable and effective. In addition, the effect of the strength of the BMI, the thickness of the BMI, and the geometrical shape of the rock blocks on the uniaxial compressive strength (UCS) of the SRM are also investigated. The modelling approach proposed in this paper is able to generate BMI in SRMs and enables the effect of the BMI on the SRMs’ properties to be better investigated in numerical simulations. This method can overcome the difficulties of preparing representative and undisturbed experimental cores while saving cost and improving efficiency. Simultaneously, the method proposed in this paper is promising to be extended to three dimensions.

An improved DEM-based mesoscale modeling of bimrocks with high-volume fraction

Block-in-matrix rocks (bimrocks), a typical heterogeneous and discrete geomaterial, are widely found in nature and may cause problems in the design and construction of projects. The generation of mesoscale bimrocks with a high volumetric block proportion (VBP) is still a challenge. This paper proposes a novel mesoscale method that can generate bimrocks models with high VBPs and can generate high-quality mesh using the finite element method (FEM). The Rigid Block discrete element method was then applied to simulate uniaxial compression tests based on the FEM mesh. The agreement between the numerical and experimental results demonstrates that the method is reasonable and effective. In addition, the effect of VBP, strength of the block-matrix interface, and friction coefficient of rock blocks on the uniaxial compressive strength of bimrocks was also investigated.

Strengthening effect of sulphoaluminate cementitious grouting material for water-bearing broken rocky stratum

A rapid-hardening sulphoaluminate cementitious grouting material (SCGM) is improved for water-bearing broken rocky stratum. Hydroxy propyl methyl cellulose (HPMC) and polycarboxylate-based superplasticizer (PCE) are used to improve fresh-state performance. Main diffusion ability, fresh-state properties, basic mechanical strengths, microstructure, etc., are investigated. A novel grouting simulation apparatus is designed to assess grouting effectiveness, the holistic reinforcement effect, compressive strength and anti-permeability of grouted specimen, typical failure mode, influence of key parameter and bonding characteristic of grout-rock interface are studied. The combination of 0.4 % PCE and 0.02 % HPMC can be applied at water-binder ratio (w/b) of 0.65–1.0. The maximal 3 d and 28 d unconfined compressive strength (UCS) of SCGM are 15.87 and 18.60 MPa, its 28 d UCS of grouted specimen can attain 14.98 MPa. The SCGM is eligible for rapid water blocking and effective reinforcement especially in water-rich and broken rocky strata. Based on the Coulomb failure criterion, relationships among UCS, internal friction coefficient and cohesion of reinforced rock were derived. Based on the linear relationship between internal friction angle (φ) or cohesion (C) and volumetric block proportion (VBP), the quantitative expression with UCS and VBP was established. In comparision with experimental data, feasibility of the quantitative formula in predicting UCS of reinforced rock is proved.

ТЕХНОЛОГИЯ БЕТОНИРОВАНИЯ БЛОК-КОМНАТ СПОСОБОМ ОПУСКАЮЩЕГОСЯ БЕТОНА

We describe the concrete deposition method for manufacturing concrete products in mobile workshops for the construction of residential buildings consisting of block rooms. A literature review was carried out in the field of volumetric block construction, modular structures, 3D block construction, and prefabricated blocks. We propose a concept of mobile manufacturing. Per this method, three-dimensional blocks of a room for a residential structure are manufactured in a mobile workshop using the patented method of concrete deposition. The workshop is located directly on the construction site or next to it. Organizational and technological solutions for block construction are provided which reduce construction time and cost per square meter.

Investigation of the effective hydro-mechanical properties of soil-rock mixtures using the multiscale numerical manifold model

This study focuses on determination of the effective hydro-mechanical properties of a widespread geological mélange, the Soil-Rock Mixture (SRM), using the multiscale Numerical Manifold Method (NMM). Influences of the Volumetric Block Proportion (VBP), block size, block shape, block orientation angle and micro-dynamics on the effective properties are investigated thoroughly. The SRM structural models are generated within the NMM framework in a statistical manner. The effective properties are extracted using the multiscale theory where micro-dynamics is fully considered based on the extended Hill-Mandel lemma. Through numerical simulations, the VBP and block orientation angle prove to be the first and second most influential factors. A growing VBP leads to increasing deformation moduli but decreasing effective permeability and Biot’s factor. Normal components of permeability and deformation tensors are positively proportional to the corresponding normal intersecting areas formed by sample cross-sections and blocks while shear components are positively proportional to sums of the normal and shear intersecting areas. Introducing micro-dynamics and diminishing the time step make the effective permeability and deformation moduli rise while Biot’s coefficient decrease. The accuracy and stability of the multiscale NMM are validated by comparing present results with those of empirical formulae and single-scale numerical methods.

Investigation of Volumetric Block Proportion (VBP) Effect on Excavation-Induced Ground Response of Talus-like Rock Mass Based on DEM Simulations.

Due to the complexity of the talus-like rock mass with different values of volumetric block proportion (VPB), it is thus crucial to explore the VBP effect on the excavation-induced ground responses. We conduct a series of 2D DEM (discrete element method) simulations on a common circular tunnel excavation in the talus-like rock mass with different VBPs (0%, 15%, 50%, 85% and 100%). For each VBP, two support scenarios, i.e., unsupported and supported by a rigid lining, are considered. The micro characteristics of the excavation-induced ground responses, including the contact force, force chain, coordination number and shear-slip contact, and the stress distribution and ground settlement are elaborated in detail. Accordingly, three types of talus-like rock masses are identified as soil-, hybrid- and rock-types, corresponding to VBP = 0-15%, 50%, and 85-100%, respectively. It is found that the lining support is essential for maintaining the ground stability of a tunnel excavation in the soil- and hybrid-type talus-like rock masses while the backbones formed by rock blocks in the rock-type talus-like rock mass can provide a certain support for the surrounding ground. Our findings have important implications for optimizing the construction scheme of tunnel excavation in different types of talus-like rock masses.

Investigation of Virtual Bimrocks to Estimate 3D Volumetric Block Proportions from 1D Boring Measurements

Serious deficiencies in ground characterization, analysis and design at engineering works can occur when working with bimrocks (block-in-matrix rocks) and bimsoils (block-in-matrix soils). Since the 1990s, serious technical problems at engineering works performed in bimrocks/bimsoils spurred practical research, which revealed that the behavior of these geomaterials is directly related to the volumetric block proportions (VBPs). However, the way that VBPs can be confidently and correctly estimated remains an ongoing critical issue that still frustrates designers, contractors and owners. Stereological techniques can be applied to overcome this challenge by inferring 3D block contents from in situ 1D and 2D measurements, but the estimates have often been demonstrated to be erroneous. This paper presents findings from a computer-aided reinvestigation, revalidation and extension of Medley’s work of 1997 and subsequent researchers to provide approachable yet statistically robust methods to limit the uncertainty associated with estimates of 3D VBPs generated from 1D boring/scanline measurements. To this aim, a specialized Matlab code was created and virtual drilling programs were performed through 3D computer-generated bimrock models. Supported by extensive statistical-based investigations, a design chart is provided that updates and extends Medley’s 1999 chart relating uncertainty in estimates of VBP as a function of total boring/scanline lengths.

Practical classification of geotechnically complex formations with block-in-matrix fabrics

The terms “bimrocks”, “bimsoils” and “soil-rock mixtures” indicate different and very common types of geological units with a block-in-matrix fabric that are also “geotechnically complex formations” and are characterized by an internal heterogeneity, and spatial variability of mechanical parameters and lithological compositions. Due to this internal complexity, the understanding of their geomechanical behavior presents a key challenge in geotechnical engineering. However, the lack of a standardized and clear terminology complicates the discrimination of different types of complex formations and their internal mechanical properties, which leads to inconsistency in the literature and research studies. This inconsistency causes misunderstandings, with possible practical implications for the characterization, analysis, design and construction of engineering works. By a combination of geological and geotechnical observations, we propose a new classification for geotechnically complex formations, with particular attention to those with a block-in-matrix internal fabric. Four properties are at the base of this new classification and have a primary role in controlling the geotechnical behavior of block-in-matrix units (bimunits): (i) the composition (i.e., lithology, degree of lithification/consolidation, nature, and rheology) of blocks and the matrix that affects the water sensitivity, (ii) the degree of internal anisotropy (DA) of the block-in-matrix fabric, (iii) the degree of stratal disruption and mixing, and (iv) the volumetric block proportion (VPB). As a result, we classified bimunits in those with “anisotropic”, “isotropic”, and “mixed” (i.e., different behavior depending on the DA of the matrix) textures and, each of these types, into block-in-matrix rocks and block-in-matrix soils (bimrocks and bimsoils in the following). According to the water sensitivity of the matrix, bimrocks are also differentiated into “hard” and “soft”. The novelty of the classification is that it is not limited to few types of geotechnically complex formations (e.g., flysch) but it can be easily applied to all field-based investigations of the different types of complex formations, regardless of their internal degree of stratal disruption, composition, and mechanical response to water sensitivity.

Influence of Block form on the Shear Behaviour of Soft Soil–Rock Mixtures by 3D Block Modelling Approaches

The influence of block forms on the shear behaviour of soil–rock mixtures with soft blocks (soft S–RMs) can be efficiently investigated by the discrete element method (DEM) on the basis of accurate 3D models accounting for the block breakage. This paper proposes a novel modelling approach, based on the spherical harmonics series, for the generation of 3D block geometries with different forms but same convexity and angularity. An already existing non-overlapping modelling approach was improved, characterized by a reduced computational cost, for the set-up of 3D block DEM models accounting for the block breakage. A number of soft S–RM DEM samples, subjected to numerical direct shear tests, were generated to analyze the influence of block forms and volumetric block proportion VBP on the mesoscopic and macroscopic behaviours. The results showed that the breakage degree is maximum for the spheroidal blocks, followed by the oblate, prolate and blade ones, due to the combined influence of the block frictional sliding and rotation. The shear strength of soft S–RMs is mainly controlled by the block interlocking and breakage, being maximum in the case of spheroidal block samples when the applied normal stress is low and in the case of prolate and blade ones for a high normal stress. It was found that a nonlinear Mohr–Coulomb criterion can provide a good description of the shear strength envelope of soft S–RMs. Soft S–RMs are characterized by a higher friction angle if composed by spheroidal and prolate blocks when the VBP is 40%, due to their elevated block interlocking, and in the case of prolate and blade blocks when the VBP is 60% at the higher normal stress, due to their lower block breakage degree.