Application and prospects of 3D printing in physical experiments of rock mass mechanics and engineering:materials,methodologies and models

The existence of joints or other kinds of discontinuities has a dramatic efect on the stability of rock excavations and engineering.As a result,a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects.In recent years,3D printing technology has become a promising tool in the feld of rock mass mechanics and engineering.This study frst reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects.Then,based on the comprehensive analysis of previous research,the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects.The frst is the printing material.Although there are many materials for 3D printing,it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited.After research,we summarize and evaluate printing material that can be used for rock mass mechanics studies.The second is the printing methodology,which mainly introduces the current application forms of 3D printing technology in rock mass mechanics.This includes printed precise casting molds and one-time printed samples.The last one is the printing model,which includes small-scale samples for mechanical tests and large-scale physical models.Then,the benefts and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed.Compared with traditional rock samples collected in nature or synthetic rock-like samples,the samples made by 3D printing technology have unique advantages,such as higher test repeatability,visualization of rock internal structure and stress distribution.There is thus great potential for the use of 3D printing in the feld of rock mass mechanics.However,3D printing materials also have shortcomings,such as insufcient material strength and accuracy at this stage.Finally,the application prospect of 3D printing technology in rock mass mechanics research is proposed.

Accuracy and Precision of Energy Dispersive X-Ray Fluorescence (EDXRF) Analysis of Trace and Major Elements in Rock Standard Reference Materials Using Fine Powder

In this work the performance of a screening analytical method for Energy Dispersive X-Ray Fluorescence (EDXRF) analysis in terms of accuracy and precision was evaluated through analysis of rock standard reference materials. The method allowed the division of elements into four groups taking into account the excitation energies and measurement conditions of the sample. Two standard reference materials were used and 15 sample replicates were prepared and analyzed, then statistics were applied to assess the precision and accuracy of analytical results. The obtained results show that major compounds or elements (SiO2, P2O5, K2O, CaO, Fe2O3, Ti) can be determined in fine powder sample with a deviation lower than 15%, and a relative standard deviation in the range (1 - 10)%. The deviation was found to be lower than 5% for major compounds such as K2O, and CaO, which suggest that the EDXRF is accurate in evaluating major elemental concentrations in rock samples. It was also found that the method seems to be more accurate and precise for major elements than for trace element investigation. This screening analytical method can be used for routine analysis with acceptable results, even though the method should be optimized to increase its precision and accuracy.

A modified damage and fracture phase field model considering heterogeneity for rock‐like materials

Damage and fracture are the most extensive failure modes of rock materials,which may easily induce disaster and instability of engineering structures.This study developed a nonlocal damage fracture phase field model for rocks considering the heterogeneity of rocks.The modified phase field model introduced the heterogeneity of fracture parameters and modified the governing equations.Meanwhile,the free energy was constructed by the elastic strain energy sphere‐bias decomposition and the plastic strain energy.As for the numerical implementation,the three layers finite elements method structure was used in the frame of the finite element method.The ability of the modified phase field model has been illustrated by reproducing the experiment results of rock samples with pre‐existing cracks under compression.

THEORETICAL MODEL OF EFFECTIVE STRESS COEFFICIENT FOR ROCK/SOIL-LIKE POROUS MATERIALS

Physical mechanisms and influencing factors on the effective stress coefficient for rock/soil-like porous materials are investigated, based on which equivalent connectivity index is proposed. The equivalent connectivity index, relying on the meso-scale structure of porous material and the property of liquid, denotes the connectivity of pores in Representative Element Area （REA）. If the conductivity of the porous material is anisotropic, the equivalent connectivity index is a second order tensor. Based on the basic theories of continuous mechanics and tensor analysis, relationship between area porosity and volumetric porosity of porous materials is deduced. Then a generalized expression, describing the relation between effective stress coefficient tensor and equivalent connectivity tensor of pores, is proposed, and the expression can be applied to isotropic media and also to anisotropic materials. Furthermore, evolution of porosity and equivalent connectivity index of the pore are studied in the strain space, and the method to determine the corresponding functions in expressions above is proposed using genetic algorithm and genetic programming. Two applications show that the results obtained by the method in this paper perfectly agree with the test data. This paper provides an important theoretical support to the coupled hydro-mechanical research.

Damage and failure characteristics of rock similar materials with pre-existing cracks

In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.

A roughness parameter considering joint material properties and peak shear strength model for rock joints

This study aims at proposing a reasonable roughness parameter that can reflect the peak shear strength(PSS)of rock joints.Firstly,the contribution of the asperities with different apparent dip angles to shear strength is studied.Then the shear strength of the entire joint asperities is derived.The results showed that the PSS of the entire joint asperities is proportional to a key parameter hs,which is related to the geometric character of the joint surface and the joint material properties.The parameter hsis taken as the new roughness parameter,and it is reasonable to associate the PSS with the geometric characteristics of the joint surface.Based on the new roughness parameter and shear test results of 20 sets of joint specimens,a new PSS model for rock joints is proposed.The new model is validated with the artificial joints in this paper and real rock joints in published studies.Results showed that it is suitable for different types of rock joints except for gneiss joints.The new model has the form of the Mohr-Coulomb model,which can directly reflect the relationship between the 3 D roughness parameters and the peak dilation angle.

Coupled GIMP and CPDI material point method in modelling blast-induced three-dimensional rock fracture

Three-dimensional rock fracture induced by blasting is a highly complex problem and has received considerable attention in geotechnical engineering.The material point method is firstly applied to treat this challenging task.Some inherent weaknesses can be overcome by coupling the generalized interpolation material point(GIMP)and the convected particle domain interpolation technique(CPDI).For the media in the borehole,unchanged GIMP-type particles are used to guarantee a homogenous blast pressure.CPDITetrahedron type particles are employed to avoid the fake numerical fracture near the borehole for the rock material.A blasting experiment using three-dimensional single-borehole rock was simulated to examine the applicability of the coupled model under realistic loading and boundary conditions.A good agreement was achieved between the simulation and experimental results.Moreover,the mechanism of three-dimensional rock fracture was analyzed.It was concluded that rock particle size and material parameters play an important role in rock damage.The reflected tensile waves cause severe damage in the lower part of the model.Rayleigh waves occur on the top face of the rock model to induce a hoop failure band.

Experimental study of polyurethane foam reinforced soil used as a rock-like material

In this study, p o ly u reth an e foam ty p e th e rm o se t polym erizing, d u e to chem ical reaction b e tw e e n itsliquid ingredients, w as teste d as b in d e r afte r solidifying and th e n a rock-like m aterial m ixing w ith asandy silt ty p e soil w as prep ared . The uniaxial com pressive stren g th s （UCSs） o f p o ly u reth an e foamreinforced soil specim ens w ere d e term in ed for different p o ly u reth an e ratios in th e m ixture. A dditionally,a series o f te sts o n slake durability, im pact value, freezing-th aw in g resistance, and ab rasio n resistance ofp o ly u reth an e reinforced soil （PRS） m ix tu re w as co n d u cted . The UCS values over 3 M Pa w ere m easuredfrom th e PRS specim ens. The testin g results show ed th a t tre a te d soil can econom ically b ecom e adesirable rock-like m aterial in term s o f slake d u ra b ility a n d resistances ag ain st freezing-thaw ing, im pacteffect an d abrasion. As a n o th e r ch aracteristic o f th e rock-like m aterial m ade w ith p o ly u reth an e foam,u n it volum e w eig h t w as found to be q uite low er th a n th o se o f n atu ral rock m aterials.

Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

The fractured surrounding rocks of roadways pose major challenges to safe mining.Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks.The aim of this study is to develop highly efficient composite ultrafine cement(CUC)grouts to reinforce the roadway in fractured surrounding rocks.The materials used are ultrafine cement(UC),ultrafine fly ash(UF),ultrafine slag(US),and additives(superplasticizer[SUP],aluminate ultrafine expansion agent[AUA],gypsum,and retarder).The fluidity,bleeding,shrinkage,setting time,chemical composition,microstructure,degree of hydration,and mechanical property of grouting materials were evaluated in this study.Also,a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock.The results have shown that the addition of UF and US reduces the plastic viscosity of CUC,and the best fluidity can be obtained by adding 40%UF and 10%US.Since UC and UF particles are small,the pozzolanic effect of UF promotes the hydration reaction,which is conductive to the stability of CUC grouts.In addition,fine particles of UC,UF,and US can effectively fill the pores,while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout.The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts.Finally,the CUC22‐8 grout was used to reinforce the No.20322 belt roadway.The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway.In this research,high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

Element geochemical characteristics of a soil profile developed on dolostone in central Guizhou, southern China: implications for parent materials

This study presents bulk chemical compositions of the Tongmuling soil profile, which developed on dolostone, and the overlying strata covering the bedrock in the central Guizhou province(southern China). The chemical weathering characteristics of the studied profile were investigated and the inheritance relationships between the terra rossa and overlying strata were discussed. The results show that there is no remarkable variation in the major elements and weathering indices from the rock–soil interface to the topsoil, indicating that the studied profile was not typical for in situ crustal chemical weathering. The terra rossa were mainly composed of Si O_2, Al_2O_3 and Fe_2O_3. Compared with the insoluble residues and overlying strata, the terra rossa are characterized by an enrichment of Y and Cs and depletion of Ba and Sr. The subsoil shows a notable Ce negative anomaly, characterized by heavy rare earth element enrichment(L/H = 1.55–3.74), whereas the topsoil shows a positive Ce anomaly with light rare earth element enrichment(L/H = 5.93–9.14). According to Laterite-forming capacity estimates, the terra rossa could not have only been formed from acid-insoluble residues from the bedrock; Al_2O_3 versus Fe_2O_3and Nb plotted against Ta show significant positive correlations between the terra rossa and overlying strata. The Eu/Eu* versusGd_N/Yb_Nand ternary diagrams for Sc, Th, Zr, and Ta suggest that the overlying strata could also provide parent materials for the genesis of terra rossa.

Weathering and soils formation on different parent materials in Golestan Province,Northern Iran

Geochemical,mineralogical,and micromorphological characteristics of soils and their relevant parent rocks including loess,ignimbrite,sandstone and limestone were investigated to identify the soil-parent material uniformity and the weathering degree of soils in Golestan Province,northern Iran.Highly developed Calcixerolls and moderately developed Haploxerepts were formed on loess and limestone,respectively.In contrast,the soils formed on ignimbrite and sandstone were nondeveloped Entisols.Illite was the dominant clay mineral found in ignimbrite and sandstone in both the A horizon and parent material.In loess derived soils however,smectite was dominant especially in the Bt horizon compared to its parent material indicating partly to its pedogenic formation.In limestone,illite and vermiculite were dominant both in the A and C horizons.Ti/Zr ratio proved that the studied soils were closely related to their underlying parent materials geochemically.Chemical index of alteration(CIA),micromorphological index of soil development(MISECA),smectite/illite+chlorite ratio and magnetic susceptibility were applied to investigate the degree of soil development.Results showed that the most and the least developed soils were those formed on loess deposits and limestone,respectively.Application of the different geochemical and pedogenetic approaches was proved to be useful in identifying the relevance of soils to their underlying parent materials and also their degree of development.

Preliminary Study on Relationship Between Soil Parent Materials and Tea Quality

Six tea plantations with different soil-forming parent materials, the same tea variety and tea age and similar landforms and management were selected to conduct a systematic study on the relationship between soil properties and tea quality. The results showed that the quality of tea grown on the soils derived from granites, arenaceous shales, argillaceous sandstones, was superior; those on the soils derived from limestones,dolomites, Quaternary red clays, were inferior. Further study showed that sandy soils were beneficial to improving amino acid content of tea, and clayey soils made it decrease; high content of bases might decrease the contents of tea polypenols, caffeine, water extracts, but promote the content of amino acids; available phosphorous was significantly positively correlated with water extracts, but significantly negatively correlated with carbine; slowly available potassium was positively correlated with amino acid content. Soil parent materials should be regarded as an important factor in evaluating the adaptability of tea to soils.

Experimental study on 3D internal penny-shaped crack propagation in brittle materials under uniaxial compression

Fractures are widely present in geomaterials of civil engineering and deep underground engineering.Given that geomaterials are usually brittle,the fractures can significantly affect the evaluation of underground engineering construction safety and the early warning of rock failure.However,the crack initiation and propagation in brittle materials under composite loading remain unknown so far.In this study,a three-dimensional internal laser-engraved cracking technique was applied to produce internal cracks without causing damage to the surfaces.The uniaxial compression tests were performed on a brittle material with internal cracks to investigate the propagation of these internal cracks at different dip angles under compression and shear.The test results show that the wing crack propagation mainly occurs in the specimen with an inclined internal crack,which is a mixed-ModeⅠ–Ⅱ–Ⅲfracture;in contrast,ModeⅠfracture is present in the specimen with a vertical internal crack.The fractography characteristics of ModeⅢfracture display a lance-like pattern.The fracture mechanism in the brittle material under compression is that the internal wing cracks propagate to the ends of the whole sample and cause the final failure.The initial deflection angle of the wing crack is determined by the participation ratio of stress intensity factors KII to KI at the tip of the internal crack.

Theory,technology and application of grouted bolting in soft rock roadways of deep coal mines

The grouted bolt,combining rock bolting with grouting techniques,provides an effective solution for controlling the surrounding rock in deep soft rock and fractured roadways.It has been extensively applied in numerous deep mining areas characterized by soft rock roadways,where it has demonstrated remarkable control results.This article systematically explores the evolution of grouted bolting,covering its theoretical foundations,design methods,materials,construction processes,monitoring measures,and methods for assessing its effectiveness.The overview encompassed several key elements,delving into anchoring theory and grouting reinforcement theory.The new principle of high pretensioned high-pressure splitting grouted bolting collaborative active control is introduced.A fresh method for dynamic information design is also highlighted.The discussion touches on both conventional grouting rock bolts and cable bolts,as well as innovative grouted rock bolts and cables characterized by their high pretension,strength,and sealing hole pressure.An examination of the merits and demerits of standard inorganic and organic grouting materials versus the new inorganic–organic composite materials,including their specific application conditions,was conducted.Additionally,the article presents various methods and instruments to assess the support effect of grouting rock bolts,cable bolts,and grouting reinforcement.Furthermore,it provides a foundation for understanding the factors influencing decisions on grouted bolting timing,the sequence of grouting,the pressure applied,the volume of grout used,and the strategic arrangement of grouted rock bolts and cable bolts.The application of the high pretensioned high-pressure splitting grouted bolting collaborative control technology in a typical kilometer-deep soft rock mine in China—the soft coal seam and soft rock roadway in the Kouzidong coal mine,Huainan coal mining area,was introduced.Finally,the existing problems in grouted bolting control technology for deep soft rock roadways are analyzed,and the future development trend of grouted bolting control technology is anticipated.

Sub-Homogeneous Peridynamic Model for Fracture and Failure Analysis of Roadway Surrounding Rock

The surrounding rock of roadways exhibits intricate characteristics of discontinuity and heterogeneity.To address these complexities,this study employs non-local Peridynamics(PD)theory and reconstructs the kernel function to represent accurately the spatial decline of long-range force.Additionally,modifications to the traditional bondbased PD model are made.By considering the micro-structure of coal-rock materials within a uniform discrete model,heterogeneity characterized by bond random pre-breaking is introduced.This approach facilitates the proposal of a novel model capable of handling the random distribution characteristics of material heterogeneity,rendering the PD model suitable for analyzing the deformation and failure of heterogeneous layered coal-rock mass structures.The established numerical model and simulation method,termed the sub-homogeneous PD model,not only incorporates the support effect but also captures accurately the random heterogeneous micro-structure of roadway surrounding rock.The simulation results obtained using this model show good agreement with field measurements from the Fucun coal mine,effectively validating the model’s capability in accurately reproducing the deformation and failure mode of surrounding rock under bolt-supported(anchor cable).The proposed subhomogeneous PD model presents a valuable and effective simulation tool for studying the deformation and failure of roadway surrounding rock in coal mines,offering new insights and potential advancements.

Non-local damage and fracture model of rock and concrete-like materials

In view of the non-local phenomena appearing in the rock and concrete-like materials, the non-local damage and fracture model of rock and concrete-like materials was established through non-local method of Gaussian weighting function. The result indicates that, the stress of one point in the material is correlated not only to its strain history, but also to the interaction of the points in its certain adjacent region of the material. Based on the established non-local model, the numerical simulation of notch containing three-point bending beam was carried out. The results show that the grid sensitivities have been avoided and the fracture direction of the material has not been influenced by the grid shape, and the model proposed can be used to better simulate the damage developing process of the rock and concrete-like materials.

An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures.In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures（a horizontal fissure and an inclined fissure） were created by inserting steel during molding the model specimen.Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servocontrolled testing system. The peak strength and Young＇s modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0？to 75？.In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process.Moreover, acoustic emission（AE） monitoring technique was also used to obtain the AE evolution characteristic of prefissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up： when a new crack was initiated or a crack coalescence occurred, thecorresponding axial stress dropped in the axial stress–time curve and a big AE event could be observed simultaneously.Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

Effect of insoluble materials on the volumetric behavior of rock salt

This paper focuses on the presence of nodules of insoluble materials within salt specimens,and their effect on the volumetric strain measurements and the dilatancy phenomenon.We analyzed experimental results of over 120 conventional triaxial compression tests,and found that in 20%of the cases,the volumetric strain measurements were atypical.We also noted that the natural variability of the specimens can lead to a non-negligible data scattering in the volumetric strain measurements when different specimens are subjected to the same test.This is expected given the small magnitude of those strains,but it occasionally implies that the corresponding specimens are not representative of the volumetric behavior of the studied rock.In order to understand these results,we numerically investigated salt specimens modeled as halite matrices with inclusions of impurities.Simulations of triaxial compression tests on these structures proved that such heterogeneities can induce dilatancy,and their presence can lead to the appearance of tensile zones which is physically translated into a micro-cracking activity.The modeling approach is validated as the patterns displayed in the numerical results are identical to that in the laboratory.It was then employed to explain the observed irregularities in experimental results.We studied the natural variability effect as well and proposed a methodology to overcome the issue of specimen representativity from both deviatoric and volumetric perspectives.

Soil Carbon Sequestrations in Forest Soils in Relation to Parent Material and Soil Depth in South-Eastern Nigeria

There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties and hence will influence how much carbon is sequestered by soil. The study was conducted in June 2019 to investigate soil carbon stock in forest soils with respect to their parent materials in three States in South-eastern Nigeria. Sampling was aided by the location map of the area and free soil survey method was used to locate sampling points. 0ne profile was dug in each location and described using the Food and Agricultural Organization guideline. A total of twelve soil samples were collected and analyzed for selected properties. Results showed that sand content was significantly higher in soils under coastal plain sands (851.96 g·kg−1) and was lowest in soils of Imo clay shale (605.60 g·kg−1). Clay content was higher in soils of Imo clay shale (277.34 g·kg−1) and was lowest in coastal plain sand (118.80 g·kg−1). Silt and clay had moderate variation in coastal plain sand (>15 ≤ 35%) and high variations in Asu River and Imo clay shale (CV > 35%). The soils studied were generally acidic with values ranging (3.52) in soils formed from coastal plain sand, followed by forest soils of Imo clay shale (3.64) and Asu river group (3.85). Soil organic carbon decreased with increase in soil depth in all soil parent materials studied. Mean values ranged from 6.14 g·kg−1 in soil underlain by coastal plain sand to 10.62 g·kg−1) in soils of Imo clay shale. Soil carbon sequestered under the three different parent materials ranged from 1575 - 4676.41 (g·cm−2). Also, soil depth had a notable impact on carbon sequestration with values ranging from 1529.42 - 4374.0541 (g·cm−2) and the thicker the horizon, the more carbon sequestered. Hence, the study concluded that more carbon is sequestered in the subsurface horizons of the soil pedons than in the epipedons.

STUDY ON DAMAGE BIFURCATION AND INSTABILITY OF ROCK-LIKE MATERIALS

The critical bifurcation orientation and its corresponding hardening modulus for rock-like geomaterials are derived by considering the effect of stiffness degradation and volumetric dilatancy under the assumption of isotropic damage. The dependency of the localized orientation on the degree of damage and initial Poisson＇s ratio of rock is examined and the bifurcation behavior of the uniaxial compression sample under the plane-stress condition is compared with that under plane-strain condition. It is shown that the localization orientation angle intimately depends on both the initial Poisson＇s ratio and degree of damage for the rock sample under the uniaxial compression condition. As the initial Poisson＇s ratio or degree of damage increases, the orientation angle of the plane on which localization tends to be initiated gets to decrease. At the same time, the localization orientation angle of a rock sample under the plane-stress condition is larger than that under the plane-strain condition.