Rock Mass Engineering Research Articles

The strain characteristics of cracked anchored soft rock under short-term creep

Abstract The short-term creep properties of cracked soft rock are the basis for analyzing and predicting the long-term deformation characteristics of engineering rock mass. Based on orthogonal test design and by means of physical testing and theoretical analysis, this paper systematically studies the short-term creep strain properties of soft rock mass with a vertical anchor form under different combinations of crack number, crack discontinuity degree and crack inclination. The results show the following: (i) as the stress increases, the growth rate of the instantaneous strain of the anchored soft rock slows down, the growth rate of the creep strain increases and the growth rate of the total strain decreases at first and before it then increases. Based on this, the idea is proposed that the stress corresponding to the turning stress of the total strain change rate, from small to large, is the turning stress of the strain rate. This stress value is approximately 50% of its uniaxial compressive strength (UCS). (ii) Statistical analysis shows that for the same cracked rock mass, the three characteristics of cracks have different effects on the instantaneous strain, creep strain and total strain of anchored soft rock, and a certain number of cracks under specific geometric conditions are beneficial to the long-term deformation control of anchored soft rock. (iii) A relative creep model based on mutation is proposed. Considering the effects of the test instrument, the model can be divided into the power function model, the logarithmic function model and the exponential function model, according to goodness of fit. All three models can describe the initial and stable creep stage of anchored soft rock with cracks.

Application of the Maximum Sensitivity Principle in the Optimization of Measuring Point Arrangement in Transversely Isotropic Rock Mass Engineering

The inverse analysis method based on in situ measurement information provides a new approach to determine the mechanical parameters of rock mass. The accurate on-site monitoring data is the prerequisite and basis for the success of displacement back analysis. To improve the accuracy of requirement parameters, a reasonable layout program should be developed to optimize the layout of the measuring position. In order to study the optimal arrangement of measuring points in anisotropic rock mass, the layout optimization of measuring points around a tunnel in the transversely isotropic rock mass is studied according to the maximum sensitivity criteria. The influence of the spatial location of the measuring points on the measurement of the tunnel deformation is obtained. The results indicate that the measuring point should be arranged close to the extreme point in the direction of the larger principal stress.

Investigating dynamic fracture in marble-mortar interface under impact loading

• Compared with the M-S-750 series specimens, the transgranular phenomenon is more common in the M-R-750 series specimens. • The crack propagation velocity in the BSCT specimen is lower than the speed of Rayleigh wave in the M40 mortar. • With the increase of loading rate, the crack propagation speed between CPG adjacent wires does not necessarily increase. • The discrepancy of wave impedance between marble and mortar results in the existence of shear stress in the interface zone of the BSCT specimen. • Compared with the BSCT specimens with smooth interfaces, the fracture properties ( K 1 and G ) of the BSCT specimens with rough interfaces are improved significantly. The mechanical property of the mortar-rock interface is a key factor in dominating the effectiveness of many reinforcement measures in rock mass engineering. Investigating the mortar-rock interface is of important practical consequences. In this paper, a bi-material single cleavage triangle (BSCT) configuration, composed of marble and mortar, was employed in a split Hopkinson pressure bar (SHPB) experiment with interface roughness and loading rates considered. The experimental–numerical method was used to obtain the crack initiation energy release rate G and the complex stress intensity factor ( K = K 1 + i K 2 ) of the onset interface crack. Besides, AUTODYN software was applied for analyzing the propagation law of stress waves in the BSCT specimen, and the failure mechanism of the mortar-rock interface was revealed. The results show that the interface crack growth rate in the BSCT specimen is lower than the P-wave, S-wave, and Rayleigh wave in the M40 mortar. The discrepancy of wave impedance between marble and mortar results in the existence of shear stress in the interface zone of the BSCT specimen. As the loading rate increases to 920 GPa/s, the fracture properties ( K 1 and G ) of all BSCT specimens are significantly improved. The improvements in the fracture properties are more significant for the BSCT specimens with rough interfaces compared to the BSCT specimens with smooth interfaces.

Application of Two Novel Acoustic Emission Parameters on Identifying the Instability of Granite.

The issue of monitoring and early warning of rock instability has received increasing critical attention in the study of rock engineering. To investigate the damage evolution process of granite under triaxial compression tests, acoustic emission (AE) tests were performed simultaneously. This study firstly introduced two novel parameters, i.e., the coefficient of variation (CoV) of the information entropy and correlation dimension of the amplitude data from the AE tests, to identify the precursor of the failure of granite. Then the relationship between the changes in these parameters and the stress-time curve was compared and analyzed. The results of this study show that: (1) There is a strong correlation between the CoV of the information entropy and the failure process of granite. The granite failed when the CoV curve raised to a plateau, which could be used as an indicator of rock instability. (2) The fluctuation of the correlation dimension indicates the different stages during the loading process, i.e., the initial compaction stage, the linear elastic stage, the yield stage, and the failure stage. Each stage contains a descending and a rising process in the correlation dimension curve, and the exhibited starting point or the bottom point at the correlation dimension curve could be selected as the indicator point for the rock instability. (3) The combined analysis of the Information entropy and Correlation dimension can improve the accuracy of rock instability prediction. This study provides new insights into the prediction of rock instability, which has theoretical implications for the stability of subsurface engineering rock masses.

Numerical implementation of rock bolts with yield and fracture behaviour under tensile-shear load

To realize the numerical analysis of rock bolt bearing-yield-fracture under tension-shear coupling and to provide an effective means for supporting the design of roadways or tunnels, a new numerical model was developed to analyse the tension-shear coupling fracture behaviour of rock bolts in engineering rock masses. Based on the study of the mechanical behaviour of rock bolts under tensile-shear coupling load, the mechanical criterion and constitutive model of the yield and fracture of rock bolts were proposed, and the secondary development of the FLAC3D platform was realized. At the same time, self-developed equipment was used to conduct the rock bolt tensile shear test. By comparing the numerical simulation results with the experimental results, we determine that the maximum difference in the shear displacement of the rock bolt does not exceed 2 mm during the yielding and breaking of the rock bolt, and the percent difference was approximately 3% and 10%, respectively. In the field of engineering, this result is generally considered acceptable. Using the numerical model we proposed, a numerical simulation experiment was conducted on the rock bolt support design of a coal mining roadway in engineering practice. The results show that under the original support scheme, a large amount of rock bolt tensile-shear failure occurs at the coal-rock interface, which makes the original support scheme unable to meet the engineering requirements with tensile-shear coupling failure tendency. In this regard, we adopted the support method of grouting anchorage at the interface of coal and rock. The results show that the deformation of the roadway surrounding rock has been effectively controlled.

Preliminary Study on Post-Peak Behavior and Fracture Characteristics of Hard Rock Under True Triaxial Stress

The post-peak behavior and fracture characteristics of hard rock are correlated with the stability and bearing capacity of engineering rock mass. However, there are relatively few research studies on the post-peak mechanical behavior and fracture characteristics of hard rock under true triaxial stress. Therefore, this study carried out relevant true triaxial compression tests and acoustic emission (AE) monitoring. It is concluded that under a true triaxial condition, the number of post-peak steps increases first and then decreases with the increasing σ2, which implies that the rock failure evolves from shear failure to a more complex tension–shear mixed failure and finally evolves into a failure mode dominated by tensile failure. The overall level of the rock fracture angle (θ) at low σ3 is higher than that at high σ3. In the range of stress level in this study, when σ3 is high, the fracture angle of granite increases with increasing σ2, and its regularity is obvious, while when σ3 is low, the regularity of the fracture angle increases with the increasing σ2 is not obvious. It is found that there are three different types of cracking processes in granite. Meanwhile, the expansion rates of three different racking types are calculated by simplified treatment, which are about the order of 10−5–10–4 m/s. The research results of this study could supply a useful reference for the understanding of deep hard rock fracture behavior.

Statistical Damage Model of Rock Based on Compaction Stage and Post-Peak Shape under Chemical-Freezing-Thawing-Loading

The deterioration of rock mechanical properties under chemical-freezing-thawing-loading will seriously threaten the stability and safety of engineering rock mass, so the study of its constitutive model has very important theoretical and engineering application significance. In view of the deficiency that the existing statistical damage constitutive model cannot describe the nonlinear characteristics of the compaction stage and the post-peak shape, the compaction index is introduced to measure the stress-strain nonlinear characteristics caused by the iso-compression of the pores in the rock, and the post-peak correction coefficient is introduced to optimize the post-peak shape of rock loading. Assuming that the strength and failure of rock microunits obey the Weibull distribution, on the basis of using the Drucker-Prager strength criterion to measure the strength of rock microunits, a statistical damage model for rock considering the compaction stage and post-peak shape under chemical-freezing-thawing-loading is established. Finally, it is compared with the test curve. The results show that the calculation curve of the established chemical-freezing-thawing-loading rock statistical damage model has the same trend as the rock uniaxial compression test curve. Furthermore, it can better describe the rock stress-strain law with different chemical solutions and different freeze-thaw cycles, which fully reflects the rationality and accuracy of the constructed constitutive model. The research results can provide a theoretical basis for the calculation of deformation and failure of rocks under chemical-freezing-thawing-loading.

Experimental Investigation of Failure Mechanisms of Granites with Prefabricated Cracks Induced by Cyclic-Impact Disturbances

Engineering rock mass is normally subject to cyclic–dynamic disturbances from excavation, blasting, drilling, and earthquakes. Natural fractures in rock masses can be reactivated and propagated under dynamic and static loadings, which affects the stability of rock mass engineering. However, fractured rock mass failure induced by cyclic-impact disturbances is far from clear, especially considering varying angles between the rock mass and the direction of impact loadings. This work investigated rock deformation and failure characteristics through cyclic impact tests on granite samples with cracks of different angles. A Hopkinson bar was employed for uniaxial cyclic impact tests on granite samples with the crack inclination angles of 0–90°. The magnetic resonance imaging technique was used to determine rocks’ porosity after cyclic impacts. The stress–strain curves, porosity, strength, deformation modulus, failure modes, and energy density of samples were obtained and discussed. Results showed that the crack inclination angles significantly affected the damage evolution and crack morphology of rocks. Under the constant cyclic impact, the dynamic deformation modulus and dynamic strength of rock samples first increased and then decreased with the increase in crack inclination angle. The failures of granite samples for inclination angles of 0 and 90° were dominated by tensile cracking, while those for the inclination angles of 30–60° were dominated by shear cracking. The energy density per unit time gradually decreased with the increase in impact cycles. The results can provide references for the stability analysis and cyclic-impact-induced failure prediction of fractured rock masses.

Stress–strain and acoustic emission characteristics of cement-based materials used to simulate soft rock with fractures

Instability failure in rock mass engineering is closely related to expansion of joint fissures. In this study, uniaxial compression tests and acoustic emission (AE) measurements were carried out simultaneously on specimens of soft rock-like material with different fracture angles and connectivity values to better understand their influence on the deformation and failure of the material. The stress–strain curve and AE signal of fractured soft rock-like material are similar to those of intact soft rock-like; specifically, they exhibit a compaction, elastic deformation, stable fracture development, and unstable fracture development. The main differences between fractured and intact material occur during post-peak failure stage. Under the combined influence of fracture angle and connectivity, the uniaxial compressive strength of fractured soft rock-like material (f_{cu}^{^{prime}}) is lower than that of the intact soft rock-like material (fcu), and can be described by the relationship f_{cu}^{^{prime}} = f_{cu} cdot alpha, where alpha is the strength reduction coefficient, fitted as alpha = 0.8228 + 0.00411x - 0.00789y. In this equation, x is the fracture angle (^circ) and y is the fracture connectivity (%). Under uniaxial compression, the main types of secondary cracks were wing cracks and secondary coplanar cracks. The specimen with a fracture angle of 30° mainly underwent tensile failure under loading, whereas those with fracture angles of 45° and 60°mainly experienced shear failure under high-connectivity conditions (45%).

Research on Generalized RQD of Rock Mass Based on 3D Slope Model Established by Digital Close-Range Photogrammetry

The traditional method of obtaining rock quality designation (RQD) cannot fully reflect the anisotropy of the rock mass and thus cannot accurately reflect its quality. In the method of calculating RQD based on three-dimensional network simulation of discontinuities, due to the limited number of samples and low accuracy of discontinuity data obtained by manual contact measurement, a certain deviation in the network is generated based on the data, which has an impact on the calculation result. Taking a typical slope in Dongsheng quarry in Changchun City as an example, in this study, we obtained the discontinuity data of the slope based on digital close-range photogrammetry, which greatly enlarged the sample size of discontinuity data and improved the data quality. Based on the heterogeneity of the rock mass, the optimum threshold of discontinuity spacing was determined when surveying lines were laid parallel to different coordinate axes to calculate the generalized RQD, and the influence of measuring blank areas on the slope caused by vegetation coverage or gravel accumulation was eliminated. The real generalized RQD of the rock mass after eliminating the influence of blank areas was obtained. Experiments showed that, after eliminating the influence of blank areas, the generalized RQD of the slope rock mass more truly represented the complete quality of rock mass and offers a new idea for the quality evaluation of engineering rock mass.

Fractal Statistical Study on the Strength of Jointed Rock Mass

The failure probability and strength of jointed and fractured rock mass under water pressure action place important constraints on the safety and stability of rock mass engineering. In this study, two strength calculation models for rock mass joint rupture failure and shear slip failure are established according to different relative sizes and working conditions, and the effects of fractal dimension, water pressure, and number of cracks on the strength and failure probability of rock mass are analyzed. The most unfavorable dip angle under shear-slip conditions is calculated. The proposed models accurately reflect the failure probability and strength of jointed rock mass, and different strength calculation methods should be selected according to the specific working conditions. The effect of water pressure on the strength of jointed rock mass is sensitive to the failure mode. Reasonable drainage should be carried out according to the different failure modes when constructing tunnels with abundant groundwater, and certain drainage or water plugging construction schemes are not necessarily applicable to all cases. The dip angle at which joint fissures are most prone to shear slip is given as π/4 + φ/2, where φ is the jointed rock mass strength parameter. An increase in the fractal dimensions, external stress, and number of fractures will enhance the rock mass failure probability regardless of failure mode. Controlled blasting and advanced grouting reinforcement measures are recommended when a tunnel traverses through a joint fissure zone to reduce the number of cracks generated in the surrounding rock and thus improve its strength and stability.

Electromagnetic radiation signal monitoring and multi-fractal analysis during uniaxial compression of water-bearing sandstone

Rockburst disasters seriously threaten the safety of deep coal mining. Electromagnetic radiation (EMR) is a powerful means of rockburst monitoring and early warning. However, the current related research often ignores the fact that the rock mass in engineering is frequently in a water-bearing state. Therefore, in this paper, the EMR signals of sandstone samples with different water contents were monitored under uniaxial compression. The experimental results showed that with the increase of water content, the EMR signals of sandstone weakened as well as the mechanical strength. Compared with dry samples, the total EMR energy and peak EMR energy of saturated samples decreased by 71.41% and 76.06% respectively. Moreover, higher moisture content would lead to lower dominant frequency and amplitude of EMR signals under various stress levels. Through multi-fractal analysis, it is found that with the rise of moisture content, the non-uniformity of signal (Δα) and the frequency diversity of minimum and maximum signals (Δf) decreased. These reflect some changes in the generation mechanism of EMR signal. The abrupt changes of Δα and Δf can be regarded as precursors of rock failure. The research results can provide guidance for the frequency band selection and precursor identification of rockburst monitored by EMR.

Investigation of 2D Seismic DDA Method for Numerical Simulation of Shaking Table Test of Rock Mass Engineering

Since the basic theory of the discontinue deformation analysis (DDA) method was proposed, the DDA open source has gone through a long development process. At present, different kinds of programs have been widely applied in rock mass engineering such as slope, dam, and tunnel. This paper introduces the solution principle of DDA motion equations in detail, as well as the development status of the 2D open-source program. Numerical simulation of shaking table test of rock mass engineering using 2D DDA program is highlighted, and investigations of seismic wave pre-processing and seismic input method are carried out. First, based on the Newmark integration scheme, the integration algorithms of synthetic or measured seismic wave time history, correction function of seismic wave, and DDA simulation are unified. Then, three seismic input methods are implanted in the DDA program, and the applicability of various seismic input methods is discussed. On this basis, using the improved seismic 2D DDA program, a shaking table test of typical rock mass engineering is simulated. Through the comparison between the theoretical/test data and simulation results, the reliability of the improved DDA program in seismic response analysis is verified; the large mass method and the large stiffness method are more suitable for rigid foundation, such as shaking table test; the propagation of the seismic wave presents a significant amplification effect due to the reflection, refraction, and diffraction in the tunnel. The research results provide DDA theory and an open-source program for analyzing the seismic response of rock mass engineering.

A Study on the Strain-Softening Constitutive Model of Cementitious Sandstone

In order to further investigate the impacts of the water environment on the mechanical properties of rocks for an engineering project, taking the water-rich conditions in a coal mine as the engineering background, a series of tests were conducted, including the uniaxial compression test, the conventional triaxial compression test, and the constant axial pressure test on the cementitious sandstone. This was conducted along with the establishment of a multi-linear strain softening constitutive model. According to the tests, the following conclusions can be drawn. Firstly, as the water content increases, the weakening effect of water on the rock mass was obvious. Under various stress paths, the water weakened the rock body to various degrees. In other words, the weakening effect of water on the rock mass was either inhibited or promoted under different stress path conditions Secondly, under various stress paths, the turning point strength and strength variance rate of the rock mass’ mechanical properties decreased linearly with the increase of water content. This further proves that water has a weakening effect on the rock mass, showing that the failure of the specimen changes from brittleness to ductility. Thirdly, the test sample demonstrated different types of damages including the tensile failure, transformation from tensile-shear composite failure to shear failure, and expansion failure under three stress path conditions. In addition, the unloading process demonstrated some dynamic failure characteristics. The research aims to provide some foundational insights for the scientific design and safe construction of the mine and other underground engineering, especially rock mass engineering in the multi-water environment.

Types and occurrence time of rockbursts in tunnel affected by geological conditions and drilling & blasting procedures

Rockburst is a difficult problem that restricts the development of deep rock mass engineering technology, and the warning of rockburst occurrence time remain a common challenge worldwide. This paper presents geological information and rockburst occurrence time in different drilling & blasting procedures collected in detail from a deep tunnel. A characterization method of MS (Microseismic) sequences has been designed to characterize the evolution law of microseismicity in the blasting cycle. An LSTM (Long Short-Term Memory) model is established to construct and augment the MS sequence samples, and a database was established based on information such as geology, excavation, support, MS sequence, and rockburst. Based on the information in 600 blasting cycles of the database, a multisource data mining method for analyzing the MS sequence formation mechanism is established. The relationship between the characteristics of rockburst occurrence time and MS sequence is established, and the formation mechanism of the MS sequence is used to interpret the potential rockburst type and occurrence time affected by geological conditions and drilling & blasting procedures. The results show that the number and spacing of structural planes have an important influence on the frequency, intensity and type of rockbursts. Rockburst may occur in each procedure of the blasting cycle. The frequency of rockburst during the danger elimination and support stage is the highest, during the drilling and charging blasting stage is the lowest. The MS sequence in blasting cycle is divided into four types, which have a good relationship with the rockburst occurrence time in blasting cycle procedures. Rockburst type and occurrence time in different procedures is mainly controlled by the rock mass structure, excavation footage, excavation rate and blasting time interval. The results have important reference value and guiding significance for rockburst time warning and hazard control.

Pre-peak acoustic emission characteristics of tight sandstone failure under true triaxial stress

In this study, experimental investigations were conducted on low-porosity sandstone specimens to reveal their pre-peak cracking characteristics under constant mean stress (σm, 100 MPa) and varying stress Lode angles (θσ, −30° to +30°). The acoustic emission (AE) characteristics 50 s before specimen failure, as well as the strengths and fracturing surface networks, are presented and discussed. The results show that the values of the three principal stresses when the specimen failure occurs change linearly with increasing θσ, in which the maximum principal stress linearly decreases. The AE energy distribution exhibits three ranges, which can be speculated as the different stages of rock cracking propagation. The AE peak frequency is distributed unevenly in seven bands, in which over 90% of the AE signals are located in the 75–95 kHz and 96–130 kHz ranges, which correspond to the tensile and shear cracks, respectively. The RA-AF dynamic evolution curves reveal that the ultimate failure is driven by shear fractures under 3D stress states (for all θσ). The pattern of macrocrack networks shows the “double-X″ through-going mode, and clear tensile and shear areas were directly observed on the fracturing surfaces. These findings are deemed essential for determining the failure mechanism of deep engineering rock masses.

Importance of Engineering Rock Mass Classifications for Rock Cut Slope Stability Analysis

Importance of Engineering Rock Mass Classifications for Rock Cut Slope Stability Analysis

Investigation on model-I fracture toughness of sandstone with the structure of typical bedding inclination angles subjected to three-point bending

The fracture mechanics behaviors of rock with bedding plane structure have considerable influences on rock mass engineering, among which crack initiation toughness (KIini) and unstable fracture toughness (KIun) play a significant role. This work first adopts the classical equivalent elastic fracture theories from different perspectives to precisely determine KIun. Then the double-K fracture criterion (DKFC) and the double-G fracture criterion (DGFC) are employed to inversely compute KIini through cohesive fracture toughness (KIc). The experimental results indicate that the crucial strength and deformation parameters show obvious weakening trends as the bedding direction varies from horizontal to vertical for stratified sandstone under standard three-point bending with a loading rate of 0.0001 mm/s. Furthermore, there are little differences in KIun among three common calculation methods, including the ASTM standard, the Guinea proposed method, and the energy release rate. The average values of KIun are 8.20 MPa·mm1/2, 7.38 MPa·mm1/2, 4.76 MPa·mm1/2, and 4.49 MPa·mm1/2 for the tested specimens with bedded orientation angles 0°, 30°, 60°, and 90°, respectively. However, there is a remarkable difference between KIiniK evaluated by the DKFC and KIiniG evaluated by the DGFC, and two relationships are satisfied as KIiniK= 0.42KIun and KIiniG= 0.30KIun. Additionally, the applicability of the DKFC and the DGFC is validated by the acoustic emission (AE) technique. The comparisons manifest that the crack initiation toughness evaluated by the AE counts and cumulative AE counts is consistent with that of the DGFC. The leading significances for this study are to explore the application of various fracture mechanics theories to three-point bending specimens and provide fracture mechanics parameters for underground engineering and tunnel engineering.

Strength Characteristics and Failure Mechanism of Granite with Cross Cracks at Different Angles Based on DIC Method

The engineering rock mass is generally composed of the rock matrix and structural plane and is an anisotropic inhomogeneous geological body. Accidents such as roof collapse and well caving caused by joint and fissure expansion occur frequently during tunnel excavation and service, resulting in serious casualties and economic losses. It is of great theoretical significance and engineering value to study the fracture mechanism of the jointed rock mass to ensure the stability of the surrounding rock and the safe and efficient utilization of the urban underground space. To investigate the effects of crossed cracks on mechanical properties and failure characteristics of rock, wire cutting equipment is employed to make rock samples with different crossed cracks, and then acoustic emission system and digital image correlation technique are used to study the fracture process of rock samples under uniaxial compression. It has been found that the strength of rock samples with a single crack is generally larger than that of samples with cross cracks, and the strength changed with the angle of the crack in a “V” shape. When the angle of preexisting crack is 60°, the rock strength reaches the lowest. The primary crack has a more obvious influence on rock strength and is the main controlling factor of rock fracture. The initiation stress of rock samples with a single crack changes more significantly with angle. When the angle of the primary crack is 45°, the rock sample is most prone to crack initiation failure, and the crack initiation stress is only 1/4 to 1/2 of the strength. There are two types of cracks: wing and anti-wing, and the tensile cracks are the main ones. It is revealed that the fracture of cracked rock has significant directional characteristics. For the samples with cross cracks, the primary crack is the main control factor of crack initiation, and the secondary crack has a certain guiding effect on the crack.

Development and validation of environmentally friendly similar surrounding rock materials and cement slurry for surrounding rock repair and reinforcement

The repair and strengthening of broken engineering rock masses usually require the use of rock-like materials and cement grouting. However, studies in this area usually focus on only one or two mechanical parameters, and it is difficult to guarantee the similarity between similar materials and surrounding rocks. In addition, a large number of experimental studies on engineering rock mass crack grouting cannot be carried out at engineering sites. The design of most materials does not consider environmental protection issues. Therefore, this article uses some waste materials to develop a high-similarity similar rock material, in which fine-grained copper powder and fine-grained gypsum replace part of the cement material. The two are combined to verify the feasibility of using such a material at the project site. The research results show that environmentally friendly rock-similar materials and cement grouting materials developed can be used for the emergency repair and reinforcement of engineering rock masses. It is highly recommended to use a variety of waste materials as environmentally friendly materials for crack grouting in engineering rock masses, which provides a feasible way to treat the above waste materials and protect the environment at the same time.