Deterioration Of Mechanical Properties Research Articles

Laser Additive Manufacturing of Layered Zr-Based Bulk Metallic Glass Composite

As a potential functional material, much effort has been devoted to enhancing the mechanical properties of bulk metallic glass composites (BMGCs). Among them, layered BMGCs are regarded as effective for achieving a strength–ductility synergistic effect. However, it is difficult with the existing metallic glass (MG) preparation technologies to obtain a decent layered structure. In addition, the fragile interface between layers formed using the traditional fabricating method always exacerbates the deterioration of mechanical properties, which restricts the wide application of layered BMGCs. In the case of laser additive manufacturing (LAM), the cooperation of coarse grains in the hot affected zone (HAZ) and fine grains in the remelting zone induced by a unique thermal history is of key importance in eliminating the fragile interface and therefore overcoming premature cracking. Thus, we successfully synthesized Nb-Zr48Cu46.5Al4Nb1.5 layered material with a yield strength of 1332 (±91) MPa and a compression ductility of 4.17 (±0.14)% via LAM. The results of the compressive curves of Nb and BMGC prepared by LAM decisively demonstrate that the layered material obtains a certain degree of plasticity while maintaining relatively high strength. This remarkable mechanical property is mainly attributed to the asynchronous deformation and the interaction of the adjacent Nb and MG layers. It is worth emphasizing that a distinctive round-way crack extension is discovered during the deformation process, which plays a significant role in breaking through the strength ductility trade-off. In addition, the source of yield strength is calculated theoretically using the rule of the mixture and the dislocation strengthening principle. The results indicate that the strength contributed by geometrically necessary dislocations is around 101.7 MPa. In addition, the strength calculated by the rule of the mixture is ~1201.9 MPa. This work offers a new paradigm for BMGCs with excellent strength and ductility as practical engineering materials.

Combined effects of freeze–thaw cycles and chemical corrosion on triaxial mechanical properties of sandstone

To study the combined effects of freeze–thaw cycles and chemical corrosion on deterioration mechanism of triaxial mechanical properties of sandstone in cold regions, triaxial compression tests were carried out on homologous sandstone specimens after corrosion action of acidic, alkaline or neutral solution and cyclic freeze–thaw action, by taking the pH value of the hydrochemical solution and the number of freeze–thaw cycles as control parameters. The failure mode of triaxial compression is shear-slip failure, and the deviatoric stress–strain curves can be divided into four stages of compaction, linear elastic, yield, and failure. The stress–strain curves and deterioration law of triaxial mechanical properties were analyzed. With the increase of freeze–thaw cycles, the peak stress, peak strain and modulus all decrease, the deterioration degree of the rock specimens increases, and the yield plateau and plastic characteristics in the yield stage become weaker. The strong acid solution shows the largest degree of damage, and the peak stress, peak strain and modulus decreased significantly. The precipitates produced by the reaction between the strong alkaline solution and the specimens adhere to the specimen surface, pores, and fissures, thereby inhibiting further damage and deterioration. Confining pressure is an essential factor affecting the rock mechanical properties. As confining pressure increases, the strength and deformation-resistant ability of specimens increase, and the yield stage on the stress–strain curve is more obvious. The sensitivity of acidic solution to the deterioration of mechanical properties of sandstone is obviously greater than that of alkaline solution. These results provide a theoretical basis for the construction of geotechnical engineering structures in cold regions.

Experimental Study on Mechanical Properties and Deterioration Mechanism of Red Sandstone from the Panjiatuo Landslide under Action of Acidic Drying−Wetting Cycles

Due to frequent water level fluctuations and complex hydrochemical environments, rock slopes in reservoir areas progressively deteriorate and become unstable. This study investigated the coupling effect of drying−wetting cycles and acidic solutions on the physical and mechanical properties, strain field evolution, failure mode, and micro-mechanism of red sandstone using a series of laboratory experiments (wave velocity tests, uniaxial compression tests, the digital image correlation method, scanning electron microscopy, and X-ray diffraction). The results showed that with increasing drying−wetting cycles, the mass, P-wave velocity, elastic modulus, and uniaxial compressive strength decreased monotonically, while the water absorption and apparent strain in the strain localization band increased. Moreover, the failure mode transitioned gradually from tensile failure to shear failure or tensile-shear composite failure. The decrease in the solution pH values aggravated the changes in the physical and mechanical parameters and contributed to an increase in the secondary cracks and the occurrence of shear behavior. In addition, the coupling effect of drying−wetting cycles and acidic solutions accelerated the worsening of the microstructure and the dissolution of minerals, resulting in a loose structure with well-developed pores and fissures. These changes provide a favorable explanation for the mechanical property deterioration of red sandstone subjected to acidic drying−wetting cycles.

Study on design, preparation, and performance of low‐temperature rising concrete with energy storage aggregate

AbstractAlleviating cracks induced by the temperature rise in mass concrete has always been a research hotspot and engineering problem. In this study, a type of energy storage phase change low‐temperature rising concrete was designed and prepared to reduce the cracking risk of mass concrete. First, a type of energy storage coarse aggregate (ESA) was prepared using a semi‐dry method with cement and fly ash as matrix materials, mixed with carbon black (CB), carbon fiber (CF), and phase change material (PCM). Furthermore, the influence of these materials on the mechanical properties, microstructure, and pore structure of the ESA was studied. Subsequently, ESA was used to prepare phase change low‐temperature rising concrete, and its mechanical properties, thermal conductivity (TC), and internal temperature rise were investigated. The research results show that, except for the compressive strength of PCM‐15‐ESA, which is only 7% lower than that of the control, PC‐P0, other samples have no mechanical property deterioration. The double‐layer protection measures can effectively avoid the mechanical property deterioration of concrete induced by PCM leakage. The maximum internal temperature rise of concrete is reduced by 9.8°C, which greatly reduces the risk of cracking of concrete.

Mechanical coupling and tuned anisotropic elasticity: Numerical and experimental material design for shear-normal and shear-shear interactions

Mechanical coupling in architectured materials has been traditionally investigated in the context of generalized continuum mechanics and is often assumed to be non-existent in the framework of classical continuum mechanics. In this paper, we challenge this misconception and study an anisotropic architectured material exhibiting shear-shear and shear-normal coupling from the standpoint of classical continuum mechanics. The material is non-regular tetrahedron lattice, a potential candidate for biomedical implants, but the lack of understanding about its anisotropic behavior and mechanical couplings has limited its application. We exploited the unit-cell definition with periodic boundary conditions and performed elastic and elastoplastic homogenizations. Non-zero coupling sub-matrices appeared in the homogenized elasticity matrix, which we further transformed into material’s natural coordinate system using elastic distance function. This allowed for anisotropy identification and determination of all the coupling parameters. Next, compression tests are conducted on laser powder bed fused Al-12Si (mass%) lattice samples with different relative densities and spatial orientations. Employing test data, mechanical anisotropy and shear-normal couplings are experimentally characterized. Both numerical and experimental results confirmed the presence of mechanical couplings and predicted a similar anisotropic tendency in the material. Finally, the role of manufacturing defects in deterioration of as-designed mechanical properties is discussed.

Effect of rare earth element Er on the microstructure and properties of highly alloyed Al-Zn-Mg-Cu-Zr-Ti alloy

By using standard melting casting, homogenization, extrusion, solid solution, and T6 aging, an Al-11Zn-3.1Mg-1.2Cu-0.2Zr-0.16Ti alloy was created, and the microstructure and mechanical properties of the alloy with various Er contents were investigated. The inclusion of Er promoted the increase in the number density and volume fraction of L12-Al3(Er, Zr) in the alloy, which greatly reduced the alloy's tendency to recrystallize, raised the internal dislocation density, and helped the alloy achieve grain refinement. To a certain extent, a moderate amount of Er added to the alloy may have helped the precipitation and phase transformation of precipitates. When the Er concentration rose from 0.15 to 0.45 wt.%, the refining effect and the density of L12-Al3(Er, Zr) were less influenced, but excessive Er interacted with other elements to form coarse intermetallic compounds, leading to the deterioration of mechanical properties. The yield strength (YS) and ultimate tensile strength (UTS) of the alloy grew first and then declined and flattened as the Er content increased from 0 to 0.45 wt.%, according to the mechanical properties test. All alloys with Er microalloying had superior elongation due to the decrease of number of high-angle grain boundary (HAGB). The optimal mechanical properties were shown in the 0.15 wt.% Er alloy, with a YS of 771.7 MPa, a UTS of 785.9 MPa, and an elongation of 9.5%.

Splitting failure and deformation evolution of the red argillaceous siltstone disc in the high humidity environment

The failure mechanism of weakly cemented soft rock under water-rock coupling effect is extremely complex. To reveal the tensile failure of red argillaceous siltstone in high humidity environment, five kinds of disc samples with different water contents were obtained through maintenance in constant temperature and humidity oven. The Brazilian test was carried out to reveal the variation characteristics of splitting behavior of rock samples in high humidity environment. Detailed analysis was conducted on the evolution law of stress-strain relationship and mechanical parameters under five different water contents. Combined with the DIC (Digital Image Correlation) investigation, the displacement evolution patterns of samples with different water content and loading stages were analyzed. Results show that he macroscopic mechanical parameters such as tensile strength and elastic modulus of weakly cemented red sandstone samples under water environment are negatively parabolic correlated with the increase of water content. The moisture content has an important influence on the disc splitting failure mode, forming the main fracture along the radial direction of loading, and showing a local crushing area in the loading area, and the crushing area increases with the increase of water content. Microstructural variation of red sandstone under a high humidity environment is the main reason for its deterioration of macroscopic mechanical properties.

Soft, Strong, Tough, and Durable Bio‐Hydrogels Via Maximizing Elastic Entropy

AbstractLoad‐bearing soft tissues are soft but strong, strong yet tough. These properties can only be replicated in synthetic hydrogels, which do not have the biocomplexity required by many biomedical applications. By contrast, natural hydrogels, although retaining the native complexity, are weak and fragile. Here a thermomechanical casting method is presented to achieve the mechanical capabilities of synthetic materials in biopolymer hydrogels. The thermomechanical cast and chemically crosslinked biopolymer chains form a short‐range disordered but long‐range ordered structure in water. Upon stretch, the disordered structure transforms to a hierarchically ordered structure. This disorder‐order transformation resembles the synergy of the disordered elastin and ordered collagen in load‐bearing soft tissues. As entropy drives a reverse order‐disorder transformation, the hydrogels can resist repeated cycles of loads without deterioration in mechanical properties. Gelatin hydrogels produced by this method combine tissue‐like tunable mechanical properties that outperform the gelatin prepared by synthetic approaches, and in vivo biocomplexity beyond current natural systems. Unlike polymer engineering approaches, which rely on specific crosslinks provided by special polymers, this strategy utilizes the entropy of swollen chains and is generalizable to many other biopolymers. It could thus significantly accelerate translational success of biomaterials.

Fabrication of carbon fiber/polyamide 6 composites with water resistance and anti-icing performance using a superhydrophobic fluorinated-polydopamine coating

With the advance of the reactive liquid molding process for mass production, polyamide 6 (PA 6)-based carbon fiber reinforced thermoplastic (CFRTP) with excellent impact resistance and recyclability has been developed, but there is still a limit to the application of external parts due to deterioration of mechanical properties in a moisture environment. This study proposes an efficient process that is advantageous for the mass production of CFRTP with improved water stability by coating fluorinated polydopamine (f-PDA) on PA 6-based CFRTP fabricated by the thermoplastic resin transfer molding process. Compared to neat CFRTP, the interlaminar shear strength and flexural strength of the CFRTP immersed in water improved by 16% and 31%, respectively, with a significant reduction in water absorption of 42%. Furthermore, the anti-icing performance of the CFRTP was verified, as evidenced by a 49% reduction in surface energy. The proposed f-PDA-CFRTP is anticipated to be applied to external parts in various transportation industries while ensuring environmental reliability.

Modification of Epoxy Compositions by the Application of Various Fillers of Natural Origin.

A series of composites based on epoxy resin filled with additives of natural origin were prepared to investigate the influence of such fillers on the properties of the epoxy compositions. For this purpose, the composites containing 5 and 10 wt.% of additive of natural origin were obtained using the dispersion of oak wood waste and peanut shells in bisphenol A epoxy resin cured with isophorone-diamine. The oak waste filler had been obtained during the assembly of the raw wooden floor. The performed studies include testing of samples prepared using unmodified and chemically modified additives. Chemical modification via mercerization and silanization was performed to increase the poor compatibility between the highly hydrophilic fillers of natural origin and the hydrophobic polymer matrix. Additionally, the introduction of NH2 groups to the structure of modified filler via 3-aminopropyltriethoxysilane, potentially takes a part in co-crosslinking with the epoxy resin. Fourier Transformed Infrared Spectroscopy (FT-IR), as well as Scanning Electron Microscopy (SEM), were carried out, to study the influence of performed chemical modification on the chemical structure and morphology of wood and peanut shell flour. SEM analyses showed significant changes in the morphology of compositions with chemically modified fillers, indicating improved adhesion of the resin to lignocellulosic waste particles. Moreover, a series of mechanical (hardness, tensile strength, flexural strength, compressive strength, and impact strength) tests were carried out, to assess the influence of the application of fillers of natural origin on the properties of epoxy compositions. All composites with lignocellulosic filler were characterized by higher compressive strength (64.2 MPa-5%U-OF, 66.4%-SilOF, 63.2-5%U-PSF, and 63.8-5%SilPSF, respectively), compared to the values recorded for the reference epoxy composition without lignocellulosic filler (59.0 MPa-REF). The highest compressive strength, among all tested samples, was recorded for the composite filled with 10 wt.% of unmodified oak flour (69.1 MPa-10%U-OF). Additionally, higher values of flexural and impact strength, concerning pure BPA-based epoxy resin, were recorded for the composites with oak filler (respectively, flexural strength: 73.8 MPa-5%U-OF and 71.5 MPa-REF; impact strength: 15.82 kJ/m2-5%U-OF, 9.15 kJ/m2-REF). Epoxy composites with such mechanical properties might be considered as broadly understood construction materials. Moreover, samples containing wood flour as a filler exhibit better mechanical properties compared to those with peanut shell flour (tensile strength for samples containing post-mercerization filler: 48.04 MPa and 40.54 MPa; while post-silanization 53.53 MPa and 42.74 MPa for compositions containing 5 wt.% of wood and peanut shell flour, respectively). At the same time, it was found that increasing the weight share of flour of natural origin in both cases resulted in the deterioration of mechanical properties.

The mechanical properties deterioration of rubberwood-latex sludge flour reinforced polypropylene composites after immersing in different water conditions

The mechanical properties deterioration of rubberwood-latex sludge flour reinforced polypropylene composites after immersing in different water conditions

Role of myofascia in the recovery of bone loss after reloading in tail-suspended rats

Astronauts experience severe musculoskeletal degradation in space. After returning to earth, bone loss recovery did not parallel muscle recovery. Fascia may play an important role as a considerable part of muscle force is transmitted to bone through fascia. However, little is known about how fascia changes in microgravity and its effect on the development of musculoskeletal degeneration. In this study, a rat hindlimb unloading model was used to simulate microgravity (21 days of tail suspension) and then reloading for 7 days, 14 days and 21 days. After different periods, bone mineral density (BMD) and microstructure of the tibia were analyzed by μCT, the mechanical properties of the tibia were determined by the three-point bending test and the mechanical properties of fascia were explored by tensile test. The results show that, after tail suspension, collagen Ⅰ in myofascia was significantly increased (p < 0.05), the myofascial elastic modulus was significantly decreased (p < 0.05), BMD of the tibia was significantly decreased (p < 0.05) and the microstructure of the tibia had deteriorated. After 21 days of reloading, there was no significant improvement in the myofascial elastic modulus as well as in the tibial maximum load. Correlation analysis results showed that the myofascial elastic modulus was significantly correlated with the tibial maximum load. In summary, the deterioration of mechanical property of myofascia induced by tail suspension did not recover when the time of reloading was the same as the time of unloading. This indicates that the delayed bone recovery after being exposed to microgravity was associated with deterioration of myofascia.

Shear and flexure of FRP-reinforced concrete beams and slabs – A review

The article reviews structural response of flexural members reinforced with fiber-reinforced polymer (FRP) as a sustainable alternative to conventional carbon steel. It overviews experimental studies and code-based models that characterize shear and flexural response of concrete beams and slabs reinforced with FRP bars. Discussion on lower resistance to fire being key limitation of FRP bars is also included. The most commonly used fibers to manufacture FRP bars include carbon, glass, basalt, aramid, or combinations of these materials. Consequently, each material plays its role in contributing to shear and flexure differently. Basalt FRP are characterized by higher tensile capacity and resistance to corrosion, carbon FRP bars can withstand exposure to harsh environments; glass FRP bars possess lower modulus of elasticity that may cause large deflection and wider cracks. FRP bars are generally preferred over carbon steel for use in concrete elements where exposure to chlorides or chemicals is expected, or places where non-magnetic properties are essential. Beams and slabs reinforced with FRP bars are likely to undergo larger deflections due to lower stiffness of FRP bars. The dominant failure mode of FRP-reinforced concrete flexural members is discussed in comparison to conventional steel-reinforced members. The article identifies increasing interest and research in using green concrete reinforced with FRP bars that helps to make construction serviceable and sustainable. However, premature de-bonding of bars remains a concern with more research needed to avoid deterioration of mechanical properties by underutilization of materials. Although concrete is practically fire-resistant, FRP is likely to undergo damage of resin due to the presence of combustible organic polymers. The bulk of research implies that the thermal instability of the resin in FRP reinforcing bars is not a disadvantage that outweighs the possible benefits of its usage in the construction industry.

Investigating the effect of fused deposition modelling on the tribology of PETG thermoplastic

A widely recognized consequence of the additive manufacturing process is the deterioration of mechanical properties through the development of macrodefects, microdefects, and chemical changes. This has particularly negative impacts on fatigue and wear resistance of components produced by additive manufacturing, which limits the utility of the technology for engineering applications. In this investigation, we find that glycol-modified polyethylene terepthalate processed via Fused Deposition Modelling (FDM) exhibits a significantly lower wear rate as compared to virgin material when subjected to slow-speed dry sliding contact, which is a rare case of an additively-manufactured material with improved bulk properties. Using pin-on-disk testing, we demonstrate favorable wear resistance for additively-manufactured pins against a surface ground 440c stainless steel counterface, which reflects potential utility of the material in light-duty, low-maintenance linear and rotary motion applications. The wear behavior observed under these test conditions corresponds to an order of magnitude decrease in wear relative to existing literature. Annealing the samples results in a further decrease in wear rate, while samples produced in a dry nitrogen atmosphere exhibit increased wear and a change in morphology and thickness of the transfer film. X-ray photoelectron spectroscopy testing validates that FDM printing results in material oxidation, that this oxidation corresponds with an improvement in wear performance, and that printing in a dry nitrogen environment inhibits this change.

Dependence of the mechanical properties of a metastable austenitic stainless steel in high-pressure hydrogen gas on machining-induced defects

The susceptibility of metastable 304L to embrittlement in a high-pressure gaseous hydrogen environment was studied from the viewpoint of changes in mechanical properties. The high pressure hydrogen gas leads to deterioration of mechanical properties, which may be accelerated by the presence of surface defects. The tensile specimens were cut with different machining parameters to change the density of the different defects caused by the machining. The maximum dislocation density caused by machining, rather than the maximum strain-induced martensite increased the sensitivity to hydrogen embrittlement.

Prediction of weld-line width and sink-mark depth of plastic injection moulded parts using neural networks

Fast-moving consumer goods companies rely on thermoplastic materials like polymethyl methacrylate (PMMA) for producing large quantities of affordable packaging products. In the current study, the experimental data of plastic injection moulding was collected from existing literature. It was found that the process parameters of the plastic injection moulding process influence the defects like weld-line and sink-mark on PMMA products. Therefore, an Artificial neural network model (ANN) was developed to estimate the permissible range for these defects. The 8–11-11–2 architecture was chosen because it yielded the least values of mean square error (MSE) and average error (AE) for training, testing and validation datasets. The predicted results were compared with experimental results to determine the accuracy of the developed model. Using performance parameters and various visual illustrations, the model has been validated. The obtained correlation coefficient (R-value) of 0.99954 signifies that the ANN model has good compatibility with the experimental dataset. This can be demonstrated by the precise prediction values produced by the ANN model. Therefore, the deterioration of mechanical properties of PMMA material can be minimized as the ANN model succeeded in predicting optimal weld-line width and sink-mark depth during the plastic injection moulding process.

Deterioration of mechanical properties at the anchor-mortar interface considering the effect of two-phase corrosion

Factors in the environment may cause corrosion of the anchor rod and mortar, thus degrading the mechanical properties of the anchor rod-mortar interface and eventually leading to failure of the anchor structure. In this paper, a method is designed to accelerate the migration of corrosive ions (Cl-，SO42-) from solution to penetrate the mortar, resulting in the corrosion of both the mortar and the bolt. Taking corrosion of the steel bar as the control, the deterioration law for the interfacial anchor-mortar bond during two-phase corrosion was studied. The mechanical properties deteriorating mechanism of the anchor-mortar interface was revealed based on changes in the composition and amount of corrosion products and the damage extent of anchor rods and mortars. The test results showed that, in acidic environments, the rib height of the bolt decreased due to corrosion, which led to a decrease in the mechanical bite force of the interface. The needle and rod-shaped ettringite generated by the mortar during corrosion can destroy the internal structure of mortar, promote more corrosive solution to participate in the chemical reaction, and reduce the radial binding force on the steel bar. In an alkaline environment, corrosion of the rebar is slow. The plate ettringite formed by the mortar during corrosion provides a filling effect and delays the corrosion reaction of the rebar. Corrosion of the reinforcement and mortar results in deterioration of the interface bond strength between the bolt and mortar. Based on the test results, the current model of bond slip was modified to include deterioration of the anchor and mortar material properties and weakening of the restraining effect of the mortar. A model for the anchor-mortar bond-slip relationship was proposed and included corrosion of both materials. The results of this research will provide guidance for future studies of the failure mechanisms of anchorage structures and evaluations of the durability of anchored slopes.

Deterioration of Mechanical Properties of Axial Compression Concrete Columns with Corroded Stirrups Coupling on Load and Chloride

To research the deterioration of the mechanical properties of stirrup-corroded concrete columns under the effect of load and chloride, accelerated corrosion and load carrying capacity tests were carried out on concrete columns subjected to long-term axial loading by means of dry and wet cycles with extra electric currents. The test results showed that under the effect of axial load and chloride, the corrosion-induced cracks of stirrup-corroded concrete columns mainly developed along the direction of the longitudinal reinforcing steel bars (cracks along longitudinal reinforcing steel bars caused by corrosion) and there were almost no corrosion-induced cracks along the direction of the corroded stirrups. The length and maximum width of the corrosion-induced cracks increased with the stirrup corrosion rate, but the average width of the corrosion-induced cracks did not change significantly. After the stirrup-corroded column reached the ultimate load, the concrete cover spalled off in pieces along the corrosion-induced cracks and loading cracks, the core concrete was crushed, and the test column produced obvious brittle failure. With the increase in the corrosion rate of stirrups, the stiffness and ultimate bearing capacity of the column decreased. Considering factors such as damage to the column section caused by stirrup corrosion, the decrease in the lateral restraint effect of the corroded stirrup on the longitudinal reinforcing steel bars, and buckling of the longitudinal reinforcing steel bars, the ultimate bearing capacity prediction model of the short column subjected to axial compression due to stirrup corrosion was established. The calculated values of the model were in good agreement with the measured values, indicating the model has good applicability.

Stir Casting Processing, Mechanical, and Wear Behavior of AA2024 +10 wt. % Flyash +5 wt. % Graphite Hybrid Composite

Metal matrix composites (MMCs) and their hybrid combinations are widely incorporated in research due to their enhanced mechanical properties and wear resistance. In this work, an investigation is made to fabricate AA2024 matrix flyash and graphite-reinforced hybrid composite for industrial applications and determine its suitability by performing testing and characterization. Tensile properties and compressive strength, wear resistance, fracture toughness, impact energy, and the hardness of the composites are evaluated. A tensile strength maximum of 300 MPa was achieved. Furthermore, the thermal analysis of a disc brake of this hybrid composite is performed using SOLIDWORKS software to identify the temperature distribution up to 469°K. The addition of flyash reinforcement shows the changes in properties with weight reduction. Although the content of graphite particles shows a deterioration in mechanical properties, it acts as a lubricant and reduces wear by friction and friction between the components. The coefficient of friction (COF) for the specimen is in the range of 0.1 to 0.3. The distribution of graphite and flyash is analyzed using the scanning electron microscope. It was found that the properties of the prepared composite are lesser than the base alloy AA2024, but the fabricated composite’s density (2.07 g/cc) is lesser than the base alloy AA2024 (2.78 g/cc).

The construction stability of large section tunnel considering the deterioration of clay mechanical properties

The stability of large-section clay tunnels is closely related to the mechanical behavior of the surrounding rock. The mechanical behavior of the surrounding rock is characterized by the coupled response of the physico-mechanical properties of the clay material and the tunnel construction conditions. Therefore, this paper proposes a numerical experimental study based on the response surface method to quantitatively link the stability of large-section clay tunnels with construction factors. It will provide a basis for quantitatively guiding the tunnel construction plan adjustment to ensure its stability. Firstly, the tunnel stability reserve is evaluated by considering the deterioration of physico-mechanical properties of clay surrounding rocks, and the relationship between the tunnel stability index and construction factors is established according to Taylor’s theorem. Secondly, the response surface method and the steepest ascent method are used to find the optimal fitting relationship between the tunnel stability reserve factor and tunnel construction factors. Finally, the analysis of a tunnel application shows that (a) the stability evaluation considering the deterioration of physical and mechanical properties of clay is well representative; (b) the “curved” region of the response of the tunnel stability reserve factor can be effectively determined by the steepest slope method; (c) for the “curved” region, a second-order response surface is more appropriate. This research will reveal the coupling relationship between tunnel stability, physico-mechanical properties of clay, and tunnel construction conditions, which will contribute to the development of intelligent tunnel construction.