Principal Stress Components Research Articles

Microseismic activity and fluid fault interactions: some results from the Corinth Rift Laboratory (CRL), Greece

The Gulf of Corinth, in western-central Greece, is one of the fastest continental rifts in the world. In its western section near the city of Aigion, the previous work has outlined the existence of a shallow dipping seismogenic zone between 5 and 12 km. This seismic activity has been monitored with a network of 12 three-component stations for the period 2000– 2007. Three, few months long, seismic swarms have been observed. They mobilize a complex structural fault system that associates both shallow dipping elements and subvertical structures with very different azimuths, some of which extend to depths greater than that of the shallow dipping zone. The swarm activity associates intensely active, short crises (a few days) with more quiescent periods. The long-term growth velocity of the seismically activated domains is compatible with a fluid diffusion process. Its characteristics are discussed in the context of the results from the 1000 m deep AIG10 well that intersects the Aigion Fault at 760 m. The vertical growth directions of the seismically activated volumes outline two different sources for the fluid and imply non-steady pressure conditions within the seismic domain. The diffusivity along the cataclastic zone of the faults is in the order of 1 m2s−1, while faults act as hydraulic barrier in the direction perpendicular to their strike. If the vertical direction is a principal stress component, the high pore pressure values that must be reached to induce slip on the shallowly dipping planes can result only from transitory dynamic conditions. It is argued that the shallow dipping active seismic zone is only local and does not correspond to a 100 km scale decollement zone. We propose to associate the localization process with deep fluid fluxes that have progressively modified the local stress field and may be the cause for the quiescence of the West Heliki Fault presently observed.

Role of interparticle friction and particle-scale elasticity in the shear-strength mechanism of three-dimensional granular media

The interlink between particle-scale properties and macroscopic behavior of three-dimensional granular media subjected to mechanical loading is studied intensively by scientists and engineers, but not yet well understood. Here we study the role of key particle-scale properties, such as interparticle friction and particle elastic modulus, in the functioning of dual contact force networks, viz., strong and weak contacts, in mobilizing shear strength in dense granular media subjected to quasistatic shearing. The study is based on three-dimensional discrete element method in which particle-scale constitutive relations are based on well-established nonlinear theories of contact mechanics. The underlying distinctive contributions of these force networks to the macroscopic stress tensor of sheared granular media are examined here in detail to find out how particle-scale friction and particle-scale elasticity (or particle-scale stiffness) affect the mechanism of mobilization of macroscopic shear strength and other related properties. We reveal that interparticle friction mobilizes shear strength through bimodal contribution, i.e., through both major and minor principal stresses. However, against expectation, the contribution of particle-scale elasticity is mostly unimodal, i.e., through the minor principal stress component, but hardly by the major principal stress. The packing fraction and the geometric stability of the assemblies (expressed by the mechanical coordination number) increase for decrease in interparticle friction and elasticity of particles. Although peak shear strength increases with interparticle friction, the deviator strain level at which granular systems attain peak shear strength is mostly independent of interparticle friction. Granular assemblies attain peak shear strength (and maximum fabric anisotropy of strong contacts) when a critical value of the mechanical coordination number is attained. Irrespective of the interparticle friction and elasticity of the particles, the packing fraction and volumetric strain are constant during steady state. Volumetric strain in sheared granular media increases with interparticle friction and elasticity of the particles. We show that the elasticity of the particles does not enhance dilation in frictionless granular media. The results presented here provide additional understanding of the role of particle-scale properties on the collective behavior of three-dimensional granular media subjected to shearing.

Mechanisms of Small-Strain Shear-Modulus Anisotropy in Soils

In this paper, experimental studies using a true triaxial apparatus and a bender element system, and numerical simulations based on the discrete element method (DEM) were used to investigate the stress- and fabric-induced shear-stiffness anisotropy in soils at small strains. Verified by experiments and DEM simulations, the shear modulus was found to be relatively independent of the out-of-plane stress component, which can be revealed by the indistinctive change in the contact normal distribution and the normal contact forces on that plane in the DEM simulations. Simulation and experimental results also demonstrated that the shear modulus is equally contributed by the two principal stress components on the associated shearing planes. Fabric-induced stiffness anisotropy, i.e., the highest G and subscript xy or G and subscript hh, can be explained by simulation findings in which more contact normals prefer to distribute along the horizontal direction. The experiments and simulations also reveal that the fabric-induced stiffness anisotropy increases with an increasing aspect ratio of the particles. The assumption of transversely isotropic fabric in soils is valid based on the DEM simulation results; however, this assumption is not completely supported by the experimental results.

Influence of intermediate principal stress on rock fracturing and strength near excavation boundaries—Insight from numerical modeling

The influence of the intermediate principal stress on rock fracturing and strength near excavation boundaries is studied using a FEM/DEM combined numerical tool. A loading condition of σ 3=0 and σ 1≠0, and σ 2≠0 exists at the tunnel boundary, where σ 1, σ 2, and σ 3, are the maximum, intermediate, and minimum principal stress components, respectively. The numerical study is based on sample loading testing that follows this type of boundary stress condition. It is seen from the simulation results that the generation of tunnel surface parallel fractures and microcracks is attributed to material heterogeneity and the existence of relatively high intermediate principal stress ( σ 2), as well as zero to low minimum principal stress ( σ 3) confinement. A high intermediate principal stress confines the rock in such a way that microcracks and fractures can only be developed in the direction parallel to σ 1 and σ 2. Stress-induced fracturing and microcracking in this fashion can lead to onion-skin fractures, spalling, and slabbing in shallow ground near the opening and surface parallel microcracks further away from the opening, leading to anisotropic behavior of the rock. Hence, consideration of the effect of the intermediate principal stress on rock behavior should focus on the stress-induced anisotropic strength and deformation behavior of the rocks. It is also found that the intermediate principal stress has limited influence on the peak strength of the rock near the excavation boundary.

Stress induced elastic anisotropy of the Etnean basalt: Theoretical and laboratory examination

A theory, the stress‐sensitivity approach, has been developed, which relates the elastic moduli of anisotropic rocks to the stress tensor and pore pressure for an arbitrary symmetry of the applied load. The theory explains the stress‐induced changes of seismic velocities in terms of stress‐induced changes of the pore space geometry. The stress dependent anisotropy is described in terms of Thomsen's anisotropy parameters ε, γ and δ. To test the theory we analyze the laboratory (high frequency) results of deformation of an isotropically crack damaged dry lava flow basalt from Mt. Etna volcano. The theory states that, under an anisotropic (i.e. axisymmetric triaxial) load and in the case of an initially isotropic rock, (1) the anisotropy parameters are linear functions of the stress exponentials (i. e. exponential functions of principal stress components) and (2) the ratio of these anisotropy parameters as a function of the stress is constant. In order to verify these relationships, the stress exponentials and the anisotropy parameters based on the measured velocities are computed as well as the expected ratio of the Thomsen's parameters. Our experimental results are in very good agreement with the theoretically predicted relations.

Hazards and health complaints associated with fish processing activities in India—Evaluation of a low-cost intervention

Fish processing is a seasonal activity in the seacoast regions. Work-related stresses and health hazards of women in fish processing works ( N=185) were examined to explore interventions to mitigate the hazards. The activities included cleaning and grading of fishes, peeling of shells, deveining, slicing, ring cutting of squid, processing for instant quick freezing, and packing of fishes and transferring to cold storage. Standing at the work desk or sitting on floor, the women in bare hands performed varieties of tasks with abundant use of ice-cold chlorinated water. A multi-method ergonomics checklist was introduced, including assessment of health complaints, musculoskeletal pain and discomfort, skin symptoms and temperatures ( T sk) of hand and fingers. A principal component analysis yielded three components of stressors related to the work environment, the methods of work, and the psychosocial variables that explained 80.4% of the total variance. Component 1 (15 items) described the work environment stressors, such as cold, wet, greasy and slippery work premises, congested work area, lack of personal protective wears and irregular work hours. The cold injuries—blanching of fingers to hand numbness, and Raynaud's phenomena in the palm areas, might be attributed to the stressors of Component 1 that explained 32.5% of the total variance. The T sk of hand areas during work were as low as 20.7±1.9 °C, i.e., 8 °C less than the pre-exposure values. One-way ANOVA showed that the T sk of the hand areas differed with the exposure conditions ( F (2,95) ranged from 44.2 to 107.3; p≪0.001 for T sk of back of hand and fingers, respectively). The drop in T sk during work were statistically significant ( p≪0.001), compared to pre-exposure T sk. Component 2 (13 items) described the stressors of the methods of work, such as unsafe hand tools, sitting on the floor, and sustained standing. About 67% of the workers complained of musculoskeletal pain and discomfort. The highest prevalence of discomfort was reported for the lower back, followed by knees, upper back, calf, and other areas, that explained the stressors grouped under Component 2. The women were at risks of repeated cut injuries from the unsafe cutting knives, and handling of fish materials. Principal component 3 (9 items)—the psychosocial variables (supervisory pressure, changing job assignments, personal job characteristics) explained about 22.8% of the total variance. The study reiterated for the much needed work design interventions to mitigate the documented risk factors. Since the hands were the most affected body parts, the regular wearing of latex gloves was advocated and in using gloves for 2 h work, the women substantially improved T sk of the hand and fingers, compared to the situations when working bare hands, and 84% of the women did not show any cold induced symptoms. An overall impression prevailed that the use of gloves gave the women good feelings of working better. Relevance to Industry The work analysis in the fish processing activities elucidates the principal work stress components, including stressors related to the environment, the methods of work, and the psychosocial variables. In view of the potential health hazards of the women workers, the study highlights the need for good work practices and interventions for sustainable development of occupational safety and health in the sector.

Complete in situ stress determination in an argillite sedimentary formation

Andra has conducted a very comprehensive investigation on the in situ stress field within an argillite formation interbeded between two stiffer limestone formations, for the development of its underground research laboratory. A series of hydraulic tests has been conducted in boreholes located in the vicinity of the future site. Borehole and shaft convergence measurements were also carried out to analyse the mechanical behaviour of the rock. Throughout the stress measurement campaign, several borehole images have shown breakouts or induced fractures, that have been analysed in terms of in situ stress field, both in the argillite and in the limestone layers. All these reliable data highlight the high dependency of the state of stress on the rheology of the formation. A high ratio between the two horizontal principal stress components – ranging from 1.3 to 2.0 – has been observed in the limestones, whereas the maximum horizontal principal stress component has been found to be close to the lithostatic stress in the clay formation at the main level of the laboratory; i.e. at the 490 m depth.

Estimating the transversely isotropic elastic intact rock properties for in situ stress measurement data reduction: A case study of the Olkiluoto mica gneiss, Finland

An anisotropy in the elastic moduli values of intact rock with a ratio of more than 1.3–1.5 has been reported to have an effect on the calculated magnitudes and orientations of the in situ principal stress components as measured by the overcoring method. Work related to the on-going site investigation for a deep radioactive waste repository at the Olkiluoto site in Western Finland has shown that the migmatic mica gneiss is anisotropic which could therefore affect the interpretation of overcoring stress measurement results. This paper includes a summary of the theory of anisotropy concerning the intact rock moduli via the strain compliance matrix, a description of the core sample testing methods, and interpretation of results for the migmatic mica gneiss from two site investigation boreholes. In this case study, 19 specimens were tested and the results showed a modulus anisotropy of about 1.4. Because such anisotropy is high enough to produce significant errors in the estimation of the in situ principal stresses, it is recommended to take this into account in the interpretation of the stress measurement results, both in the context of the current work in Finland and in other projects where similar anisotropy is encountered.

Generalized Coulomb's Criterion for 3-Dimensional Stress Conditions

The Coulomb's Failure Criterion for materials is commonly and implicitly applied to the stress components on failure plane. In this paper, it was attempted to apply the Coulomb's Criterion not only to the failure plane but also to general planes which have various directions relative to the principal stress components at failure conditions, and it was shown that the previously proposed well-known criteria for materials could be expressed by an unified simple equation. This fact indicates that the direction of the plane for the Coulomb's Criterion is a material property as well as the friction ratio and cohesion. The revised Coulomb's Criterion was applied to simulate test results, and it was shown that the model could reproduce the test data fittingly.

Unified Yield Criterion for Masonry and Concrete in Multiaxial Stress States

In this paper, failure test results of brick masonry and concrete under biaxial stress state, and of concrete under triaxial stress state, are analyzed. In particular, in the biaxial compression stress state masonry is found to behave as an isotropic material. The pertinent failure interaction curve in terms of principal stress components can be expressed by an ellipse or a parabola. Because masonry can be conceived as a conglomerate material, as a concrete, formed by coarse aggregates (bricks) and cement paste (mortar joints), a generalized failure criterion in the form of an elliptical curve valid both for masonry and concrete in compression biaxial state is provided. In the case of the triaxial compression stress state, from an analysis performed on the test results available for concrete, a prediction of the hydrostatic compressive strength is derived, and a possible form of the limit surface in the principal stress space is hypothesized.

Prediction of stress directionality from pile-up morphology around remnant indentation

Abstract The directionality and magnitude in surface stress was scrutinized from non-symmetrical morphology of Brale indenting deformation on artificially strained specimen. A non-equibiaxial stress applied brought about different pile-up variations along two orthogonal straining axes and the asymmetric deformation behavior was related with a ratio of its two principal stress components.

Constitutive equations for 3-D anisotropy in jointed rocks and its effect on tunnel closure

Joints occurring in regular sets not only make the rock mass more deformable but also induce anisotropy in it. The rock mass has a special anisotropy in which the shear modulus is very low compared to its modulus of deformation. The assessment of the anisotropic deformational behaviour of the jointed rock thus becomes an important aspect in tunnel design. The constitutive equations for elastic-anisotropic-dilatant rock mass have been suggested in order to compute the strains for the following situations: * Plane strain deformations under a uniaxial loading condition, * Plane strain deformations under a biaxial loading condition, * 3-D deformations under a triaxial loading condition. The rock mass may have any number of joint sets with representative values of normal stiffness kn, shear stiffness ks and the joint spacing S. The dilation of the joints is considered through the dilatancy factor λ. An approximate method is proposed to assess the tunnel closure in different directions. The equations derived are applied to estimate the closure of the tail race tunnel of Salal Hydel Project Stage-II (India). The tunnel is aligned through a single litho unit of dolomite rocks and three joint sets with dip and dip directions of 53/340, 25/180 and 75/090° traverse through the rock. The computed horizontal closure of the tunnel wall is compared with the observed closure and the value of the parameter λ is adjusted to match the results. After calibration, the model is used for parametric analysis to observe how the tunnel closure responds to the variation in in situ stresses. It is concluded that the tunnel closure is highly anisotropic (Fig. 1) and all the three principal stress components have a significant effect on the tunnel closure. The proposed method may be used to analyse anisotropy of tunnel closure which can then be monitored by instrumentation carefully, so that one is able to record the maximum closure.

Estimation of biaxial surface stress by instrumented indentation with sharp indenters

The influence of non-equi-biaxial surface stress on the shape of indentation load versus depth curve was studied experimentally by instrumented sharp indentation tests on artificially strained samples of API X65 steel. The shifts in the indentation loads for several stressed states from that of the unstressed state had a linear relationship with average equi-biaxial stresses separated from the biaxially applied stresses. Micromechanical contact analyses for the stress-induced load shifts yielded stress values comparable to the applied in-plane stresses except for the pure shear stress state, where the effect of the applied stress on indentation plasticity is negligible. This study supports the proposition that the surface stress in an arbitrary biaxial state can be evaluated through a theoretical model combined with the ratio of two principal stress components.

Azimuthal anisotropy of the P-wave velocity in the hypocentral volume of the Krn Mt. (Slovenia) earthquake sequence

Azimuthal anisotropy of P-wave velocity in the hypocentral volume of the Krn Mt. (Slovenia) earthquake sequence is measured using the differences of travel times and of travel paths of the Pg-phase towards the recording stations of the local and regional networks. The observed velocity varies between 6.0 km/s in the ENE–WSW direction and 6.4 km/s for waves propagating NNW–SSE. These directions closely match those of the mean regional principal stress components obtained from individual fault-plane solutions for events from the Krn Mt. sequence. A large part of observed anisotropy may be explained if hypocentral volume is assumed to be pervaded by a system of vertical/subvertical extensive-dilatancy anisotropy (EDA) cracks aligned under the influence of local tectonic stress field.

Electrical imaging and hydraulic testing for a complete stress determination

A complete stress determination has been performed in Lodève (southern France) by conducting hydraulic tests in a 200 m deep borehole, with a probe combining electrical imaging with an inflatable straddle packer. Both classical hydraulic fracturing and hydraulic tests on pre-existing fractures have been conducted. The normal stress acting on the tested fracture planes was determined from the simultaneous analysis of both hydraulic and electrical signals observed during shut-in phases. Values derived from quasi-static reopening pressure tests are systematically larger than those derived from shut-in and have been discarded. Hydraulic fractures provide information on the principal stress directions orientation as well as on the minimum principal stress magnitude. HTPF tests provide information on the vertical and the maximum horizontal principal stress components magnitude and are unaffected by any pore pressure effect. At a depth of z=165 m , the vertical stress component is principal and is given by S v =4.0±0.5 MPa . The maximum horizontal principal component is oriented N155°±10° and is given by S H =10.0±0.2 MPa . It is almost twice the value found for S h , S h =5.8±0.1 MPa . These results are consistent with the results obtained nearby. They show that hydraulic properties of faults (discontinuities with length larger than 1 km and offsets larger than 100 m ) do not depend simply on the relative orientation of the fault with respect to the principal stress directions.

The role of the 1999 Chamoli earthquake in the formation of ground cracks

The moderate magnitude Chamoli earthquake that occurred in the Garhwal Higher Himalaya, in the early hours of March 29, 1999, caused intense damage to the ground and mountain slopes of the Alaknanda–Mandakini river valley and adjoining region. A systematic survey of this induced damage was conducted immediately after the earthquake occurred. Prominent shallow cracks of significant length, negligible width and indeterminate vertical extent, conspicuously tensile in nature, with little or no slip across the crack planes, were observed in the ground at several places along the surveyed route. These cracks had formed in the dynamic phase of the Chamoli earthquake process that is in the period of time during which the earthquake-generated seismic waves were passing through the geographic region of interest. However, we use the theory of earthquake-induced static (or long time) stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation.Based on the results of our analysis we conclude that, just prior to the earthquake occurrence, under the influence of the local ambient stress field, the ground at these sites was already near failure in tension. To this, in its dynamic phase, the Chamoli earthquake induced stress perturbations, having, across the planes of the cracks, (i) shear components which were nearly equal and opposite to similar components of the ambient stress field and (ii) normal (tensile) components, necessary for triggering tensile failure of the ground. The σ3 (or minimum principal stress) component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant. This facilitated formation of major tensile cracks in the ground there. Our static estimates of the tensile stress changes at the different sites are, in essence, estimates of the minimal triggering stress perturbations that was provided by the Chamoli earthquake in the dynamic state for the formation of the tensile cracks there.

Morphometry of late Pleistocene‐Holocene faulting and volcanotectonic relationship in the southern Andes of Colombia

Diffuse seismicity and the active Galeras Volcano characterize the southern Andes of Colombia, whose inhabitants are prone to a high natural risk. We used field geological, structural, and quantitative morphological data to define the geometry and kinematics of late Quaternary faults and the volcanotectonic relationships in this area. The main NE‐SW Buesaco Fault has a late Pleistocene‐Holocene 29‐km rupture length. Offset of dated landforms yields 188 ± 13 m of horizontal, right‐lateral, long‐term cumulative component of slip, the vertical component of uplift of the NW block being 67 ± 12 m. The long‐term net slip rate is 1.48 ± 0.12 mm/yr. The other main structure, here named Aranda Fault, also strikes NE‐SW and is 13 km long. Offset of landforms yields 160 ± 10 m of horizontal, right‐lateral, long‐term component of slip and 3.9 ± 1.9 m of vertical component of uplift of the NW block. The long‐term net slip rate is 1.19 ± 0.08 mm/yr. On the Galeras edifice E‐W to NW‐SE faults have normal motions and slip rates from 0.02 to 0.23 mm/yr. Both the Galeras and a late Pleistocene pyroclastic cone lie along the ideal extension of the Buesaco Fault. Magma uprising in the crust can occur along the NE striking fractures when magma pressure (σmp) is greater than the normal‐to‐fault component of tectonic σ1. Magma uprising in the uppermost crust (i.e., in the cone) can occur by rock cracking along E‐W planes with σmp > σ3 up to NW‐SE planes with σmp greater than shear stress component of the horizontal greatest principal stress (σHmax).

Discussion

Although plastic potential functions considering an intermediate principal stress component are widely employed for elasto-plastic analyses, its effect on excavation-induced stress re-distribution is not adequately examined and verified based on in-situ stress measurements. The present study addressed this issue by not only examining the analytical solutions of elasto-plastic models but also conducting a case study based on large cavern excavation and the continual measurement of the in-situ stress at a great depth. The analytical solutions indicate a clear difference in volumetric plastic strain increment between different plastic potential functions with the same yield function. Specifically, when σ2/σ1 exceeds 0.6, the Drucker–Prager (DP) plastic potential function produces an increase in volumetric strain rate larger than that of the Mohr–Coulomb (MC) potential function, hence suggesting the increase in confining stress in the surrounding rock mass. For the case study, the numerical analyses of the large cavern excavation with the different potential functions demonstrated that both the potential functions yield comparable excavation-induced stress change at the stress monitoring point, however the failure state transition of the surrounding rock mass is non-identical. When the MC potential function is employed, the surrounding rock mass continuously undergoes failure throughout the excavation stages, whilst for the model with the DP potential function, unloading takes place due to the volumetric expansion of failed rock masses associated with the intermediate principal stress component, as the excavation stage proceeds. This was found to be more consistent with field observations. Thus, we concluded that the intermediate principal stress in a plastic potential function plays a vital role in the evolution of volumetric plastic strain, thereby exerting an influence on the overall stability of rock mass structures, especially for a fractured rock mass and when the intermediate stress is relatively large, compared to the minor principal stress value.

Modification of the regional stress field by magma intrusion and formation of tabular granitic plutons

Granitic intrusions typically have large aspect ratios, with an horizontal major axis about 4–8 times the vertical one. Combined structural and geophysical (gravity) data allows distinction between two main types of plutons. Flat-floored plutons (the most represented) are rather thin (3–4 km) and extend in every horizontal direction with a gently dipping floor toward several root zones. These contrast with the thick (>10 km) wedge-shaped plutons, more elongated in one direction with a few root zones. We interpret the shape of flat-floored plutons as the result of a switch in the stress pattern caused by the emplacement of magma. Magma is preferentially emplaced into the plane ( σ 1– σ 2) perpendicular to the least principal stress component ( σ 3). This plane is initially vertical, except for compressional conditions. This dilation causes a local re-organization of the stress field, by increasing the minor and intermediate principal stress components. When they overcome the lithostatic load, a drastic change in the orientation of the opening plane results, switching from vertical to horizontal. This constitutes a change from vertically-oriented, dike-shaped intrusions to sub-horizontal laccoliths. Crustal anisotropies (vertical faults or horizontal zones of different rheology) also contribute to modify the shape of the intrusions. The continual exchange of the intermediate stress components also explains the rounded shape of intrusions in strongly extended regions. Our analysis suggests that the concept of magmas rising to a level of neutral buoyancy is not applicable to many settings. Rather, we suggest that the feedback between displacements resulting from magma intrusion and the local stress pattern controls the geometry of magma emplacement.

Two-dimensional stress-relaxation behavior of human skin as influenced by non-enzymatic glycation and the inhibitory agent aminoguanidine

In order to simulate the in vivo stress alterations of diabetic skin in an in vitro model, we examined the viscoelastic properties of long-term glycated human skin samples. Since skin is subjected to biaxial tension, we used two-dimensional multiaxial testing which better reflects the in vivo situation than the uniaxial testing mode. For native skin samples from the abdominal region we found a direction-dependent elastic stress–strain behavior. The viscous stress component was separated from the elastic stress component by relaxation tests at consecutive incremental steps of radial strains. We hypothesize that glycation-induced changes in the tissue stiffness are generated in a direction-dependent mode. A marked increase of the direction-dependent stiffness was found upon long-term incubation with glucose-6-phosphate. This increase was statistically significant for the maximum principal elastic stress component which was highly correlated with the degree of non-enzymatic collagen modification. The viscous fractions obtained from twodimensional relaxation tests at consecutive radial strains were inversely correlated with non-enzymatic modification. Only at 30% radial strain a significant decrease of the viscous fraction engendered by glucose-6-phosphate was observed together with a directiondependent significant increase of the expectation value of the time constant. The biomechanical and biochemical effects of long-term glycation could be partially reversed by aminoguanidine, a potential therapeutic agent for patients with diabetes mellitus. Our findings suggest that additional cross-links generated by long-term glycation cause two-dimensional biomechanical alterations in human skin, which can be unequivocally detected by multiaxial testing.