Stiff Rock Research Articles

Effects of mechanical layering of host rocks on dike growth and arrest

Many dikes intruding the layered host rock of Miyakejima and Piton de la Fournaise are arrested, segmented, and show variation in thickness. These geometric factors can be largely attributed to the mechanical layering of the host rocks that constitute these volcanoes. Some dikes are arrested at the base of stiff (high Young's modulus) rock layers, whereas others are segmented in the layers. We use finite-element models (FEM) to simulate a typical dike arrest at the base of a stiffer layer. The dike may become arrested when it reaches at the base of the stiffer layer for several reasons. First, the dike-induced tensile stress may not be high enough to break the rock. Second, the stiff layer may act as a “stress barrier”. Third, the material toughness of the layers may be unfavorable for vertical dike propagation and result either in dike arrest or dike deflection. When the magmatic overpressure (driving pressure) is sufficiently high dike can intrude into the overlying layer. Some deflected dikes resume their vertical propagation, thereby generating offset segments. The layering of a volcano thus commonly controls the dike propagation paths and if and where the dikes become arrested. Our measurements show that the dikes in these volcanoes tend to be comparatively thick where they dissect “soft” pyroclastic layers, and thin where they dissect stiff lava flows and sills. Numerical FEM simulations indicate that the variation of dike thickness observed in Miyakejima and Piton de la Fournaise can be broadly explained in terms of layer-stiffness differences of one or two orders of magnitude.

Seismically damaged regolith as self-organized fragile geological feature

[1] The S-wave velocity in the shallow subsurface within seismically active regions self-organizes so that typical strong dynamic shear stresses marginally exceed the Coulomb elastic limit. The dynamic velocity from major strike-slip faults yields simple dimensional relations. The near-field velocity pulse is essentially a Love wave. The dynamic shear strain is the ratio of the measured particle velocity over the deep S-wave velocity. The shallow dynamic shear stress is this quantity times the local shear modulus. The dynamic shear traction on fault parallel vertical planes is finite at the free surface. Coulomb failure occurs on favorably oriented fractures and internally in intact rock. I obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock extending all the way to the surface. The imposed dynamic shear strain in stiff rock causes Coulomb failure at shallow depths and leaves cracks in it wake. Cracked rock is more compliant than the original intact rock. Cracked rock is also weaker in friction, but shear modulus changes have a larger effect. Each subsequent event causes additional shallow cracking until the rock becomes compliant enough that it just reaches Coulomb failure over a shallow depth range of tens to hundreds of meters. Further events maintain the material at the shear modulus as a function where it just fails. The formalism provided in the paper yields reasonable representation of the S-wave velocity in exhumed sediments near Cajon Pass and the San Fernando Valley of California. A general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking. This process causes transient changes in S-wave velocity, but not strong nonlinear attenuation of seismic waves. Wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock.

Probabilistic seismic hazard of Pakistan, Azad-Jammu and Kashmir

The seismic hazard study for Pakistan and Azad Jammu and Kashmir has been conducted by using probabilistic approach in terms of peak ground acceleration (PGA) in m/s2 and also seismic hazard response spectra for different cities. A new version of Ambraseys et al. (Bull Earthq Eng 3:1–53, 2005) ground acceleration model is used, and parameterization is based on most recent updated earthquake catalogs that consisted of 14,000 events. The threshold magnitude was fixed at Mw 4.8, but seismic zones like northern Pakistan–Tajikistan, Hindukush and northern Afghanistan–Tajikistan border had Mw 5.2. The average normalized ‘a’ and ‘b’ values for all zones are 6.15 and 0.95, respectively. Seismicity of study area was modeled, and ground motion was computed for eight frequencies (0.025, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 s) for different annual exceedance rates of 0.02, 0.01, 0.005, 0.002 and 0.001 (return periods 50, 100, 200, 500 and 1,000 years) for stiff rocks at the gridding of 0.1° × 0.1°. Seismic hazard maps based on computed PGA for 0.02, 0.01 and 0.002 annual exceedance are prepared. These maps indicate the earthquake hazard of Pakistan and surrounding areas in the form of acceleration contour lines, which are in agreement with geological and seismotectonic characteristics of the study area. The maximum seismic hazard values are found at Muzaffarabad, Gilgit and Quetta areas.

The Elastic Strain Energy of Damaged Solids with Applications to Non-Linear Deformation of Crystalline Rocks

Laboratory and field data indicate that rocks subjected to sufficiently high loads clearly deviate from linear behavior. Non-linear stress–strain relations can be approximated by including third and higher-order terms of the strain tensor in the elastic energy expression (e.g., the Murnaghan model). Such classical non-linear models are successful for calculating deformation of soft materials, for example graphite, but cannot explain with the same elastic moduli small and large non-linear deformation of stiff rocks, such as granite. The values of the third (higher-order) Murnaghan moduli estimated from acoustic experiments are one to two orders of magnitude above the values estimated from stress–strain relations in quasi-static rock-mechanics experiments. The Murnaghan model also fails to reproduce an abrupt change in the elastic moduli upon stress reversal from compression to tension, observed in laboratory experiments with rocks, concrete, and composite brittle material samples, and it predicts macroscopic failure at stress levels lower than observations associated with granite. An alternative energy function based on second-order dependency on the strain tensor, as in the Hookean framework, but with an additional non-analytical term, can account for the abrupt change in the effective elastic moduli upon stress reversal, and extended pre-yielding deformation regime with one set of elastic moduli. We show that the non-analytical second-order model is a generalization of other non-classical non-linear models, for example “bi-linear”, “clapping non-linearity”, and “unilateral damage” models. These models were designed to explain the abrupt changes of elastic moduli and non-linearity of stiff rocks under small strains. The present model produces dilation under shear loading and other non-linear deformation features of the stiff rocks mentioned above, and extends the results to account for gradual closure of an arbitrary distribution of initial cracks. The results provide a quantitative framework that can be used to model simultaneously, with a small number of coefficients, multiple observed aspects of non-linear deformation of stiff rocks. These include, in addition to the features mentioned above, stress-induced anisotropy and non-linear effects in resonance experiments with damaged materials.

Seismicity associated with the 1991–1995 dome growth at Unzen Volcano, Japan

From May 1991 until February 1995, seismicity in the crater area of Unzen Volcano, southwest Japan, intensified in conjunction with the growth of a dacite lava dome. We used data from seismic stations located near the crater to identify approximately 580,000 summit earthquakes with maximum amplitudes equal to or greater than 1 × 10 − 3 cm/s. The temporal characteristics of the seismicity level were different for exogenous and endogenous periods of dome growth. Periods of solely exogenous growth were accompanied by several days or weeks of increased seismicity, and levels of seismicity were notably reduced between successive seismically active periods. In contrast, levels of seismicity were generally high during periods when the dome grew endogenously, with repeated cycles of increasing and decreasing seismicity of one to two months duration. We classified the waveforms of summit earthquakes into high-frequency (HF), medium-frequency (MF), and low-frequency (LF) types on the basis of spectral analysis. Dominant waveform types varied significantly over time: HF was dominant in May 1991, LF from June 1991 until August 1993, MF during September and October 1993, and HF and MF from November 1993. HF and MF events are mainly distributed at depths of 500–1100 m above sea level (ASL), just below the lava dome, while LF events are widely distributed at depths from 500 m ASL to the interior of the dome itself. To efficiently detect earthquake families, we conducted a cross-correlation analysis of waveforms. Using the events one-by-one as reference events, we calculated peak correlation coefficients between each reference event and events that occurred within 24 h either side of the reference event. The results show that many earthquake families of all waveform types occurred throughout the growth period of the dome. The durations of most families were less than two weeks and were not related to the intensity of seismic activity. The incidence rate of events within each family reached a peak in the middle of the respective activity period. The results also suggest that the waveforms in several analyzed families gradually evolved over time. During periods when HF events intensified, several families appeared contemporaneously. In contrast, during periods when LF events intensified, the occurrence pattern of earthquake families was relatively simple: a new family became active only once the activity of the previous family had declined or ceased completely. A possible source mechanism for families of HF events is stick-slip within the stiff rocks surrounding the conduit; however, several different types of source mechanisms should be considered for families of LF events.

Adaptive solid wave propagation—influences of boundary conditions in high-speed train applications

Wave propagation in solid materials is of great interest in many engineering applications. The fact that the area of interest changes with time creates a number of computational problems such as the need for a mesh density varying in space and time. This means that the mesh must be continuously updated and controlled, rendering a large demand of computer effort. In certain applications like railway mechanics there are mobile loads. A load speed close to the natural speed in the underlying soil causes specific problems, shock waves being one of them. The transmitted waves have to leave the defined finite element domain without reflection, which imposes a need for certain modelling methods. The paper will deal with quality controlled FE-procedures for wave propagation including error estimation and mesh refinement/coarsening. As an application an important problem from railway mechanics is considered. When a high-speed train approaches an area with decreasing thickness of underlying soft soil on a stiff rock it is expected that the reflection of the wave will increase the total amplitude of the wave. We will study this problem with the procedures described above in full 3D with partly absorbing boundaries.

A preliminary probabilistic seismic hazard assessment in terms of Arias intensity in southeastern Spain

A preliminary probabilistic seismic hazard assessment in terms of Arias intensity is presented for the first time in southeastern Spain. In the calculation, the spatially smoothed seismicity procedure has been used, considering four seismic models, and a seismic catalog updated up to 1999. One of the models that include the most significant seismicity, considers earthquakes above 5.5 M S in the last 700 years. Maps for a return period of 475 years, that is, for a 10% probability of exceedance in 50 years, and for different soil conditions, have been computed. The uncertainty in the final result is shown by depicting maps for the mean and mean+ σ attenuation curves. Independently of the geological soil conditions, higher Arias intensity values have been obtained along the Betic Cordilleras. The most significant result is the value obtained in the Granada Basin, the most active and hazardous Spanish seismogenic area. It is of the order of 0.4 m/s for shallow soils, 0.3 m/s for deep soils, and 0.2 m/s for stiff rock conditions, for the return period quoted above. These are typical values for a moderate seismic hazard region.

Modelling of cutting tool – soil interaction – part I: contact behaviour

The unknown interaction of the cutting tools with geological settings represents an interesting problem for the excavation machinery industry. To simplify the non-linear aspects involved in the numerical analysis of such phenomena a strategy for an accurate soil modelling has to be defined. A possible approach is the discrete one, by considering the soil as an assembly of rigid spheres. In this work this strategy is adopted. The basic idea is to concentrate at the contact level between the spheres the real mechanical behaviour of the soil. For this purpose suitable contact models have been developed, where specific elasto-plastic laws have been implemented in the node-to-segment contact formulation. The framework for the plastic behaviour consists of a failure criterion, a one-dimensional, rate-independent elasto-plastic flow rule for the normal and the tangential force and a non-linear yield criterion. The final aim of this paper is to develop mechanical models to study the behaviour of stiff soils and rocks under different loading conditions.

The deformation evaluation of Kızlaç T3A Tunnel (Osmaniye, Turkey)

This study covers the graphical analysis of deformation values measured in the Kızlaç T3A tunnel (Osmaniye, Turkey), which was built as a part of the Tarsus–Adana–Gaziantep Motorway Project. Excavation was performed through a sequence which was composed of sandstone–shale alternation, sandstone and dolerite dyke. Horizontal, longitudinal and settlement deformation values were optically read and recorded daily on a computer. These data were evaluated according to New Austrian Tunneling Method. Total deformation measurement, risky area determination and forecast of transitions between weak and stiff rock, stiff and weak rock were assessed as a result of deformation evaluation for tunnel stability, safety and economy.The largest resultant deformation value (13 mm) was measured in the sandstone–shale alternation between chainage 500 and 550 m, which was highly weathered by groundwater and affected by local tectonic disturbance. The smallest deformation value was observed in a stiff dolerite dyke between 370 and 430 m, where at times the deformation values decreased to zero. In the sandstone, small resultant deformation values (2–4 mm) were also recorded. The 500–550-m interval of tunnel alignment had the highest risk for tunnel instability in the studied section but the deformation values (maximum 13 mm) were within the tolerable deformation range (10 cm). Small negative longitudinal deformation values decreasing between chainage 320 and 370 m and small positive longitudinal deformation values decreasing between 420 and 480 m indicate the sandstone–shale alternation (weak rock) and the dyke (stiff rock) and sandstone (stiff rock), and the sandstone–shale alternation with a fault gauge zone (weak rock), respectively. These longitudinal deformations needed probable to predict the lithological transitions ahead of the face, which in timely were used to determination of the tunnel support system.

Tensile Fracturing of Stiff Rock Layers under Triaxial Compressive Stress States

In an attempt to reduce the Li+ concentration polarization and electrolyte depletion from the electrode porous space, sulfonated polyether ether ketone with pendant lithiated fluorinated sulfonic groups (SPEEK-FSA-Li) is prepared and attempted as ionic conductivity binder. Sulfonated aromatic poly(ether ether ketone) exhibits strong adhesion and chemical stability, and lithiated fluorinated sulfonic side chains help to enhance the ionic conductivity and Li+ ion diffusion due to the charge delocalization over the sulfonic chain. The performances are evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, charge–discharge cycle testing, 180° peel testing, and compared with the cathode prepared with polyvinylidene fluoride binder. The electrode prepared with SPEEK-FSA-Li binder forms the relatively smaller resistances of both the SEI and the charge transfer of lithium ion transport. This is beneficial to lithium ion intercalation and de-intercalation of the cathode during discharging–charging, therefore the cell prepared with SPEEK-FSA-Li shows lower charge plateau potential and higher discharge plateau potential. Compared with PVDF, the electrode with ionic binder shows smaller decrease in capacity with the increasing of cycle rate. Meanwhile, adhesion strength of electrode prepared with SPEEK-FSA-Li is more than five times greater than that with PVDF.

The shear strength of reinforced rock joints

Abstract The evaluation of the shear strength of rock joints, reinforced by means of steel dowels, by both experimental measurements and numerical modelling with the aim of determining a provisional tool for optimization of dowel design is presented. The influence of some important parameters of both the rock and the steel type on the mechanical behaviour of the reinforced structure has been studied. The analysis of the mechanical behaviour of the discontinuous rock mass-dowel system presented in this paper involved the following theoretical and experimental studies: • •|laboratory tests on reinforced rock joints, • •|Finite Element Method (FEM) modelling of the laboratory tests, • •|analytical models for determination of the reinforced joint shear strength, • •|comparison between the experimental and analytical results. The tests have been carried out in order to evaluate the influence of some important parameters on the mechanical behaviour of the reinforced structure: • •|steel type, • •|bar diameter, • •|reinforcement type (bars and tubes), • •|rock material type. Shear resistance is heavily influenced by the quoted parameters. Yielding steel provides the highest contribution to the global reinforced joint shear resistance when using bars or tubes. Stronger and stiffer rock materials lead to higher shear stresses in the steel and consequently lower overall resistance. Two different mechanisms of reinforcement failure have been observed while varying the rock material characteristics. The analytical model has been set up in order to reproduce these two failure mechanisms, one involving a strong and stiff rock material with bar failure determined by shear and tensile stresses at the joint intersection; and the other involving weaker rock and the formation of two symmetric plastic hinges in the bar, with failure being due to either the tensile strength or the ultimate elongation of the reinforcement being reached. Finally, the analytical model has been validated by comparison with experimental results.

Modest movements, spectacular fabrics in an intracontinental deep-crustal strike-slip fault: Striding-Athabasca mylonite zone, NW Canadian Shield

Geometry and strain partitioning within lower-crustal intraplate strike-slip shear zones can be extremely complex, compared with analogous structural levels of interplate strike-slip shear zones sited at plate margins. Striding-Athabasca mylonite zone, Canadian Shield, is a spectacular ca. 500 km long granulite facies continental intraplate shear zone. The shear zone is composed of Middle Archean granulite facies annealed mylonites ( ca. 3.13 Ga) and Late Archean ( ca. 2.62-2.60 Ga) granulite facies ribbon mylonite belts, which thread a sinuous course along a chain of crustal-scale ‘lozenges’ cored by relatively stiff rocks of mafic to intermediate composition. To the northeast, the mylonites form a N-S-trending, 5–10 km thick, dextral strike-slip belt. To the southwest, this bifurcates into a pair of conjugate strike-slip shear zones, overlain by a contemporaneous dip-slip shear zone. Striding-Athabasca mylonite zone was kinematically inefficient as a strike-slip fault and cannot have accommodated large wallrock displacements. Nevertheless, spectacular granulite facies ribbon mylonites were formed throughout the shear zone, reflecting the very high temperatures ( ca. 850–1000 °C), high recrystallization rate/strain rate ratios, and the transpressive nature of the deformation ( W k < 1), possibly accommodated by significant volume loss by magma migration.

Effect of stress change on the bond strength of fully grouted cables

Abstract The bond strength of fully grouted cable bolts is primarily frictional and depends on the pressure at the cable-grout interface. Thus, any change in this interface pressure must affect the bond strength. The interface pressure increases with (load induced) dilation and may increase or decrease with the stress change due to nearby mining activities (excavation induced). In this paper, the effect of stress change on the bond strength is studied in the context of the bond strength model (BSM) previously established in a companion paper. A laboratory testing program was executed to evaluate the stress change effect on the frictional resistance of the steel-grout interface of a smooth bar and the laboratory results confirm the theory. It is concluded that mining induced stress change is one of the most important parameters controlling the cable bond strength. Theoretical results indicate that cables should be most affected by stress change in relatively soft rocks. Stress reductions of −40 MPa, often measured in deep mines, can cause the cables to lose most of their bond strength in low to medium stiff rocks. This study provides a new perspective on cable design and provides a methodology to increase the stability of openings.

Analysis of the variability of unconfined compression tests of rock

The laboratory testing program reported herein describes the statistical correlations of unconfined compressive strength (σ c ), Young's modulus (E t50), and modulus ratio (MR) to their coefficients of variation (CV(σ c ), CV(E t50), and CV(MR)). Negative correlation of bothσ c andE t50 to CV(σ c ) indicates that data scatter tends to decrease with increasing strength and stiffness. A positive correlation between MR and CV(σ c ) indicates that stiffer rocks are more variable for a given compressive strength.

New modified borehole jack for stiff rock : Azzam, R; Bock, H Rock Mech Rock EngngV20, N3, July–Sept 1987, P191–211

New modified borehole jack for stiff rock : Azzam, R; Bock, H Rock Mech Rock EngngV20, N3, July–Sept 1987, P191–211

New modified borehole jack for stiff rock : Azzam, R; Bock, H Rock Mech Rock EngngV20, N3, July–Sept 1987, P191–211

New modified borehole jack for stiff rock : Azzam, R; Bock, H Rock Mech Rock EngngV20, N3, July–Sept 1987, P191–211

Regla Steam Electric Station

Paper describes design of 4-unit, high viscosity oil fueled steam electric station; design of foundations to cope with stiff clay, rock strata, and slag deposits; aspects of outdoor type construction, strengthening gantry crane, and ventilating louvres for turbogenerator housings; outdoor type of construction was found ideal for ventilation but had disadvantages during driving rains, therefore sides were enclosed with corrugated asbestos.

Regla Steam Electric Station

Paper describes design of 4-unit, high viscosity oil fueled steam electric station; design of foundations to cope with stiff clay, rock strata, and slag deposits; aspects of outdoor type construction, strengthening gantry crane, and ventilating louvres for turbogenerator housings; outdoor type of construction was found ideal for ventilation but had disadvantages during driving rains, therefore sides were enclosed with corrugated asbestos.