Understanding the time-dependent deformation behavior of rock joint is important when evaluating long-term stability of structures built on or in jointed rock masses. This study focuses on the ...time-dependent strength and deformation of unweathered clean rock joints. First, five grain-scale joint models are established based on Barton’s standard joint profiles using the GBM-TtoF creep material model. Barton’s non-linear shear strength criterion is adopted to determine the short-term shear strength of the joints. Second, a series of creep simulations are conducted to investigate major factors (normal stress, shear loading ratio, and joint roughness) that influence the long-term shear strength and the sliding velocity of the joints. The results reveal that normal stress has more influence than joint roughness on resisting creep slipping of the joints. Third, an equation for the prediction of creep sliding velocity is developed by fitting the simulation results and the equation is verified by experimental data. Finally, a creep slipping model for simplified flat joints is proposed, which can be used to model the long-term shear strength and sliding velocity of joints under creep deformation conditions. The creep slipping model, which can be used in both stationary and variable stress conditions, is useful for simulating time-dependent behaviors of jointed rock mass using the distinct element method.
•A new monitoring method for overlying strata failure height in Neogene laterite caused by underground coal mining is presented, solving the inapplicability of traditional monitoring method in clay ...layer.•The monitoring method applicability based on FMI is verified by numerical simulation, and the shapes of water flowing fractured zone in laterite and bedrock are arch-shaped, not saddle-shaped.•The evolution mode of WFFZ in laterite layer and bedrock is different, and Neogene laterite layer has inhibitory effect on the WFFZH.
Determination of the overlying strata failure height, that is, water flowing fractured zone height (WFFZH), is critical to underwater coal mining, especially in the fragile geo-environment areas. Due to the property discrepancy of rock and soil, WFFZH penetrating the clay layer in the Jurassic coalfield cannot be accurately determined by conventional measurement method, a new formation micro-scanner image (FMI) method was presented and verified in the paper. Taking the N1208 coalface in the Shennan mining area, Shaanxi, China, as a case study, FMI based field test for monitoring WFFZH was carried out firstly. The scanning results show that subtle changes of drilling sidewall cracks could be presented intuitively in FMI scanning image, and the WFFZH was be determined as 145.15 m. Secondly, the whole evolutionary process of WFFZH is simulated using UDEC, whose maximum height of WFFZ is calculated as 147.0 m. Comparison results between on-site measurement and numerical simulation suggest that FMI technology is applicable to monitor the WFFZH in laterite layer. Thirdly, in order to illustrate the discrepancies in WFFZH developed in laterite and bedrock, a comparative numerical simulation tests results show that laterite layer has an inhibitory effect on WFFZH.
The studies on the performance of tunnels under static loads are reported extensively in the literature but their performances under dynamic loads are limited. The present study highlights some of ...the important aspects of jointed rock tunnels during seismic loading. The literature review provides a shake table experimental study of a jointed rock tunnel. A Universal Distinct Element Code (UDEC) model is developed from this shake table experiment. The model tunnel is subjected to a scaled input motion of the 1985 Mexico earthquake. The numerical results are validated systematically with the findings of the shake table experiment. Further, the developed numerical model is used to perform parametric studies to understand the effect of in-situ stress, joint angles, joint stiffness, and joint friction angle on the deformation and stability of the tunnel under the same earthquake input motion. It is observed that some joint angle combinations form a wedge that yields excessive deformation and subsequently a complete failure. An exponential decrease in deformation occurred in the tunnel as the joint stiffness increases. It is found that the shallow tunnels are more susceptible to damage under the action of earthquake loads.
Rock bursts have recently become a serious problem in the horizontal section mining of steeply inclined extra-thick coal seams (SIETCSs). However, few studies have been carried out to investigate ...their mechanisms and prevention. In this study, numerical simulation and field measurements were carried out to investigate the mechanism of rock bursts in the horizontal section mining of an SIETCS. A Universal Distinct Element Code (UDEC) Trigon model was built, based on the Yaojie No.3 Coal Mine, and calibrated through laboratory tests and RQD methods. The results demonstrate that the coal in the elastic zone around the roof is in a high static stress state, due to the asymmetric clamping and squeezing of the roof and floor. Strong dynamic loads are formed by breakage of the roof and the failure of multiple hinged beam structures during the evolution process of the overlying strata. Rock bursts occur on the roof side when the superimposition of the static stress σs and stress increment σd induced by such dynamic loads is greater than the critical stress σmin of the coal and rock. We propose a technical prevention scheme for the considered mine. Field studies suggest that the proposed technology can effectively prevent and control rock bursts in the horizontal section mining of SIETCSs.
فرآیند تخریب در روش استخراج جبههکار طولانی به طور مستقیم بر پایداری و پیوستگی عملیات استخراج تاثیر میگذارد. از این رو پیشبینی رفتار تخریبی سقف از دو دیدگاه گامهای تخریب و مقدار تنشهای القایی ...ایجاد شده در طی آن مسالهای ضروری در طراحی پروژههای استخراج جبههکار طولانی است. در این راستا فرآیند تخریب اول که در آن گام تخریب و تنشهای القایی بیش از تخریب دورهای است، اهمیت ویژهای دارد. بر این اساس در این مقاله به بررسی تنشهای القایی ناشی از فرآیند تخریب اول از طریق شبیهسازی عددی گسسته پرداخته شده است. برای این منظور تاثیر تغییرات 5 پارامتر مقاومت کلی سقف بلاواسطه به صورت تابعی از مقاومت فشاری تک محوری لایهها و ضخامت آنها، ارتفاع سقف بلاواسطه، فاصله لایهبندی در سقف بلاواسطه، عمق معدنکاری و نسبت تنشهای برجا بر روی بیشینه تنشهای القایی قائم و افقی جلو و پشت جبههکار با استفاده از نرمافزار UDEC مجموعا برای 62 مدل تحلیل شده است. نتایج حاصل شده نشان میدهد که به جز برای نسبت تنشهای برجا، روند تغییرات فشارهای پایهای قائم و افقی جلویی و عقبی نسبت به تغییرات پارامترها یکسان است. همچنین رابطه تمام پارامترها با تنشهای پایهای به جز ارتفاع سقف بلاواسطه به صورت مستقیم است.
Laboratory tests showed that the average direct tension strength (DTS
0
) of the Lac du Bonnet granite was 6.9 MPa, and significantly less than its average Brazilian tension strength (BTS
0
), i.e., ...8.8 MPa. In this paper, a grain-based model (GBM) with a 2D universal discrete element code (UDEC) was used to explore factors that could control the difference in the direct tension strength (DTS) and Brazilian tension strength (BTS) of the Lac du Bonnet granite from the micromechanical point of view. Micro parameters of the grain contacts were investigated, i.e., the tensile strength (
T
), cohesion (
c
), friction angle (
φ
), and the ratio of the shear to normal stiffness (
λ
). Results show that both BTS and DTS highly depended on log(
λ
). With an increase in log(
λ
), the BTS first increased nonlinearly and decreased instead after achieving a peak while the DTS always increased nonlinearly. The BTS was sensitive to
T
and
c
, while the DTS was mainly sensitive to
T
. The ratio of DTS to BTS first decreased with the increase of log(
λ
) and then increased instead from a minimum. It was found that the GBM with UDEC can well reproduce the uniaxial compression, direct tension and Brazilian tests of the Lac du Bonnet granite simultaneously only on condition that
λ
= 2.51. This indicated that the shear stiffness of the grain boundary in the Lac du Bonnet granite may be several times larger than its normal stiffness. This may be the main factor controlling the difference in the BTS and DTS of the Lac du Bonnet granite.
The deterioration of rock mass in the hydro-fluctuation belt and reservoir-induced earthquakes in the Three Gorges Reservoir Area (TGRA) have great impact on the stability of bedding rock slope. The ...cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt, when subjected to repeated seismic loads, were investigated using the shaking table model test and Universal Distinct Element Code (UDEC) numerical simulation. Under the continuous action of seismic loads, the peak ground acceleration (PGA) amplification coefficient clearly weakens; the cumulative displacement, pore water pressure and earth pressure of the slope show a change trend of increase, increase and decrease, respectively; the damping ratio and damage degree (
D
G
) of the slope increase, while the natural frequency of the slope decreases gradually; the nonlinear cumulative damage mechanical models of the slope in the stages of microseism—small earthquake action and strong earthquake action can be characterized by the cubic function of “S-type” and the exponential function of “steep rise type,” respectively. Based on the good agreement between the experimental observations and numerical simulation results, the evolution process of the dynamic cumulative damage—instability and typical failure modes of the slope (including the hydro-fluctuation belt) was observed. Furthermore, the stability of the slope increases with the decrease of the slope height (A), slope angle (B), seismic load amplitude (C), seismic load frequency (D), or deterioration depth of rock mass in hydro-fluctuation belt (E), while it decreases with the increases of the strength degradation ratio of the rock discontinuities in hydro-fluctuation belt (F); the ranking of sensitivity of the mentioned-above influence factors is C > A > D > E > B > F according to the orthogonal analysis method (OAM).
The city of Matera, as several other ancient historical cities and towns, is recovering a large part of its ancient parts developing a policy of urban regeneration. In the early 90s, during the ...restoration works of the main square, Piazza Vittorio Veneto, it was re-discovered a huge underground space used as water reservoir named
Palombaro Lungo
. It was built linking ancient pre-existing smaller caves and completed at the end of the nineteenth century making it impermeable with the
cocciopesto
(opus signinum) technique. The hypogeum is dug in a Plio-Pleistocene rock called Gravina Calcarenite. It is a calcareous sandstone weak rock with good mechanical properties, low permeability and easy to be dug. The internal geometry of the hypogeum and the rock thicknesses above the caves was reconstructed by the integration of topographic and GPR surveys. The paper presents a geo-mechanical model of
Palombaro Lungo
underground reservoir and evaluation about the stability of this structure. The stability analysis were developed using the numerical code UDEC for several transect of
Palombaro Lungo
assuming the calcareous sandstone blocks as deformable, trying to address the evolution of the stress–strain conditions. The case study can be considered as an example of general interest for the study of rupestrian underground reservoir of a longed form, where one planimetric dimension strictly prevails over the other. Numerical simulations showed a stress–strain state compatible with the fractures detected in situ and confirmed the absence of instability problems in the groundwater reservoir.
The shear characteristics of rock joints under constant normal stiffness (CNS) boundary condition are critical to the stability of underground engineering rock mass. Five different rock joint ...profiles with random morphology were constructed using the independent segmentation method of the Hurst exponent. Based on the continuously yielding joint model, the discrete element calculation models of double rough parallel joints with different joint surface roughness and spacing of joints under CNS boundary condition were established using UDEC software to investigate the shear effect of joints under CNS boundary condition. The results show that under CNS boundary condition, the shear stress, normal displacement, normal stress, and surface resistance index (SRI) all increase with the increase of joint surface roughness coefficient (JRC) for both single- and double-joint specimens, and these of the single-joint are greater than these of the double-joint. With the increase of the joint spacing
d
, the peak shear stress
τ
y
, and the peak surface resistance index (SRI
p
) show a gradually increasing trend, and the influence of
d
on
τ
y
and SRI
p
is greater with the increase of JRC, and both
τ
y
and SRI
p
show a linear increasing trend with the increase of JRC. With the increase of
d
for the same JRC, both normal displacement and normal stress show a gradually increasing trend, and also, the increased amplitudes gradually increase; with the increase of JRC for the same
d
, the two parameters also show an increasing trend.
Landslide is a natural hazard which carries water, mud, debris and sometimes large boulders. Earthquakes, heavy rainfall and tectonic forces are natural responsible factors for landslides, whereas ...overpopulation and rapid development in the hilly region are unnatural factors which involve human activities such as construction/maintenance of roads, highways, railways and buildings by the unplanned excavation of rock slopes. Both natural and unnatural factors have been accountable for the increase in the probability of landslides in the past few decades. In the present study, stability analysis of rock slopes has been carried out along Kulikawn to Saikhamakawn road section of Aizawl. Kinematic analysis has been performed to identify the road cut slopes which have the potential to fail, and mainly two types of failures were found, i.e., wedge and topple failure. In order to check the stability of road cut slopes, Geological Strength Index, slope mass rating (SMR) and continuous slope mass rating (CoSMR) have been used in this study. Numerical modelling has also been performed to assess the stability of the road cut slope. The maximum displacement of 0.79 m with a maximum velocity of 0.78 m/s has been found for rock slope at location L1 using numerical modelling which confirms the finding from kinematic analysis, SMR and CoSMR analysis.
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