Creep effect and type of landslides, the sites observed .
The soft rock and wet slopes increase landslides over 50 m long creep slide and risk assessment for long steep slide in Şırnak open-pit coal mining should be searched in asphaltite quarries. The Avgamasya quarries No1 and 2 at critical depths and road bench sites in Şırnak, reaching over 120 m height with 60–65° shale slopes, developing major creep factors and other factors for landslide in the deep quarry locations is resulting debris rock falling or free sliding. The pore pressure measurements by measurements of water levels in four wells and water flow counting as the mining safety in recent years. This research provided rock slope stability patterns and crack propagation control of the hazardous location and formation cracks. The stages of creep experimentation explored the geophysical characteristics and thaw and freeze testing of rock samples. For this aim, two different long sliding areas with similar geoseismical conditions, two main analyzing methods, and patterns of researches were developed. Firstly, data on crack propagation in situ rock shale faces over certain time periods were determined. Displacement measurements over highly saturated shale—limestone contacts over the base of crack counting in a meter scale such as Rock Quality Designation (RQD) scoring of drilling logs. Secondly, hydrological water level logs were taken into consideration. On the other hand, due to that creep effect over freeze crack propagation unseen cause instability over wet sliding surfaces over 50 m, long sliding surface matter over slopes, poly linear or circle type creep sliding or rock tumbling falling failure types, and GEO5 slope stability, slice analysis will be advantageous instead of Finite Element Method (FEM) method.
- landslide analysis
- Şırnak asphaltite quarry
- active potential landslide
- creep failure
- geotechnical stability
- GEO5 slope stability
The time-dependent failure propagation occurs on the local mountainous natural rockfalls in the hard winter conditions of freezing and thaw cycles observed on road slopes. Hazardous deep quarries in the Şırnak will make a great concern in asphaltite production as significant to the local economy. The hydrology of the area, few months hard fill snow on the quarry avoiding production is important in creep failure or landslides as illustrated in Table 1  due to loosen rock fallings and free slide of saturated shale slopes over safety limit grade zone [1, 2, 3]. Formations such as shale in the regional quarries allow crack propagation by freeze and thaw cycling in the winter climates [4, 5]. The pore structure and low mechanical strength cause a negative effect on creep-dependent breakage quality and stone falling [6, 7, 8, 9]. For this reason, the freeze-thaw cycling time and crack texture were critical for creep behavior at the local slope durability [10, 11, 12].
Although the 65° (72°gr) of bench slopes of quarries 1 and 2 as steeper will reduce the excavation costs, it has a negative effect on the creep stability of the quarry at the end of winter, opening the excavation over melted ice period. The highly fractured rock masses have undergone crack propagation, extremely fractured, and showed counting effects on RQD values. The geological strength index GIS, Rock Mass Rating (RMR), and RQD points were determined, by creep texture properties of rock mass in the classification ensured long-term planning stability in the coal quarry excavations. 
It is quite difficult to creep the block samples depending on the quarry development. Various rock mass classification methods have been proposed. The high groundwater levels and water pressure make ease landslides in the quarry caused major problems in terms of safety. The creep effect in rock mass assessment by freeze and thaw test method is proposed. Q classification system and the Hoek–Brown empirical failure criterion [6, 7, 8] were most frequently used by researchers. By the high creep matter, the geomechanical properties critically change the sawing rate resulting in failure by lowering the shear strength and similar methods are used.
The creep failure in rock masses is dependent on discontinuity features that controlled crack face filling and roughness. The slopes failures and discontinuity-controlled failures can be divided into creep discontinuity failures that critically occur in heterogeneous rock conditions as alluvial shale mixed formations. Those creep failures cannot be controlled. The failures are severely fractured and cracked and time depended propagated unseen. It mainly occurs in highly weathered rock masses [6, 7, 8, 9, 10].
In the stability analysis, the shear strength of the rock mass at the time of failure was determined. The water pressure parameters for all sliding geometry of the failure surface should be analyzed by the calculated block weight slice method. This method is used in soft rock and heterogeneous rock masses although it describes the failures that occur [1, 2, 3, 4, 5], the rock masses are also linear or irregular failure envelopes in different soft rock mass and heterogeneity. However, this cannot fully calculate by the medium the shear strength.
Therefore, The Mohr–Coulomb method is not a preferred measure of instability for rock mass in creep propagation. In the failures that occur in soft and heterogeneous rock masses, Hoek–Brown [6, 7, 8] failure criterion is more preferred for the determination of geomechanical strength change.
On quarries no 1 and 2, the south side shale and altered alluvial debris covers and groundwater levels increase in September and reach the highest level in April. December-February period of mining is a closed and active time for creep crack propagation even saturation time [11, 12, 13, 14]. The water level increase and freeze and thaw cycle causes of the rock failures occur determined by extensive
1.1 Geology in asphaltite quarry in Avgamasya, Şırnak
Study area geology sedimentary alluvial, shale, and calcareous rocks of the Gercus Massif formation Jurassic aged in the Avgamasya, Şırnak province. There are highly disseminated chlorites and calcites are exposed (Figure 1). In the southern part, the late Mesozoic aged limestone anticline zone, in the northern part early Eosin age altered porous limestone calcite are located heterogeneous shale contact to Cudi formation and Cizre formation.
In the field studies, the study including the open-pit area has a very heterogeneous layered shale and alluvial contact with vertical asphaltite structure. (Figure 1). The hazardous areas of asphaltite quarries are studied as slopes S1, S2, S3, and S4 over the excavation area. The discontinuity intervals were determined. The creep act by freeze and thaw effect is critical for time-dependent rock loose and free landslides developing in mining quarries and urbanization lands in the Southeastern Anatolian regions at height over 1400 m attitudes by high tectonically soft ground conditions [10, 11, 12, 13, 14]. The instability of rock loss in the asphaltite coal quarry area creep cracks were developed with advanced mining operations over decades and loosen geotechnical characters of soft heterogeneous formations determined. The detailed investigations in the quarries during mining operations have two fundamental causes of free sliding over freeze and thaw effect on the geotechnical conditions [15, 16, 17, 18, 19, 20, 21]. First of all, the tumbling rock falling landslides occurred at the top of the quarries by groundwater saturation and hard rainwater taking surface conditions as clearly seen. In terms of the past, fatal disasters of instability were observed widely in the different quarries. Secondly, free flow sliding land rocks as debris flows as land flows were similar to the other high deep quarries [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34]. Therefore, stability conditions and soft rock properties causing past landslides and rock tumbling were so important in order to evaluate and criticize that may develop in the mining excavation areas and even urbanization areas [34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44]. Debris areas or possible free flow loosen landfill areas in mountainous and high-steep rocks were evaluated for free creep flow and tumbling depending on the topology. The unsuitable land use for urbanization over hills increases the creep probability for the development of free land flows [45, 46, 47, 48, 49, 50, 51, 52, 53]. In the case of creep landslides, the stability analysis revised by time and related to crack propagation can be achieved and change the safety factor on avoiding the fatal disasters of the quarry or urbanization area concerned [54, 55, 56, 57, 58, 59, 60].
The stability analyzes of the top benches in quarries 1 and 2 south side slopes are managed to protect the asphaltite coal excavation equipment and fatal casualties caused by landslides. For this aim, in the quarries 1 and 2 slopes S1, S2, S3, and S4, the free slide top benches three over 35 m long sliding surface excavation area are considered. The fatal experiences of Şırnak Avgamasya and Silopi open-pit mining were carrying high landslide or rock falling risk (Figure 1) [11, 12, 13, 14]. The creep effect over soft mechanical properties of the soft rock formations of soft limestone, alluvium, and shale layers heterogeneously oriented in the vertical belt form where creep rock falling or free top land flows occurred in the asphaltite quarries. The poly linear surface or circle shape slope stability analyzes for top benches are carried out with GEO5 Slope stability software and GEO5 FEM methods. The slice weight charts of the GEO5 program on the scope of this investigation regarding creep effect, a 1/5000 scale quarry no 1 bench isocontour map covering 3.7 km2 of the study area are shown in Figure 1a and b. The high risk of tumbling top rocks and free flow uncohesive sliding over the asphaltite excavation zone is seen as shown in Figure 2a and b. The blackish zone area is representing a wet asphaltite coal extraction area.
The asphaltite excavation is carried out over 2–4 m thick asphaltite seam placed vertical whirled form in the limestone rock with approximately somehow 1/2 m thick at 62° to SE and approximately 10–25 m for shale 87° to NW and completely changed the orientation to horizontal layer (Figures 2
In the scope of this study, Şırnak asphaltite quarries 1 and 2 in the 940–830 m elevations and 920–810 m elevations. The slope stability analysis for the critical shale slopes were made. The shear stress change corresponding to the creep parameters of rock masses were concluded with tests
2.1 Rock mass properties in asphaltite quarry in Şırnak
2.1.1 RMR and RQD
Determination of rock mass properties by RMR method as a result of field studies, RMR and RQD crack counting for shale Jurassic alluvial unit of Pliocene aged are carried out to provide rational stability analysis on creep base regarding two months saturation time cycle. The study area has a lot of facing cracks and cores suitable for determining RQD from the field. RQD value measured as a result of discontinuity in a meter scale line as standard studies is given in Figure 5.
RMR score was determined for the determined RQD value and scoring is shown in Figure 4. Uniaxial compressive strength UCS and RMR scores of discontinuity gap measurements (Figure 5) and RMR value and rock classification are presented in Tables 2 and 3.
|Rock formations||Thickness (m)||RQD (%)||c′ (kPa)||φ′||Pı (MPa)||Iı (MPa) (50 mm)||Shear strength (mm/s)||γsat n (g/cm3)||γdry (g/cm3)|
|γsat max (g/cm3)||2.92||2.85||2.87|
|Permeability (k) (cm/s)||5.3 × 10–4||3.0 × 10−5||6 × 10−5|
RQD value as scoring for two soft limestones of early Eosins’ and Miocene aged in Avgamasya were determined as 45 and 40 scores, respectively. It is concluded that the limestone unit is of medium rock quality and the shale and alluvial unit Pliocene aged is of poor rock quality.
2.2 Pore pressure
The geological rock classification method is useful for slope stability analysis even for complex rock and soil formations. There was a real issue for alluvial pore pressure and rock pore pressure difference and even crack propagation changes the pore pressure in the rock layer put in the calculation. The alluvial soft rock properties are given in Table 3.
The pore pressure changing the strength of limestone is illustrated in Figure 6.
2.3 UCS compression strength
Samples with volumes 0, 1, 3, and 5% are soaked in water-filled jar. The advantage of this experiment is that it minimizes the errors of the course over 50 mm according to the standard freeze-thaw propagation [15, 16, 17, 18, 19, 20]. The UCS change with pore content changing the two limestones, alluvium, and shale in the quarry is illustrated in Figure 7.
Considering inferences, extreme deformations can be observed undersaturated with water of pores depending on time. Due to these negative weight effects, various stress changes on complex texture are required for the stable sliding surface in order to reduce cracking and prevent the negative consequences of permeability on the slippery creep. Lower porosities and cracks are seen in two soft limestones. The alluvium and shale reached 22 and 45% cavities by cracking effects of creep.
The pore content of the shale sample containing 30% saturation was determined as 30.5% strength reduction and the maximum dry unit volume weight was 2.85 kN/m3. Altered limestone reaches a pore saturation of 25% and the maximum dry unit weight of 2.6 kN/m3 for Şırnak asphaltite quarry (Figure 8).
2.4 Shear strength
Considering filling material by creep moves, extreme deformations can be observed under saturated sliding surfaces depending on time till 35–40 mm scale relative control length at 10 m wire. Due to slippery filling shale mud fines affected uncohesive free slippery surfaces, even internal change on internal friction angle loses caused for the instable sliding surface with increase cracking and prevent the negative consequences of instability on the slippery creep surface.
After this shear process at 70 mm cylindrical disks, the strain amount of the box was determined from the electronic measuring stick on the device. Some samples taken from the submerged part of the box were dried in the oven and the water content corresponding to the pore saturation at the end of the test was found (Figure 9).
3. Creep failures of rocks
The stability is provided by water discharge resulted in low deformations of 10–20 mm can be observed under low water pressures of 10 mmw depending on time. The higher weight load of slope slices increases resistive stress change on complex sliding surface texture for the stability with reduction cracking and prevents the negative consequences of permeability on the slippery creep. Eq. (3) shows shear stress with deformation amount at time t :
4. Results and discussions
4.1 GEO5 slope stability analysis on creep theory
slice weights the load Fi kN, anisotropic cohesion value of , free creep slope angle. The free slip surface stability weights show resistance by load chart slice calculations depending on slip surface angle and creep effect. Safety scorings calculated by this resistance to shear should be over 1.35 confirming the stability.
About 2–3 m length slice at discontinuity at the angle of crack and creep propagated crack density and percentage distribution on slip surface change of was calculated by integral as given below Equations 5, 6.
The studied areas shear loads were regressed as exponential functions given below:
The stability mechanism and control by creep crack propagation and creep pore pressure effect for each slice as given in Eq. (7)
The safety scoring in toppling and creep flow or landslide is calculated by following the shear force and resisting load over the slope as shear deformations based on the lowered internal friction angle patterns. Rock falling caused by cohesion-free bottom cracking and propagated shear dislocations and pore pressures can be observed in free-fall displacements above 40 mm displacements. The stability analysis carried out by calculations depending on the crack propagation overslip surface for each slice was calculated by the Eqs. (8)–(15) sequentially as below:
The safety scoring of water-saturated effective mechanical strength parameters regarding creep failure.
5. Slope analysis of S1, S2 and S3 shale soil/rock face slopes
The top alluvium shale heterogeneous benches of S1, S2, and S3 benches following closed excavation period of winter December and January term started deformation shears at 10 mm sized and the cracks propagated at 11% more and 2 mm widened size gaps caused the little movements that observed and measured in field studies. In quarry No 2, S3 showed free developed slip with top alluvium bench covered with alluvium 10 m sliding depth at steep bench rock stability analyzed by GEO5 programs. The results showed a slip failure problem due to heterogeneous structure and complexity with the wet saturated sliding surface over high 40% saturation on slip surface as given in Table 4 (Figures 7 and 10). In quarry No 1, top shale bench S2 showed similar lowered stability as given in Table 5 and shown in Figure 11. The top bench of soft limestone at slice showed better stability safety factor as given in Table 6 and illustrated in Figure 11 as the higher stack and even the maximum height difference between the heel points 30–35 m, the slope of the maximum height of 50 m, the slope of the surface tilt angle is 60°.
|Chart||Block height||Block width||Block weight ton||Block weight (kN)||Block shear (MPa)||Resistance to shear (MPa)||Safety||Creep|
|Chart||Block height||Block width||Block weight (ton)||Block weight (kN)||Block chart share (MPa)||Resistance to shear (MPa)||Safety||Creep|
|Chart||Block height||Block width||Block weight (ton)||Block weight (kN)||Block shear (MPa)||Resistance to shear (MPa)||Safety||Creep|
The calculation style given in Tables 4
The safety risk parameter was calculated as 1.42 stable for 40° slopes, but 50° and 60° slopes the safety factors decreased to 1198 and 1060. As given in figure the equation slope 44.2° has given the safety factor for a stable slope as 1120 is shown in Figure 11.
Data obtained as a result of GEO5 steep discontinuity line studies regarded by shale and alluvial contact layers. The lower internal friction angle and cohesion was giving the safety factor of safety below 1.35 due to a sharp 15–25 m long sliding surface.
In this study, in the estimation of rock mass strength, RQD value for shale and alluvial zone as a result of RQD as an alternative to the method specified forward 41 and 35, respectively (Table 1). Use the normal stress(s) value when determining the strengths; m value to be used in GEO5 circle sliding surface analysis on creep base with defeat criterion from 3 for shale, 2 for alluvial clay, and a 35° slope are calculated as a function of RMR shale unit its value be 30 RMR crack propagation as determined at the end of creep period for limestone and shale alluvium.
In laboratory experiments for soft limestone rock, uniaxial test strength 42 MPa, dry unit weight 25.8 kN/m3, shale uniaxial compressive strength of the rock 12 MPa, dry unit volume and its weight was determined as 24.45 kN/m3.
2-4 month periods in the winter term results in severe weathering. RQD score is determined as the sum of the cracks and cracks filling points.
In this study, two different slope instabilities occurring in the enterprise were investigated. Extremely fractured, fractured, and altered creep saturated units were loaded to software as fill material as sliding saturated creep evaluated by the GEO5 slice analysis method.
The rock mass creep was based on the shear. It was demonstrated using the Hoek–Brown failure criterion. GEO5 FEM analysis was not chosen for the heterogeneous sliding manner. The shear stress-normal stress graphs gave higher safety values for long sliding surfaces. The slice charts as seen from Figure 11, the Avgamasya slopes 1, 2, 3, and 4 in the quarries 1 and 2 for two-dimensional (2D) and three-dimensional (3D) evaluation carried out. The hazard of the sharp slopes in the deep quarry was controlled with the slope stability analyses. The safety coefficients over 1.35 should be considered for steep bench slopes and improved safety working area in bench slopes prepared in Avgamasya asphaltite mining operations. There is also a great creep issue in slope stability is one of the biggest problems. The high pore water saturation comes out of hazardous free sliding. Before instability results arise on slopes various precautions and reinforcement methods or appropriate slope design preventing creep failures by applying top alluvial layer geometry, lower slope angels will be necessary for the security of production. For this reason, the displacement on the slopes that are likely to be defeated your angels regularly followed up with monitoring systems.
Finally, the high rainwater conditions or hard and long winter conditions are forced to creep analysis with slope stability charts practiced over the study area.
The 10–40 m long slip surfaces may cause free landslides unexpected in the quarry. The possibility of creep failure land flows may cause fatal accidents for asphaltite coal excavation areas. The stability analysis calculation should be carried out over highly shattered representative specimens at wet saturated effective strengths geotechnical parameters and the results should consider free land flows and tumbling rockslide prevention. The precautious methods appropriate for the asphaltite quarry were water discharge on the site to prevent instability within the scope of the creep in the quarries in the region.
Freeze-thaw cycling in 60 days or two months period decreased the strength values by about 34% over a month period for shale and alluvium. The pore ratio was also similar in the limestone samples. It was increased saturation by 27%. The creep values were also obtained in the shear box strength test.
Creep conditions depending on the pore density in the development of cracks and consequently the formation of wet saturated surfaces and lower shear resistance were observed.
Water discharge over alluvium and shale infiltration of rainwater through the rock slope mass will slow down creep matter and reduce free landslide or flow.
|c′||effective cohesion (kg/cm2)|
|Φ’ο||effective internal friction angle|
|Φο||internal friction angle|
|τ||shear stress (kg/cm2)|
|σ||normal stress (kg/cm2)|
|Is||point load index|
|Wopt||optimum water content|
|γNatural||natural unit volume weight (g/cm3)|
|γSaturated||saturated unit volume weight (g/cm3)|
|γDry||dry unit volume weight (g/cm3)|
|γkmax||maximum dry unit volume weight (g/cm3)|
|γs||grain unit volume weight (g/cm3)|
|S1, S2, S3, S4, C1, C2||south and north landslide risk slopes no. 1, 2, 3, 4|
|S11, C11||sample taken from south and north landslide risk slopes no.|