مجله زمین شناسی مهندسی
سال چهاردهم شماره 2 (تابستان 1399)

Rock masses have an enormous geometrical discontinuities such as void, notch, crack and flaw. These geometrical discontinuities which play as stress concentrator, cause to reduce the load bearing capacity of rock masses. In rock masses, the crack is the most important geometrical discontinuity assessed frequently by civil, mechanical and mining engineers and researcher. The fracture mechanics which is a branch of mechanical engineering science, has been often used for investigating the cracked rock samples. The fracture toughness is one of the important parameters in the fracture mechanics which describes the resistance of materials against the crack growth. On the other hand, since orientation of cracks relative to the loading directions can be arbitrary, brittle fracture in rocks may happen due to a combination of two major fracture modes, i.e. crack opening mode (mode I) and crack sliding mode without any opening or closing the crack flanks (mode II). In order to obtain the fracture toughness of rocks, several test configurations under pure mode I have been proposed. One of the parameters that has the influence on the fracture toughness of rocks and other materials is the thickness of test sample. Previous experimental results showed that the fracture toughness of rocks increases by increasing the specimen thickness until a specific thickness. After that, the fracture toughness decreases for thicker samples until plane strain condition occurs. Then, the fracture toughness becomes a fixed value when the thickness of sample varies. The all preceding studies have been dealt with considering the effect of specimen thickness on fracture toughness focusing only the mode I fracture toughness and there is few research concerning the thickness effect on the mode II fracture toughness of rocks. Therefore, the aim of this paper is to investigate experimentally the effect of specimen thickness on the mode II fracture toughness.

To investigate the thickness effect on the mode II fracture toughness of rocks, several fracture tests were conducted on the semi-circular bend (SCB) specimens. The SCB specimen is a semi-disk of radius R and thickness t including an edge crack of length a loaded under three-point bending. When the crack is along the applied load and the bottom supports are symmetric relative to vertical crack, the SCB sample is under pure mode I loading. One of the methods for achieving the mixed mode loading in SCB sample is the asymmetry distances of bottom supports from the vertical crack located at the middle of bottom edge (see Figure 1). The pure mode II in this type of SCB sample is attained at a specific distances, i.e. at specific values of S1 and S2. These values of supporting distance can be obtained from finite element analysis. Figure 1. The schematic of SCB sample. The fracture tests were done both on pure mode I and pure mode II, for the sake of comprehensiveness. Therefore, 32 SCB samples with 4 different thicknesses and 4 repetition for each specimen size were tested for both pure mode I and pure mode II. The specimens were cut from Ghorveh marble sheets with different thicknesses by water jet machine. Then, the specimens were cracked artificially by a high speed rotary diamond saw blade. The specimen dimensions and loading conditions are presented in Table 1. Finally, the cracked SCB samples were tested by using a 300 kN ball-screw universal test machine. Table 1 also gives the average of four fracture loads (Pf) obtained for each thickness of specimen. Table 1. The specimen dimensions and loading conditions.   S.D.  (N) Pf  (N) S2 (mm) S1 (mm) a (mm) t (mm) R (mm) Pure mode I 150 3220 57 57 28.5 15 95 Pure mode II 350 4726 11 57 Pure mode I 360 6711 57 57 28.5 25 95 Pure mode II 882 9445 11 57 Pure mode I 1450 20285 57 57 28.5 50 95 Pure mode II 4179 25441 11 57 Pure mode I 4672 31810 57 57 28.5 80 95 Pure mode II 4686 36848 11 57

The mode I and mode II fracture toughness (KIc and KIIc) can be calculated for SCB samples from following equations:(1) (2) where Pf is fracture load, R and t are the radius and thickness of SCB sample, respectively KI* and KII* are geometry factors which depend on geometrical ratios a/R, S1/R and S2/R and independent of specimen dimensions and magnitude of applied load. These dimensionless parameters are often obtained from finite element analysis. For tested SCB samples, the values of KI* and KII* were extracted from previous studies as shown in Table 2. Substituting the fracture loads and specimen dimensions from Table 1 and the values of KI* and KII* given in Table 2 into Eqs. (1) and (2), the mode I and mode II fracture toughness were calculated as listed in Table 2. Figure 2 also shows the variations of mode I and mode II fracture toughness with respect to specimen thickness. As seen from this figure, the fracture toughness for both pure modes increases for thicker samples until a specific thickness. After that, the values of KIc and KIIc decrease by increasing the specimen thickness. For plane strain condition in which the thickness of specimen is relatively large, the values of KIc and KIIc are nearly constant. Table 2. The dimensionless parameters KI* and KII* for tested SCB samples and their corresponding fracture toughness.   KIIc (MPa.√m) KIc (MPa.√m) KII* KI* t R Pure mode I 0.0 1.125 0.0 0.644 15 95 Pure mode II 0.897 0.0 0.35 0.0 Pure mode I 0.0 1.411 0.0 0.644 25 95 Pure mode II 1.075 0.0 0.35 0.0 Pure mode I 0.0 2.126 0.0 0.644 50 95 Pure mode II 1.448 0.0 0.35 0.0 Pure mode I 0.0 2.083 0.0 0.644 80 95 Pure mode II 1.311 0.0 0.35 0.0 The other point assessed in the present study is the dependency of fracture path on specimen thickness in mode II loading. It was shown that the fracture trajectory becomes more curvilinearly when the thickness of specimen increases. Figure 2. The variations of KIc and KIIc versus the specimen thickness.

The effect of specimen thickness on the mode I and mode II fracture toughness of rock was investigated experimentally using the SCB specimens. The experimental results showed that the fracture toughness for both pure modes increases when the thickness of specimen increases until a specific thickness. After that, the values of KIc and KIIc decrease by increasing the specimen thickness. For plane strain condition in which the thickness of specimen is relatively large, the values of KIc and KIIc are nearly constant. Also, it is shown the crack grows more curvilinearly for thicker SCB samples../files/site1/files/142/1.pdf

Soil dynamic properties are used to evaluate the dynamic response of soils at different strain levels in geotechnical engineering. The shear modulus (G) and damping ratio (D) are among the most important dynamic properties of soils. In general, the factors affecting the dynamic behavior of soils are divided into two categories: first; soil type and characteristics such as water content, void ratio and soil plasticity and second; parameters of loads applied on the soil such as the number of loading cycles, loading frequency and loading waveform .Therefore, it is widely believed that the dynamic response of soils partially depends on the characteristics of the load. In this paper, 1-g shaking table tests were employed to investigate the effect of loading waveform and frequency content on dynamic properties of dry sands. The response obtained from soil samples during loading with different frequencies, input accelerations and waveforms were used to generate hysteresis loops of tested samples at different strain amplitudes. Then, hysteresis loops were used to determine the damping ratio and shear modulus at different strain levels. Finally, the effects of loading frequency and waveform on the changes of each parameter (G and D) were investigated.

A hydraulic shaking table with a single degree of freedom, designed and constructed at the Crisis Management Center of Urmia University, was used to conduct the experiments. Firoozkuh No. 161 sand was used in all the experiments. The Firoozkuh sand gradation curve is similar to that of Toyoura sand. In this study, accelerometers were used to measure the acceleration of the input to the sample as well as to record the acceleration caused by the input excitation at different depths of the soil sample. The displacement transducers (LVDT sensors) were also used to measure linear displacement. Each soil sample was constructed using dry Firoozkuh sand poured uniformly into the container from four equal heights of 150 mm to reach a total height of 600 mm. During the compaction process, the accelerometers A1, A2, and A3 were placed at a depth of 150, 300 and 450 mm with respect to the bottom of container. Also, one accelerometer, A0, was attached rigidly to the container base to measure base acceleration. A displacement transducer (L1) was placed on the soil surface at a height of 600 mm from the floor of the container to measure the vertical displacement of the surface of the soil. In this study, 42 shaking table tests were performed to study the effect of loading frequency and waveform on dynamic properties of dry sand. The test samples were subjected to rectangular, sinusoidal and triangular loading at frequencies of 0.5 to 9 Hz and at input acceleration of 0.1g and 0.3 g.

Given the importance of G-γ and D-γ curves in dynamic analyses, the changes in shear modulus with shear strain has been studied. The results show that the shear modulus increases as the frequency increases in all cases, and this increase is observed at lower frequencies and increases with increasing frequency. On the other hand, the shear modulus decreases with increasing shear strain. At a constant testing frequency, soil samples subjected to the rectangular waveform exhibited the largest shear modulus while the samples subjected to the triangular waveform showed the least shear modulus. The shear modulus of the samples under the sinusoidal waveform is barely more than the shear modulus of samples under triangular waveform. Moreover, by increasing the shear strain, the shear modulus values ​​of samples with different waveforms have become closer and the waveform effect is reduced. As for the effect of input acceleration on the shear modulus , increasing the input acceleration increases the shear strain and consequently, decreases the shear modulus in all states (the values ​​of shear modulus in various frequencies and the waveforms under the input acceleration of 0.1 g are larger than the shear modulus values ​​under the input acceleration of 0.3g). In the case of the damping ratio, the results show that, in all cases, damping ratio increases with shear strain. At low strain levels, the damping ratio values at various frequencies and waveforms are low and yet very close. At higher strain levels, the increase in frequency increases the damping ratio. This increase is more significant at higher frequencies. Also, the effect of waveform on the damping ratio is more apparent at larger shear strains, and at such shear strain levels, soil samples under rectangular loading exhibit the largest damping ratio. The damping ratio associated with the sinusoidal and triangular loading are also close to each other and it is a slightly larger for sinusoidal loading. On the other hand, the damping ratio increases with input acceleration. In addition, the effect of increased input acceleration on the increase in the damping ratio is more obvious at higher frequencies mainly due to the increase in shear strain.

In the present study, the effects of loading frequency and waveform on the dynamic properties of dry sand were investigated using shaking table tests. The following conclusions were drawn: The shear modulus increases with frequency. The trend is more obvious at larger frequencies. The effect of loading frequency on the damping ratio of the soil at low levels of strain is negligible, and at relatively large strain levels, damping ratio increases with loading frequency.  Soil samples exhibit the highest shear modulus and damping ratio under rectangular loading. Therefore, in all the tested frequencies and input accelerations, the values of G and D for the rectangular waveforms are greater than those of the sinusoidal and triangular waveforms. The shear modulus and damping ratio for the sinusoidal waveforms are marginally greater than those of triangular waveforms, yet one can consider them practically similar.
In all cases, the shear strain increased by increasing the amplitude of the input acceleration, and as a result, the shear modulus decreased and the damping ratio increased../files/site1/files/142/2.pdf

Dispersive soils are problematic and they cause a great many of local damages and destructions in hydraulic structures such as dikes and irrigation channels. The correct identification and recognition of divergence are fundamental measures taken in line with preventing the early destruction of the hydraulic structures. The soil improvement using lime, especially in clayey soils (CL), brings about an increase in the optimum moisture percentage, reduction of the maximum dry unit weight, reduction of swelling potential, increase in the strength and elasticity module. The effect of lime on soil can be classified into two groups, namely short and long-term stabilization. Raise of the soil’s workability is counted amongst the short-term modification measures and it is the most important factor in the early improvement stages. The increase in the strength and stability can be considered as the lime utilization on long-term results occurring during curing and afterwards. Also, according to the reports, swelling and damages occur in the lime-stabilized soil containing sulfate. The effective role of the iron furnace slag has been well recognized in increasing the strength against sulfates and corrosive environment conditions of the mortar containing lime and sulfates.

Adding the slag products of the melting furnaces and lime is a method used to stabilize dispersive soils. The present study makes use of a mixture of clay featuring low plasticity with 1% and 2% lime and slag, for 0.5%, 1%, 3% and 5% of the weight, to improve dispersivity, shear strength and plasticity. The samples were kept in constant temperature and humidity for a day and then were subjected to direct shear, uniaxial strength and pinhole tests.

It was observed based on pinhole experiment of the initial dispersive soil sample, denoted as D1, that the sample, shown by ND2, containing lime, for 2% of the weight, and slag, for 5% of the weight, turned out to have become non-divergent. The results of the direct shear test showed that the adhesion coefficient of the slag-free samples stabilized using 1% lime has been increased from 0.238 kg/cm2 to, respectively, 0.251 kg/cm2, 0.373 kg/cm2, 0.41 kg/cm2 and 0.48 kg/cm2  per every 0.5%, 1%, 3% and 5% slag added. The adhesion of the samples stabilized using 2% lime as determined in the direct shear experiment were 0.615 kg/cm2, 0.671 kg/cm2, 0.724kg/cm2 and 0.757kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. Also, the internal friction angle of the samples stabilized using 1% lime was found an increase from 14.3° for slag-free samples to 18.11°, 21.3°, 21.86° and 21.92° per every 0.5%, 1%, 3% and 5% added slag. As for the samples stabilized using 2% lime, the internal friction angles were found in direct shear test equal to 23.15°, 23.53°, 23.76° and 24.12° per every 0.5%, 1%, 3% and 5% slag added. The uniaxial strength of the slag-free samples stabilized using 1% lime was found an increase  from 1.0014 kg/cm2 to, respectively, 1.0616 kg/cm2, 1.0782 kg/cm2, 1.2127 kg/cm2 and 1.2246 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. The uniaxial strength rates has been determined in the direct shear test of the samples stabilized using 2% lime were 1.1367 kg/cm2, 1.1885 kg/cm2, 1.2322 kg/cm2 and 1.2872 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added. The amount of axial strain of the slag free samples stabilized using 1% lime was found decreased from 9.6842% to, respectively, 9.3333%, 9.2683%, 9.6364% and 8.4444% per every 0.5%, 1%, 3% and 5% slag added. Moreover, the axial strain amounts obtained for the samples stabilized using 2% lime were 7.7333 kg/cm2, 7.6316 kg/cm2, 7.1517 kg/cm2 and 4.7619 kg/cm2 per every 0.5%, 1%, 3% and 5% slag added.The study results indicate that slag and lime have the capacity of improving the studied soil’s dispersivity. Furthermore, it was figured out that adding slag to the soil causes an increase in the soil strength and improves the shear strength parameters. It can be stated according to the observed results that the use of slag, a byproduct of iron smelting industry, as a substitute for a given percentage of lime is effective on the reduction of the clay soil’s divergence potential. The results of the experiments carried out to determine Atterberg limits are suggestive of the idea that the increase in the slag and lime fractions brings about a decrease in the liquid limit and plasticity and improves the plasticity properties of the soil. The reason why the soil plasticity has been reduced after being mixed with lime and slag is the cationic exchange and coarsening of the soil texture. Addition of lime to the soil causes an increase in the plasticity limit and a reduction in the liquid limit. Therefore, the plasticity index is decreased and the plasticity characteristics of the soil are improved. Adding 1% lime to the dispersive soil leads to small reduction of the liquid limit from 32.43% to 31.73%, a small increase in the plasticity limit from 13.42% to 14.66% and a insignificant decrease in the plasticity index from 19.01% to 17.07%.

Solid waste is one of the unavoidable products of every society that necessitates the establishment of municipal solid waste management system. Because of variability in quantity and composition of municipal solid wastes, several management scenarios are considered. Assessing the environmental impacts of the life cycle of these scenarios will have a significant role in reducing and resolving urban service management problems. The aim of this study was to compare different scenarios of municipal solid waste management in Sirjan city using life cycle assessment (LCA) approach. LCA methodology is used to evaluate the environmental performance of the waste management of Sirjan for different scenarios, according to the ISO standards 14040 series 2006.

After identifying the quantitative and qualitative characteristics of the produced wastes within the scope of the study, the quadratic steps of the LCA method are followed in relation to each of the scenarios. The stages of life cycle assessment in the present research are as follows: 1. Determining goals and scope: Our goal is to compare environmental impacts of scenarios that include different methods of disposal. The boundaries of the study start from the collection of municipal solid wastes from the transfer station and ends with the final disposal of waste (Figure 1)
Figure 1. System boundary
Four scenarios have been investigated and evaluated in the environmental field (Table 1).
Table 1. Disposal solid waste scenarios
Scenario
Compost (%)
Recycle (%)
Incineration (%)
Landfill (%)
1
2
3
4
0
68.4
17.1
0
0
19.2
15
19.2
0
0
55.9
69.8
100
12.4
12
11

2. Collecting data and life cycle inventory (LCI): Various tools have been developed for LCI, one of which is the IWM-2 model. The IWM-2 model is one of the lifecycle assessment models that can be used to define different scenarios and then to compare the environmental impacts of each scenario. At this stage, the data from physical analysis, the amount of waste produced, the stages of separation at source, collection, transportation and final disposal, were collected and analyzed and the amount of contamination caused by each of the scenarios and energy consumption were determined.
3. Life cycle impacts assessment (LCIA): Assessing the impacts of the life cycle is a step of life cycle assessment, aimed at understanding and assessing the magnitude and significance of the potential environmental impacts of a product or service. At this step, the various information and data obtained at the LCI stage are reduced to less indicators and impact categories in order to facilitate the interpretation of this information and provide clearer outcomes to decision makers and managers. In this step, input data are allocated to the five impact categories of energy consumption, greenhouse gases, acid gases, photochemical gases and toxic emissions.
4. Interpretation of results: At this stage, the results of the LCI and LCIA will be evaluated so that the stages or points which have the greatest and least harmful impacts on the environment in the production and consumption of the product have been determined. Finally, conclusions and solutions are explained.

Results of the model were allocated to five categories consisting of energy consumption, greenhouse gases, acid gases, photochemical gases and toxic emissions. In every category, the ecological index as a quantitative measure to compare scenarios was calculated.

In this study, the life cycle assessment approach was used as a decision tool for choosing the appropriate waste disposal scenario in Sirjan city. The second scenario (68.4% compost, 19.2% recycling, 12.4% landfill) was selected as the preferred option for municipal waste disposal in Sirjan city. Also the results of this study show that in an integrated municipal waste management system, increasing the rate of separation and recycling will significantly reduce the release of environmental pollutants../files/site1/files/142/5.pdf

Landslide is known as one of major natural hazards. Landslide susceptibility mapping is known as efficient approach to mitigate the future hazard and reduce the impact of landslide hazards. The main objective of this research is to apply GIS spatial decision making systems for landslide hazard mapping in the 5th segment of Ardebil-Mianeh railroad. Evaluation of the landslide criteria mapping and their relevancy for landslide hazard can be also considered. To achieve the research objectives, an integrated approach of Fuzzy-Analytic Hierarchy Process (AHP), Fooler Hierarchical Triangle and Fuzzy logic methods were employed in GIS Environment.

Within this research, we also aimed to apply GIS spatial decision making systems and in particular GIS multi criteria decision analysis which are available in Arc GIS and Idrisi softwares. We have identified 8 casual factors (including: density of vegetation, land use, faults desistance, distance from rivers, distance from roads, slope, aspect, geology) based on literature review. Accordingly, these layers were prepared in GIS dataset by means of applying all GIS ready, editing and topology steps. The criterion weighting was established based F-AHP approach. The criteria weights was derived and rank of each criterion was obtained. Accordingly, the landslide susceptible zones were identified using GIS-MCDA approaches.

Finally the functionality of each method was validated against known landslide locations. This step was applied to identify most efficient method for landslide mapping. According to the results and based on the values derived from Qs, P, and AUC, the accuracy of fuzzy method was accordingly about 0.33, 0.74 and 0.76, respectively. In context of Fuzz-AHP the accuracy of 1.08, 0.88 and 0.94 were obtained. While, the accuracy of Fooler Hierarchical Triangle were obtained 0.78, 0.84 and 0.91, accordingly.

As results indicated integration of Fuzzy-AHP represented more accurate results. Results of this research are great of important for future research in context of methodological issues for GIScience by means of identifying most efficient methods and techniques for variety of applications such landslide mapping, suitability assessment, site selection and in all for any GIS-MCDA application.

The use of various additives to improve the properties of soils from past years have been studied by different researchers. Such additives are lime, cement, fly ash and fiber which have been used frequently in combination with soil. Lime is one of the oldest additives that it is utilized with different types of soils. Lime has positive impact on geotechnical properties of soil that alter some of the soil characteristics. Adding lime causes to reduce plasticity ranges, enhanced efficiency, strength and shrinkage of the soil. Extensive researches in the field of sustainability of clay with lime indicate that the optimum percentage of lime in the soil modification is between 1 to 3% by weight of the soil. But some researchers believe 8% by weight of lime are effective for soil stabilization. The presence of lime in clay soil yiels to occur some reaction, that it improves the soil properties. Reactions are included cation exchange flocculation, carbonation and pozzolanic reactions. Cation exchange between the clay cations and calcium cations takes place in lime. Cation exchange causes clay particles to get closer to each other creating complex structures in the clay soil and this improves the   clay soil features. In recent years the use of nanoparticles is considered in civil engineering field. The investigations have demonstrated that the use of nanomaterial increases cement reactivity and also improves density because it is filled with particles. Recent research has shown that the use of montmorillonite nano-clay soils to control swelling and to reduce failure potential in the soil. A number of researchers have expressed the use of nanoparticles causes to decrease the hydraulic conductivity of soils. In this paper, the effect of nano-clay and lime on the important soil parameters is evaluated. For this purpose, lime at 2 and 4 percentage and nano-clay at 0.5, 1 and 2 percentages have been added to clay soil and their impact on parameters such as optimized moisture, Atterberg limits, unconfined compressive strength and self-healing properties of soil is evaluated. Self-healing properties is one of the features, to repair damages due to internal erosion in the clay which is very efficient and important.
Materials and experimental

In the present research, the effect of lime and montmorillonite nano–clay to soil strength is evaluated. For this purpose, samples of clay soil (CL) has been used. In the experimental study, the percentages of additives mixed with the dry soil and then the optimum moisture and maximum specific weight of soil are determined with different percentages of additives. Soil Atterberg limits based on the ASTM D4318 standard have been determined.   Dry samples have been mixed together and then the water is added and mixed well with each other. Then the sample has been prepared in the form of a steel cylinder (cylindrical specimens) with a diameter of 50 mm and a height of 100 mm. Specimens were molded immediately and the weight and dimensions were carefully measured and then placed in plastic to prevent moisture loss and put them at 20 °c and 90%  moisture curing room.

In this study, the percentage of lime is between 0, 2, 4 percent by weight and nanomaterials percentage is between 0.5 and 1 and 2 percent that can be varied in order to analyze the effect of various additives on the properties of the soil samples. The results indicate that increasing the nano-clay and lime percentage can enhance the optimum specific gravity of soil. The optimum moisture content of sample without any additive is equal to 19.5%. However, samples contain 2% nano-clay and 4% lime, the optimum moisture content increases to 23.5%. But the presence of lime reduces the maximum dry density of soil while adding nano-clay increases this amount. In samples with 4% lime and with no nano-clay, maximum dry density is 17  but in case of lime with 4% and nano-clay with 2% it is increased to 17.5 . In addition, adding lime without the presence of nano-clay only increases strength of soil. When 2 percent of lime is added, the strength of soil increases about 39 percent. As mentioned before, the effect of lime and nano-clay on increasing of unconfined compressive strength is almost the same which means by adding 2% of lime or nano-clay the strength of the soil increases about 40 percent. Using both lime and clay nanoparticles simultaneously (each 2%), a significant increase in strength of soil occurs in approximately 77 percent.

The use of nano-clay and lime improves soil strength parameters. But economically lime is more affordable than nano-clay. Therefore, if you need to increase only unconfined compressive strength, then the nano-clay is not recommended.
When it comes to self-healing in clay, the nano-clay can improve resistance rupture of the soil. By adding 2% of nano-clay in soil, healing of soil resistance after the break and after 24 hours can reach up to 60% of the ultimate strength of the soil. This property can be used to repair of locations that are subjected to internal erosion and scouring.