Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
The Study of Cementation Level Effect on the Strength Characteristics and Shear Wave Velocity of Coarse-Grained Alluvium in Eastern Areas of Tehran, Iran
581
608
FA
Maziar
Hosseini
Y
Majid
Taromi
majid.taromi@yahoo.com
N
Mahdi
Saeidi
majid.taromi@yahoo.com
N
Vahid
Soleimani
majid.taromi@yahoo.com
N
Mehdi
Soltani Negar
N
10.52547/jeg.14.4.581
Introduction
Series A of coarse-grained alluvial deposits of Tehran are extended in eastern and north-eastern areas of Tehran. Analyzing and studying of these alluvial deposits from a geological point of view as well as their creation time and general characteristics such as the deposits’ mineral types, their source, and formation conditions, gives a better point of view to geotechnical engineers about exploring their characteristics as well as geotechnical aspects in underground structure design, excavations, and foundation design processes. On the other hand, in order to analyze stability, estimating the factor of safety and the seismic design of these structures, considering their location, which is in Tehran with a high seismic hazard area, the necessity of knowing the exact mechanical and dynamic properties of Tehran's alluvium is felt more than ever.
Material and methods
Due to the grain size of Tehran’s coarse-grained alluviums (series A) as well as high level of cementation of them, it is impossible (or maybe so difficult) to make undisturbed samples in order to do experiments. Such that it is excavated 23 boreholes with 30 to 140 meters depth as well as 17 test wells with 20 meters depth in an area which was extended in 10 kilometers in long which were located in Tehran’s No. 13 and No. 14 districts (as it can be seen in Figure 1). During the excavation of the entrance ramp and tunnel of eastern highway of Tehran, in-situ tests have been done in different sequences. Since it was important to investigate real behavior of these alluviums, different in-situ tests such as plate load test, in-situ shear test, pressuremeter test, and downhole test have been done as well as many laboratory and field tests. Furthermore, (1) X-Ray Diffraction (XRD) and (2) X-ray Fluorescence (XRF) as well as (3) Scanning Electron Microscopy (SEM) methods, have been used to explore the type of minerals and those used in cementation.
(ب)
Figure 1. a) Geological plan and the location of boreholes and test wells in the alignment of East Tehran Freeway
Results and discussion
Based on the results of XRD tests, it is quite clear that the largest weight percentages of tested samples are lime and silica.
Calcium and magnesium levels-as the high-power cations in flocculation process-in soil sample No. 1 (soil with high cementation level) are much more than soil sample No. 2 (soil with moderate cementation level).
This is the cause of high cementation level of soil sample No. 1 comparing with soils sample No. 2. A rapid increase in stress level can be seen in in-situ shear test results, in low shear displacements, up to reaching a maximum of τp (peak point) and afterwards reduction in shear stress with softening behavior.
Cohesion and shear strength levels also increase by increasing the depth. According to the plate load tests results, an increase in soil modules changes can be seen in different depths by depth increasing.
Large tendencies to increase in volume and dilation can be seen in under shear load cemented soils, after applying a primary compression on them. A brittle behavior with the occurrence of a certain peak can be seen in cemented samples. The significant increase in strength is directly related to the severe dilation rate, which can be seen in cemented samples results. The shear strength would be decreased, if this cement is broken during the particles’ displacements.
The results of downhole tests are shown in Figure 2. According to this figure, it has been explored that Vs,30 is about 600 m/s in moderate cemented soils while it is about 850 m/s in highly cemented soils. Because of the homogeneity and uniformity of sedimentary deposits, shear wave velocity is increasing due to the higher density of the layers and high level of cementation in both of the soil types. However, this increase is not significant at depths above 25 meters.
Conclusion
Based on the results, cementation level of the eastern coarse-grain-alluvium of Tehran is moderate to high and minerals used in cementation of this type of soil are generally carbonated and especially calcite.
Investigating the level of cementation of soil as well as the results of chemical analysis and in-situ tests, it can be found that the strength and deformation parameters of the soil are directly related to the degree of its cementation.
Based on the obtained results, the deformation modulus increases by about 25%, the cohesion by about 55% and the shear wave velocity by about 30% with increasing the degree of cementation (Table 1).
Increases of these parameters are directly related to depth. However, the cementation level does not significantly affect the internal friction angle of the soil.
Table 1. Average results of in-situ shear tests
Deformation Modulus (MPa)
Peak Friction Angle (deg.)
Cohesion
(kPa)
USCS
Depth
(m)
Sample
50-60
39
30-35
GW-GM
5
Moderately Cemented Soil
(M.C. Soil)
75-85
41
50-60
SP-SC
10
85-90
41
50-60
GW-GC
15
95-105
41
50-60
GW-GC
20
60-70
39
35-40
GW-GM
5
Highly Cemented Soil (H.C. Soil)
75-85
39
50-60
GW-GC
10
110-120
42
65-75
GW-GC
15
125-140
41
110-120
GC
20
Tehran eastern alluviums, In-situ tests, Chemical analysis, Cementation, Shear wave velocity.
http://jeg.khu.ac.ir/article-1-2909-en.html
http://jeg.khu.ac.ir/article-1-2909-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
The Assessment of Zeolite and Sepiolite Effect on Elastic Modulus and Hydraulic Conductivity of Clayey Soils with the Emphasize on Microstructure
609
634
FA
Ali M.
Rajabi
amrajabi@ymail.com; amrajabi@ut.ac.ir
Y
Shima
Bakhshi Ardakani
shima.bakhshi@ymail.com
N
10.52547/jeg.14.4.609
Introduction
Improving the geotechnical characteristics of soils including superficial or deep soils has always been a challenge to geotechnical engineers. Therefore, various physical and chemical methods are used to improve different types of soils. In general, any physical, chemical, biological or combination of methods are used to change the characteristics of natural soil mass in order to achieve engineering goals which is defined in the "soil stabilization." Among different types of additives for soil stabilization, the use of pozzolans has been investigated by researchers because of their chemical compatibility with the environment and the cementation products due to chemical reactions. Todays, a lot of researches has been done on the use of natural or artificial zeolites as pozzolanic materials for the production of cement mixtures. This material, as a pozzolan, increases the speed of the pozzolanic reactions and reduces the density of cement products. However, many studies have been done to investigate the effect of zeolite and sepiolite on the resistance of cement products such as concrete, but so far, the use of these additives has been less considered for soil improvement. On the other hand, because of the compatibility of zeolite and sepiolite with the environment and their unique physiochemical properties, it is necessary to pay attention to these additives in order to improve the soil. Therefore, in this research, the effect of zeolite and sepillot additives with different percentages at different treatment times have been investigated to determine the elasticity modulus and hydraulic conductivity with focus on soil microstructure behavior.
Materials and methods
1. The properties of the soils
In this research, two types of soil including clayey sand (with 20% clay) and sandy clay (with 51% of clay) were used. The studied soils were a mixture of clay and sand of Firoozkouh (a typical type of sand located in north of Iran). Some physiochemical properties of zeolite and sepiolite are presented in Table 1.
Table 1. Physiochemical properties of zeolite and sepiolite used in this study
L.O.I.
Na2O
K2O
MgO
CaO
Fe2O3
Al2O3
SiO2
Chemical component
25.11
0.02
0.01
15.73
0.01
o.61
0.3
55.3
Sepiolite (%)S
11.94
0.13
-
0.87
2.45
1.26
13.54
69.74
Zeolite (%)
2. Experiments
The uniaxial compressive strength tests were performed at 0.1 mm/min according to ASTM D2166 standard. The stabilized soil samples were compacted at percentages of 0, 5, 10, 15, 20 and 25 in cylindrical molds (38mm × 76mm) in five layers to achieve the desired density. In order to investigate the effect of curing time, the samples were placed inside sealed containers and underwent the test at instantaneous, 7, 14, and 28 days and at the desired additive percentages. To investigate the effect of additives on the soil hydraulic conductivity, clayey sand soil with additives 5, 10, 15, 20, and 25% was prepared using dry mixing method. Then, the prepared mixture was poured from a specific height into the permeability mold with a height of 8.65 cm and diameter of 5 cm. In this way, the specific dry unit weight of all samples was obtained as 1.47 g/cm3, close to the minimum specific dry unit weight. In this research, concerning the considerable effect of fine-grained soils on hydraulic conductivity, falling head test was used to determine the permeability coefficient.
In order to the morphology of the clayey sand soil without additives and stabilized with additives 15% was examined through SEM test.
Discussion and results
1. Modulus of elasticity
In this study, after uniaxial tests in different percentages and ages, the stress-strain graphs were plotted and then the elasticity modulus was calculated. The results showed that, with increasing zeolite content, the modulus of elasticity has been increased and, with increasing curing time, except for a slight decrease, after 7 days, the modulus of elasticity increased. During the initial treatment (7 days), the hardness of the sandy clay soil decreased and then increased with increasing time. In general, hardness in both soils in the high percentages of zeolite is significantly is increased.
Also, the effect of sepiolite on the modulus of elasticity has been studied. The results indicate that with the increase in the percentage of additive and lengthening the curing time, the modulus of elasticity is increased. This increase in the stabilization of both sandy clay and clayey sand soil is almost the same. In addition, in the case of sepiolite modification, the elasticity of sandy clay and clayey sand is approximately equal to 5 times in comparison to the initial value of unstabilized soil. However, in zeolite, the modulus of elasticity in clayey sand soils is almost 2 times, and sandy clay is nearly 5 times higher.
2. Permeability
To investigate the effect of additives on the soil hydraulic conductivity, clayey sand soil with additives 5, 10, 15, 20, and 25% was prepared using dry mixing method. The samples were saturated in a short period and permeability test was carried out immediately. Permeability coefficient changes were mostly influenced by physical factors. Therefore, due to the fineness of both types of additives, the hydraulic conductivity decreases with increasing additive content. The amount of reduced hydraulic conductivity in sepiolite stabilization is greater than zeolite due to the structure of the sepiolite (fiber-shaped) compared to zeolite.
3. SEM imaging
In this study, attempts were made to examine the reasons behind the obtained results more carefully through SEM imaging.
c b a
Figure 1. SEM image of non-stabilized clayey sand soil (a) soil stabilized with zeolite 15% (b) soil stabilized with sepiolite 15% (c) during the curing time of 28 days at magnifications 10000X
Figure 1a displays the SEM image of non-stabilized clayey sand soil. As can be seen in the figure, the soil structure is clear as layered and clay scales can be seen as laminated. Figure 1b demonstrates the SEM images of clayey sand soil stabilized with zeolite 15% during the curing time of 28 days. The sample has lost its layered structure in response to stabilization with zeolite during the curing time and changed into an integrated structure. This can be due to incidence of chemical reactions such as ion exchange and pozzolanic reactions in response to adding zeolite. Figure 1c demonstrates the SEM images of clayey sand soil stabilized with sepiolite 15% during the curing time of 28 days. As shown in the figure, the sepiolite has a fibrous-shaped structure that is longitudinally twisted. Also, with curing time increase, complex structures have emerged that could be due to the occurrence of chemical reactions.
Conclusion
This study examined the effect of zeolite and sepiolite additives on strength parameter of clayey soils. Accordingly, uniaxial compressive strength test was performed on clayey sand and sandy clay soil at percentages of 0, 5, 10, 15, 20 and 25% of zeolite and sepiolite with instantaneous curing times of 7, 14 and 28 days. Further, permeability test was conducted at different percentages on stabilized clayey sand soil. Also, to investigate the effect of these materials on soil microstructure, SEM imaging was performed at 28 days. The results show that both additives increase the elastic modulus of clayey sand and sandy clay soils. Also, the results indicate a steady increase in the stiffness of the cured soil with sepiolite during processing time. However, reducing soil hardness can be seen in stabilizing with zeolite at lower rates and lower percentages. In permeability test, hydraulic conductivity decreases with increasing additive content. The rate of permeability reduction in sepiolite is higher than zeolite. SEM images show that chemical reactions create an integrated structure that ultimately increases uniaxial compressive strength and modulus of elasticity. Also, SEM imaging depicts physical changes along chemical reaction in soil stabilized with sepiolite. Ultimately, increasing soil strength resulting from additive alongside environmentally friendliness is recommended in superficial and deep improvement of soil../files/site1/files/144/Rajabi.pdf
Elastic Modulus, SEM, Zeolite, Sepiolite, Hydraulic Conductivity, Soil Improvement
http://jeg.khu.ac.ir/article-1-2757-en.html
http://jeg.khu.ac.ir/article-1-2757-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
Analysis and routing of basic parameters of foreshocks and aftershocks in Zohan earthquake, 2012 in south khorasan
635
668
FA
Ali
Saket
alisaketgeo@yahoo.com
N
Seyed Mahmud
Fatemi Aghda
fatemi@khu.ac.ir
Y
Ahmad
Fahimifar
N
Hossein
Sadeghi
N
10.52547/jeg.14.4.635
Introduction
Analysis of time, location and magnitude of foreshocks and aftershocks has been one of the most important cases for experts in various scientific fields such as: seismology, structural engineering and crisis management, and other interrelated fields. Since this analysis and the result of studies on seismotectonic and cases of earthquakes help us identify the foreshocks and aftershocks with the goal of decreasing losses and nervious stress of the injured community in quake-stricken areas and skilled crisis management. The cause fault of earthquake plays the important role in foreshocks and aftershocks of the earthquake. So, study on fault behaviour is a suitable method for analyzing and routing the basic parameters of foreshocks and aftershocks. Also, foreshocks and aftershock are important parts of any earthquake in a seismic area. The analysis of the basic parameters of the foreshocks is one of the most practical researches for reducing the risk of earthquakes. The identification of behavioral pattern of foreshocks can help researchers detect the active fault conditions for the occurrence of earthquakes in different areas. The present study is concerned with the study of behavioral patterns earthquakes, foreshocks, and aftershock of Zohan earthquake. Experience of large aftershocks in different parts of the world indicates that, following earthquakes and depending on seismic-tectonic conditions, large aftershocks are likely to occur in the earthquake-effected zone, which will aggravate the damage caused by earthquakes (Omi et al., 2013). The main factor contributing to the worsening of damage caused by aftershocks is the performance of structures that are weakened but not destroyed by main earthquakes and are, thus, highly likely to be destroyed by large aftershocks (Saket and Fatemi Aghda, 2006).
Material and methods
The present paper makes use of data collected in a real earthquake and similar expriences in other earthquakes for presenting a practical pattern for predicting primary earthquake patterns, determining the location, magnitude, and time of aftershocks. The target of this case is decreasing the effects of earthquake. To this end, we used the results from studies on basic parameters of foreshocks and aftershocks of Zohan earthquake, and 2012 earthquake in South Khorasan province. The rationale for selecting the aforementioned studies is: location of event, the Zohan earthquake, had been identificated as an area with high risk for the occurrence of earthquakes, although there has been no wide-scale earthquake in this area in the last two decades. These conditions are important causes for more concentrated studies on this area because there is a high chance for wide-scale earthquakes striking this area.
Result and Discussion
In this part of research, we conduct a study on the location, magnitude and depth of foeshocks. Some of the world-wide research suggested that these data can help to predict the time of mainshocks. Studies conducted on the variations of frequency in foreshocks can follow this goal.
In this paper, the available statistical data such as periodical variations of seismicity in the weeks leading up to the main shock can be used as a tool for estimating the approximate time of a future important earthquake. The weekly variations of seismicity before Zohan earthquake indicate a relative increase and then decrease within a 100 km radius around the epicenter of the main shock.
Table 1: Variations of frequency of foreshock based magnitude before Zohan earthquake
Week before main shock
Frequency of foreshock in the Radius of 100Km from main shock
Frequency of foreshock(with M>2.5) in the Radius of 100Km from main shock
6
0
0
5
1
1
4
1
0
3
2
0
2
5
3
1
2
0
Studies on numerous earthquakes in Iran and other regions in the world show that the distribution of aftershocks can be related to fault type or the direction of principal stress (Saket and Fatemi Aghda, 2006) and (King et al., 1994). Whereas maximum Coulomb stress change is related to maximum principal stress in earthquakes, the concentration of aftershocks can coincide with the direction of maximum principal stress (σ1) of the causative fault in mainshock. Considering the direction of maximum principal stress and its adaptation to the scattering of aftershocks, the above hypothesis is confirmed.
Also studies on frequency changes and seismic quiescence of small aftershocks help us in predicting future aftershocks. The results the of presented research by Itawa (2008) on the World earthquake catalogue suggest that seismic quiescence theory is true for different regions of the world. Based on the results of the study mentioned above, this case can be used as a tool for predicting large aftershocks in Zohan earthquake.
Fig 1. Adaptation of direction of maximum principal stress with scatering of the aftershocks of Zohan earthquake. a: direction of maximum principal stress (σ1) of the causative fault in mainshock. b- scaterring of the aftershocks
Table 2: Seismic sequience versus magnitude of aftershocks
Row
Seismic Quiescence for aftershocks
Aftershock Magnitude
Data and Time of aftershocks
1
13
3.0
2012/12/05
17:21:03
2
36
3.4
2012/12/05
17:57:03
3
161
3.1
2012/12/05
20:38:09
4
3906
3.9
2012/12/08
13:44:19
In addation, frequency of aftershocks and certain time distance (seismic quiescence) between their can use precursors for detecting the time of large aftershocks. The relevant analysis in this study showed that methods such as: time series beside seismic quiescence can help in conducting a more accurate time forecast of large aftershocks.
Conclusion
The results of this research suggest that we can identify some of the charactristics of the main shock by focusing on location, magnitude and depth of foeshocks.
In Zohan earthquake, the direction of maximum principal stress is adpated to the scattering of aftershocks, and this case suggests that there is a specific relationship between them.
The relevant analysis in this study showed that the methods such as: time series beside seismic quiescence can help conduct a more accurate time forecast of large aftershocks../files/site1/files/144/saket.pdf
Zohan earthquake, Routing aftershock, Foreshock, Seismic quiescence, Causative fault, Maximum main stress, Risk management
http://jeg.khu.ac.ir/article-1-2691-en.html
http://jeg.khu.ac.ir/article-1-2691-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
Evaluation of Excavation Stabilization by the Top-down Approach in the Control of Excavation Wall Deformation based on Numerical and Field Studies
669
702
FA
Vahid
Shirgholami
vsh1371@yahoo.com
N
Mahdi
Khodaparat
khodaparast@qom.ac.ir
Y
Abolghasem
Moezi
ghasemmoezi@yahoo.com
N
10.52547/jeg.14.4.669
Introduction
Excavation in urban areas occasionally is accompanied by the improper performance of the support system for even small deformations. In this regard, deformation control design based on force-based approaches provides a more realistic reprehensive of excavation performance. Top-down deep excavation techniques are among the modern excavation stabilization methods in urban areas. In this method, unlike the conventional methods, it is possible to perform the excavation and construction operations simultaneously. The present study aims to investigate excavation stabilization using the main structure through the top-down approach. For this purpose, field and numerical evaluations of the stabilized project were conducted based on the top-down approach in the downtown of Qom city, Iran. This research reports the information obtained through monitoring and modeling using the finite element ABAQUS software, predicting the occurred deformations until the end of excavation operations using the calibrated model, and offering an initial estimation of the required stiffness for the support system with respect to the lateral deformations in four sites proposed, according to the studies of Line A Qom Subway.
Project specifications
Based on the geological studies of Line A Qom Subway Tunnel, the geological layers are classified into four soil classes. Qc-1 consists of gravely sand with fine content of 5 to 20%; Qc-2 is silty and clayey sand with fine content of 35 to 60%; Qf-1 is clayey silt with fine content of 60%; and Qf-2 is a silty clay layer with fine content above 60%. Line A of Qom subway passes the study area of the present study, which is located in Ammar e Yaser Street (Station A6). Based on the geotechnical studies of the project site, the site in the levels near the ground consists of Qc-2 but in the lower elevations, it is composed of Qc-1 and Qf-2.
Salam Trade Complex, located in the downtown of Qom city, has 6 underground stories and 6 above-ground stories. It is limited to the main street in the south and to urban decay in the three other directions. The final excavation depth, length, and width is -21, 36, and 32-52 m, respectively. The project structure consists of a steel moment frame with a retaining wall in the negative elevations and metal deck frame for ceiling construction. In this project, excavation wall deformation was monitored in three important sections (A, B, and C). Due to the vicinity to urban decay, a total station TS02 was used for monitoring these sections. According to the field surveys, the maximum horizontal deformation of the walls in sections A, B, and C is 24.10, 42.16, and 47.21 mm, respectively, which were measured in the 0, -1.5, and 0 m elevations.
Monitoring process and numerical simulation
To calibrate the prepared model, a sensitivity analysis was performed on geotechnical parameters including modulus of elasticity (E), internal friction angle (φ), and cohesion (C) of the layers by simulating 60 numerical models. Based on the sensitivity analysis results, an increase in internal friction angle and elasticity modulus for layer 1 (i.e., φ1 and E1) and elasticity modulus of layer 3 (E3) results in a decrease in lateral deformation. Finally, using the sensitivity analysis results and after several trials and errors, the numerical models for sections B and C were calibrated when reaching the depths of -8 and -11 m, respectively. Using these models, then, it is possible to predict deformations up to the end of the project.
To determine the required stiffness for the excavation support system, regarding the acceptable deformation of the adjacent soil mass, 160 numerical models were built and their results were analyzed. Based on the results of Brason and Zapata (2012), relative stiffens (R) were used to develop a relationship between the maximum lateral deformation of the wall and the required stiffness of the support system. R is a dimensionless parameter that represents the stiffness of a solid support system; the greater this value is, the more flexible the system would be. In this study, caisson pile length, excavation width, and buried depth of the wall were used for determining the R.
R = (1)
Figure 2 presents the maximum occurred deformation in terms of depth versus the relative stiffness for sites QC and QF.
Figure 2. Maximum deformation in terms of depth versus the relative stiffness for sites QC and QF
Conclusion
According to the monitory data, the maximum lateral deformation in sections B and C until the end of the project was 42.16 and 47.2 mm, respectively. Moreover, the deformation of the other points inside the excavation was 30 mm.
Considering the occurrence of maximum lateral deformations in the higher elevations in the monitored sections, it is inferred that excavation support at the ground level plays a key role in this approach. Hence, the lack of completing the structural frames and slabs for facilitating the excavation operation can lead to an increase in deformation levels.
Based on the prepared graphs, the top-down approach in sites QC-2 and QF-2, compared to sites QF-1 and QC-1, provides a more desirable performance for deformation control.
Top-down excavation, Deformation assessment, Total Station TS02, FEM, Line A Qom Subway Tunnel
http://jeg.khu.ac.ir/article-1-2886-en.html
http://jeg.khu.ac.ir/article-1-2886-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
Laboratory Studies of Nanoparticles Hybrid Effects on the Improvement of the Soil around the Razavi Holy Shrine
703
728
FA
Soheil
Ghareh
ghareh_soheil@pnu.ac.ir
Y
Kimiya
Yazdani
kimiya_yazdany@yahoo.com
N
Fatemeh
Akhlaghi
faakhlaqi@gmail.com
N
10.52547/jeg.14.4.703
Introduction
The existence of problematic soils due to their geotechnical properties, such as low strength and stability, high compressibility, and swelling, is one of the most important issues and challenges that geotechnical and civil engineers are faced in urban environments, especially in metropolises. Various methods are used to stabilize and to improve the behavior of problematical soils such as compaction, consolidation, stone columns, jet grouting, biological procedures, and additive materials including nanomaterials. Because of their high specific surface, the use of nanoparticles is very effective to increase the shear and mechanical strength parameters of soil. Mashhad city is located on alluvial deposits of Mashhad Plain. A wide area of this city, especially the central and eastern areas where the Imam Reza holy shrine is located, has been built on weak and fine-grained deposits. Considering constructing high-rise buildings such as hotels and commercial complexes in these areas, as well as the need for restructuring the urban decay, the soil improvement will be inevitable. Given the significant application of these nanoparticles, the purpose of this study is to investigate the effects of nanoclay and nanosilica on each other and to find their optimal composition as a suitable alternative for traditional materials to improve the weak and problematic soils. This not only increases the bearing capacity and strength properties but also reduces the cost and time of project implementation.
Method and Materials
To achieve a hybrid with maximum strength and bearing capacity in executable projects, laboratory tests were performed on the soil picked up from the vicinity around Razavi holy shrine in Mashhad mixed with nanoclay and nanosilica. The type of soil is classified as CL-ML based on sieve and hydrometer tests. The nanoclay used in this research is the type of montmorillonite- K10, and the nanosilica is as a powdered shape with 99% purity.
At first, nanoclay and nanosilica were mixed independently with soil in six different weight ratios (0%, 0.1%, 0.5%, 1%, 2.5%, & 5%) and (0%, 0.1%, 0.25%, 0.5%, 0.75%, & 1%). Soil mechanical and strength properties, including compressive and shear strength, settlement, plasticity index, and swelling, were studied by standard laboratory tests on all specimens. After determining the optimum ratio of each nanoparticle, four hybrids consisting of nanosilica and nanoclay were made in four different combinations and then the effects of these four hybrids were investigated on the soil in the laboratory scale (Table 1).
Table 1. Composition of hybrids made with different percentages of nanomaterials
Nanomaterials composition
Hybrid Name
5% Nanoclay + 0.25% Nanosilica
5NC + 0.25NS
5% Nanoclay 1% Nanosilica
5NC + 1NS
2.5% Nanoclay + 0.25% Nanosilica
2.5NC + 0.25NS
2.5% Nanoclay + 1% Nanosilica
2.5NC + 1NS
Conclusion
The results of the Atterberg limit test on improved and pure soil indicate that the addition of nanoclay and nanosilica and the optimized ratios of these nanoparticles hybrid to increase the soil resistance parameters did not change the soil swelling index.
Evaluation of shear strength test results showed a significant synergistic effect of these nanoparticles on increasing the shear strength parameters. The nanoparticles hybrid of 2.5% nanosilica and 1% nanosilica increased the cohesion up to 106% and also hybrids of 5% nanosilica and 1% nanosilica increased the internal friction angle of soil up to 32%.
Examination of unconfined compressive strength tests presented a 134% increase in the compressive strength of the specimen improved with 2.5% nanoclay and a 620% increase in soil improved with 1% nanosilica. The optimum hybrid compositions of 5% nanoclay and 1% nanosilica increased significantly the compressive strength of the studied soil up to 785% and reduced the settlement of the soil by 60% compared to pure soil.
Laboratory studies of electron microscopy examination on pure and improved soil samples with nanoparticle hybrid revealed the presence of these particles in pores of the improved soil. On the other hand, the high specific surface area of the nanoparticles increased the interaction of the soil particles, and the effect of adding these nanoparticles on the refining process is observed in compressive strength increase.
As the nanoclay, nanosilica, and hybrid of nanoparticles are the results of soil processing, these particles are very effective to solve the environmental problems because of good compatibility with soil environments. In addition, low volumes of nanoclay, nanosilica, and hybrid in these nanoparticles are necessary to increase the compressive strength and decrease the settlement of soil. Therefore, using these nanoparticles at the project site reduces significantly the cost and execution time of the project.
Soil improvement, Hybrid, Nanoclay, Nanosilica, Bearing Capacity.
http://jeg.khu.ac.ir/article-1-2896-en.html
http://jeg.khu.ac.ir/article-1-2896-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
Evaluation of Hole Inclination Effect on the Response of Holed Sandstone Rocks against Compressive Static and Tensile Dynamic Loads
729
748
FA
Ali Akbar
Moomeni
ali_moomeni@yahoo.com
Y
Ming
Tao
mingtao@csu.edu.cn
N
Alireza
Taleb Beydokhti
beydokhti@sci.ikiu.ac.ir
N
10.52547/jeg.14.4.729
Introduction
Shallow tunnels have a vital role in urban planning, railway and highway transportation lines. The presence of underground cavities can leads to stress concentration and consequently, instability of the spaces against static and especially dynamic loads. Therefore, the aim of this study was to evaluate the effect of elliptical cavity and its inclination on sandstone rock behavior under compressive static and tensile dynamic loads. In order to evaluate the effect of the cavity under static stress conditions, two groups of intact and hole-bearing sandstone cores with 0, 30, 60, and 90 degrees of hole inclination were prepared and tested under uniaxial compressive loading test. During the test, in addition to the stress recording, damage and deformability of the samples were recorded by using the strain gauge, acoustic emission sensor and camera. Split Hopkinson pressure bar (SHPB) test apparatus was used for doing dynamic loading test. Furthermore, the damage process was recorded using a high-speed camera with 10 micro-seconds interval of frame capability. The obtained results showed that presence of the cavity reduced the rock strength in maximum state (θ=0) up to 55% and in minimum state (θ=90) up to 77% of its initial uniaxial compressive strength. Dynamic tensile loading tests illustrate that the elliptical hole near the free end of sample (reflection boundary of compressive wave to tensile wave) is stable due to locating in superposition area, while the other cavity out of the area with each inclination was undergone to spalling failure. Assessment of failure surface using scanning electron microscope and thin section study indicates that the dominant fracture is grain-boundary type and iron oxide cement has a vital role in developing of this type of fracture.
Sandstone, Elliptical hole, Stress concentration, Dynamic loading, Spalling failure.
http://jeg.khu.ac.ir/article-1-2907-en.html
http://jeg.khu.ac.ir/article-1-2907-en.pdf
Kharazmi university
Journal of Engineering Geology
2228-6837
2981-1600
14
4
2021
1
1
The Influence of Engineering Geological Properties of Carbonate Aggregates on Artificial Stone Properties
749
776
FA
Tayebeh
Mirjalili
Tarbiat Modares University,Thran,Iran
mirjalilitayebeh@gmail.com
N
Mashala
Khamechian
Tarbiat Modares University,Thran,Iran
khamechm@modares.ac.ir
Y
Mohammadreza
Nikudel
Tarbiat Modares University,Thran,Iran
nikudelm@modares.ac.ir
N
10.52547/jeg.14.4.749
Abstract
This study aimed at evaluating the effect of calcic aggregates of engineering geological properties on the artificial stones properties, non-resin cemented and then, to make a comparison between the engineering properties of artificial and natural stones. To investigate the effect of calcic aggregates properties on artificial stones, seven samples of building stones including black limestone, three samples of marble (Chinese stone, marble and crystalline marble) and two samples of travertine and onix were used. Engineering geological properties of the samples were then determined. In the next stage, after designing mould for constructing artificial stones, aggregates with the same grading and mixture design were provided. Then two samples including coarse and fine grained artificial stones were made for all of the mentioned aggregates under the same vibration, pressure and vacuum conditions. Next physical, strength and durability tests were conducted, and the obtained results were compared. The results of engineering parameters showed that Hojjat Abad travertine artificial stones have similar engineering quality to own natural stone and Crystaline Marble and Turan Posht travertine artificial rocks have about 11 to 32% increase in quality but Chinese stone, Black limestone, onix and marble have a 6 to 33% lower quality than own natural stone. However, the samples made of other stones in view of the compared parameters related to artificial stones have lower quality than natural stones; however, they are placed in the acceptable range as building materials.
Introduction
Given the variation of construction materials, the importance of the economy in its supply and large use of natural stone mines and the production of seemingly unusable slags, it is necessary to reuse these slags. One of these reusing methods is to make artificial stones and its application as construction materials. Rock powder, aggregate, a small amount of cement or resin and other chemicals are used for producing artificial stone. In this study, carbonate minerals, rock powder and white cement in the first phase are mixed and wet. Then, in the next stage, to form the sample in a cubic mold, they have been compacted under three physical processes of vibration, vacuum and pressure. The aim of this study is to investigate how to make artificial stone, to evaluate the engineering properties of artificial rock and the effect of limestone engineering properties on artificial stone properties of non -resin cement and then comparing the properties of artificial rocks made with natural stones
Material and methods
In this study, in order to investigate the effect of calcic aggregates properties on artificial stone properties, seven samples of building carbonate rocks including crystalline marble, two samples of marble, black limestone, and two samples of travertine and onix were used.
Engineering geological properties of the used samples were then determined. In the next stage, after designing mold for constructing artificial stones, aggregates with the same grading and mixture design were provided. Then two samples including coarse and fine grained artificial stones were made for all of the mentioned aggregates under the same vibration, pressure and vacuum conditions. After construction, physical, strength and durability tests were conducted, and then the results were compared.
Results and discussion
Investigation of the effect of engineering geological properties of carbonate aggregate on artificial stone properties showed that the artificial stones made of travertine aggregates have higher quality than natural travertine in terms of physical, strength and durability properties. Due to the existence of pores on the surface of travertine aggregates, the used cement can result in reducing effective porosity and increasing strength and durability in the artificial stones.
In Table 1 a proposed research has been used for rating rock engineering parameters based on the degree of importance for building stones. Then, according to this table, the score of each natural stone and related artificial stones were determined. For building stones, the importance of durability and strength is more than the density. Also, the density shows its effect on durability. At the same time, with increasing the percentage of water absorption, the durability of rock has decreased. Therefore, the rocks with less water absorption are more important.
Table 1. Scoring of building stones based on the engineering parameters
Parameters
Description
Excellent
Good
Marginal
Poor
Total score
100
75
50
25
Water absorption (%)
Range
0-2
2-3
3-5
>5
Score
25
20
15
10
Unit weight (kN/m3)
Range
>24
22-24
18-22
<18
Score
15
10
5
3
Uniaxial compressive strength (MPa)
Range
>50
40-50
30-40
<30
Score
20
15
10
4
Tensile strength (MPa)
Range
>20
15-20
10-15
<10
Score
20
15
10
4
Durability (%)
Range
<1%
1%-2%
2%-3%
>3%
Score
20
15
10
4
The total score of fine-grained artificial stones (65%) is almost similar, indicating that the type of carbonate grains does not affect the characteristics of fine-grained artificial stones, but the total score of coarse artificial grains are in the range of 58 to 74%. This range of score indicates that structural weakness, especially the cleavage surface, porosity, lamination, vein and acetylolite of aggregates have more influence on engineering properties in coarse-grained artificial rock.
Conclusion
Comparison between the engineering properties of artificial and natural stones were studied. The following conclusions were drawn:
- The artificial stones of Hojjatabad travertine have similar engineering quality with their natural stone.
- Both Crystaline marble and Turan Posht travertine artificial rocks have about 11 to 32% increase in quality but Chinese stone, black limestone, onix and marble have 6 to 33% decrease in quality compared to natural stone but in acceptable ranges when they are considered as construction materials.
- The samples made of other rock samples have lower quality than natural stones; however, they are placed in the acceptable range as building materials../files/site1/files/144/Mirjalili.pdf
Building stone, Artificial stone, Aggregate, Calcic, Engineering Geological properties
http://jeg.khu.ac.ir/article-1-2862-en.html
http://jeg.khu.ac.ir/article-1-2862-en.pdf