assessing sedimentary basin effect on compressibility of city of …. appl. environ. biol... ·...

J. Appl. Environ. Biol. Sci., 3(10)132-141, 2013

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*Corresponding Author: Mohammad Reza Aminizadeh Bazanjani, Department of Geology and Geology Engineering, Ferdowsi University of Mashhad (FUM), Iran. E-mail: [email protected]

Assessing Sedimentary Basin Effect on Compressibility of City of Kerman Sediments Using Stress Sensitivity and Standard Penetration Test

Mohammad Reza Aminizadeh Bazanjani1, Gholamreza Lashkaripour1, Mohammad Ghafoori1,

Naser Hafezi Moghadas1, Mohammad Bahrami2

1Department of Geology and Geology Engineering, Ferdowsi University of Mashhad (FUM), Iran 2 Soil Mechanics and Technical Laboratory of Kerman Province

Received: July 16 2013 Accepted: September 3 2013

ABSTRACT

Stress sensitivity is an index that shows effect of geological history and sedimentary basin on the formation of fabric and structure in fine soils. In this research, the necessary studies for determining stress sensitivity in deposits of city of Kerman deposits were done by comparing behavior of natural and reconstituted soils. Thus, initially, undisturbed soil samples were mixed with high moisture content between 1.25 and 1.5 times of their liquid limit and, using the results of reconstituted soil consolidation tests, intrinsic compression line of city of Kerman sediments (Kerman city-ICL) was extracted. Then, some of co-sensitivity intrinsic compression lines were drawn on Iv-Log(σ`v) space. For evaluating soil sensitivity, the proposed method which was more applicable in this subject was used [29, 34] In this model, comparison of natural sedimentation compression curves with the intrinsic compression line of Kerman sediments (Kerman city-ICL) was done; then, the required model parameters were extracted and stress sensitivity index was calculated for every sample. Comparison of the results showed that range of stress sensitivity in Kerman deposits was less than unit; therefore, it can be concluded that soil structure and fabric did not superabundantly develop and probably effect of sedimentary model caused compression and over-consolidation phenomena to be more predominant than fabric and structure. KEYWORDS: Stress sensitivity, sedimentary model, natural sedimentation compression line, intrinsic compression

line, fabric, over-consolidation, city of Kerman.

INTRODUCTION Sensitivity index (St) is ratio of strength of undisturbed structured soil over that of the same soil in a

corresponding reconstituted state at the same void ratio [31, 33]. The term `soil structure' is used here to mean arrangement and bonding of soil constituents. In recent years, there have been numerous studies in which a theoretical framework has been formulated for describing behavior of structured soils [8, 20, 15, 10]. The authors have investigated virgin compression behavior of structured soils [21]. Sedimentary basin model and geological conditions have an important role in the formation of soil structure and fabric. Overall, sedimentary basin is a part of the earth's surface that has physical, chemical and biological specific properties and is distinct from adjacent areas. Therefore, sediments are deposits in every environment have nearly common physical and mechanical property and vary with their surrounding areas. Environmental conditions have a major influence on the formation of sedimentary basins [3]. The important influence of soil structure on the mechanical properties of soil has long been recognized [9]. Formation of soil structure is an extremely complicated process that depends on geological and stress histories of soils. These are features which cannot be usually traced accurately for most natural soils. There is a significant body of experimental data which suggests that soil structure as well as stress history has great influence on mechanical behavior of natural soils [28, 30, 8, 20]. In situ soils usually possess a natural structure, which enables them to behave differently from the same material in a reconstituted state [8, 20, 12]. Some researchers have performed important developments in formulating constitutive models by incorporating influence of sedimentary basin on soil structure, [15, 36, 35, 27, 19]. Soil structure has impacts on geotechnical parameters of soil and increases its shear strength [4]. Based on the impact soil property on vulnerability of structure against moisture, it can be concluded that stability of soil structure is an indicator for representing quality of soils [6]. Chemical admixture materials such as cement and lime affect engineering properties (such as uniaxial compression strength) of organic soils of tropical zone [7]. It must be mentioned that cement and lime increase engineering properties of soil but reduce the liquid limit. The importance of history of sedimentation and digenesis was investigated in estimating and interpreting geotechnical property in Vienna sedimentary basin in Austria [24]. Effect of soil

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structure on compressibility and resistance of Pluka glacial tills was examined by comparing natural and reconstituted clay soils [5]. Analyzing effect of silt deposition on deformation behavior of semi-saturated and unsaturated soils showed that types of deposition had an important role on mechanical behavior of materials [2]. Soil sensitivity is an indicator that could be determined by development of fabric and structure. Sedimentary basin model

Physiographic shape of Kerman plain's sedimentary basin was obtained due to tectonic movements of Quaternary period. Kerman plain is located in depression between Kuhbanan-Mahan mountain ranges in the east and Badamo-Davaran in the west and has a Graben structure formed by circumferential reverse faults (Figure1). Kerman city is a part of Kerman plain and, in the present research, all of the assessment and analysis were done in Kerman city soils. Kerman deposits are constituted of fine grained alluvial materials that are mainly silt and clay (CL-ML). Kerman plain, during Pleistocene and four major glacial periods as a closed basin, received all the flood sediments that were issued from high areas. Sedimentation rate can be controlled by many known factors such as watershed basin physiography, sediment supply and sediment texture [1]. Transportation and deposition of flood materials has been done proportional to flood energy in depression and low land areas and has formed Kerman plain. In upper Pleistocene, due to tectonic movements, conditions of closed basin has been varied and Kerman sedimentary basin gently sloped to the north and north-west direction [17].

Figure 1 Kerman sedimentary basin reproduced from 1:500000 geological maps.

Soil erosion is one of major threats for conservation of soil and water resources in semi-arid and arid regions

of Iran [13]. Factors such as slope, slope direction, lithology and distance from waterway have an important impact on occurrence of soil erosion [25].

MATERIAL AND METHODS

In this research, first, results of consolidation tests that were performed previously on Kerman soils were

collected. In addition, for complete coverage of information, a number of undisturbed samples were prepared from

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different depths and locations and the virgin consolidation tests were performed on them. Then, some of the previous samples were reconstituted and one-consolidation tests were performed on them. Finally, intrinsic compression line of Kerman sediments was extracted. To obtain stress sensitivity in Kerman city, deposits were confined using the stress sensitivity model which was proposed for this subject [29, 10, 34]. Based on the above model, natural sedimentation compression curves (SCCs) were compared with intrinsic compression line (ICL) of Kerman sediments. Eventually, the required model parameters were extracted and stress sensitivity was calculated for different parts of Kerman city.

Intrinsic compression line of Kerman sediments

To plot intrinsic compression line for Kerman city's fine grained soils (Kerman city's soils-ICL), 25 disturbed samples (Table 1) were prepared from 11 proper sites in Kerman city (Figure 2). Then, the samples were mixed with high values of water content, usually between 1.0 and 1.5 times of liquid limit of the material (preferably 1.25 times), without air or oven drying prior to the reconstitution.

The prepared slurry was poured in a one-dimensional consolidation laboratory model and was consolidated by vertical static loads applied to the samples. Values of void ratios were calculated for different levels of stress and consolidation curves of all the samples were drawn together in a void ratio – vertical stress space or e-log (σ´v) space. Then, two important quantities were obtained and used when dealing with intrinsic compression curve. They were e*100 and e*1000, in which mean intrinsic void ratios corresponded to values of effective stress σ′v = 100 kPa and σ′v = 1,000 kPa, respectively. Intrinsic compression index Cc* was defined as e*100 - e*1000.

Due to differences of void ratio, liquid limit and mineralogy of sediments in various depths, intrinsic compression curves for reconstituted clay soils plotted in e-logσ´v space were different from each other and covered a wide range (Figure 3).

Figure 2 characteristic of sites that soil samples are reconstituted in Kerman city.

Therefore, in order to achieve a single intrinsic consolidation line as a basis for comparing natural and reconstituted soils, the proposed normalizing parameter called void index ( Iv) was used [8] and defined as: IV = ( e – e* 100 ) / ( e* 100 – e* 1000 ) The normalized results were plotted in the Iv-Log (σ'ν) space and the best fitted line called intrinsic compression line (ICL) was obtained for city of Kerman's fine grained sediment (Figure 4) with the following equation. Iv = 1.998-0.43Ln (σ'ν) Equation of intrinsic compression line of Kerman deposits ha suitable overlap with ICL proposed in [8] and they had slight differences in primary parts in the range of low stresses (Figure 5).

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Table 1. Characteristic of sites that soil samples are reconstituted.

Figure 3. Intrinsic compression curves of Kerman fine grained sediments in e-Log(σ`v) space.

Borhole No Site Location Depth (m) Longitude Latitude

1

Kerman Potck company

8 502715 3350784

2

Kerman Potck company

18 502715 3350784

1

Sound and Aspect 4 508517 3347346

2


3


4


1


1

Forensic Medicine

12 502330 3352324

2

Forensic Medicine

18 502330 3352324

3 Forensic Medicine

20 502330 3352324

4 Forensic Medicine

26 502330 3352324

1

Abouzar Bridge

5 505595 3347973

2

Abouzar Bridge

10 505595 3347973

1

Koohpayeh four way

13 508179 3353925

2

Baghodrat four way 18 507789 3346876

1

Abaas Sabahy Avenue 7 506818 3351388

3

Abaas Sabahy Avenue 14 506818 3351388

1

Kousar four way 8 501962 3351323

2

Kousar four way 24 501962 3351323

4

Kousar four way 30 501962 3351323

1

Council Park 10 507183 3351530

2

Council Park 30 507183 3351530

3

Council Park 40 507183 3351530

1 Firozeh Avenue 5 504601 3350111 1 Jahad Avenue 15 505007 3352222

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Figure 4. Extraction of intrinsic compression curves of Kerman city sediments in e-Log (σ`v) space.

Figure 5. Comparison of Burland [8] intrinsic compression line to Kerman city sediments-ICL Evaluating stress sensitivity in Kerman sediments

To assess soil structure in city of Kerman city, initially, undisturbed soil samples were mixed with high moisture content between 1.25 and 1.5 times of their liquid limit; therefore, the one-consolidation tests were performed on reconstituted soils and, using the proposed normalizing parameter [8] or void index, intrinsic compression line of Kerman sediments (Kerman city-ICL) were extracted and plotted in Iv-Log(σ'v) space.

According to the investigations, natural consolidated curves are approximately parallel by intrinsic compression line with sensitivity degree of unit (St = 1) [10]. Accordingly, different co-sensitivity intrinsic consolidation lines were drawn on Iv-Log(σ'v) space (Figure. 6). These lines were used as a reference to assess degree of soil sensitivity when comparing sedimentation compression curves to intrinsic compression line for every site. The samples selected for the analysis had appropriate dispersion in city of Kerman and the obtained results could be generalized to the entire of area of city of Kerman.

Sensitivity model [29, 34, 10] was used as a framework (Figure 7) for expressing behavior of fine soils in city of Kerman arena. Based on stress sensitivity model, natural sedimentation comparison curves were compared with intrinsic compression line of Kerman city sediments and the required indicators such as stress sensitivity (Sσ), yield stress ratio (YSR) and in situ stress ratio (isSR) were extracted. Finally, the soils's sensitivity degree was calculated for subzone of Kerman city sediments.

Some examples of calculation that was carried out are shown in Figures 8 to 11 and the overall computation is given in Table 2. The model parameter was defined as follows:

Stress sensitivity (Sσ) on Iv-Logσ'v space is the distance between natural yield stress and vertical stress on intrinsic compression line (ICL) at the same void ratio that is shown in the following equation [9]. Sσ =σ'vy / σ'e* In stress sensitivity model, the in-situ stress ratio ((IsSR) and yield stress ratio ((YSR) are geometrically defined according to the following equations [11]. YSR = σ'vy / σ'v0 and isSR = σ'v0 / σ'e* According to the results obtained in this model, the following relationship was established between these parameters. Sσ= YSR. IsSR

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Figure 6 Co-sensitivity graphs of Kerman city deposits.

The results of stress sensitivity analysis showed that, in soils of Kerman city, natural consolidation curves were

mainly located on the left of intrinsic compression line. On the basis of the proposed model, stress sensitivity of most samples in Kerman city soils was less than unit (Figure 12). Therefore, it can be concluded that soils of Kerman city subzone mostly lacked a specific structure and fabric. So, soil strength was due to compaction and consolidation of sediments. High distance between some samples and intrinsic compression line confirmed that the Kerman city soils were mainly over-consolidated owing to the influence of sedimentary basin on soil consolidation.

Figure 7 zoning of stress sensitivity based on intrinsic compression line [34]

Figure 8 stress sensitivity analysis in Alghadir Stadiume site, depth 8 m

σ´v0=40Kpa σ´vy=50Kpa σé* =6.25Kpa Sσ= σ´vy/ σé*=50/6.25=8 YSR= σ´vy/ σ´v0=50/40=1.25 isSR= σ´v0/ σé*=40/6.25= 6.4

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Figure 9 Calculation of stress sensitivity index in Valfajr Avenue site, depth 14 m

σ´v0=75Kpa σ´vy=100Kpa σé* =100Kpa Sσ= σ´vy/ σé*=100/100=1 YSR= σ´vy/ σ´v0=100/75=1.33 isSR= σ´v0/ σé*=75/100= 0.75

Figure 10 Calculation of stress sensitivity in Aspect and sound administration, site depth 8 m

σ´v0=180Kpa σ´vy=200Kpa σé* =550Kpa Sσ= σ´vy/ σé*=200/550=0.36 , YSR= σ´vy/ σ´v0=200/180=1.11 , isSR= σ´v0/ σé*=180/550= 0.32

Figure 11 stress sensitivity analysis in Forinsic Medicine site, depth 20 m

σ´v0=175Kpa σ´vy=200Kpa σé* =3000000Kpa Sσ= σ´vy/ σé*=200/3000000=0.00006 YSR= σ´vy/ σ´v0=200/175=1.14 isSR= σ´v0/ σé*=175/3000000= 0.000058

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Figure 12 Position of natural consolidation curves related to intrinsic compression line (ICL) of Kerman city soils

Assessing standard penetration test (SPT) To confirm the results of stress sensitivity analysis, standard penetration data were used in subzone of Kerman city. Standard penetration test (SPT) is one of the common methods for evaluating mechanical and engineering properties of soils in the field. Standard penetration data which were collected from different points of Kerman city were about 961. In Table 3, the comparisons between stiffness and standard penetration number of clay soils are shown [18]. According to this criterion, standard penetration numbers of soils of this range were divided into three classes which were relatively homogenous (Figure 13) and about 85 percent of soils were placed in the category of "very stiff to hard" (Table 3).

Table 2 stress sensitivity analysis of Kerman city sediments

No Site Location Depth (m) Longitude Latitude σ´vy σ´*e Stress sensitivity degree(S σ) 1 Abas sabhi street 16 506818 3351388 50 3000000 0.000016 2 Abozar bridge 12 505520 3347958 50 700000 0.000071 3 Kuhpayeh four way 14 508017 3353909 60 500000 0.00012 4 Cuncil park 30 507183 3351530 100 6000 0.016666667 5 Sound and vision 16 508517 3347346 200 550 0.36 6 Shriaty street 12 506952 3350284 150 1000 0.15 7 Esteghlal avenue 12 505425 3349972 80 80 1 8 22 Bahman Boulvard 16 508600 3349074 100 20000 0.005 9 Valfajr avenue 14 503739 3350845 100 100 1

10 Forensic medicine 16 502330 3352324 100 200000 0.0005 11 Kusar four way 20 501433 3351621 300 100000 0.003 12 Coal company 18 502212 3349053 100 30000 0.003333333 13 Pars Hotel 17 502371 3349640 120 10000 0.012 14 Shfa avenue 14 503013 3350536 70 3000 0.023333333 15 Besat town 8 497850 3348070 70 30 2.333333333 16 Kerman airport 8 496150 3347724 100 200 0.5 17 Shukoh town 8 497612 3348313 100 3000 0.033333333 18 Elaheyah1 8 499845 3348580 200 10000 0.02 19 Elaheyah2 8 499499 3348613 300 80000 0.00375 20 Beheshty hospital 8 501365 3349467 150 100000 0.0015 21 Seven Garden 8 514097 3341606 25 1 25 22 Alghadir Stadium 8 498724 3348855 50 6.25 8 23 Shafa four way 12 503302 3350221 50 5 10 24 Esteghlal avenue 8 505450 3350125 100 180 0.555555556 25 Bazargani four way 8 504692 3347713 50 100 0.5 26 Asiabad avenue 8 506375 3349452 100 420 0.238095238 27 Baghodrat four way 18 506632 3347872 100 2150 0.046511628 28 Sound and Aspect 20 508517 3347346 100 6812 0.014679977 29 Forinsic medicine 20 502330 3352324 200 3000000 0.000058

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Therefore, it can be concluded that soils of this arena were compact and over-consolidated due to effect of sedimentary basin model. Kind of soil classes in terms of stiffness and percent of every class are given in Table 4.

Table 3 Comparison of standard penetration tests and stiffness in fine soils [18].

Figure 13 Distribution of stiffness classes in Kerman city sediments range.

Table 4 Stiffness classifications of Kerman city soils based on standard penetration tests. Conclusion

Results of stress sensitivity analysis showed that natural sedimentation consolidation curves for most samples in the arena of Kerman city were mainly located on the left of intrinsic compression line. Based on the proposed model, stress sensitivity was less than unit, which confirmed over-consolidation of fine sediments in city of Kerman. Due to over-consolidation phenomenon of fine grained soils of city of Kerman and lack of structure development in these sediments, it was expected from most of the tested samples to have stress sensitive of less than unit. But, for some soil samples, yield point in Iv-Log (σ'v) space was located at the interface between ICL and SCL lines; therefore, stress sensitivity was larger than unit. Generally, fine grained soils of city of Kerman city have poor structural sensitivity according to depositional environment and geologic history. Results of SPT analysis indicated that soil of city of Kerman was relatively uniform and about 85 percent of it was in "very stiff to hard" class. These results confirmed that soils of this range are generally compact and consolidated and the soil structure has great development. Probably, the reason of soil over-consolidation is influence of sedimentary basin model in Kerman area. During the Pleistocene periods, Kerman sedimentary basin as a shallow closed basin received all the sediments carried by flood processes originating from high mountains. During the Wurm glacial period, due to upper Pleistocene movements, Kerman sedimentary basin lost the closed basin condition, gently sloped to the north and north-west direction and deposited sediments gradually shifting along the downstream. So, it can be concluded that the present deposits of Kerman plain have been consolidated by upper layers that today shift in downstream of the plain. Therefore, results of stress sensitivity analysis confirmed role of sedimentary basin in the engineering properties and over-consolidation process of soils in sediments of this range. It can be concluded that sedimentary basin has a very important effect on engineering property of soils in the range of city of Kerman. Acknowledgment

The authors declare that they have no conflicts of interest in the research.

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