Arab J Geosci DOI 10.1007/s12517-014-1345-7

ORIGINAL PAPER

A typical weathering profile of granitic rock in Johor, Malaysia based on joint characterization S. V. Alavi Nezhad Khalil Abad & Edy Tonnizam Mohamad & Ibrahim Komoo & R. Kalatehjari

Received: 11 May 2013 / Accepted: 19 February 2014 # Saudi Society for Geosciences 2014

Abstract One of the most important challenges in the study of slope stability, foundation, and excavation in rocks is understanding the weathering states. This issue is more important in tropical climates, where severe weathering produces thick weathering profiles. Thick weathering profiles are normally classified or graded differently based on some field observations, geological studies, and material properties of rock. This paper considers the relationship between joint characterization and the state of weathering of granitic rock as an important factor to describe the mass weathering. A total of 24 panels of rock exposures was studied in two active granite quarries located in Johor, Malaysia. This region has a tropical climate condition. A typical profile was proposed for granitic rock, mainly based on joint characterization, topography, and geological condition. This profile includes a common weathering ranging from fresh rock to residual soil. Based on the presence of corestones, two additional subgrades were introduced in completely and highly weathered zones. It is believed that the proposed weathering profile may contribute to engineering design and classification of weathered granitic rock in tropical region. Keywords Granite . Weathering profile . Discontinuity . Corestone . Tropical region . Joint spacing . Joint trace length

S. V. Alavi Nezhad Khalil Abad (*) : E. T. Mohamad : R. Kalatehjari Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM), Skudai 81310, Johor, Malaysia e-mail: [email protected] I. Komoo Universiti Malaysia Terengganu, Terengganu, Malaysia

Introduction Defining a typical weathering profile of different rocks is of interest to all geoscientists and geotechnical engineers. This profile is most useful for preliminary engineering designs and planning in civil engineering and mining projects involved with slope stability, excavation, blasting, and foundation (Verma and Singh 2009; Salari-Rad et al. 2012; Jahed Armaghani et al. 2013; Kalatehjari et al. 2013). Weathering profile in rocks is derived from the geological classification for engineering applications (Moye 1955; Ruxton and Berry 1957). In tropical regions, weathering is more intense and occurs to greater depths than elsewhere (Komoo 1995). Weathering profile in tropical regions have a specific feature such as the presence of rock blocks (corestones) that are difficult to be predicted. In addition, sudden changes may take place between different mass weathering grades. Despite the mentioned complexities, the study of weathering profiles is still in the early stages in these regions. Therefore, it is important to define a typical weathering profile in different types of rock in tropical climate conditions to better understand the behavior of weathered rock. A number of studies have been conducted to give a complete description of rock weathering based on the type of rocks and the associated engineering problem (Moye 1955; Ruxton and Berry 1957; Dearman 1976; Matula 1981; Murphy 1985). Generally, the classification systems of engineering geology have been qualitative, and they have been typically related to granitic rocks (Arel and Önalp 2004). In addition to these qualitative approaches, other schemes have been used such as rock mass and rock mass weathering classification, which were based primarily on some simple tests carried out using available field data as well as some statistical procedures (Wei and Liu 1990).

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Two of the initial approaches for classification of weathered rocks have been derived from the Ruxton and Berry (1957) geological classification that had been done in the case of Hong Kong granite and the Moye (1955) engineeringpurposed classification in based on the Snowy Mountains Scheme in Australia. It should be noted that essential elements of physical disintegration have been also observed in both regions; however, chemical weathering and decompositions were dominant in both of them. Ruxton and Berry (1957) studied the sequence of weathering of granite caused by both physical disintegration and chemical decomposition to present a weathering profile. Little (1969) modified the classification proposed by Moye (1955). He graded the rock soil ratios numbered from one to six for fresh rock and for the residual weathered soil, respectively. The Moye’s classification was also modified by Newbery (1970) to be applied to the granite of Cameron Highlands, Malaysia. The approach proposed by Ruxton and Berry (1957) was adopted by Fookes and Horswill (1970); they employed both mass and material features as diagnostic characteristics of distinctive mass weathering grades. Fookes et al. (1971) published this classification in which an indication of the engineering properties of each grade was added based on Little (1969). Later on, it was recommended for mapping purposes (Anon 1972). Lee and De Freitas (1989) reviewed the schemes that have been introduced for classification of granitic rocks, and they also discussed the common problematic areas of classification and description of weathering grades and their distribution in the rock masses. Dearman (1974, 1976) played an important role in classification of weathering grades by demonstrating that for complicated conditions, weathering zones could be mapped into rock mass based on weathering grades. In the beginning, for granitic rocks, morphology of the weathering profiles was studied based on the division of the remarkably different zones into rock mass. For this purpose, regardless of the rock matrix changes, three parameters were specified: rock discoloration degree, soil/rock ratio, and the presence of the original texture. However, the philosophy of study altered and the rock matrix became more focused, partially for two issues: First, the field behavior was not completely expressed by the model; second, there was some confusion over how the model could be used. Several technical associations, institutions, and authors have proposed their schemes for weathering classification by taking into consideration the rock matrix as proposed by ISRM (2007), Matula (1981), and Anon (1995). Weathering classification schemes are mostly proposed based on some important factors such as the condition and appearance of the rock material (e.g., its friability), the weathered materials’ engineering properties, the condition of individual minerals (e.g., the extent of micro-cracking), the staining degree on the joint surfaces and/or the how much the

staining is extended from joints into the rock, and alterations to the mineral composition (e.g., the appearance of new minerals and disappearance of existing ones). However, joint characterization such as spacing, trace length, orientation, and inclination (horizontal, inclined, and vertical joints) that significantly control the engineering properties of rock mass have not been considered (Sharifzadeh et al. 2011; Ghazvinian et al. 2012; Zadhesh et al. 2013). This paper addresses the relationship between joint characterization and the state of weathering in granitic rock in Johor, Malaysia. This area is located in a tropical region. The joint characterization including spacing, trace length, orientation, and inclination were considered in 24 panels of rock exposure located in two active quarries, Masai and Putri Wangsa. The results of the study were used to propose a typical weathering profile for granitic rock in the studied region. This weathering profile may contribute to the establishment of rock mass classifications and engineering designs in regions with the same climate and geological condition.

Site investigation Site investigation including observation and joint survey such as joint orientation, joint spacing, and trace length were measured in two areas of weathered granitic rock located in southeastern Asia. These areas were located in Johor Bahru, the southern province of Malaysia. The geological map of this area with the age of late Cretaceous to early Tertiary is presented in Fig. 1 (Rajah S. Senathi et al. 1982). The required field data for this study have been collected from the quarries of Putri Wangsa and Masai that are shown in the mentioned figure. In the studied areas, a total of 24 exposures were measured and investigated including 11 panels in Masai quarry and 13 panels in Putri Wangsa quarry. Figure 2 shows the overviews of panels in Masai and Putri Wangsa quarries. The rock exposure in panels ranged from 5 to 24 m in height and from 10 to 12 m in length. The rock exposure in each panel was divided into different zones based on the existed mass weathering grades. In both quarries, a complete range of mass weathering grades from fresh rock (F) to completely weathered rock (CW) was present. This type of classification is based on the most widely used scheme proposed by, International Society of Rock Mechanics (ISRM 2007). Joint study is usually carried out by two sampling schemes known as scanline and window survey (Song 2006). In both techniques, the mapping is only involved with exposed surfaces. Consequently, they cannot represent the structural features behind the mapped surfaces. Although window survey method produces more data over a larger area than scanline method, it requires more engineering decisions during data collection. Furthermore, scanline is simpler to use and

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Fig. 1 Geological map of the studied area (Rajah et al. 1982)

provides more detailed data compared with window method in the same location (Gumede and Stacey 2007; Şen 2013). The scanline sampling scheme was used to measure joint properties in this study. Joints to be measured were intersected with scanline in the outcrop, where a measuring tape was utilized as a scanline. Orientation of the joints including dip and dip direction, spacing, and trace length were surveyed for each mass weathering grade in each panel. The other

geological features including faults and corestone were identified by visual inspection of the outcrops.

Data analysis In order to classify panels based on different mass weathering grades, the classification of ISRM (2007) were used which is

Fig. 2 Overview and the boundaries of panels in: a Masai quarry; b Putri Wangsa quarry

Arab J Geosci Table 1 ISRM suggestion for classification and description of rock masses Term

Description

Class

Sound rock (SR) Slightly weathered rock (SW)

No visible sign of matrix weathering; some rock discoloration may be present along main discontinuities. Discoloration of rock indicates beginning of rock matrix weathering and along discontinuities surfaces. All rock matrices can be discolored by weathering and can be slightly softer externally than in sound condition. Moderately weathered rock (MW) Lower than half of rock matrix is decomposed or disintegrated to soil condition. Sound or discolored rock is present forming discontinue zones or as corestones. Highly weathered rock (HW) More than half of rock matrix is decomposed or disintegrated to soil condition. Sound or discolored rock is present forming discontinue zones or as corestones. Completely weathered rock (CW) All rock matrices are decomposed or disintegrated to soil condition. Original structure of rock mass is commonly preserved. Residual soil (RS) All rocks are transformed into soil. Geological structure of rock mass is destroyed. There is a great volume variation but no significant soil transport is present

presented in Table 1. The resultant mass weathering grades were sketched for all panels. The measured data were combined in order to analyze joint characterization in different mass weathering grades by using Dips 5.0 software package (Rocscience 2000). The datasets were compiled from the raw field data by simple statistics. In addition, the distribution of joint properties among different mass weathering grades were determined by frequency histograms. Percentage of different types of joints including horizontal (<30°), inclined (30–70°), and vertical (>70°) were calculated. Orientations of joints were input in Dips data sheets, and major joint sets were determined for each mass weathering grade. The results were plotted by rose diagrams.

I II

III IV V VI

Sketches of panels of both sites were prepared regarding identified weathering zones and observed geological features. Finally, the typical weathering profile for granite in a tropical region was proposed based on joint characterization, topography, rock appearance, and panel sketches.

Joint characterization in different mass weathering grades Based on site observation and classification of ISRM (2007), weathering profiles were sketched for selected panels in each site. Figure 3 shows the sketches of weathering profiles and rose diagrams of joints encountered in both Masai and Putri

Fig. 3 Sketch of mass weathering grades of different panels with their rose diagrams in: a Masai quarry; b Putri Wangsa quarry

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Wangsa quarries. The overview of Masai quarry was divided into two groups based on panel topography. Panels A to H were categorized as ‘side,’ and panels I to K were identified as ‘crest’. In Putri Wangsa quarry, three topography features as ‘crest,’ ‘side,’ and ‘valley’ were assigned respectively for panels A-B-C-K-L-M, D-E-I-J, and F-G-H. Geological features in Masai quarry were observed as corestones in panels B-C-D-E-G with section sizes from 0.5×0.5 to 5.5×3 m2, and normal faults in panels F-G-H. The same features were identified in Putri Wangsa quarry including corestones with section sizes from 1.5×1.5 to 6×10 m2 in panels A to D, and normal faults in panels A-I-K. It was observed that weathering state ranges from fresh to completely weathered zones at both sites studied. The

thickness of fresh, slightly weathered, moderately weathered, highly weathered, and completely weathered zones in Masai quarry is up to 21.5, 7, 8.5, 11, and 8 m, respectively. In Putri Wangsa quarry, the maximum thickness of different mass weathering grades from fresh to completely weathered zone is 11, 10, 3.5, 15, and 13 m, respectively. In Masai quarry, the thickness of fresh zone decreases from ‘crest’ to ‘site’ panels (up to 70%). In addition, slightly weathered rocks were observed with various thicknesses at ‘side’ panels (3 to 7 m). Moderately weathered rocks were present mostly at ‘side’ and rarely in ‘crest’ panels (up to 8.5 m). Highly weathered rocks were identified scattered in ‘side’ and ‘crest’ panels with different thicknesses (up to 11 m). The thickness of completely weathered zone decreases from ‘crest’

Fig. 4 Joint spacing distribution in different mass weathering grades including: a fresh; b completely weathered

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to ‘site’ panels (up to 60 %). Corestones were recognized in highly weathered rocks at ‘side’ panels with almost equal dimensions (about 1×1 m2). The upper parts of exposures were partially covered by residual soil and vegetation. In Putri Wangsa quarry, fresh rocks were only observed at ‘crest’ panels with different thicknesses (1 to 11 m). Slightly weathered rock was seen at ‘side,’ ‘valley,’ and infrequently at ‘crest’ panels with an almost constant thickness (about 8 m). Moderately weathered rock was observed as small zones at ‘crest’ panels (up to 3.5 m). Highly weathered rock existed

with various thicknesses at ‘crest’ to ‘valley’ panels (up to 15 m). The thickness of completely weathered rock decreased from ‘crest’ to ‘side’ (up to 60 %). In addition, corestones were mapped in highly weathered and completely weathered zones at ‘crest’ panels (up to 6×10 m2). It was also observed that the tops of the completely weathered and highly weathered rocks were covered partially with residual soil and vegetation. The scanline survey was applied to all panels to obtain joint characterization. Joint spacings were measured as the distance

Fig. 5 Trace length distribution in different mass weathering grades including: a fresh; b completely weathered

Arab J Geosci Fig. 6 a Mean spacing versus mass weathering grade. b Mean trace length versus mass weathering grade

between two joints which have intersected a measuring line. The minimum spacings measured were 10, 5, 5, 13, and 2 cm in fresh, slightly, moderately, highly, and completely weathered rocks, respectively. Joint trace lengths were measured for those joints which intersected with scanline. The minimum trace length captured for fresh to completely weathered rocks were respectively 23, 15, 14, 18, and 8 cm. In addition, a descending trend was observed in joint spacings from crest to valley. The distributions for joint spacing and joint trace length are presented for each mass weathering grade. Figure 4 shows two samples of the frequency of joint spacing versus mass weathering grade. Moreover, two samples of the frequency of joint trace length versus mass weathering grade are presented in Fig. 5. It can be seen that the frequency of joint spacing and joint trace length pursues the lognormal distribution as stated by several authors (Zadhesh et al. 2013; Sousa Luís 2007; Ehlen 2002; Hudson and Harrison 1997; and Priest 1993). Based on distributions of joint spacings in different mass weathering grades the maximum frequencies of spacing in fresh to completely weathered rocks occurred respectively in ranges of 1.95–2, 0.5–0.55, 0.25–0.3, 0.4–0.45, and 0.45– 0.5 m. The distributions of joint trace lengths in different mass weathering grades show that the maximum frequencies were

respectively in ranges of 3.5–4, 2.5–3, 1–1.5, 0.5–1, and up to 0.5 m in fresh to completely weathered zones. Figure 6 shows the mean spacings for the granite in different mass weathering grades where the summary of statistical work is presented in Table 2. Mean spacing decreases surprisingly from fresh to slightly weathered and continues faintly to moderately weathered rock, then increases through highly weathered to completely weathered. The maximum mean of spacing occurs in fresh rock, while the minimum mean of spacing is in moderately weathered rock. The mean trace length of granite in different mass weathering grades is presented in Fig. 7 based on statistical results of Table 3. The graph shows a slight decrement in mean trace length from fresh to slightly weathered rock and a sharp decline to moderately weathered, then continues to decrease to completely weathered rock. The overall trend of mean trace length is decreasing along with weathering progress from fresh to completely weathered rocks. Table 4 and Fig. 8 show respectively the percentage and trend of joint inclination in different mass weathering grades. The result of statistical analysis of joint inclination shows an increasing trend in the percentage of horizontal joints from fresh to completely weathered rocks. In contrast, a decreasing

Table 2 Statistical results of joint spacing in different mass weathering grades Mass weathering grade

F SW MW HW CW

Masai

Putri Wangsa

Combined

n

Mean (m)

Standard deviation

n

Mean (m)

Standard deviation

n

Mean (m)

Standard deviation

294 203 165 253 326

1.57 0.61 0.4 0.53 0.73

0.74 0.35 0.37 0.33 0.58

281 305 132 314 253

1.88 0.51 0.33 0.49 0.95

0.47 0.13 0.12 0.22 1.26

575 508 297 567 579

1.73 0.55 0.37 0.51 0.83

0.65 0.25 0.29 0.27 0.95

Arab J Geosci Fig. 7 Percentage of joint inclinations versus mass weathering grade

trend was found in the percentage of vertical joints for the same weathering progress. The percentage of inclined joint fluctuated in different mass weathering grades.

Typical weathering profiles Study of joint characterization, topography, rock appearance, and sketches of the panels makes it possible to propose a typical weathering profile for granitic rock in Johor, Malaysia (Table 5). The proposed profile includes a range of identified mass weathering grades based on ISRM (2007), their thickness, topography, color, and joint specifications. A full range of weathering states from fresh rock to residual soil exhibited in the profile was fully described. In the fresh rock zone, there is no visible sign of matrix weathering. However, some rock discoloration may be visible along discontinuities. The range of rock color in this zone is from light gray to light green. Based on the results of joint study, a maximum number of three joint sets were determined with dominant vertical joints. The discontinuities found in fresh rock were mainly joints, faults, and cracks. As a result

of statistical analysis, mean spacing and trace length of the joints are respectively about 1.7 and 4 m. The thickness of this zone is up to 16 m. In slightly weathered zone, rock matrix weathering begins with discoloration of rocks along discontinuities surfaces. The range of rock color in this zone is from light pink to light gray. Four major joint sets are predicted in this zone in which more than half of the joints are vertical. Moreover, average spacing and trace length of joints are respectively about 0.5 and 3.4 m. The thickness of slightly weathered rock is up to 8.5 m. In moderately weathered zone, less than half of the rock matrix is decomposed or disintegrated to the soil. The color of rock in this zone ranges from light brown to dark gray. A maximum of four joint sets can be found, and less than half of the joints are vertical. Mean spacing and trace length of the joints are respectively about 0.4 and 2 m. The thickness of this zone is up to 6 m. The highly weathered zone is divided into two grades based on the presence of corestone. In both grades, more than half of the rock matrix is decomposed or disintegrated to the soil. Corestones exist in grade (a) whereas in grade (b) no corestone is visible. A maximum number of three joint sets are

Table 3 Statistical results of joint trace length in different mass weathering grades Mass weathering grade

F SW MW HW CW

Masai

Putri Wangsa

Combined

n

Mean (m)

Standard deviation

n

Mean (m)

Standard deviation

n

Mean (m)

Standard deviation

294 203 165 253 326

4.13 3.36 2.14 1.45 1.39

2.47 2.2 1.83 1.07 1.48

281 305 132 314 253

4.02 3.39 1.82 1.64 1.37

2.17 2.18 1.52 1.43 1.56

575 508 297 567 579

4.07 3.38 2.00 1.55 1.38

2.33 2.19 1.71 1.28 1.52

Arab J Geosci Table 4 Percentage of different joint inclinations in each mass weathering grade Mass weathering grade

Joint inclination Horizontal (%)

Inclined (%)

Vertical (%)

F

12.00

27.13

60.87

SW MW HW CW

18.50 24.92 52.91 59.76

26.18 30.30 24.51 26.60

55.31 44.78 22.57 13.64

visible in this zone, and approximately half of the joints are horizontal. Average spacing and trace length of the joints are respectively about 0.5 and 1.5 m. The maximum thickness of this zone is 13 m. In completely weathered zone, two grades are identified based on presence of corestone. In grade (a), uniform weathering leads to a gradual decrease of weathering to a depth where no corestone can be found. However, the presence of corestones surrounded by decomposed rock disturbs the uniformity of weathering in grade (b). All rock matrices are decomposed to the soil but the original structure of rock mass is commonly preserved in this zone. A maximum number of two joint sets may be found, and horizontal joints are dominant. Mean spacing and trace length of the joints are respectively about 0.8 and 1.4 m. The thickness of this zone is up to 10.5 m.

Fig. 8 Trend of joint inclination in different mass weathering grades

In residual soil, parent rock completely decomposed to the soil. Consequently, there is no rock texture or mass preserved. This zone may be partially covered by vegetation. The maximum thickness of this zone is 4 m.

Conclusion This paper studied the relationship between joint characterization and the state of weathering in two areas of weathered granitic rock in Johor, South Malaysia. In the mentioned study, different joint parameters including spacing, trace length, orientation, and inclination were considered. The results of statistical analysis showed that frequency of joint spacing and joint trace length follow the normal distribution. This finding coincides with the results of Sousa (2007), Ehlen (2002), Hudson and Harrison (1997), and Priest (1993). The minimum and maximum means of spacing were respectively in moderately weathered and fresh rocks; however, the overall trend of mean spacing versus mass weathering grades did not follow any specific pattern. In contrast, mean trace length changed with decreasing trend over weathering states from fresh to completely weathered. Another finding of the present paper was the relation between joint inclination and mass weathering grades. The results revealed an increasing trend in the percentage of horizontal joints along with the progress of weathering from fresh to completely weathered rocks. Also, a decreasing trend was noted in the percentage of vertical joints for the same

Arab J Geosci Table 5 Proposed typical weathering profile for granite in Johor, Malaysia

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weathering progress. No specific relation was found between the percentage of joint inclination and the progress of weathering. In order to propose the typical weathering profile for the mentioned areas, the sketches of 24 panels of rock exposures were mapped based on site observation and classification of ISRM (2007). A typical profile was proposed based on descriptions of joint characterization, topography and geological condition, and rock appearance. It includes a complete range of weathering from fresh to residual soil and two subgrades for completely weathered and highly weathered zones. The extra subgrades were defined based on the presence of corestones. Regarding to the corestone weathering, the finding of the present study is similar to the weathering profile of Price (2009). It is believed that the results of this paper may contribute to rock mass classification and engineering design. Acknowledgments The authors would like to thank Universiti Teknologi Malaysia (UTM) for its financial support. We appreciate the cooperation of site managers and technicians of Putri Wangsa and Masai quarries during the site investigation of this study.

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