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Cases and solutions

A classification system for the assessment of slope stability of terrains along highway routes in Jordan A. S. Al-Homoud 7 Y. Masanat

Abstract The establishment of comprehensive development plans, in general, and the proper selection of highway routes, in particular, require an assessment of landslides or instability hazards in the project sites. The frequent landslides that occurred along the routes of major highways in Jordan, and particularly along the Amman-Na’ur-Dead Sea highway and Irbid-Jerash-Amman highway, have substantially increased the cost of construction and caused a considerable delay in the completion of work. The study of many landslides that occurred in the last 25 years along the highway routes and in the sites of some major civil engineering projects in Jordan has led to the recognition of major factors that affect the stability of slopes, and thus the safety and economics of these projects. The geological formation, structural features, topographic characteristics, geometry, and climatic conditions were adopted as the basis for the classification of terrains in terms of their stability. Each factor has been assigned a rating to indicate its relative contribution to the overall stability according to engineering judgment and past experience. The areas have been classified into 5 groups according to their total stability rate. The simplicity, comprehensiveness, and accuracy are the main characteristics of the proposed classification. Its significance stems from its helpfulness as a guide to the geotechnical and highway engineers in assessing the overall stability of the alternative routes of proposed highway projects. Key words Classification System 7 Landslides 7 Stability class 7 Geological and geotechnical parameters 7 Hazard maps

Received: 3 December 1996 7 Accepted: 29 April 1997 A. S. Al-Homoud Civil Engineering Department, Jordan University of Science and Technology, P.O. Box 3030, Irbid, Jordan Y. Masanat Civil Engineering Department, Jordan University, Amman-Jordan

Introduction There is a growing awareness among civil engineers, in general, and those involved in highway design and construction, in particular, of the importance of the role played by the engineering geologist in securing reliable data that can be efficiently used for the safe design and construction of highways. Site investigations are not restricted any more to the specific sites of engineering projects but they should be expanded to include wider zones surrounding these sites. A progressively increasing number of highways are being constructed in areas of unfavorable geotechnical conditions. Large sections often suffer from different forms of slope instability such as falls, slides, flows, erosion, etc. Such problems often cause considerable increase in the cost of construction and delay in the execution of work in addition to associated risks to human life and construction equipment. For example, due to landslides, the cost of construction of section 3 of Amman Na’ur Dead Sea highway increased by more than 100%, and the delay in the completion of sections 2 and 3 of Irbid-Jerash Amman highway (Fig. 1) by more than 30%. This demonstrates the need to efficiently translate the qualitative geologic statements into quantitative engineering geological parameters that can be adopted for the establishment of design criteria of civil engineering works or even the selection of their sites. This is particularly true in the evaluation of the different alternative routes of highways. Therefore, the proper selection of a highway route which involves minimum slope stability problems has paramount importance in the economics of the project. Many studies have been done to classify and map slope hazard. Anbalangan (1992), derived a classification system which combines past experience of causative factors and their impact on landslides. This classification, was called the landslide hazard evaluation factor (LHEF). It is similar to the rock mass rating (RMR; Bieniawski 1974) and Q Index (Barton and others 1974) rock mass classification systems. Jade and Sarkar (1993) used the information theory and regression analysis in developing a slope instability classification. Juang and others (1992) used the fuzzy sets to map slope failure potential. Mckean and others (1991) used the remote sensing and Geographic Information System (GIS) to assess landslide hazards.

Environmental Geology 34 (1) April 1998 7 Q Springer-Verlag

59

Cases and solutions

bility of terrains along different alternate routes of a proposed highway. The preference of a specific route is indeed the result of analysis of many combined factors, such as geometric, economic, social, political, environmental, and geotechnical. In this study the geotechnical aspect of the selection process will be emphasized.

Landslides in Jordan Jordan is morphologically distinctive, it is divided into seven physiographic provinces which coincide with the geologic provinces, (Fig. 2; Bender 1975) as follows: (1) southern mountainous desert, (2) mountain ridge and northern highlands east of the rift, (3) Central Plateau, (4) Northern Plateau Basalt, (5) Northeastern Plateau, (6) Wadi Araba-Jordan Rift, and (7) highlands west of the rift. Most of the landslides occurred in the second physiographic province. The population is concentrated in that region. Also, this area is characterized by hard topography draining towards the Jordan valley. In this province four geologic units outcrop (Table 1): (1) The Kurnub Group, (2) The Ajlun Group, (3) The Belqa Group, and Fig. 1 (4) recent Quaternary covering deposits. Location map showing the Irbid-Jerash-Amman and The Upper Kurnub Group is a Lower Cretaceous seAmman-Na’ur-Dead Sea highways quence consisting predominatley of varicolored interbedded friable sandstone, claystone and shale together with gypsum bands. The upper contacts are clearly marked by Objective of the Study a change from sandstone to nodular limestone, dolomite and marl. The overlying Ajlun group is a carbonate domAcquisition, interpretation, evaluation and utilization of inated sequence. The lower section of the group (A1–A3) geotechnical data are often better accomplished by estab- is composed of marl and clay intercalated with marly lilishing the methodology for acquiring the data and quan- mestone and dolomite. The upper section (A4–A7) is a litifying them on the basis of a classification system to en- mestone marl sequence. The lower Belqa group consists sure consistency, comprehensive acquisition of data, and of chalky marls intercalated with marly limestone whereobjective evaluation of the stability of the terrain under as the upper part consists of silicified limestone, chalk, study. Such a study would be the basis for developing phosphate and chert. The Cretaceous deposits are overspecific purpose zoning maps like landslide hazard maps. lain to a varying degree by Quaternary fluvial, lacustrine The main objectives of this research is to propose a clas- and eolian loess sediments. sification system of the geotechnical data which would The most critical landslides, however, occurred along the enable the geotechnical engineer to objectively assess the Irbid-Jerash-Amman highway which is a transport route anticipated slope stability problems in specific areas of national importance connecting northern Jordan and along highway routes, particularly in the sections involv- the Syrian frontier with the Jordanian capital city of Aming deep cuts, high fills, or the construction of heavy man. This highway has recently been opened for traffic, structures. This would help in choosing the alternate replacing a narrow, and often steeply graded, two-lane route that involves minimum anticipated slope stability single carriageway road. The newly constructed highway problems, and consequently minimum required volume is a dual carriageway which follows a hilly route varying and cost of preventative, control, and correction measin elevation between about 200 m and 650 m above the ures. It follows that such a route would naturally involve sea level essentially within the same corridor as the old minimum risks to traffic safety and minimum future road. The design of this road which calls for a side by maintenance costs. side carriageway has resulted in deep cuts and exceptionDue to the intricate relationship between the many geoally high fill sections especially in the mountainous tertechnical and environmental factors that affect the stabili- rain. These cuts were made into deeply weathered rock ty of slopes, subjective quantitative evaluation of the sig- masses, alternating sequences of sandy, silty sand, clayey nificance of any factor is unavoidable. However, the use rock and low strength colluvium which is subject to a of such a proposed classification system would ensure slumping behavior. The embankment traverses side consistency and objective correlation of the relative staslopes and is founded on relatively thick soils and low 60


Cases and solutions

Fig. 2 Physiographic-geologic Provinces in Jordan (after Bender, 1975)

strength colluvium. Although as noted by Ruef (1964) records of slope failure affecting highways and residential areas span the last forty years prior to construction of this road, no intensive geological investigations of either slopes or embankment foundations were made even though the road was being constructed in areas of inherent instability. Construction is often accomplished during relatively dry periods, and landslides then occurs after a subsequent period of rain. The most serious landslides occurred during and after the very exceptional winter of 1991–1992 when heavy rain and snowfall caused catastrophic embankment and cut slope failures that destroyed or severely damaged sections of the road (Fig. 3). A number of other slopes experienced less significant failures, and still many others showed signs of instability. Field and laboratory investigations into the landslides by the Government authority, consulting firms and others to determine the cause of the instability and to design remedial measures have been limited in extent and directed towards stabilizing the most serious slope failures. While no extensive movement has occurred at some locations, it is clear that the slope failures have already occurred and that movement is currently taking place. Slopes

which are apparently stable today could be a catastrophic risk in the future.

Geological and hydrogeological conditions along Irbid-Jerash-Amman highway Landslides have been recorded along the mountainous section of the Irbid-Jerash-Amman highway since 1966 (Fig. 4). It is an area of horizontally to slightly inclined bedded Cretaceous marine sediments (Table 1) cut by a number of east-west trending shear faults. In its course, following the valleys of Wadi Jerash and subsequently the Zerka River, the highway passes through the top of the Ajlun Group in the north, down into the top of the Kurnub Group in its central section, before rising back into the Ajlun Group in the south. The uppermost Belqa Group of sediments outcrops on surrounding hills but is not exposed within highway excavations. Overlying this group is a variable thickness of colluvium consisting of clay with boulders of limestone


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Cases and solutions

Table 1 A correlation of the different designations used in the description of the stratigraphy of the Upper Cretaceous in Jordan Period

Epoch

Group a

Formation b

Units (Member) c

Early Paleogene

Paleocene

Belqa Group (B)

B3 Muwaqar

Chalk-marl

Upper Cretaceous

Mastrichtian Campanian

B2 Amman

Phosphorite

Santionian Coniacian Turonian

Silicified limestone Ajlun Group A

Cenomanian

B1 El-Ghudran A7 Wadi Sir

Massive limestone

A6 A5 Shueib

Echinoidal limestone

A4 Hummar A3 Fuheis

Nodular limestone

A1–2 Na’ur Lower Cretaceous a

McDonald and others (1965),

Kurnub (Hathira) Sandstones b

Burdon (1959), and Masri (1963),

and marly clay materials. This material also contains sheared surfaces. The mean annual rainfall during the period 1940–1992 is shown in Fig. 5. The movement of groundwater takes place mainly through fractures. The water table rises only during heavy rainstorms and then falls very rapidly. The deep incision of the Zerka Valley drains off much of the groundwater in the form of baseflow. The springs observed in the area mainly issue from fault zones and generally cease to flow within a few months after the rainfall period, confirming the limited extent of the aquifers.

c

Bender (1974)

particularly wet year (Fig. 5). The main geological materials exposed at the site are silty clays alternating with grey shale belonging to the Upper Kurnub Group. A major rotational failure followed by a mudflow near the toe occurred at location OL2 in the slope of Zerka River Valley in 1969 and in April 1971. The annual rainfall in 1969 was 438 mm; in 1971 it was 524 mm; and in April 1971 it was almost the highest recorded value in the preceding ten years. This was about five times the monthly average over this period. The rock unit involved in the landslide area is part of the Upper Kurnub Group that consists mainly of brown or green silty clays, grey to greenish clays and black shale, with varicolored sandstone at the base. A translational failure occurred at location OL3 intermitDescription of landslides along tently between March 1969 and April 1971. The rock Irbid-Jerash-Amman highway units exposed at the site were 130–150 m thick, highly weathered, and tectonically disturbed marly clays and liOld road mestones and clays belonging respectively to the Ajlun In the period1966–1971 four landslides took place along a and Upper Kurnub Groups. The initial failure, which 35-km section of the old main road connecting Amman took place immediately after rainfall which was twice the with Syria (Fig. 1). Three were of a rotational type while monthly ten-year average, led to bulging and cracking of the fourth was of a translational character (Strieble and the soil above and below the level of the road. The main others 1969; Saket 1974. All of them took place during movement occurred along a plastic clay layer at an averwinter when the mean annual rainfall was more than age depth of 22 m. 423 mm (see Fig. 5). A rotational landslide followed by a mudflow at the crest Slope location OL1 (Fig. 3) underwent successive rotaof the slide at location OL4 occurred in 1967. The annual tional failure in December 1966 and failed again 4 years rainfall was 612 mm but during the month in which the later. The first failure occurred after rainfall that averaged landslide took place, rainfall was approximately twice the 612 mm per month. This was 2.5 times the December av- ten years monthly average. The bedrock in the region of erage for the ten preceding years. The 1970 failure also the landslide area consisted of a marly clay unit of the followed a month of heavy precipitation (211 mm) in a Lower Ajlun Group while the movement itself occurred

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Cases and solutions

The details of these failures are indicated in Table 2. Figures 6 and 7 show sections along the axis of landslides II and VI, respectively. As indicated in Table 2 the failures consist either of rotational failure where embankments are constructed on thick (greater than 8 m) colluvium overlying bedrock, or translational where failure has occurred along a thin clay seam within bedrock sequences. Where the weak horizon is thicker, the style of failure is rotational. It is significant that landslides I, II, and V occurred during periods of severe weather. A program of laboratory testing was carried out to classify and determine the shear strength parameters for the critical materials involved in the slides. Field work and testing was carried out by the local geotechnical companies in Jordan, while other tests were conducted at Dames and Moore laboratories in Saudi Arabia and Western Australia. The results are shown in Table 3. The physical and engineering properties of sandstones and claystones associated with the landslides (Table 3) are in full agreement with the fact that these rocks are highly weathered, having the character of a soil. Dames and Moore (1993) studied the landslides along the Irbid- Jerash-Amman highway. They assigned the risks for each slope as low, medium, and high. Also they divided the slopes into five distinct groups: limestone-marl slopes, weak marl-shale slopes, sandstone-shale slopes, nodular marl slopes, and clay-marl slopes.

Summary of landslides in Jordan Fig. 3 Location of the 1991–1992 landslides (I–VII) and the 1966–1971 landslides OL1–OL4 along the Irbid-Jerash-Amman highway

in beds from near the top of the A1–2 unit. The presence of major shear faults contributed to the weakening of the strata. Other minor earth movements took place between the years 1971 and 1990. However, the affected sections of the highway were reconstructed. Other than the geotechnical investigations relating to the four slides, none were made prior to the 1991–1992 failures. The weak, clayey horizons have contributed to the problems and several slopes have become unstable due to the unfavorable orientation of the bedding planes and joints (Dames and Moore 1993). Clearly, precipitation has had a major influence on the incidence of failure and it was about 2–6 times the monthly ten-year average when the landslides occurred. In addition, field observations and investigations made by Saket (1974) revealed that the lower part of the Ajlun Group is implicated in all the landslides. New road As mentioned previously a series of major landslides (Fig. 3) affected the new Irbid-Jerash-Amman highway.

The factor of safety (SF) against slope failure was evaluated for many slopes in Jordan, especially for slopes along the Irbid-Jerash-Amman and Amman Nau’r-Dead sea highways. Accordingly, the slopes can be classified as follows: 1. Stable, SF 1 1.5 and no signs of instability; 2. Marginal stable, 1.0~SF~1.5 with minor signs of instability; 3. Potential stable, 1.0~SF~1.5 with major signs of instability; 4. Critical, SF~1.0; and 5. Failed, Large-scale movement. The signs of instability were classified into two categories: 1. Signs of minor instability - cracks of limited length relative to the slope, rock falls, and mud flows; and 2. Signs of major instability - cracks of considerable length relative to slope, undercutting of slope and/or the presence of a soft layer within the slope face; developed jointing giving rise to the possibility of wedge failure, block slide, or toppling failure. Considering the available data on landslide occurrence in Jordan, Fig. 8a shows a histogram of landslide occurrence versus slope height, while Fig. 8b shows a histogram of landslide occurrence versus slope angle. In reviewing the geological, hydrological, and geotechnical aspects of landslides that occurred in the last 25 years


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Cases and solutions

Fig. 4 Geologic map showing the four landslides that occurred between the years 1966 and 1971 along the Irbid-Jerash-Amman highway

Fig. 5 Average rainfall for the last 50 years in the Jerash Area

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in Jordan, it was found that the landslide areas are characterized by the following: 1. More than 50% of the landslides are associated with plastic marls and about 20% with shales. The rest of landslides occurred mainly in fill materials placed over metastable colluvial deposits, and in saturated superficial deposits composed of clays, silty clays, and sandy silts. Most of the landslides occurred in the marls of the Na’ur and Fuheis Formations, A1–2 and A3 of the Ajlun Group (Table 1), and about 28% of the slides occurred in the weak recent superficial deposits. About 20% of the slides occurred in the claystones and shales of the Kurnub Sandstones (Lower Cretaceous). Most of the major landslides in Jordan are linked with the

Cases and solutions

Table 2 Brief description of the major landslides along the new Irbid-Jerash-Amman highway Slide No.

Mode of failure

Formation

Failed mass

Notes

I

Rotational

Fill material consists mainly of granular, compacted, very weak sandstone overlaid by colluvial material

16 m high embankment

Failed after a period of intense continuous rain and snowfall in 1991–1992

II

Rotational

Marl, green silty clay, block shale or greenish and multicoloured sandstone of Upper Kurnub Group of rocks

Rocks of Upper Cretaceous

Failed during winter 1991–1992 as above

III

Rotational

Colluvial deposits

Embankment

Ancient landslides took place at the same location

IV

Translational

Highly weathered, very weak sandstone and claystone

Large block of rock

Slide was caused by excess surface runoff resulting from removal of a culvert, after the heavy rain and snowfall of 1991–1992

V

Translational

Colluvial deposits, dark brown soil with embedded sandstone and dolomite boulder

Embankment

Area has steep slopes, rock scarp and gullies

VI

Rotational

Embankment constructed over a thin cover of colluvium material overlying limestone, marl and marlstone

Embankment

Block moved down the slide of a hill towards the road

VII

Translational

Highly weathered limestone formation

Huge rock block of 70 m!50 m dimension

2. 3.

4.

5.

A1–2 (Na’ur Formation) and A3 (Fuheis Formation) of the Ajlun Group, and fewer are linked with either the silty shale and claystone intercalations within the Kurnub Sandstone Formation or the recent deposits composed of colluvium, silty clays, and clayey silty sands. It is interesting to note that the marls and shales which constitute more than 70% of the sliding materials are moderately to highly plastic. Such materials generally have moderate to high swelling potential. Most of the slides occurred in the rugged areas of old landslides with moderate to steep topography where the shear strength approximates the residual one. Most of the slides occurred during or shortly after the winter season. Few slides occurred shortly after excavation in summer. However, all the slides were associated with the presence of wet or saturated layers or perched water. Most of the slides occurred in the areas of high annual precipitation, i.e., in north and central Jordan, and in years of exceptionally high annual precipitation. Table 4 shows the annual precipitation corresponding with the occurrence of major landslides. Most of the slides occurred in areas characterized by their poor surface and subsurface drainage conditions. Scour erosion at the toe of some natural slopes and highway embankments contributed to the occurrence of slides through the reduction of resisting forces.

6. Most of the old landslides exist in areas close to the Jordan Valley where most of the geologic layers dip unfavorably with respect to most highway cuts. The rocks are generally of very poor quality as indicated by their intense jointing and weathering.

Classification system for slope stability assessment In order to enable highway engineers to choose a highway route that involves minimum landslide hazards, and thus minimum delay in the completion of work and minimum construction costs, a quantitative classification system of the geological and geotechnical parameters that affect slope stability is proposed. This system is based on the consideration of five major parameters that are believed to substantially affect the stability of slopes. Therefore, rates were assigned to each parameter according to past experience and engineering judgment. Table 5 shows the considered parameters and the assigned rates. The overall slope stability can be obtained by summing the rates of all contributing parameters, then the state of the slope can be expressed in five stability categories (classes) according to Table 6.


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Cases and solutions

Fig. 6 Section along the Axis of slide II along the Irbid-Jeash-Amman Highway (after Dames and Moore Int., 1993)

Fig. 7 Section along the axis of slide VI along the Irbid-Jeash-Amman highway (after Dames and Moore Int., 1993)

Table 3 Summary of laboratory tests for sites II and IV (modified after Dames and Moore Int., 1993) Material type

Tested W.C. Wet Dry Liquid Plastic PI % by % Den. Den. Limit Limit % % % %

Grain size distribution

Gravel Sand Silt % % %

Clay %

Direct shear UU (undisturbed)

Triaxial UU (undisturbed)

Peak

c f (7) (kPa)

Residual

c (kPa) f

c (kPa) f

(7)

Peak cb fb (kPa)

Residual (7)

cb fb (7) (kPa)

Colluvium D&M* 14 II P IV 21

18.2 16.0 P P 19.6 21.5

35 P 58

17 P 27

18 P 31

7 P 6

37 P 20

31 P 25

23 P 49

13 P 75

31 P 4

4 P P

32 32 P P P P

17.5 12 P P P 29

29 P 22

16 P P

25.5 P P

Green clay D&M II VI

27 P 20

18.1 14.3 P P 20.1 16.5

81 P 61

43 P 23

38 P 38

0 P P

0 P 9

48 P 29

52 P 63

50 P 72

18 P 14

44 P P

11 P P P P 27

P P 17

12 P P

18 P P

12 P P

18 P P

Sandstone

D&M II VI

3 2 P

17.6 19.1 21.7 21.2 P P

P 25 P

P 12 P

P 13 P

P P P

98 53 P

P 31 P

P 17 P

P P P

P P P

15 P P

34 P P P P P

P P P

P P P

P P P

P P P

P P P

Claystone

D&M II VI

P 7 P

P P 22.3 21 P P

P 42 P

P 18 P

P 24 P

P P P

P 23 P

P 37 P

P 40 P

P P P

P P P

P P P

P P P P P P

P P P

25 30 P

12 15 P

P P P

P P P

* D&M: Dames and Moore Int. (1993)

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(7)

Triaxial CU (undisturbed)


Cases and solutions

erage annual precipitation in the region where the landslide occurred is 355 mm/year. Applying the proposed classification system, the rates assigned for items (parameters) are given below:Item Rate

1 20

2 3

3 8

4 4

5 4

The total rating is 39, i.e. poor slope. This is in full agreement with the fact that the slope has suffered large slope failure. Example II The station at km 56c400 - this slope has suffered a large “block” slope failure. The formation of the slope is highly weathered, medium to very strong, fractured limestone. The height of the slope is 38 m and slope angle is 227. The average annual precipitation in the region where the landslide occurred is 430 mm/year. The slope still suffers from continuous sliding. Applying the proposed classification system, the assigned rates for the items (parameters) are given below: Item Rate Fig. 8 Histograms showing occurrence of landslides versus a slope height (m), and b slope angle (degree)

1 20

2 3

3 6

4 13

5 4

The total rating is 4650, i.e., poor slope. This is also in full agreement with the fact that the slope has suffered large “block” slope failure.

Summary and conclusions

Table 4 Landlide occurrences related to total annual rainfall

1. Available geological, geotechnical and rainfall data on major landslides that occurred along major highways in Jordan in the last 25 years were analyzed. This included seven major landslide failures that occurred in 1991–1992 along the Irbid-Amman highway. On the basis of anaLandslide OL1 Jerash-Sweileh 1966–1967 612 Landslide OL1 Jerash-Sweileh 1971–1972 524 lyses, interpretations, discussions, and observations of Landslide OL2 Jerash-Sweileh 1969–1970 438 data related to these landslides the following conlcusions Landslide OL2 Jerash-Sweileh 1969–1970 433 may be drawn: Landslide OL3 Mastaba-Nourth 1969–1967 507 a. More than 50% of the landslides are associated with Slide OL4 Nau’r, 1st subsidence 1954–1955 639 plastic marls and about 20% with shales. The remainder Slide OL4 Nau’r, 2nd subsidence 1955–1956 621 of the landslides occurred mainly in fill materials placed Silde OL4 Nau’r, main subsidence 1963–1964 610 over metastable colluvial deposits. Amman-Irbid highway slide north 1991–1992 669 Amman-Irbid highway slide south 1991–1992 807 b. Most of the slides occurred in the rugged areas of old landslides with moderate to steep topography where the shear strength approximates the residual value. c. Most of the slides occurred during or shortly after the Verifying examples winter season. All the slides were associated with the Two examples of landslides that occurred along Irbid-Jer- presence of wet or saturated layers or perched water. ash-Amman highway are as follows: Most of the slides occurred in the areas of high annual precipitation, i.e., in north and central Jordan. Example I d. Most of the old landslides exist in areas close to the The Station at km 27c300 - this slope has suffered a Jordan Valley where most of the geologic layers dip unfalarge, shallow, circular slope failure. The height of the vorably with respect to most highway cuts. The rocks are slope is 45 m and angle of the slope is 557. The formation generally of very poor quality as indicated by their inis a highly fractured sequence of limestone, marly limes- tense jointing and weathering. tone and chert bands. The structure is intensively broken e. Most of the slides occurred in areas characterized by by short, very closely spaced joints and bedding. The av- their poor surface and subsurface drainage conditions. Event

Year

Total rainfall, mm


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Cases and solutions

Table 5 Classicifcation system for slope stability assessment, a Identification of parameters Item

Parameter

Class number 1

2

3

4

5

Limestone

Sandstone

Shale

Miscellanous

Marl and clay

1

Geologic formation

2

Dipping a

3

Avg. ann. precipitation, mm

~50

90–100

100–200

200–400

1 400

4

Inclination, deg.

~ 7

7– 15

15– 30

30– 60

1 60

5

Hight, m

~ 5

5– 11

11– 19

19– 26

1 26

a

Dip slope (30–707)

Vertical dipping

Non-bedding

Only three categories exist

b Assigned rate Class number Item 1 2 3 4 5

1 20

2

3

16

10 7 10 13 13

15 20 22 23

15 16 16

Table 6 Slope stability categories (classes) Total rate

State of stability

1 85 65–85 55–65 30–55 ~30

Excellent (v. stable) Good (stable) Fair (fairly stable) Poor (unstable) V. poor (v. unstable)

2. A quantitative classification system of the geological, topographical, rainfall and geotechnical parameters that affect slope stability is proposed. Five major parameters that affect slope stability were considered: geologic formation, dipping, average annual precipitation, inclination, and height. Rates were assigned to each parameter. The overall slope stability state was expressed in five stability categories (classes). The proposed classification system was verified and proved to be successful with confidence. 3. The developed classification system can be used by highway and geotechnical engineers in assessing the overall stability of alternative routes and for selection of a highway route that involves minimum landslide hazards.

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4

5

7

5 3

8 9 9

6 4 4

Acknowledgements The author would like to acknowledge Geotechnical Engineering and Materials Testing Company (GEMT), Toukan and Saket Geo-Research and Foundation Engineering Office, and Dames and Moore International for providing the geotechnical data used in the study. The authors sincerely thank the Deanship of the Scientific Research at Jordan University of Science and Technology for financing this study under grant No. 36/96. The contents of this paper reflect the views of the authors and do not necessary reflect the official views or policies of governmental authorities in Jordan.

References Anbalangan R (1992) Landslide hazard evaluation and zonation mapping in mountainous terrain. J Eng Geol 31 : 267–277 Barton N, Lien R, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mech Journal 6 : 189–236 Bender F (1974) Geology of Jordan. Supplementary Edition in English with Minor Revision of Vol. 7, Gebr. Borntraegger, Berlin Bender F (1975) Geology of the Arabian Peninsula, Jordan. Central Water Authority, Amman, Jordan Burdon DJ (1959) Handbook of geology of Jordan to accompany and explain the three sheets of the 1:250 000 geological map east of the rift by AM Quennell Bieniawski ZT (1974) Geomechanics Classification of rock masses and its application in tunneling. In: Proceedings of 3rd Cong. ISRM, Denver, Vol. ZA, p. 27

Cases and solutions

Dames and Moore International (1993) Geotechnical studies Amman-Jerash-Irbid highway. Submitted to Jordanian Ministry of Public Works and Housing, Report No. 25478–002–57, Ammran, Jordan Jade S, Sarkar S (1993) Statistical models for slope stability classification. J Eng Geol, 33 : 91–98 Juang CH, Lee DH, Shue C (1992) Mapping slope failure potential using fuzzy sets. J Geotech Eng ASCE 118 : 115–128 Masri MR (1963) Report on the geology of Amman-Zarga area. Central Water Authority, Amman, Jordan McDonald M and Partners, In Cooperation with Hunting Geological Survey Ltd. (1965) East Bonk Water Resources. Central Water Authority, Amman, Jordan

Mckean J, Buechel S, Gagdos L (1991) Remote sensing and landslide hazard assessment. Photog Eng Remote Sensing 57 : 1185–1193 Ruef M (1964) Geology of the landslides at km 20c800 of Amman-Jerusalem highway. Technical Report, Submitted to Jordanian Ministry of Public Works and Housing, Amman, Jordan Saket SK (1974) Slope instability on the Jordanian highways. PhD thesis, University of London, UK Strieble X, Tal AB, Sabbah AS (1969) Mastaba landslide. Geological Engineering Report, Natural Resources Authority (NRA), Amman, Jordan


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