Geo Tour to Malekhu Report

TRIBHUWAN UNIVERSITY

INSTITUTE OF ENGINEERING A FIELD REPORT ON

GEOLOGICAL AND ENGINEERING GEOLOGICAL STUDIES ALONG PRITHVI HIGHWAY AND IN THE MALEKHU AREA

SUBMITTED BY: Krishna Prasad Shrestha Laxman Nakarmi Rajan Maharjan Ratna Prasad Twayana

Downloaded From http://www.shresthakp.com.np/

SUBMITTED TO: Prakash Chandra Ghimire Mahesh Singh Dhar Department of Science and Humanities Pulchowk Campus

Field Report on Geology tour to Malekhu -2063. ---------------------------------------------------------------------------------------------------------------------

A Field Report on GEOLOGICAL AND ENGINEERING GEOLOGICAL STUDIES ALONG PRITHVI HIGHWAY AND IN THE MALEKHU AREA

Submitted By: Name Krishna Prasad Shrestha Laxman Nakarmi Rajan Maharjan Ratna Prasad Twayana

Roll No. 062BCE053 062BCE057 062BCE088 062BCE096

Submitted To: Prakash Chand Ghimire Mahesh Singh Dhar Department of Science and Humanities

Acknowledgement Downloaded From http://www.shresthakp.com.np/

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Pulchowk Campus 2064/01/64


The study of Engineering Geology remains incomplete without its practical knowledge. In real life we have to face a lot of practical problems that can’t be solved if we don’t have practical knowledge. For Civil engineering student the practical knowledge of the subject is essential. It is a matter of pleasure to have opportunity to field visit and field work in Engineering Geology It helped us to build up confidence and have practical knowledge about the theories we studied in class. This document contains the field studies that we have made in Malekhu and the corresponding theoretical backgrounds to understand it. We would like to express our gratitude to our respected teachers Mr. Mahesh Singh Dhar, Mr. Prakash Chandra Ghimire, Ananta Man Singh Pradhan and Dipendra Laudhari for their kind support to make this tour informative. We would also like to thank the Department of Civil Engineering for providing us such an opportunity.

Krishna Prasad Shrestha Laxman Nakarmi Rajan Maharjan Ratna Prasad Twayana

Contents


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Chapters 1. Introduction

Page No.

2. Mass Movement and their Types 2.1. Definition and Types of Mass Movements 2.1.1. Introduction 2.1.2. Types of Mass Movements 2.2. Case Studies 2.2.1. Case 1 (Ch 17+075) 2.2.2. Case2 Juge Khola 2.2.3. Belkhu Khola 2.2.4. Gajuri 2.2.5. Malekhu(Ch 68+000) 3. Rock Exposure and Measurements 3.1. Planner Features at the Rock Outcrop 3.2. Attitudes of the Geological Structures 3.3. Handling of the Geological Compass 3.4. Measurement of the Attitudes of the Planner Features at the Rock Outxrop Using Geological Compass 4. River Channel Morphology 4.1. Types of River Channel 4.1.1. Straight 4.1.2. Mandering 4.1.3. Braided 4.2. Land Forms Developed by River 4.3. River Channel Morphology at the Trisuli-Thopal Confluence 5. Identification of Rocks in the Field Downloaded From http://www.shresthakp.com.np/

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------5.1. Igneous Rocks 5.2. Metamorphic Rock 5.3. Sedimentary Rock 5.4. Major Rock types of the Field Study Area 6. Geology of the Study Area 6.1. Geology of the Malekhu Area 6.2. Recognition of the Geological Units in the Field

7.

6.2.1.

Benighat Slate

6.2.2.

Malekhu Limestone

6.2.3.

Robang Formation

6.2.4.

Raduwa Formation

6.2.5.

Bhaise Dhovan Marble

Recognition of the Geological Structures in the Field 7.1. Fold 7.2. Fault 7.3. Unconformity 7.4 Joints 7.5.Veins

7.6. Thrust 7.7.Engineering Geological Significance of the Geological Structures 8. Engineering Geological Studies of the Rock Outcrop 8.1.Introduction 8.1.1. Intact Rock 8.1.2. Rock Mass


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------8.1.3. Characteristics of Discontinuities in Rock Mass 8.1.3.1.Rock Type 8.1.3.2.Orientation 8.1.3.3.Intact Rock Strength 8.1.3.4.Spacing 8.1.3.5.Aperture 8.1.3.6.Roughness 8.1.3.7.Seepage 8.1.3.8.Infilling Materials 8.2.Rock Mass Rating of the Rock Outcrop 9. Conclusive Remarks


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1. INTRODUCTION Geology is the study of earth, its origin, composition, interior, exterior, the processes acted upon it that resulted into its present state. The word geology comes from Greek work “geo” (earth) and “logia” (study). Geology gives us the knowledge about the world around us and its behavior. Study of geology is also important to understand and predict natural disasters and other geological activities. Engineering Geology is an applied discipline of geology that relies heavily on knowledge of geologic principles & processes. It is now established as an interdisciplinary branch of science & engineering. Engineering geology provides a unique opportunity for the productive, co-operative interaction between two disciplines to solve many problems facing us today. Engineering Geology has much more scope over the civil engineering. Firstly because, the natural condition of the area determines the design, cost and proper location for any constructional project, secondly because, constructional and developmental works can alter the natural processes that may result to undesirable effects such as landslide. The third and the most important point is that the geological structures (major or minor) such as thrusts, faults, folds, joints, unconformity, lineation etc. play vital role not only in increasing the cost but also on failure of the engineering projects. Geological site investigation and field studies are the primary means of obtaining geological knowledge. The field study helps to acquire the actual field condition such as topography, bedding conditions and so on. Without field study the study of geology remains incomplete. For this purpose a three day geological tour to Malekhu was organized for civil second year students. The tour was mainly intended to provide practical knowledge about various types of landslides, planar features, river channel morphology, types and nature of rocks identification etc. Nepal, as a whole is naturally enriched with various geological structure and topography. One of the place that is enriched with natural bless is Malekhu that lies west to the Kathmandu basin. It is one of the best places for study of geological structures to a depth in short time and less expense. That is why it is selected as the destination for geological tour each year.


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2. MASS MOVEMENT ACTIVITIES AND THEIR TYPES 2.1. Definition and Types of Mass Movements 2.1.1 Introduction The study of hill slope process and mass movement has important significance for civil engineers in Nepal. The geographical location of Nepal lies in the heart of the tectonically active and fragile Himalayan belt. The hill slopes are mostly steep and unstable. So, before planning the civil engineering projects, it is important to know about the geology of the project area and the hill slope process of the area. The different hill slope process occurring is shown in the organization chart shown below:

HILL SLOPE EROSION

Land Slide

MASS MOVEMENT

Flow Debris

Fall

Topple

Slope failure

The activities of the slope such as topsoil erosion, slope failure, landslide and debris flow are the major hill slope processes in Nepal. Water induced activities such as heavy flooding and mass movement may cause in the lowland and upper catchments. The increasing rate of hazardous hill slope processes may increase the rate of mass destruction and casualties in Nepal. Erosion of topsoil and rock surface is one of the challenging hill slope process for civil engineers in Nepal. The surface runoff, river water and ground water are the major erosion agents in hilly area. Higher rate of erosion increases the sediment rate in the storage type dams and reservoirs and irrigation canal. We studied hill slope processes along the Prithvi Highway from Nagdhunga to Malekhu on the first day of our field trip. We observed different types of mass movements along the Highway during study.

2.1.2. Types Of Mass Movements Mass movement is one of the most challenging hill slope processes related to the potential energy developed by the gravitational force of attraction. Stresses may or may not influenced by the pore


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------water pressure. Slope failure, landslides and debris flows are the major mass movement activities in Nepal. a) Slope Failure Relatively small dimensional movements of weathered rock or soil layer in the slopes are called as the slope failure. Slope failure may redistribute the rock materials in less steep slopes and it relief the stress by reducing the high concentration of stress usually present in the bottom. The slope failure loosen the rock mass and open the stress relief joints or fractures which may lead huge landslide. Slope failure depends upon the mainly in the following Factors. a. Angle at which it is sustaining. b. Height c. Material d. Strength e. Water stress in the pores etc. F

mgcosβ β

mgsinβ mg

β

For equilibrium, mgsinβ = F + µmgcosβ where, µ is the coefficient of static friction. Removal of deposited material may be the solution of the slope failure. b) Landslide The term slides refer to the mass movements with a distinct surface of rupture or zone weakness separating the slide material from the more stable underlying materials. It consists comparatively large dimensional, that may be slow or fast continuous movement of huge weathered rock or soil on a clear slide surface. The sliding surface usually contains clay and the activities are influenced by groundwater. The Two major types of slides are Rotational and Translation slides. The mechanism occurs at the angle of 35degree to 65degree. Treatment of landslides is expensive and site specific. Detail information of slip surface is very important for the treatment of landslide. c) Debris Flow When the shear strength of the hill slope material considerably reduced, the rapid movement of the solid earth-material including large volume of the water can take place; such a flow including complex debris is called debris flow. If the material is fine the phenomenon is called earth flow. The slow but continuous movement of the slope containing the thicker soil layer without any distinct slip surface is recognized as creeping. The major role in debris flow is by gravity and pour water, so, generally occurs in monsoon. The stability measures against flow, spread and creeping are complex and demands considerably high costs. Downloaded From http://www.shresthakp.com.np/

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------d) Fall and topple Falls are abrupt movements of slope materials that detach from steep slopes of cliffs. Movements occur by free fall of a series of leaps and bounds down the steep slope. The relatively free characters and lack of a slide plane differentiates the rock fall and landslide. Depending upon the type of slope materials involved, it may be a rock fall, soil fall, debris fall earth fall, boulder fall and so on. Toppling is a process in which blocks of rock tilt or rotate forward on a pivot of hinge and then separates from the main falling on the slope and subsequently bouncing of rolling down the slope.

2.2. Case Studies On the duration of the trip, we studied different types of mass movements along the Prithvi Highway. We observed the overview of problem, causes of problem, effectiveness of applied control measures etc. These studied cases are described as case study of the mass movements as follows: 2.2.1. Case 1 (Ch 17+075) This was the first field for our three day tour. The major causes of the landslides and erosions in the area are weathering of rock, slope and water pressure. The erosion is stabilized by construction of gabion wall. Gabion wall is the wall constructed of stones kept inside mesh of wire. Similarly masonary retaining wall that is constructed using stones and cement is also constructed to stabilize that area. The weep holes are provided in the stone masonary wall for the outflow of excessive water in order to maintain hydraulic pressure. At one side of this area, there was another mass movement. It was a narrow gully in the steep slope. The gully is formed due to the flow of water at high speed along the steep slope. Though it seems very small, it may cause devastating effect. For safety crip wall has been constructed in this area. Similarly, to prevent the interruption of the highway from the debris, catch wall has been constructed. There is no sign of vegetation in this area(area of mass movement). Thus we can minimize the erosion by vegetation as well. 2.2.2. Case 2 Juge khola (Mahesh Khola) It was the second station we observed during our study. It was the huge mass movement area above Mahesh Khola. There were different parts of that mass movement. There was scarp in the left down side of the mass movement. The mass movement and younger exposure rock surface was just above the scarp of the area. There was comparatively gentle slope and the older rock exposure surface just above the part two in the area. Some vegetation was also there in this area. There was again comparatively steep slope in this part above part three. There was also rock exposure in the surface. By the side of the rock exposure there is debris flow. The upper part of this site is inhabited and thus is in risk of collapse. There may be permeable soil in that area which may lead for slipping of the huge mass movement in the rainy season. There may be the possibility of a numbers of slip surfaces in that area. There were gully erosions both sides of the mass movement, which may help to slip it down. Toe cutting by Mahesh Khola may be another cause of this mass movement. The major factor of the mass movement of this area is due to steep slope. It has only caused the environmental impact but no socio-economic impact. No preventive measures are used in this site but natural vegetations have acted as a preventive measure.

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2.2.3. Case 3 Belkhu Khola It was the third station of our study. It was the place where Belkhu and Trishuli River combine together in perpendicular manner. The site, in spite of being unsafe from flood is inhabited by the local people. There is possibility of casualty and mass destruction in case of heavy flood in Trishuli River. We observed old broken abutment of Belkhu Bridge that occurred in 1993. The foundation of the bridge was strong but the height of the bridge was insufficient. During the flood its level was so high that it reached the upper part of the bridge that is not designed for any such forces (force of flood). The presence of huge boulders by the side of the broken bridge supports the fact. There was huge amount of debris flow in the Belkhu River at that time. The catchment area of the river is also very large and this is also one of the reason for the flooding away of the old bridge of small height. The sand in the river consisted high quartz and low mica and was famous as “Sand of Belkhu River” used in different constructional purposes and imported to Kathmandu basin as for constructional purposes at that time. But these days the sand’s quality has degraded and the sand from the surrounding area is being used as the sand of Belkhu River. We observed another bank of Trishuli Rivet that was almost vertical. It was on the opposite side of the bridge. There were different layers in the scarp of vertical slope. The top layer was of coarser materials with flat cultivated land. We can see some linear vegetation in the middle layer. It is because of the fact that the lower layer was relatively impermeable as compared to the middle so that water content releases from the middle layer making it we and favorable for vegetations. As a result we can see the vegetation at the middle of the vertical landscape. The vegetation in turn has reduced the possibility of landslide at the site. The red, highly oxidized old soil at the site shows that it has been a stable structure for a very long period of time.Similarly its high angle (<60 o) and high binding capacity of the material of the site reduced the possibility of the landslide to very low. For the preventive measures of the debris potentiality of the Belkhu Khola we can adopt the high technology for the control of rate of erosion and trapping of debris before flow but due to low economic status, no any preventive measures are adopted in practice.

2.2.4. Case 4 Gajuri It was out fourth station of study. Here we can mainly see the mass movement due to the improper surface water drainage. The major cause of mass movement in this area was the high slope, low strength and less cohesion of the soil, excessive pore water pressure, formation of cracks due to live load and penetration of water from these cracks.. As preventive measures various types of the walls and drainage systems have been constructed. Gabion walls, breast wall, concrete walls as toe wall on toe of landslide and stone masonry walls with weep holes have been constructed. But as the major cause of the mass movement in this site is the improper drainage system, side drainage, reel and cascade wall have been constructed that reduces the rate of perculation. Except this Bio engineering technique has been applied in this


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------area. For this Amleso that is a small but deep rooted plant has been planted which also helps stabilizing the soil in this area. Although the applied solution measure was proper, it did not work as required. The improper management of drainage system, the blockage of weep hole and unequal and miscalculated placing of the weep holes in retaining wall is the major cause for the failure of such a so called well planned construction. There might be low quality of construction materials or workmanship for the cause of failure. Also the dynamic load viz. vehicle movement load may help to fail the area.

2.2.5. Case 5 Malekhu (Ch 68+000) Malekhu was the last site of our study of mass movement. There was rock mass failure in the roadside. The huge masses of rocks were deposited on the roadside and some of the rock mass was removed away from the road surface. There was rock exposure in the scarp of the mass movement. The failure masses of rock in the form of stone, boulder or gravel were deposited in the lower part of mass movement and road surface. There was rock instability in that area. The rock mass of this area is heavily jointed and fractured. There are multiple joints causing a wedge failure. The weathering is also important point to be noted that caused the rock failure. The site is a good example to prove that the geology of the place cannot be said to be the most stable simply because it has a strong foundation, the foundation of rock etc. Moreover it also details that for the stability of the structure there must be balance among the force acting over it. As the preservative measure trimming of hanged mass, bolting , spay of cement concrete, anchoring, wire netting, interlocking etc can be done but nothing so far mentioned have been applied to check the rock

3. ROCK EXPOSURES AND MEASUREMENTS Naturally solid rock is not exposed anywhere on the surface of the earth; it is often covered by the thin or thick layer of alluvium or soil. In some places, alluvium or soil may be spread for thousands of square kilometers and the bed rock may not be visible anywhere. If the rock are exposed naturally it is called exposure while if it is exposed artificially it is called outcrop.

3.1. Planner Features at the Rock Outcrops Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------The distinct visible marks or features of the rock outcrops are known as the planner features of the rock outcrops. The planner features have the significance importance for the study of the structural features of rocks. There are different planner features, which we can see in the rock outcrops. Bedding Plane The layer which is easily distinguished on the basis of variation in color, composition and grain size is known as bed. The plane of this bed or strata is known as bedding plane. It has fundamental significance in the study of structural features of sedimentary rocks. The different beds are distinguished from each other by difference in mineral composition, variation in grain size or texture, difference in color and variation in thickness etc. Foliation Plane The segregation of minerals into layers or bands of contrasting mineralogical composition is known as foliation. The plane of these different bands occurred in metamorphic rock is known as foliation plane. Foliation plane is generally formed by dynamo-thermal metamorphism of coarsegrained igneous and sedimentary rocks at progressive stages of the process. Joints The rupture surface presented after the cracks is known as joints. These are the divisional planes or fractures, which divide rocks into parts or blocks without transverse movement of the blocks. There may or may not be small movement in the blocks perpendicular to the fracture surface.

3.2. Attitudes of the Geological Structure Attitude refers to the three dimensional orientation of some geological features such as a beds, joints, folds etc. These may be measured by considering the two schools of thought: • •

Linear features Planner features

3.2.1 Orientation of linear features: Trend The orientation of horizontal projection of the linear feature measured with respect to the north is called Trend. Plunge The angle of inclination measured of its own linear feature horizontally is called plunge 3.2.2 Orientation of Planner features Strike The line of intersection of an incline plane with its own horizontal projection is called Strike line and the orientation of the strike line is called Strike with respect to the universal North (bearing of the strike line.) Dip direction The orientation of the maximum inclination of a planner surface with reference to universal North (the bearing of max. inclination.) Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Dip amount The angle of maximum inclination of an inclined plane with respect to its own horizontal projection.

3.3. Handling of Geological Compass Dip and strike at the rock outcrops can be measured with the help of geological compass. Geological compass is the combination of clinometers and magnetic compass. The dip angle is measured with a clinometers ant its direction is measured with compass. There are different types of geological compass. 3.3.1 Types of Geological compass 1. Clinometer Compass It is simply the combination of clinometers and the magnetic compass. Demerit: There is possibility of error if it is not hold horizontal. Merit: Easy to handle. 2. Brunton Compass It is same as clinometers compass but to reduce the error, there is a circular level marker and a level drum. There is a mirror to get the readings quickly. 3. Ptyberger Frager Compass Combination of clinometers and prismatic compass, with the help of this compass both the dip amount and dip directions components can be measured simultaneously in a single measurement. 4. Digital Compass with P.C It is comparable to P.C. It gives the attitude in digital form. Handling of the Geological Compass

The chief compasses used by geologists for field workare Clinometers compass and Brunton compass. But again due to comfortability in handling Brunton compass are popular. The Brunton compass consists of (a) a clinometers used for measuring dip angles’ (b) a compass used for measuring direction, and (c) a sighting device used in taking bearings and in hand leveling. While measuring dip, not only angle but also direction of dip must also be noted. The sides of the body of Brunton are made plane and parallel. One of these sides is placed on an inclined bending plane in the direction of dip. In this position the dial of the instrument lies in the vertical plane. The tube bubble of the clinometers is then centered by rotating a lever. The amount of dip is read on the inner scale in degrees The compass direction of the horizontal line on an inclined plane is called “strike”. In order to measure a compass direction, the Brunton is held face up and it is then leveled by using the circular level bubble. The hinged mirror and sight help in taking bearing of selected points. The readings of direction are taken on the outer circular scale.

3.4. Measurements of the Attitudes of the Planner Features at the Rock Outcrops Using Geological Compass 3.5.1 Measurement of Attitudes We measured the attitudes of the planner features at the rock outcrop on the left bank of Malekhu River near bridge site. The attitudes of the foliation plane and joint plane at that place are as follows: Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Dip direction(o)

Dip amount(o)

1

162

84

162/84

Bed

2

161

84

161/84

Bed

3

089

56

089/56

Joint

4

262

56

262/56

Joint

5

162

83

162/83

Bed

6

161

84

160/84

Bed

7

096

44

096/44

Joint

8

162

82

162/82

Bed

9

162

82

162/82

Bed

10

302

05

302/05

Joint

11

075

61

075/61

Joint

12

149

71

149/71

Bed

13

157

87

157/87

Bed

14

262

44

262/44

Joint

15

155

88

155/88

Bed

16

161

49

161/49

Bed

17

076

39

076/39

Joint

18

153

87

153/87

Bed

19

157

88

157/88

Bed

20

164

86

164/86

Bed

21

084

46

084/46

Joint

22

085

45

085/45

Joint

23

090

58

090/58

Joint

24

251

45

251/45

Joint

25

169

82

169/82

Bed

26

164

78

164/78

Bed

27

161

79

161/79

Bed

28

82

67

082/67

Joint

Serial no


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Attitude(o/ o)

Remarks

Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------29

81

67

081/67

Joint

30

162

81

162/81

Bed

31

161

81

161/81

Bed

32

145

80

145/80

Bed

33

262

72

262/72

Joint

34

261

75

261/75

Joint

35

161

83

161/83

Bed

36

95

49

095/49

Joint

37

169

82

169/82

Bed

38

99

79

099/79

Joint

39

166

87

166/87

Bed

40

165

87

165/87

Bed

41

130

65

130/65

Bed

42

71

34

071/34

Joint

43

165

85

165/85

Bed

4. RIVER CHANNEL MORPHOLOGY The surface waters flowing in courses of their own are known as streams and the large stream flowing through extensive area and receiving water from smaller side streams is known as river. The defined course followed by the river is known as the river channel.

4.1. Types of River Channel When the river flows in its way, it follows a definite path, the path followed by the river during its flow is called river channel. The river follows different path according to the energy level, the velocity of river and the gradient of riverbed. There are three different types of river channel.

4.1.1. Straight Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------The river follows a straight path in it's high energy level. In this case erosion is predominant and the velocity of river is maximum. In hilly region, the river follows straight path.

Figure: Straight River 4.1.2Meandering In this type of flow, the river follows the path like as snake's movement. In valley region, the river follows the meandering path. Erosion and deposition take place side by side in the same time.

Figure: Meandering River

4.1.3Braided In this type of flow, the river follows multiple channels. Deposition is predominant in this flow. The braided river tends to be very wide and relatively shallow. The river follows this type of path in Terai region. Figure: Braided River

4.2 Land Forms Developed by the River Due to continuous flow of the river, deposition and erosion takes place continuously forming some characteristic shapes or lands. Following are major land forms developed by the river: Higher Terrace It is the land formed by the river as it was flowing in these area in the past history. The higher terrace is over the high flood level of the river in present. There may be finer and coarser material layers alternately in the higher terrace. Middle Terrace As its name it is the middle part of the higher and lower terrace. This terrace will also over the high flood level of the river. Lower Terrace (Flood Plain)


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------During floods a river overflows its bank and submerges the adjacent low-lying areas where deposition of alluvial material takes place. A wide belt of alluvial plain formed in this way on either side of a stream, is called 'flood plain'. Channel Bar Many rivers are forced to rope a part of their load along their beds, especially in the flatter regions along their course. Most commonly the deposits so formed tale the shape of long narrow ridges called channel bars. Since they are made up of sand, they are also called sand bar. The river will flow from both side of the channel bar. They are temporary in nature because an increase in velocity, the river may cut down and take the sand along with it. Oxbow Lake The meanders grow by eroding its outer bank and depositing sediments at the inner bank. During this process the sharpness of the river bends increases progressively and the neck of meander becomes narrow and narrow. Finally a stage comes when the river cuts through the neck and starts flowing straight leaving behind its roundabout course. Such left out old meanders which remain filled with stagnant water, are called “oxbow lakes”. Alluvial Fans The alluvial material, which flows down from mountains, accumulates at foothills where the stream enters a plain. The deposition occurs due to abrupt change in the gradient of river valley. Such deposits spread out in the shape of flat fans and are called “alluvial fans”. Usually the coarse material is dropped near the base of the slope while finer material is carried further out on the plain. Alluvial fans from many adjacent streams along a mountain may merge to form a long wedge of sediment called “alluvial aprons”. Natural Levees “Natural levees” are the low ridges, which are formed on both sides of a river channel by the accumulation of sediment. They tend to confine the flow of river water into its channel between flood stages. The natural levees occur in rivers, which have broad flood plains. During floods the river overflows its bank and its velocity decreases rapidly. As a result most of the coarse sediment is deposited along the area bordering the river channel and finer sediments are deposited more widely over the flood plain. In this way, successive floods build up ridges on both sides of a river channel, which are called “natural levees”. Point Bars In meandering rivers, sediment deposits occur as point bars. The point bars are the crescent shaped deposits, which occur at inside bends of a river channel. Deltas Deltas are deposits built at the mouths of streams. The deltas are usually triangular in shape with their apex pointed upstream. When a stream enters an ocean or lake, the currents of the flowing water dissipate quickly. This results in the deposition of the series of sedimentary layers, which make up the delta. The material of most deltas is well sorted and many deltas are uniformly graded. Figure: Delta Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Island They are hard rocks forming a small island in the river channel.

4.3. River Channel Morphology at the Trishuli-Thopal Confluence We studied the river channel morphology of the Trishuli-Thopal confluence from the higher terrace of the river located about 200m towards Dhading Besi along old track from the suspension bridge. There was channel bar in the left side of the river. The discharge of the Trishuli river was high with compared the Thopal river. There was side bar in the right bank of the river. At the confluence point there was erosion band in the right side of the river. There was an island at the confluence of these two rivers. The site study of the field fortified us with the knowledge about the morphology of the river, the activities of the river, various landforms formed by the river cutting, deposition and erosion. Moreover the site provided us with the knowledge about the appropriate site for the construction of the bridge, i.e. the bridge must be constructed where the effect of river cutting is the minimum and it should be somewhere near the deposition bank so that we can easily get the constructions required. The site must also have a strong foundation bed to resist the impact due to river.

5. IDENTIFICATION OF ROCKS IN THE FIELD Rocks are identified in the field by the study of its size of grain or texture, shape of grain layers, colour, composition of minerals etc. as they exposed naturally or artificially on the surface of the earth.

5.1. Igneous Rock These types of rocks are formed by the solidification of magma either under the surface of earth or over it. These are of three types according to the solidification process. Plutonic Rock :- The rocks, which are formed underneath the surface of the earth, are called the plutonic rocks. Volcanic Rock :- The rocks, which are solidified on the surface of earth, are called volcanic rocks. Hypabyssal Rock :- The rocks, which are solidified on the way of extrusion process, are called hypo basal rocks. Igneous rocks are commonly identified in the field by the study of their interlocking crystallization of a number of mineral grains. Igneous rocks are generally hard, massive, compact, having no bedding plane and interlocked grains. It usually contains much feldspar. By the study of these properties we identified the igneous rocks in the field. e.g., Granite Gabbro Dolerite

- generally equigranular texture, light colour appearance - coarse grain and dark colour - containing dark minerals in good proportion with medium


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------grain sized

5.2. Metamorphic Rock These are formed by alteration of alignment, texture, structure, chemical composition etc. in preexisting rocks due to the action of temperature, pressure and chemical reaction. Metamorphic rocks are generally hard and having of interlocking grains. • • • •

Contact Metamorphic Dynamic Metamorphic Dynamo Thermal Metasomatic

Metamorphic rocks are distinctly distinguished from other types of rocks by the development of features like cleavage, foliation, schistosity and by the presence of such minerals which are known to be of metamorphic origin. Metamorphic rocks often exhibit an interlocking texture of the constituent minerals grains. Thus these rocks are basically identified in the field on the basis of colour, texture as well as structure. e.g., Slate Phyllite Schist Gneiss

- slate cleavage - soapy feeling - rough, irregular and undulated plane, unequal growth of minerals - band of contrast colour, composition and texture (mica band)

5.3. Sedimentary Rock These rocks are derived from pre-existing rocks through the process of erosion, transportation and deposition by various natural agencies such as wind, water, glacier etc. The loose sediments undergo compaction and form resulting products as sedimentary rocks. According to the mode of transportation the sedimentary rocks are divided into three different types. Clastic Rocks :- The rocks which are formed by deposited mechanically are known as clastic rocks. Chemical Deposits :-The rocks which are formed by chemical precipitation are known as chemical deposits. Organic Deposits :-The rocks which are formed by deposited organically are called organic deposits. Sedimentary rocks are identified in the field by the study of different layers, which are originally bedded or laminated under suitable conditions. There may be the impression of fossils in sedimentary rocks. The colour and the grain size of the rocks may be different in different layers. By the study of these properties also the rocks may be identified. e.g., Conglomerate Sandstone Clay stone

- grain size greater than 2 mm - grain size is equal to sand (i.e. 1/16 mm –2 mm), quartz is common - formed by deposition of clay, shale is common example

5.4. Major Rock Types of the Field Study Area During our study we found different rocks in our study area.

A. The metamorphic rocks found in the field are described below:


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Slate: Slate is an extremely fine-grained metamorphic rock characterized by a slaty cleavage, by virtue of which it can be split into thin sheets as roofing material .Due to its low crushing strength it is also used as building material. It was found at a distance of 500m north of highway. Phyllite: It is a medium to fine-grained metamorphic rock of complex silicate composition. The rock shows a foliated structure and represents an intermediate stage in the metamorphic transformation of slates to schist with the unaided eye. In the field the presence of muscovite was found in the rock. This is found at the south from the highway along the stream. Dark green type of phyllite was found in the Robang formation (rb). Schist: Schists are megascopically crystalline metamorphic rock characterized by a typial schistose structure. The constituent platy and flaky mineral and are arranged in irregular parallel layers of bands.

Marble: Marble is essentially a granular rock composed chiefly of recrystallised calcite. It is characterized by a granular structure. Marble often show banded structure. Marvels are commonly used in building constructions in the form of blocks, slabs, aches and as chip for flooring. It is also used as decorative and ornamental purpose. In Malekhu it was found at a distance of 3275m south from the highway. Gneiss: Gneiss is a megascopically crystalline metamorphic rock characterized by segregation of constituent minerals into layers of bands of contrasting color, textures and composition. Feldspar and quartz are more common in gneiss than in schists. Dark minerals of amphibole and pyroxene group are also common. The compact, dense massive varieties of gneisses are used in building and road metal. In Malekhu it was found at a distance of 4650m south from the highway. The gneiss was found in the boulder as an eye structure and so called Augen Gneiss. This was found on the Kulekhani formation (ku) of Bhimphedi group. Quartzite:Quartzites are granular metamorphic rocks composed chiefly of intersatured grains of quartz. The name Orthoquartzite is used for a sedimentary rock of similar composition but of different origin; it has siliceous cement. It contains subordinate amount of micas, feldspars, garnet and some amphiboles which result from the impurities of the original sandstone during the process of metamorphism. The rock is generally very hard, strong, dens and uniformly grained. It finds extensive use in building and road construction.

B. The different types of Sedimentary Rocks found in the field are as follows: Limestone: Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------These are the most abundant sedimentary rock formed from the non-elastic group and are composed chiefly of calcium carbonate. However the presence of dolomite, quartz, feldspar and iron oxides is rather a common texture. Limestone is a primary source of material for the manufacture of Portland cement and for a wide variety of limes. Its other uses are in the metallurgical industries as a flux. It was found along the Prithivi highway towards Gajuri as the Robang formation (RB) as a Malekhu limestone formation (ML) in the upper Nawakot Group and Sandstone Sandstone is a mechanically formed sedimentary rock. it is formed by the cementation of the sand particles between 1/10 mm to 2 mm in diameter. Sandstone is, perhaps, the most familiar of all the rocks as it is usually quarried and used more than any other rock, for all types of buildings. The various varieties of sandstones are named after the cementing material. e.g. Siliceous sandstone, ferruginous sandstone, calcareous sandstone, argillaceous sandstone.

Breccias Breccias are mechanically formed sedimentary rocks, consisting of angular fragments. These sediments are heterogeneous in nature; cemented together by clay, iron oxide, silica or calcium carbonate and are generally more than 2 mm size. Because of the heterogeneous character they are not used as building stones but some of the varieties which are susceptible to polish can be used for ornamental works.

C. The Igneous Rocks found in the field are described below: Granite: Granite may be defined as plutonic light coloured igneous rock. These are among the most common igneous rock. Two most common and essential mineral constituents of granite are; quartz and feldspars. The first is always easily recognized by its glassy lustures, high hardness (H=7) and cleavage less wide transparent appearances. Feldspars making granites may be of two types; the potash feldspars, commonly orthoclase and the soda bearing plagioclase feldspar like albite and oligoclase. Feldspars microcline may also occurred in some granites. Agra granite was found in the right bank of Malekhu Khola south west of "Chhapan Danda".


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6. GEOLOGY OF THE STUDY AREA 6.1. Geology of Malekhu Area Malekhu is an important area from geological point of view. Malekhu is teeming with much geological peculiarity like joints, faults, folds, different types of rocks, streams and amazing flow direction of the Malekhu River. Malekhu lies in the region of lesser Himalayas, one of the morho-tectonic zone of Nepal. Siwaliks and higher Himalayas are its neighboring morpho-tectonic zones. Main boundary thrust (MBT) in south separates the Siwaliks and the Lesser Himalaya and the Main Central Thrust (MCT) in north separates the Higher Himalaya and Lesser Himalaya. The MBT is itself an active fault that has brought older rocks of lesser Himalayas to Siwaliks. The lesser Himalayas are mostly composed of unfossiliferous, sedimentary and metasedimentary rock such as slate, phyllite, schist, quartzite etc. There are also some intrusions of granite. The lesser Himalayas of Nepal vary from east to west in stratigraphy, structure and magmatism. The eastern Nepal is characterized by development of extensive thrust sheet of crystalline rocks that have traveled southward. In central Nepal, a large thrust sheet called Kathmandu Nappe covers a wide area around the Kathmandu region. Malekhu lies in the vicinity of Mahabharat thrust, which lies between Indian and Tibetan plates and thus landslides are quite common here. In few places the Mahabharat range is intercepted by major rivers through which all the water from Nepal originating from north drain to south. The Mahabharat region is characterized by concentration of population along the ridge and gently dipping northern slopes. Major Rock Types


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------The Malekhu area consists of lower grade as well as higher grade of metamorphic rocks. The igneous and the sedimentary rocks are less found in the area than the metamorphic rocks. The area is regionally metamorphosed and it has youngling litho logy pattern. The different rocks found in this area are Quartzite, Slate, Limestone, Dolomite, Phyllite, Schist and Marble with some specific names like Benighat Slate, Malekhu Limestone, Balse dobhan Marble, etc.

6.2. Recognition of the Geological Units in the Field The geology of Malekhu area is very complicated and comprises of large structures to microscopic structures of various origin. The area includes the two complexes of Central Nepal, i.e., Kathmandu complex and Nuwakot Complex. Both complexes built up the Mahabharat synclinorium. The lithological difference between the Nuwakot Complex and Kathmandu Complex is the grade of metamorphism. During our study, we observed and recognized different geological units in the field, on the basis of bed member formation and complex. These units are described as follows. 6.2.1 Benighat Slate The name is derived from the village 'Benighat' at the confluence of Budhigandaki and Trishuli River. This formation consists of grey to black slate. In some places it is highly carbonaceous (graphitic). Also it is calcareous and dolomitic at the lower part. Inter collation of quartz vein 2 cm to 4 cm thick is also observed in some places. The beds are not thicker than 5 cm to 7 cm in this formation. This formation is about 500 m to 300 m thick. It is found along Thopal Khola and Dhading Road After 300 m from suspension bridge over Trishuli river, calcareous beds of Benighat slate is observed which is fine grained yellowish grey in colour and highly fractured and jointed. The difference in attitude in Benigaht slate indicates that these may be fault or fold in this formation. 5.2.2 Malekhu Limestone The name is derived from the village 'Malekhu' along Prithvi Highway. The Malekhu Limestone has a transitional contact with Benighat slate near the suspension bridge along Malekhu Dhading road on right bank of Trishuli river. It is composed of light yellow coloured silicious limestone of fine grained to dense, crystalline and massive. In the middle and top part of this formation, the dolomitic limestone is observed; bounding structure in quartz veins is also observed in limestone, which shows contemporary pressure-temperature conditions. Drag fold at the top part of this formation on the left bank of Malekhu Khola is observed. Weathered rock is blackish in colour and fresh exposure is brown in colour. The average thickness of this formation is about 800m. It is found along Malekhu Khola Towards Upstream

About 400 m. far from the Bridge over Malekhu Khola, we observed nearly vertical beds of dolomitic limestone of grayish white or elephant skin colour. About 200 m. from the previous location along Malekhu Khola towards upstream, we observed a fault plane. Left side of the fault plane composed of limestone of whitish yellow colour and the Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------right side of the fault plane composed of grayish white phyllitic limestone. The fault plane composed of mylonite bressia. Nearly 200 m. from the fault plane, there is a transitional contact between Malekhu Limestone and Robang Formation.

5.2.3 Robang Formation The name derived from the village 'Robang' in Dhading district. Along Malekhu Khola, on the right bank about 500 m. from the Prithvi Highway near Malekhu Bazzar contact between dolomitic limestone of Malekhu Limestone and dark green phyllite of Robang Formation was observed from where river bends sharply. Main lithology is phyllite and yellowish quartzite called 'Dunga Quartzite' which is highly jointed. Phyllite is gradually replaced by massive yellowish quartzite towards south. Some phyllite beds are black in colour due to graphite. Nearly middle part of the formation, we observed was Amphibolite, a metamorphic product of basic intrusive rock-dolerite. The thickness of this formation is about 200 m. to 1000 m. It is found along Prithvi Highway Towards Gajuri About 500 m. far from the Malekhu Bridge, the contact between Robang Formation and Malekhu Limestone is found which is transitional contact. About 100 m. far form the contact, Amphibolite a metabasic rock is observed which is weathered and is olive and muddy in colour with contact of metabasic rock and quartzite is observed. It may be Dunga Quartzite. 5.2.4 Raduwa Formation The name is derived from the village 'Raduwa' in Dhading district. This name was first used by Stocklin and Bhattarai at 1971. A highly fractured zone of Mahabharat Thrust exposed at right bank of Malekhu Khola, every fine, grey to black mylonite is observed. This separates Robang Formation of Nawakot Complex and Raduwa Formation of Kathmandu Complex. The main rock type of this formation is mica-schist of coarse crystalline of dark grey colour due to predominant micaceous minerals. Near M. B. T. garnetiferrous schist is also observed which is perfectly foliated. This formation is about 1000 m. thick. 5.2.5 Bhainse Dovan Marble The formation is named after the village Bhainsedovan on the tribhuvan highway. IT is in contact with Raduwa formation. Well exposed marble is in front of Dharapani. It is metamorphic equivalent of limestone and so white in color, crystalline in texture associated with pyrite mineral. It is about 800 m thick


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7. RECOGNITIONS OF THE GEOLOGICAL STRUCTURES IN THE FIELD The term structural geology deals about the genesis and geometry of the structural features present in the rocks. The geometry of arrangement of the rocksand the geometry preserved in the rocks/sediments/soils are the Geological Structures. These geological structure are classified as follows:

Geological Structures

Primary Geological Structures

Secondary Geological Structures

These geological structures are formed mainly due to tectonic activities in the area. The major primary geological structure includes cracks, fractures and the major secondary geological structures includes fold, fault, joint and so on. In the study area we observed the different geological structures which are described as follows:

7.1. Fold Folds are wavy undulations developed in the surface of the rocks as a result of stresses to which these rocks have been subjected from time to time in the past history of the earth. The folds may develop in any type of rock and may be of any shape, from simple symmetrical upwarping or down warping to complex geometrical patterns. The ultimate shape and extent of folds depend upon a number of factors like the nature, magnitude, direction and duration of forces involved in the process and the nature of the rocks subjected to such a process. The characters of folds found near to Malekhu bridge, along Malekhu Khola towards upstream side are • Color of rock is brown. • Plastic deformation • Drag folds • Formed by pushing of younger rocks by older • Rock is purely sedimentary and identified as Dolomite. • Formation of inside cavity is seen in the rock. • The rock is affected by physical weathering and has weathering pattern like elephant skin. • The rock is marble like and its reaction with acid is vigorous.


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7.2. Fault A fault is a planar discontinuity between blocks of rocks that have been displaced past one another in a direction parallel to the discontinuity. The faults are distinguished on the basis of following factors: a) The apparent movement of the disrupted blocks along the fault plane. b) The relation of the fault attitude (dip and strike) to the attitudes of the displaced beds . c) The direction of the slip. We observed the evidence of the fault as major structure. Location at right bank of Malekhu Khola • Mylonite(micro breccia) present. • Yellowish white in colour. • Small course grains due to angular fragments of rocks. • Occurrence of small fault. • Black coloured fine clay particles are also present at the side.

7.3. Unconformity An unconformity is defined as a surface of erosion or non depositing occurring within a sequence of rocks. It indicates a gap or interval of time in the geological history of the area duting which the normal process of deposition was inturupted. It is a structural feature in the sense that rock formations lyig avobe and below it generally represent different conditions under which they have been formed. Unconformities are recognized in the field as follows: • Visual inspection of the angular relation between the sequence. • Presence of Basal Conglomerate. • Availability of the residual soil within the sequence of rocks. • Exposure of the erosional surface. • Conatrasting behavior of the rocks from a particular surface. • Variation or gap in the geological age of the rocks of the sequence.

7.4. Joint The rupture surface presented after the cracks is known as joints. These are the divisional planes or fractures, which divide rocks into parts or blocks without transverse movement of the blocks. There may or may not be small movement in the blocks perpendicular to the fracture surface. The joints may be open or closed. These may be smooth and straight or rough and curved in outline. Joints are caused due to tectonic stress, residual stress, contraction due to shrinkage, surface movement and blasting and explosion. The joints are recognized in the field as follows: • • • •

Fractures observed in the rocks without considerable displacement. Visual inspection and thorough geological study of the site. Dimension of joints varies from short in extension to miles together. It sometimes controls the drainage pattern of an area, shape of the coastline.

7.5. Veins Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------The narrow strips generally found in metamorphic rocks are called veins. They are small, usually discordant or concordant to the original bedding planes, and formed by the silica secreted by country rocks. During our study we observed the quartz vein near Trishuli-Thopal confluence view point at the suspension bridge side of Trishuli River. The presence of vein in the rock has great significance in civil engineering activities. The vein may reduce the strength and may cause to parting the rocks.

7.6. Thrust The Mahabharat thrust lies in the south of the main central thrust and towards the north of the main boundary thrust. It is produced due to pushing of the Indian plate on the Tibetan plate. The reverse fault in which the hanging wall is actually moved up relative to the footwall is known as thrust fault or simply thrusts. The fault angle is quite low in thrusts. These are very common occurrence in folded mountains and seem to have originated as a further step in the process of adjustment of rocks to the imposed stresses.

7.7. Engineering Geological Significance of the Geological Structures These Geological Structures plays the significant role in civil Engineering purposes. Following are the engineering significances of the various geological structures: Joint • Evaluation of rock mass for specific purpose is based on intensity of joints. Presence of joints in the rock reduces its strength. • Interrupts the transfer of stresses. • Variation in the porosity and permeability of the rock mass. • Stability of slopes and engineering structures develops on the nature, type and orientation of joints Fold • • • • •

Change in attitude may result variation in evaluation of beds to structures. Due to shattering of rocks, axes of folds are weak. Variation in porosity and permeability. Formation of arches during the transformation of stresses. Variation in water pressure.

engineering

Unconformity • Source of surprises or considerable errors in qualitative as well quantitative judgement of the site. • Variation in the stability of the rock sequences adjacent to the unconformity surface.


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------• •

Unconfirmities are the weak contacts which may inturrept the stress transfer or deviate the stress path. The unconformity surface can result the permeability contract.

Fault The fault has great significance in civil engineering works. A civil engineer has to ascertain for the presence of faults and investigate thoroughly their effects on the construction site. The construction site should be located far from an active fault. Faults are always associated with earthquakes. Thus tectonic history of the area under consideration must be studied thoroughly. • Change in attitude may result variation in evaluation of beds to engineering structures. • Variation in porosity and permeability • Fault zone serves as easy pathways for the water which can cause leakage when let untreated in dams and reservoirs and can become source of great trouble when encountered across highways. • Faulting products like gauge and breccias create additional problems always adding to the condition that cause instability and the failure.

Veins •

The presence of veins cause the decrease in the strength of rocks

•

Since it is a type of fault it has the same significance as described in the fault.

Thrust

8. ENGINEERING GEOLOGICAL STUDIES OF THE ROCK OUTCROPS 8.1 Introduction It is essential for civil engineer to study the rock outcrops. To study the rock outcrops it is necessary to collect the engineering geological data. Downloaded From http://www.shresthakp.com.np/ -

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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------The purpose specific geological information that can be quantified is known as engineering geological data.

8.1.1. Intact rock The intact rock is the rock material without discontinuities. They have greater strength than the rock mass. Their strength can be determined in the following ways: Check in lab: Required size of intact rock can be taken from the rock mass and checked in the lab. Check by hammer striking: This is the cheapest and easiest way to find out the approximate strength of rock material and this can be done directly in the field. For this, rock material is struck by geological hammer and the sound is identified. If metallic sound comes then the rock material is strong having strength more than 100Mpa and if sound is as in soil then the rock material is weak having strength less than 10Mpa.If sound is in between metallic to soil, then strength is also in between 100Mpa to 10Mpa. Schmidt hammer: it is also an easy but nearly accurate method to check the intact strength. It can give numerical value of strength of rock material. Actually the hammer is a special type of hammer, which measures the rebound value.

8.1.2 Rock Mass The large volume of rock intersected by the discontinuities is known as rock mass. The rock mass is considered in between two discontinuities. In civil engineering practice, rock mass is considered as construction site where as rock is considered as construction materials. Rock mass as construction site provides foundation for building, reservoir, base for road alignment etc. Rock mass = Intact rock +discontinuity The following parameters are related to the intact rock. The rock mass is classified on its outcrop on the basis of following characteristics of intact rocks.

8.1.3. Characteristics of Discontinuities in Rock Mass Discontinuities are the structural features of rock, which are developed due to the existence of different stresses on the periphery of the earth. It separates the two rock masses to each other. The classification of rock mass is based on the characteristics of intact rocks as well as the discontinuities. The following are considered influencing parameters for the discontinuities: 8.1.3.1. Rock type The rocks are classified on the basis of the characteristics of intact rock as well as the discontinuities present. • Cleavage/foliation plane, bedding plane • Materials • Particle size • Textures etc.

8.1.3.2. Orientation:


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Orientation of discontinuities is the attitude of the discontinuities. Depending upon the slope of the discontinuity rock has different strength at different direction. If the direction of the discontinuity is in the same direction as the rock mass, it is an unfavorable condition. But if the discontinuity is in an opposite direction to the rock mass, it is a favorable condition. 8.1.3.3. Intact Rock Strength The strength of the intact rock is tested by Schmidt Hammer rebound test. Schmidt Hammer is the instrument used to test bearing capacity of site rock mass by rebound test. There are two ways of testing by Schmidt Hammer. One is uniaxial test and the other is triaxial test. 8.1.3.4. Spacing: It is the perpendicular distance between the two adjacent discontinuities of the same set. The space between the discontinuities set in the same direction also causes variation in the strength of the rock. The rock material in between the discontinuity is intact material. The volume of the intact material governs the strength of the rock.

8.1.3.5. Aperture: Aperture is the open spacing present in the rock due to discontinuity present in it. The crack due to any means like alkaline water has high tendency to dissolve calcite material may get widened up. Depending upon space it is classified as widely open(>1cm), open(2mm-1cm), close(<2mm), tight(<1mm). The apertures wide and open cause the mechanical discontinuity as no stress is transferred all over the rock. However if the open discontinuity is filled with any other material then strength is transferred. The open and close aperture if is filled by any other material then the strength and the stability of the rock increases depending upon the material type filling the aperture. 8.1.3.6. Roughness: It is one of the characteristics of the discontinuity surface. In rough discontinuity surfaces due to low friction shear strength is high. It is generally of two types - rough planar (rough surface with a plane flow) and rough wavy (rough surface with a wave like flow). 8.1.3.7. Seepage: Seepage is the flow of water under gravitational forces in a permeable medium. Flow of water takes place from a point of high head to a point of low head. The flow is generally laminar. A flow line represents the path taken by a water particle. 8.1.3.8. Infilling materials: These are the materials filled in the open apertures of discontinuities. If there is no fill material it is called clean material, if the rock has mineralized discontinuity (rock fragment) the strength may be considerably high. If the rock is powdered material (e.g., soil) and mineralized both, the rock may be either cohesive or non-cohesive. Tensile strength of soil is low.

8.2. Rock Mass Rating(RMR) The geology of the earth is not so simple. The rocks consisted in and on the earth are not of same quality, strength, bearing capacity and class. The properties of the rocks varies with many circumstances including the various environmental parameters and physiochemical activities


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Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------going in the earth. So the classification of the rock is key factor affecting the construction activities in and above it. The quality of the Rock depends upon two factors: The strength of intact rock mass and the discontinuities in it. Rock mass rating is the process of calculating the rock strength on the basis of the study of the parameters affecting it and classifying the rock into different standard rock class. Parameters for RMR 1. Intact Rock Strength: The rock is composed of large numbers of integrated pieces of rock the strength of which determines the strength of overall rock. 2. Rock quality designation(RQD): RQD is the measured volume of discontinuities which is calvculated as percentage of core drilled pieces of length greater than 10cm. 3. Spacing: The perpendicular spacing between the discontinuities affects the RMR. 4. Ground water condition: The ground water condition which may be dry, wet, dripping, seepage, flowing affects the RMR 5. Others: Other factors affecting the RMR value are • Infilling marerial • Roughness • Aperture • Length of discontinuity

Rock Mass Rating Observation Table Site A Parameter Uniaxial compressive strength RQD Spacing of Discontinuity Condition of Discontinuity • • •

Persistence Separation Roughness

•

Infilling

• •

Weathering Ground water

Value

Rating 12 3 8

Site B Parameter Uniaxial compressive strength RQD Spacing of Discontinuity

Value


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Rating

Field Report on Geology tour to Malekhu -2063. --------------------------------------------------------------------------------------------------------------------Condition of Discontinuity • • •

Persistence Separation Roughness

• • •

Infilling Weathering Ground water

9. CONCLUSION Finally as a conclusion of the three day geological tour to the Malekhu site , we realized the engineering geology has wide scope in civil engineering field and is very much important in both theoretical and practical point of view. Since Malekhu has various geological features, different types of mass movement activities like slope failure, landslides and formed with different types of rock, river morphologies and different rock formations, it has proved that it is oned of the best site for the geological studies and we were able to explore it to its maximum depth though to explore any geologically important place to totally is impossible. Now, we have knowledge to identify and cause measure about such field. We are now, able to identify different type of rocks weather sedimentary, metamorphic or igneous and different types of mass movement activities, its cause and nature, slope stability measurement for stability analysis Also, this geological tour gave the knowledge about morphology of river channel such as external appearance of river channel, their structures like Delta, Side bar or Point bar, Island, River valleys and nature of river etc. The gain knowledge of rock mass rating and determining the quality , strength and class of the rock at the site. Finally, the Geological tour to Malekhu is more fruitful and from that we achieved knowledge and process of documentation of different geological activities, geological boundaries, geological units, technique of rock mass rating etc. It is better to say that Engineering geological tour for a civil engineer is one of the most essential aspect for his skill, practical knowledge about the field and in overall career development.


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Geo Tour to Malekhu Report

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