Geolog ical Study Of Malekh u Area, Central Nepal
A Field Report.
Submitted To:
Submitted By: Group: B-f
Department of Civil Engineering, Kathmandu Engineering College, Kalimati
Rakesh Kr Yadav (069-BCE-080)
Table Of Contents: S No. 1. Acknowledgement.
Title
Page No. 2
2. 3. 4. 5. 6. 7. 8. 9. 9 10.
Introduction. Location of study area. Objectives Methodology Study of rocks and minerals Major rocks types of field area. Observations Geological Structures. Engineering Significance of the Geological Structures. Conclusion
3 3 6 7 8 10 14 18 22 25
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List Of Figures
Lime stone (Page No. 14) Psammitic Schist (Page No. 14) Marble (Page No. 15) Granite (Page No. 16) Phyllite (Page No. 16) Amphbolite (Page No. 17) Slate (Page No. 17)
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ACKNOWLEDGEMENT The geological field knowledge and field visit is very important especially for a civil engineer. The main work of a civil engineer is to study the feasibility of the construction and stability of structures in different types of land feature including rock, their slope, riverside and clayey portions. Literature alone cannot assist in producing any satisfactory results. Therefore a thorough knowledge of actual field visit counts for its credit. As the geology deals with rocks and stones along with their origin including types of soil, strike, dip-direction and other geological discontinuities such as faults, folds, joints, landslides, use of topography map for proper location of site and other activities. It is therefore very essential to make a field visit. From the field visit we came to know much about structural geology including the above mentioned features. For the basic knowledge of field work of structural geology the two days from 19th of Poush to 20th of Poush we were taken to Malekhu for geological excursion. This performance was very effective for the partial fulfillment of knowledge and experience. However the two days of tour was not sufficient to fulfill the requirement. We are very grateful to the teachers who helped us during the field trip and taught many important things within the limited time period.
INTRODUTION The geological field visit to Malekhu was organized by the Department of Civil Engineering under Kathmandu Engineering College, in order to accustom knowledge about the geological structures, their engineering significance and distribution of different rocks, soil types and study of mass movement activities. The time duration being two days from 3rd to 4th January 2014 was spend in geological field study in Malekhu, 75 Km. west from Kathmandu. Engineering geology is defined as the branch of geology which deals with the application of geological knowledge in the field of civil engineering for the construction of infrastructure such as roads, bridges, dam, tunnel etc. Engineering geology is defined in the statues of IAEG as the science devoted to investigation, study and solution of different types of engineering and environmental problem which arises as the result of interaction between the geology and the work or activities of man, as well as the prediction and development of measures for prevention remediation of geological hazards.
LOCATION OF STUDY AREA The study site lies on the Malekhu river banks, which extends from its confluence to the Trishuli River to about 2.5 Km. upstream. The Site itself is called Malekhu which lies on 71 Km. towards south-west along the Prithivi Highway, in Dhading district, Central Nepal. Malekhu lies on lesser Himalayan unit of Nepal. It has peculiar geological features within a small range of area. The Malekhu V.D.C. is located at latitude of 27°50'38'' to 27°45'50'' and longitude of 24°49'5'' to 84°50' 50’’. It is situated on the bank of Trishuli and Malekhu river. The Trishuli river is running from the eastern direction to the western diredtion and the
Malekhu river from south to north which mingles into the Trishuli river. Also, the Malekhu river has a tributary namely the Apakhola which meets the Malekhu river at a distance about 3 kms from the Malekhu bazar. Climatically Malekhu is a sub-tropical zone. Mainly the rainfall is during the monsoon. The site was selected due to availability of different rocks, the river morphology, natural topography in small extent of area and different types of mass movement along the route. The study site is easily accessible from the Kathmandu valley, a three hours bus travel along the Prithivi Highway from Thankot can easily take us to site. The study trip was facilitated by logging and fooding at the Malekhu chowk.
1.1 Importance of engineering geology in the field of civil engineering Geology in civil engineering concerned with the engineering behavior of earth materials. It includes investigating existing subsurface conditions and materials; assessing risks posed by site conditions; designing earthworks and structure foundations; and monitoring site conditions, earthwork and foundation construction. A typical Geo-technical engineering project begins with a site investigation of soil, rock, fault distribution and bedrock properties on and below an area of interest to determine their engineering properties including how they will interact with, on or in a proposed construction. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place. Investigations can include the assessment of the risk to humans, property and the environment from
natural hazards such as earthquakes, landslides, sinkholes, soil liquefaction, debris flows and rock falls. 1.2. Geological and Mechanical Principles
Geological time Rock forming minerals Rock types, Soil Types Mechanical fundamentals for Engineering Geology Soil and rock properties
1.3 Geological Structure Analysis
Geological structures (faults, folds) Discontinuities Hemispherical projection (basics and borehole analysis)
1.4 Applied Engineering Geology
Landslides classification for slopes in rock and soil Mass movement in rock Mass movement in soil Excavation Principles in Rock and Soil
1.5 Engineering Geology in Practice
Site characterization and investigation techniques Case histories and examples
Objective: The main objective of the geological field trip was to learn the basic geotechnical skills in civil engineering regarding river morphology, site investigation, landslide and petrology. The study aimed at learning general tactics regarding identification of rocks determining their major chemical contents, determining the various geotechnical parameters such as attitude of rock bedding and the observation of various physical features regarding river channel morphology and landslides. The main objectives of our field visit were: Identification of different rock types Identification of different minerals Identification of different primary secondary structures Identification of different secondary secondary structures Measurement of dip and strike Study of bedding foliation Handling of compass for documentation of Engineering geological data Study of landslides Study of morphology of river channel Identification of geological units of the Lesser Himalaya and Kathmandu Nappe Engineering geological studies along the large scale geological discontinuity (The Mahabharat Thrust) Study of the rock slope along the road corridor To know the rock mapping techniques of the rock outcrops
METHODOLOGY The common methods used in the geological excursion were the site selection and the field observations. Different places suitable for the geological study was selected and their location was determined by the map and the observation related to such structures were taken and copied such as physical appearances, orientation, geological structures. Photographs were taken at many sites. In some, sketches were also plotted to assist the better understanding. In still some cases graphs were also plotted like in rock outcropt observation. The geological field study of the ascertained area was carried out in the following ways:
Field reconnaissance and geological traverse of the study site. Sketch of the field topography and rocks. Photographs of the field topography and rocks. Description of the field topography and rocks.
2. Study Of Rocks And Minerals Rock Identification Rock is a relatively hard, naturally occurring mineral material. It consists of a single mineral or of several minerals that are either tightly compacted or held together by a cement like mineral matrix. 2.1 Types of rock The three main types of rock are Igneous, Sedimentary, and Metamorphic. 2.1.1 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- generally equigranular texture, light colour appearance Gabbro- coarse grain and dark colour Dolerite- containing dark minerals in good proportion with medium grain sized
2.1.2 Metamorphic Rock These are formed by alteration of alignment, texture, structure, chemical composition etc. in pre-existing 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- slate cleavage Phyllite- soapy feeling Schist- rough, irregular and undulated plane, unequal growth of minerals Gneiss- band of contrast colour, composition and texture (mica band) 2.1.3 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- grain size greater than 2 mm Sandstone- grain size is equal to sand (i.e. 1/16 mm –2 mm), quartz is common Clay stone- formed by deposition of clay, shale is common example
2.2 Major Rock Types of the Field Study Area Following are the different types of rock that we found during our study in malekhu area. 2.2.1 Metamorphic rocks 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 typical 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. Amphibolite: Amphibolite is a grouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. It is typically dark-colored and heavy, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. 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 intersaturated 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. 2.2.2 Sedimentary Rocks Limestone: 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. Dolomite: Dolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate found in crystals. Dolomite rock (also dolostone) is composed predominantly of the mineral dolomite. Limestone that is partially replaced by dolomite is referred to as dolomitic limestone, or in old U.S. geologic literature as magnesian limestone. Dolomite was first described in 1791 as the rock by the French naturalist and geologist, Déodat Gratet de Dolomieu (1750–1801) for exposures in what are now known as the Dolomite Alps of northern Italy. The mineral dolomite crystallizes in the trigonalrhombohedral system. It forms white, gray to pink, commonly curved crystals, although it is usually massive. It has physical properties similar to those of the mineral calcite, but does not rapidly dissolve or effervesce (fizz) in dilute hydrochloric acid unless it is scratched or in powdered form. 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. 2.2.3 Igneous Rocks 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".
Observations: Location 1. The rock was located on the left bank of the river. It was situated near the broken bridge and 200m downstream from the bridge. The rock was found to be of yellowish color. When the fresh surface of the rock was treated with HCL it produced white fumes. Hence the rock was concluded to be limestone The attitude of the rock was found to be S 5º W/ 86 º SE
Location 2. The rock was situated at the left bank of the river about 400m away from Mawatar Gaun.Two types of rocks were found in the location i.e Psammitic Schist and Pellitic Schist. Psammitic Schist: The weathered color of rock was found to be grayish black. The fresh color of the rock was found to be white. The rock was hard and produced metallic sound when hammered. The rock was non crystalline and produced metallic sound when hammered. The deposition of quartz was seen. Therefore, the rock was concluded as Psammatic schist. The attitude of the rock was found to be S 25 º W/ 89 º SE
Pellitic Schist: The weathered color of rock was found to be whitish grey. This rock was comparatively softer than Psammatic schist and didn’t produce any metallic sound when hammered. There was maximum concentration of mud and clay.There was no reaction with 10% HCL. The attitude of the rock was S 75º W/ 82º SE
Location 3 It was located to the left bank of the river opposite to the tar. The color of the rock observer here was milky white and crystalline in form. It readily reacted with 10% HCL so it was concluded to be a calcite rock. As crystalline structures were also observed and other properties being similar to that of lime stone, the rock was concluded to be Marble. The attitude of the rock was S 25º W/ 84º SE
Location 4 It was also situated to left bank of the river. We observed folds in this region. Basically Ptygmatic fold and Boudinage. Folds were formed to the compression and tension. Folds formed due to compression are known as ptygmatic fold and the folds formed due to tension are known as Boudinage.
Location 5 It was located on the right bank of the river and by the side of the motor way. In this place we observed the igneous rock and the type of the rock was granite which is a plutonic/intrusive rock which were originally from Agra area. It was composed of white and black minerals with majority of minerals white. It was characterized due to the presence of xenolith which is relatively older than the surrounding rock. The rock constitute of the following minerals:
Quartz Feldspar Mica: Biotite & Moscobite Tourmaline Location 6 The rock was located on the right bank of the river and 1000m downstream of location 5. The weathered color of the rock was yellowish and the fresh color of the rock was greenish grey. It was weak and had soapy touch. The rock reacted with 10% HCL. The surface was typically lustrous and wrinkled. It was concluded as phyllite.
Location 7: The
rock was located on the left bank of the Malekhu river. The weathered color of the rock was blackish and the weathered color of the rock was greenish. The rock didn’t react with 10% HCL both in fresh as well as crystalline form. The smelt like gun powder when hammered and was mainly composed of Amphibole mineral.
The attitude of the rock was S 5º W/ 85º SE Thus the rock was concluded to be Amphibolite.
Location 8. The black colored, hard,-light weighted rock was observed. The weathered color of the rock was found to be gray and the fresh color of the rock was found to be black colored. The graphite content was maximum In the rock. It had sharp edges. It was light weighted and specially used in roofing in the house. The altltude of the rock was found to be N 75 E/81 SE. Therefore, the rock was concluded as Slate.
3. GEOLOGICAL STRUCTURES 3.1 Mahabharat Thrust (MT) The Mahabharat thrust lies in the south of the main central thrust and towards the north of the main boundary thrust. It separates Nuwakot complex and Kathmandu complex. 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.
RECOGNITIONS OF THE GEOLOGICALSTRUCTURES 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 rocks and 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: 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 up warping 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 FAULT Faults are well- defined cracks along which the rock- masses on either side have relative displacement along the fracture plane. The attitude of faults is defined in terms of their strike and dip. The strike and dip of a fault are measured in the same way as they are defined in terms of their strike and dip .The strike and dip of fault are measured in the same way
as they are for bedding. RECOGNITION OF FAULT IN THE FIELD To recognize the faults in the field, a number of criteria are used. The faults may be directly seen in the field, particularly in artificial express such as river-cuttings, road Cuttings, etc. But is majority of cases, faults are recognized by stratigraphic and physiographic evidences as:
Discontinuity of structures Repetition or omission of strata Solidification and mineralization Presence of features characteristic of fault-planes (slickenside, gouge, fault breccia)
3.4 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 during which the normal process of deposition was interrupted. It is a structural feature in the sense that rock formations lying above and below it generally represent different conditions under which they have been formed. RECOGNITION OF UNCONFORMITY IN THE FIELD 1. 2. 3. 4. 5.
Visual inspection of the angular relation between the sequences. Presence of Basal Conglomerate. Availability of the residual soil within the sequence of rocks. Exposure of the erosion surface. Contrasting behavior of the rocks from a particular surface.
6. Variation or gap in the geological age of the rocks of the sequence
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. Veins: 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 TrishuliThopal 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. 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.
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 engineering 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. Unconformity Source of surprises or considerable errors in qualitative as well quantitative judgment of the site. Variation in the stability of the rock sequences adjacent to the unconformity surface Unconformities are the weak contacts which may interrupt 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
Thrust Since it is a type of fault it has the same significance as described in the fault.
CONCLUSION Finally as a conclusion of the two days 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 one 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. In short this visit gave us lots of ideas regarding engineering works and geology. We also gained knowledge to analyze the engineering significance of various landforms. So the visit was fruitful.
