Mir F Karim

Bangladesh is a very densely populated country and tectonically located in the active part of the Indian subcontinent. The country occupies a major part of the Bengal Basin, the largest fluvio-deltaic sedimentary system on earth, laid by the Ganges, Brahmaputra, and Meghna (GBM) river systems. The tangential tectonic forces exerting from Indian, Eurasian and Myanmar plate movements put the country under a complex state of tectonic stress and strain situation. Bangladesh needs to adopt an intelligent and rational seismic understanding and management system due to the rapid urban and industrial expansion (the Dhaka Megacity population density ≈87,000/sq mile). Several researchers made predictions of megaearthquakes based on hypothetical simulation models that are highly conjectural due to lack of sufficient geological evidence. This study comprises available geological, geophysical, geodetic, rheology, micro-seismic, structural, and geometrical datasets to differ the hypothetical catastrophic earthquake predictions from presumed megathrust, concealed under ≈15 miles thick sedimentary sequence of the Bengal Basin. Historically the Srimangal fault, located about 120 miles east of Dhaka city, generated the largest earthquake of Mw ≈7.5 in Bangladesh and no other seismogenic structures have been detected in the studied area that can generate larger earthquakes than the Srimangal Earthquake. In the present study geological, magnetic, gravitational anomaly maps and subsurface data published by the Geological Survey of Bangladesh are used in comprehending the crustal configuration and tectonic scenario of Bangladesh for determining the potential structures and active faults for an appropriate seismic hazard analysis.

DOI Number: 10.1130/abs/2022AM-381409

TECTONIC EVOLUTION OF BENGAL BASIN: A PARADIGM SHIFT OF PRESUMED BLIND MEGATHRUST AND PREDICTED GREAT EARTHQUAKES

Present geotectonic study is focused on the assessment of seismic risk and hazard in the world's youngest and most active delta formed by the Ganges-Brahmaputra-Meghna River system, a major part of the Bengal Basin, consisting of thickest pile of sediments (~25 km) in the planet. Present state of geological and geophysical knowledge points out that the northern stable shelf of Bengal Basin consists of a multi-fractured, undulated basement at shallow depth. During continental convergence, the buried crustal slope suddenly dipped down to 20 km abyssal topographic trench formed of huge grabens and horsts, crushed, pushed, and dumped remnant of transitional and thin continental crust to shape up a deep and uneven to a planer basement in the present central part of Bengal Basin. The geological, geotechnical field investigations, analysis of available seismic and deep core samples of folded belt and deltaic plains revealed the structural pattern as well as differential velocity vectors, those resulting from the dynamics of all the concealed geological processes. The analysis of Chittagong Tripura Fold Belt in the east uncovered the snapshot of the kinematics of the active deformation in the subduction front of plate boundary in the Indo-Burmese wedge. In the north-east edge of Bengal Basin, the north-south compression out of regional torque sets the folds obliquely following the trend of tectonic convergence. The asymmetric sinusoidal folding of Chittagong Tripura Fold Belt diminished in intensity due to release of compressional energy through intense deformation during the active phase of Indo-Burmese plate convergence. Results of field investigations and analysis of gravity and magnetic anomaly of Bengal Basin eliminates the possibilities of existence of oceanic crust in Bengal Foredeep, and absence of large and continuous slips in the subsurface that can release required energy for generating great earthquakes in Bengal Basin.

The assessment of frequency and magnitudes of regional seismicity in comparison to the plate motion vectors and crustal geometry revealed that the decollements are fragmented and inactive due to high angular friction and enormous gravitational load, which is not favorable for the development of any deep megathrust that can generate very high magnitude catastrophic earthquakes in the region.

Session No. 3

T34. Crustal Deformation: How and When? Linking Long-Term Landscape Signatures with Earthquakes and Seismic Hazard
Sunday, 9 October 2022: 8:00 AM-12:00 PM
507 (Colorado Convention Center)


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An engineering geological evaluation for renewable low-head hydroelectric, solar and wind energy across the Jamuna (Brahmaputra) River at Sariakandi-Pakuria Section, Bangladesh
Mir Fazlul Karima, Nazre Sobhanb, Md. Zillur Rahmanc
a GeoEastern Inc., 700, Massachusetts Ave., Boxborough, MA 01719, USA
b Independent Consultant, 7 Phyllis Frost St, Forde, ACT 2914, Australia 
c Department of Disaster Science and Management, University of Dhaka, Bangladesh
Corresponding author, Mir Fazlul Karima Email: mfkarimazad@gmail.com
ICEEST use only: Received Date here, revised date here, Accepted Date here
Keyword: renewable energy, electricity, geo-engineering, low-head hydroelectric dam, 

Abstract
The demand for electricity in Bangladesh has been projected to reach 34 gigawatts (GW) by 2030. This study identifies that Bangladesh is rich in water resources and an intelligent and operative river water management can increase power generation to meet the expected demand. Construction of multipurpose geo-structures for low-head hydroelectric power generation is identified as an alternative renewable energy sources to meet the future energy demand of the country and green infrastructure development plans. Present engineering geological and geomorphological research recognizes several locations along the Jamuna (Brahmaputra) River where enormous amount of clean energy can be harnessed by constructing multipurpose mega geo-structures. The Sariakandi-Pakuria Section of the river is considered to be one of the best and advantageous locations for such structure and a detailed study is accomplished thereby. The study includes digital remote sensing analysis of water intensity, discharge volume and temporal stability pattern of the banks for last 34 years. The slope and gradient pattern analysis along and across the river for possible design of dam, sluice gates and navigation options are done. The maximum ground elevation in the proposed area is measured to be 23 m and the lower elevation is less than 10 m while the bank-slopes vary between 3.5% and 8% with elevation difference between 15 m and 23 m. The unique geomorphology of the river will aid in constructing a multipurpose 1200 sq. km lake. A conceptual geo-structural design of the low-head hydroelectric dam is proposed and presented in this paper. Given the ground conditions, dynamicity and openness of the river course, it is also contemplated for installation of anchored multi-megawatt solar energy panels and mounting of numerous wind turbines to capture wind energy covering a large area over the common infrastructures. A thumb-rule estimation indicates that a combined low-head hydroelectric, solar and wind power generation system across the selected river section will add more than 1000 MW of electricity to the national grid of Bangladesh. A geo-engineering methodology is proposed in this paper for further studies.

Bengal basin is a classic example of an active natural laboratory because of its complex geological-setting in an active depositional environment, in multidimensional differential stress conditions, resulting from the relative motion of three tectonic plates. The earthquake risks in Bangladesh  (a greater part of Bengal Basin) are poorly predicted due to lack of relevant geological information, insufficient representative and instrumental seismic data acquisition systems.

An attempt is made here to standardize the engineering geological parameters of different geological materials of Bangladesh. For a rational seismic risk assessment, it is necessary to prepare both regional and local seismic zoning maps based on ground response analysis and engineering design parameters, the gravity, magnetic and reflection seismic data. Seismic source areas are identified from historical earthquakes (Max Recoded Mag in Bangladesh was 7.2). The ranges of Peak Ground Acceleration and Amplification Factors are compiled and correlated with different geological units. Three types of earthquake source areas are identified: a. Intra-plate source areas, b. Transitional source area and c. Inter-plate source area. The seismic behavior of these source areas is deeply related to the tectonic pattern and crustal configuration of the basin. The Basin is divided into five major geotechnical provinces: 1. Continental slope along Hinge Zone, 2. Stable shelf, 3. Deep central trough (Sylhet-Hatiya), 4. Eastern Fold Belt of Chittagong-Tripura and 5. Dauki Fault Zone.

The local ground condition and geomorphological attributes are responsible for seismic spectral responses. The geological mapped units are classified accordingly. The geological structures, geotechnical indices of respective deposits, strength and settlement characteristics are described.  This paper a will help determine seismic response spectrum and help modify and update the Building Codes accordingly.

The annual quantity of surface and ground water in Bangladesh is estimated to be about 115 Mham and 2.0 Mham respectively. 80% of the surface water flows out during monsoon and make the country over-flood. During lean period there is shortage of surface water causing draught in the northwest part of Bangladesh. For skewed water distribution, it is essential to have rational and effective water management plan. This paper presents some geological attributes that are required along with ecological and socioeconomic factors for sustainable water management. Two Holocene delta systems are identified in Bengal basin, which are designated in this paper as Old Delta and Modern Delta. The geomorphic attributes of these delta parts have typical environmental and topographic characteristics having distinct variations in the sedimentary sequences. The delta deposits are strained due to regional tectonic movement producing distinct structural features. For these geological phenomena the flow and distribution of ground water in the Bengal basin is not simple as it is analyzed before. The ground water models for different studies do not include geo-structural boundary conditions like regional folding, fault, upheavals and stratigraphic lenses of aquifers. This study identifies that geological setting influences the groundwater regimes and aquifer system of Bangladesh. The geological structures contend the size, shape, depth and extent of aquifers as it is seen along Padma Fault and Buriganga Fault where the groundwater table contours follow the boundary conditions derived from expected fault or structural discontinuity. Bangladesh occupies a major part of the Bengal basin. The basin is filled with thick sedimentary deposits to form one of the largest deltas of the world. The Ganges-Brahmaputra-Meghna river system brings not only water but also about 1-2.5 x 10 9 tons of sediments to the delta annually. The sediments consist mostly of sand, silt, clay and some gravel, which are used as construction materials. Present study reveals that the delta building process has direct relationship with the tectonics of Bengal basin and Quaternary sea level changes which led to formation of three overlapping delta lobes out of diverged river systems. The lower plains of the delta

Keynote Speech: Workshop on Earthquake Disaster Preparedness and Mitigation Organised by Identification Mission Consultants to the EU Delegation-Bangladesh February 18, 2004, Dhaka, Bangladesh

ABSTRACT
Seismic hazard assessment of an earthquake prone region involves a wide range analysis of seismological and geological data and engineering characterization of geological materials. The earthquake history of Bangladesh and surrounding region indicates that the country is seismically active. The regional geological setup of the landmass is complex due to the juncture of Himalayan Arc of northeast India and the India-Myanmar plate subduction to the east. The plain-land topography of Bangladesh musk the subsurface depositional variations and all geological structures except in the hilly region. Seismic hazard assessment is not simple for such covered complex geological environment.
This paper present the basic factors related to geology, tectonic environment and geotechnical conditions for rationale seismic hazard assessments. An attempt is made to understand the relationships among tectonic setting, structural and crustal configuration of Bengal basin to classify the earthquake source areas. Three types of earthquake sources areas are identified: a. Intra-plate source areas, b. Transitional source area and c. Inter-plate source area. The seismic behaviour of these source areas is deeply related with the tectonic structure and basement or crustal configuration of Bengal basin.
Epicenter locations of recent earthquakes in Bangladesh indicate that there are number of active faults in these source areas. The physical attributes and exact locations are not known. A detailed investigation on the geometry and mechanics of these active faults is essential to determine the relationship among geo-technical behaviour of materials, local geological constraints and ground response. An account on these relationships are presented in this paper.

STATE OF EARTHQUAKE AND TSUNAMI VULNERABILITY OF BANGLADESH: SOME GEO-SCIENTIFIC STRATEGIES FOR RISK REDUCTION

Mir Fazlul Karim1, Sirajur Rahman Khan1, AKM Kourshed Alam1 and Nasima Begum2
Geological Survey of Bangladesh, Dhaka, Bangladesh


Extended Abstract

After the Andaman-Sumatra earthquake of 26 December 2004 it has become essential to re-evaluate the regional and global seismogenic hazard maps. The devastating megathrust earthquake generated a massive tsunami causing death of millions and destruction of huge livelihood in the Indian Ocean region. The 9.0 magnitude (RS) earthquake has made unprecedented changes in the seafloor configuration, mostly along the India and Burma plate boundaries. Following the event of this extraordinary earthquake an attempt is made by the Geological Survey of Bangladesh to investigate the reasons of insignificant affects in the coastal belt and delineate the state of tsunami vulnerability of the country. The unique seafloor configuration, consisting of about 200 km continental shelf helped to deflect the massive tsunami waves that strike the continental slope after two and half hours of the main thrust. 

Geologically Bangladesh is a very young landmass having an active delta building system into the tectonic framework of Bengal basin. Due to the geographical location, pattern of geomorphic facets and an active tectonic plate interface along the eastern boundary, the country has always been prone to various natural hazards. The geodynamic adjustment due to tectonic plate movements along the interfaces of Indian and Eurasian Plates stretching from the Himalayan Mountains to Sunda Trench caused the country to be a part of a most active platelet (Bengal Platelet?).

Though the frequency of large earthquakes is low, the country and the surrounding region experienced number of great earthquakes during the last century. Most of the epicenters of these great earthquakes are located outside the territory.  The occurrence of these earthquakes and the recent Asia Earthquake of December 26, 2004 make the landmass to be exposed to most deadliest and destructive natural hazards related to regional tectonics. Fortunately the physical damages due to these tectonic hazards are very limited and insignificant in Bangladesh. But at every event tremendous panic and concern develop throughout the country causing disruption in normal activity. Similarly after the Andaman-Sumatra tsunami the nation was uncertain about the Indian Ocean situation due to lack of any seismic observatory and acceptable monitoring system. Manifold increase in population, urban clusters and rapid infrastructure development has increased the earthquake risk scenario of the country. This paper presents the state of earthquake and tsunami vulnerability of Bangladesh for identification of some geo-scientific strategies for risk reduction and disaster management.

A modified Seismic Hazard Map and a Tsunami Vulnerability Map of Bangladesh is proposed in this paper. The maps are prepared by considering all possible correlations of tectonic framework and basin configuration, geological boundary condition and ground characteristics. The country is divided into six seismic hazard zones in this map and into three tsunami vulnerable coastal belts.

Infrequent occurrence of tsunamis in the Bay of Bengal kept the geoscientists of this region almost unconcerned about the potentiality of tsunami hazard.  There are some evidences of Paleo-Tsunamis and low height tsunamis. So far evidences of devastating tsunamis are not available but threats of tsunamis in the coastal belt of the country cannot be ruled out. The 200 km long continental shelf is possibly susceptible to earthquakes and landslide / slump failures along the margins of continental slopes. These locations are extremely potential for generation of local tsunamis. Unfortunately the local tsunamis are more destructive than regional tsunamis as the time difference between the tsunami generation and arrival time at the coastal livelihood is very short.

Considering the state of tsunami vulnerability and potential seismic sources the coastal belt of Bangladesh can be divided into three Tsunami Vulnerability Coastal Belts.
1. Tsunami Vulnerability Belt - I of Chittagong-Teknaf coastline – Most vulnerable.
The intra-deltaic coastline is very close to the tectonic interface if Indian and Burmese plates. The active Andaman-Nicobar fault system is often capable to produce tsunami waves.
2. Tsunami Vulnerability Belt - II of Sundarban-Barisal coastline – Moderately vulnerable. This old deltaic belt is extremely vulnerable to local tsunamis due to presence of Swatch of No Ground.
3. Tsunami Vulnerability Belt - III of Barisal-Sandwip estuarine coastline – Low vulnerability due to presence numerous islets and shoals. 

However, for sustainable development processes of the country it is essential that a rapid seismic observatory system be developed, as it is an integral part of tsunami early warning system.  Inter-organizational and regional cooperation of the warning systems for detection of local, regional and ocean wide tsunamis is prime requisite to reduce earthquake and tsunami risk in the region. A multi-professional research activity and action plan will help in capacity building, education and awareness of the people of Bangladesh and thus an efficient disaster management system will be ensured.

Email: mfkarimazad@gmail.com

1 Director, Geological Survey of Bangladesh
2 Assistant Director, Geological Survey of Bangladesh
2005, Dhaka, Bangladesh

Summary :

The City of Dhaka occupies a unique geological location in terms of the geological set up and ground condition. Geologically the city landmass is a part of an old terrace that is raised considerably up than the surrounding floodplains. The general elevation in the axial part of the city reaches up to about 6 to 7m above mean sea level (AMSL) whereas the surrounding floodplains are at about 4m AMSL.  The ground of the terrace is composed of Madhupur Clay (Pleistocene), consisting of very stiff to hard, reddish brown, highly ferruginous, plastic Clay-Silt with some minor contents of fine quartz-sand and iron concretions. The shear strength properties are considerably high and the average value of un-drained shear strength is ≈ 2 kg/cm2. The settlement characteristics indicate that the red clay to be an over-consolidated stratum. The geological history indicates that due long run erosion about 20m of materials have been removed from the top of the city ground. This indicates that an amount of ≈ 1 kg/cm2 of vertical stress has removed from the top of the existing ground surface. At present the average thickness of Madhupur Clay in the main urban area is about 7 meters.  The upper clay-silt stratum overlies a firm sand bed, geologically known as Dupitila Formation (Upper Tertiary). The geological and geotechnical properties of Dupitila  Sand (Upper Dupitila  Sandstone) tends to behave as soft rock. This soft sedimentary rock acts as  dense bedrock to hold most of the pile tips of all deep foundation which is uniformly distributed throughout the axial part of the city.

In terms of hydro-geological environment the Madhupur Clay Formation acts a wonderful cap over the Dhaka terrain. The top material is low in permeability and no ground water recharge occurs in the city area at ambient condition. The surface materials and natural topography with unique natural drainage system the flash-flood water has excellent run-off characteristics. The permanent and confined ground water level is located below 70m from the surface. The existing geo-hydrological environment provides better options for underground excavation. 

The existence of Madhupur Clay and Dupitila Sand below the urban feet turns the ground condition of Dhaka city to the best comparing the ground condition of many other cities of the world. Though Bangladesh is located at edge of most seismically active global zone, in terms of the ground condition the apparent seismic hazard* is relatively low in Dhaka city than most of other parts of the country (expected maximum Peak Ground Acceleration is 0.5g). A correlation on Shear Wave Velocity (Vs) of the geological materials underneath Dhaka city indicates that the value of Vs would be > 350 m/sec. Considering the geological and geotechnical aspects, the city of Dhaka has advantageous ground condition for construction of underground engineering structures including underground rapid transportation system.

What 26 December 2004 Tsunami did in the Indian Ocean States? Death of about 300,000 people in the region.
Washed away peaceful livelihood.  Demolished some small Islets. And….. Created PANIC where it could not affect!!!!!! As in BANGLADESH…. What to do?
 
IT HAS BECOME ESSENTIAL TO RE-EVALUATE THE REGIONAL AND GLOBAL SEISMIC HAZARD AND DEVELOP WARNING SYSTEM.

This work proposed and designed technical options for Tsunami Early Warning System for Bangladesh. IT SHOULD BE A MULTI-HAZARD APPROACH  · Risk assessment, including tsunami inundation modeling and evacuation map development;
· Warning Guidance, including seismic and sea level monitoring, data evaluation, processing and interpretation, forecasting methods and warning dissemination;
· Mitigation and Preparedness, including education and awareness  programmes, structural and non-structural mitigation, and government policy and emergency management procedures.

Cities without the use of underground space are unthinkable in a modern urban environment. Mega-city Dhaka in Bangladesh has yet to step into the underground construction world to take advantage of its underlying unique and firm soil, the stiff-to-hard Madhupur Clay Residuum, which overlies dense-to-very dense sandstone of the Dupi Tila Sandstone Formation. Dhaka is very densely populated and continues to be among the fastest growing city in Asia. Uncontrolled growth including skyward expansion have caused tremendous overcrowding and exasperating traffic congestions. However, use of underground space is still ignored and largely unexplored. The possibility of building an underground rapid transit system will relieve many of the present urban stresses. The city was developed on an uplifted tectonic block (anticlinorium) of Plio-Pleistocene age, which is isolated from the surrounding floodplains of active Ganges-Brahmaputra delta system. The top 20 ft of ground is composed of stiff-to-hard over-consolidated clayey soil (Layer 1), that overlies thick moderately lithified sand (Layer 2, drilled to 200 ft). A 3D geological model is prepared to illustrate the spatial distribution of these stratigraphic layers. Extensive geophysical and geotechnical exploration data including hydrogeological conditions are compiled to give insights and engineering options for shallow and deep underground construction. The geotechnical and geophysical properties of the geological strata include vertical consistency, density, undrained shear strength, consolidation and settlement characteristics, and shear wave velocity. A plot of geotechnical properties with depth indicates improved ground conditions occur with the increasing depth. The 3D geological model shows that strata are homogenous and uniformly distributed. The increase of density, shear strength and shear wave velocity (>1400 ft/s below 20 ft) with depth is a strong advantage for planning of safe tunnels and underground structures.

Geologically, the Dhaka-Tongi area consists of parts of high inlier, along narrow tract of older sediments hosting the major parts of the city and surrounded by very young riverine sediments occupying the surrounding valleys. The drainage patterns of this tract consist of two types, dendritic and trellis. The older sediment sequence consists of sandstone of Dupi Tila Formation overlain by by the Madhupur Clay. The Clay is overlain by alluvium, but is locally exposed in stream valleys. The region can be divided into three types of landforms – a central high area, a complex of high and lowareas band a complex of low areas. The ground condition with respect to construction can be rated as: favourable, poor and hazardous. The techniques for ground improvement depend on the ground conditions which are intimately related to the geology (sediment type and structure) and geomorphology (landform and elevation). The type of site preparation techniques applicable during pre-construction development are variable from simple removal of the surficial soft soil followed by a sand fill and compaction to more complex techniques of using geotextile, grouting, preloading and surcharge. Taking account of above, a model is suggested which can be used to choose the appropriate ground improvement technique.

The expansion of Dhaka city is taking place rapidly. A large number of engineering projects are in progress. Consequently, there is an increase in the generation of waste. The quality, quantity and distribution of municipal and industrial wastes have been studied. The results indicates that the wastes are adversely affecting the environment,
The effect on the environment due to interaction amongst the geological aspects, existing engineering structures and waste disposal has been studied. A geoengineering model to identify environmental hazards is proposed in this paper. It reveals that a detailed geoengineering mapping and geotechnical database may help for safe urban planning and waste management.

NOTE: THIS IS AN SCANED COPY OF AUTHOR’S ORGINAL MANUSCRIPT

ABSTRACT:
Tectonically Barkal-Rangamati and Chittagong region occupies a crucial part of India-Myanmar Mobile Belt. The regional tectonics indicates that at the edge of Indian Plate subduction the Barkal-Rangamati folds suffer optimum stress from the westward push of Myanmar plate. This tectonic movement caused generation of a moderate earthquake of Magnitude 5.1 that struck the districts of Chittagong Hill Tracts and Chittagong in the early morning of July 27, 2003. The earthquakes generated numerable large landslides, ground subsidence and even small-localized jolts or micro-earthquakes in the regions. Presence of active faults like  the Subhalang-Kasalang and Barkal Thrust System causes the region to be prone to moderate earthquakes.  This paper is based on  the geological field investigation, carried out immediately after the earthquake which jolted the entire south east Bangladesh. The locations of fault scarps, landslides, ground fissures are explored in the field, measured their attitudes and mapped. The affected or partially damaged buildings are investigated for understanding of causes of failures. The Chittagong city and Rangamati Town are developed on folded and faulted terrain of Tertiary sedimentary. Due to the complex geological structures the grounds are susceptible to landslide and slope failure and needs consideration in engineering designs and construction. The young deposits of the valleys and floodplains are prone to liquefaction and many buildings in these regions are at the risk of earthquake damages. The affected engineering structures need immediate attention for repair and retrofitting as next earthquake of similar magnitude will cause severe damage to these buildings. The repetitive low magnitude earthquakes pose slow damage process (cyclic) to the building or other engineering structures. An individual geo-engineering investigation was carried out for an immediate understanding of seismic vulnerability of Kaptai Hydroelectric Power Dam site.  The Kaptai dam occupies a greater part of a syncline and forms stable basin where a firm ground condition exists and no sign of damage could be found in the dam. The dam design is consistent to the geological structure but needs engineering maintenance and geological monitoring.

The port city of Chittagong is situated at a junction of sea, hill range and plain land and subject to heavy rainfall along with a number of natural hazards like cyclones, tidal surges and flash floods.

Due to a complex geological environment it has been potentially susceptible to erosion. During the last two decades, an increase in human interference like deforestation and cutting of slope, has triggered massive erosion. The erosion, in the city area, is graded into severe, moderate and low. It has also resulted in various types of landslides in the dipping and fractured strata.
Proper management is imperative to control this erosion. A model is proposed on which a management plan may be developed.

Geologically Bangladesh is composed of young fluvio-deltaic deposits of Mio-Pleistocene age. Most of this landmass is inundated during monsoon. Due to intricate river system and flooding, innumerable bridges and drainage structures are integral component of the highways. Till seventies, bridges were normally constructed on masonry caisson foundations. Presently instead of caissons bored cast-in-situ reinforced concrete pile is widely adopted in bridge foundation because it is found cost-effective, it saves appreciable construction time and the equipment and technology is readily available.

The varied and difficult sub-soil condition and uncontrolled construction procedure frequently cause defects in piles. This paper identifies the cause of defects and suggests quality control measures for bored cast-in-situ piles.

The rapid growth of population, urbanization, communication and infrastructure development in Bangladesh has sharpened the need of understanding the geological processes that some times cause severe natural and man-made disasters. The natural landscape of Bangladesh can distinctly be portrayed as active plains of fluvial, deltaic and coastal environments, having few strips of low hills in the east and northeast. The country is prone to annual flood and other climatic hazards. The general elevation of the deltaic and coastal plain land is only 2 to 4m above mean sea level. 

There are number of large and small clusters of urban growth throughout the country, among these the capital city of Dhaka, the port cities of Chittagong and Khulna (Mongla Port), Rajshahi, Sylhet, Mymensingh, Bogra and Barisal are important. Most of the urban centers are located on naturally raised land facets. The physical growth of these urban centers is so fast that it has become difficult to maintain a systematic land-use pattern of these clusters. The geological disadvantages or advantages for economic and rational engineering design are overlooked. For this many of the newly grown areas have incurred severe damages due to flood, cyclone and tidal surges, riverbank and coastal erosions, landslides, soil collapse and foundation failures. Due to increased frequency of failures in different projects and structures, the concerned authorities are paying attention to the inherent causes of the failure or taking measures to avoid further disruptions.

After the independence of Bangladesh the development activities started so rapidly that a time lag remained between the planners and developers in interchanging the necessary geo-information and data for rational designing or formulation of the projects. In recent years, the city planners and other national organizations like the city improvement authority, the roads and high ways department and the public works department have extended hand for geological information for proper understanding of geological aspects of their projects.  Considering these, the Geological Survey of Bangladesh (GSB) has taken up a National Mapping Programme for preparation of geological maps in the scale of 1: 50,000 and engineering geological maps in the scale of 1: 20,000 of different cities and town of the country. So far the GSB has completed about 35% of country's geological mapping and engineering geological mapping of seven cities and towns, among these the urban geological maps of Dhaka and Chittagong cities are most significant achievements. These maps are yet to be published.

This paper describes the present status, prospects and types of geological or geo-environment data, maps and other information available to planners and developers. The means for optimum utilization of hard achieved geological and geotechnical data for rational utilization in the urban and infrastructure developments are proposed.

Foreword

A request was made to the Director General, Geological Survey of Bangladesh (GSB) by The Louis Berger Group, INC and Bangladesh Consulting Ltd. to provide a geological evaluation of Dhaka City for understanding of and planning of underground transportation system under Strategic Transportation Planning Project of the Government of Bangladesh. This evaluation report is prepared using geological investigation reports and technical papers available in the GSB. Emphasis is given to provide some concept on the sub-terrain environment and ground condition of Dhaka city. An interpretation on the engineering geological advantages and disadvantages for planning, designing and development of underground transportation system is done.

Summary

The City of Dhaka occupies a unique geological location in terms of the geological set up and ground condition. Geologically the city landmass is a part of an old terrace that is raised considerably up than the surrounding floodplains. The general elevation in the axial part of the city reaches up to about 6 to 7m above mean sea level (AMSL) whereas the surrounding floodplains are at about 4m AMSL.  The ground of the terrace is composed of Madhupur Clay (Pleistocene), consisting of very stiff to hard, reddish brown, highly ferruginous, plastic Clay-Silt with some minor contents of fine quartz-sand and iron concretions. The shear strength properties are considerably high and the average value of un-drained shear strength is ≈ 2 kg/cm2. The settlement characteristics indicate that the red clay to be an over-consolidated stratum. The geological history indicates that due long run erosion about 20m of materials have been removed from the top of the city ground. This indicates that an amount of ≈ 1 kg/cm2 of vertical stress has removed from the top of the existing ground surface. At present the average thickness of Madhupur Clay in the main urban area is about 7 meters.  The upper clay-silt stratum overlies a firm sand bed, geologically known as Dupitila Formation (Upper Tertiary). The geological and geotechnical properties of Dupitila  Sand (Upper Dupitila  Sandstone) tends to behave as soft rock. This soft sedimentary rock acts as  dense bedrock to hold most of the pile tips of all deep foundation which is uniformly distributed throughout the axial part of the city.

In terms of hydro-geological environment the Madhupur Clay Formation acts a wonderful cap over the Dhaka terrain. The top material is low in permeability and no ground water recharge occurs in the city area at ambient condition. The surface materials and natural topography with unique natural drainage system the flash-flood water has excellent run-off characteristics. The permanent and confined ground water level is located below 70m from the surface. The existing geo-hydrological environment provides better options for underground excavation. 

The existence of Madhupur Clay and Dupitila Sand below the urban feet turns the ground condition of Dhaka city to the best comparing the ground condition of many other cities of the world. Though Bangladesh is located at edge of most seismically active global zone, in terms of the ground condition the apparent seismic hazard* is relatively low in Dhaka city than most of other parts of the country (expected maximum Peak Ground Acceleration is 0.5g). A correlation on Shear Wave Velocity (Vs) of the geological materials underneath Dhaka city indicates that the value of Vs would be > 350 m/sec. Considering the geological and geotechnical aspects, the city of Dhaka has advantageous ground condition for construction of underground engineering structures including underground rapid transportation system.

(*Caution: The low seismic hazard does not mean lower seismic risk, as the risk is directly related to human activity and response to seismic issues.)

Seismic hazard assessment of an earthquake prone region involves a wide range analysis of seismological and geological data and engineering characterization of geological materials. The earthquake history of Bangladesh and surrounding region indicates that the country is seismically active. The regional geological setup of the landmass is complex due to the juncture of Himalayan Arc of northeast India and the India-Myanmar plate subduction to the east. The plain-land topography of Bangladesh musk the subsurface depositional variations and all geological structures except in the hilly region. Seismic hazard assessment is not simple for such covered complex geological environment.

This paper present the basic factors related to geology, tectonic environment and geotechnical conditions for rationale seismic hazard assessments. An attempt is made to understand the relationships among tectonic setting, structural and crustal configuration of Bengal basin to classify the earthquake source areas. Three types of earthquake sources areas are identified: a. Intra-plate source areas, b. Transitional source area and c. Inter-plate source area. The seismic behaviour of these source areas is deeply related with the tectonic structure and basement or crustal configuration of Bengal basin.

Epicenter locations of recent earthquakes in Bangladesh indicate that there are number of active faults in these source areas. The physical attributes and exact locations are not known. A detailed investigation on the geometry and mechanics of these active faults is essential to determine the relationship among geo-technical behaviour of materials, local geological constraints and ground response. An account on these relationships are presented in this paper.

Bangladesh is one of the densely populated country of the world. There are various type of geological hazards in this small landmass which cause serious damage to the lives and property of the country every year. The geological hazards like floods, erosion, landslides, subsidence and earthquake are discussed in this paper. It is necessary to identify the geological aspects in mitigation of these hazards for an effective land use planning and development. The possible relationship between the hazards and geological processes are delineated in this paper.

Abstract
The demand for electricity in Bangladesh has been projected to reach 34 gigawatts (GW) by 2030. This study identifies that Bangladesh is rich in water resources and an intelligent and operative river water management can increase power generation to meet the expected demand. Construction of multipurpose geo-structures for low-head hydroelectric power generation is identified as an alternative renewable energy
sources to meet the future energy demand of the country and green infrastructure development plans. Present engineering geological and geomorphological research recognizes several locations along the Jamuna (Brahmaputra) River where enormous amount of clean energy can be harnessed by constructing multipurpose mega geo-structures. The Sariakandi-Pakuria Section of the river is considered to be one of
the best and advantageous locations for such structure and a detailed study is accomplished thereby. The study includes digital remote sensing analysis of water intensity, discharge volume and temporal stability
pattern of the banks for last 34 years. The slope and gradient pattern analysis along and across the river for possible design of dam, sluice gates and navigation options are done. The maximum ground elevation in the proposed area is measured to be 23 m and the lower elevation is less than 10 m while the bank-slopes vary between 3.5% and 8% with elevation difference between 15 m and 23 m. The unique geomorphology of the
river will aid in constructing a multipurpose 1200 sq. km lake. A conceptual geo-structural design of the low-head hydroelectric dam is proposed and presented in this paper. Given the ground conditions,
dynamicity and openness of the river course, it is also contemplated for installation of anchored multimegawatt solar energy panels and mounting of numerous wind turbines to capture wind energy covering a
large area over the common infrastructures. A thumb-rule estimation indicates that a combined low-head hydroelectric, solar and wind power generation system across the selected river section will add more than
1000 MW of electricity to the national grid of Bangladesh. A geo-engineering methodology is proposed in this paper for further studies.

The seismic or earthquake risk management in Bangladesh is one of the major socio-economic concerns owing to its high population density together with tectonic setting due to complex syntaxial stress-strain and multidimensional differential deformation conditions from Indian, Tibetan and Burmese tectonic plates. This study finds the landmass to be the world’s youngest active delta building system fully controlled and trended by the regional or distal tectonic influence. The Bengal basin is divided into the northern stable shelf consisting of the multi-fractured, undulated basement at shallow depths and the buried continental slope that suddenly drops down to the twelve miles abysmal topographic trench formed of crushed remnant of oceanic crust pushed and dumped during the last and final stage of continental drift and gave the extreme shape of a deep and successively undulate to planer basement of Bengal basin. It is identified that the slowed down tectonic stress helped to accommodate the thick Tertiary folded sedimentary belt out of thrusts from the Burmese plate while the energy of the thrust suddenly reduced and helped in keeping the petroleum deposits of Bengal basin less disturbed. The gradually merging folded sediments started pushing the NE-SW trending hinge zone, tilted and raised the deeper basin deposits including Madhupur Tract. The terrain analysis portrayed a unique westward sinusoidal progression of the folds due to steady and uniform compressional stresses from the east with a convergence vector (∼N27°E). The resultant force pushed the Shillong massif in the north and sank down the Surma basin segment to preserve the petroleum rich structures. This study and analysis reveal new insights of tectonics of Bengal Basin and a compelling resolution for a safe and sustainable development of the country. A rational assessment of seismic threats are determined from the locations, depths, intensity of local, regional seismicity, differential tectonic stress conditions and possible highest energy impact. Amplification factors are predicted from the average shear wave velocity to a depth of 30 m (Vs30), which are estimated using various geophysical and geotechnical investigations and a 3D case study on site-specific earthquake hazard characterization of Dhaka Megacity presented. Present study, detailed field investigations throughout the region, seismic sources identifications and geotechnical analysis found that most of the seismic sources and crustal or clastic layers, and both lateral and vertical discontinuities are subjected to multiple segmentation. The segmentation was later facilitated by tectonic movements to weaken the giant structures and will not produce any earthquakes larger than magnitude 7.5 in Bangladesh. This state of structure gives a relief to the Bengal basin from destructive threats. It is also discovered that the seismic damping ground conditions of Bengal Basin provided us a relatively safer land to live. This finding will provide an improved understanding and considerations in the geo-engineering and structural engineering design options, construction practices, factors of safety in respective geological environment, maintenance and continuing sustainable development provided the norms of Bangladesh National Building Codes are maintained. The tectonic and structural geological analysis also postulated to identify the causes of finding petroleum and other unexplored mineral deposits in the country.