Geo-Technical Design for Bridge Crossing a River - Coursework Example

By The of the The of the School The and where it is located The Contents An overview of the site geology 3 Anticipated soil profile (geotechnical cross-section) 5 River alluvium 5 River terrace gravels 6 Till 6 Cornbrash 6 Great Oolitic limestone 6 Upper and lower estuarine series 7 The Northampton sandstones ironstone 7 Upper lias clay 7 Numerical analysis 8 SinӨ=3/4=0.75 10 FAB=320 11 Design of a representative section 11 Appreciation of the uncertainties of parameters and Recognition of how they can reduced 12 Identification of existing underground services 14 Evaluation of environmental issues and risk assessment 14 Practicality of building the chosen option 17 Geo-technical design for bridge crossing a river An overview of the site geology The project falls geographically in the lower Thames sections of the east London. Thames region has a stoneless soils structure that mainly consists of calcareous clayey soils that is hugely affected by the groundwater. The region is mostly Flat land and is thus exposed to risk of flooding. The soil contents of the region consists mainly river alluvium. The governmental assessment of the project resulted in in mainly three option possible or potential for commissioning of the project. The route connecting M2 with the A13 and M25 between junctions 29 and 30 will pass through sections such as Chafford Hundred, Greys, Tilbury, Gravesend, Istead rise or Shorne Higham areas . These areas are prone to good development and thus enhance trade in the area. The construction of other crossing sections is projected to decongest Dartford and thus create a long term solution to the current transport hurdle in the region. The success of ever option taken in design and geographical siting of the project is majorly comparable and contrasted in terms of merits and demerits of each model- highlighting on distance shortness, lower financial incurrence and decongestion level of the existent crossing. Geographical redesign and expansion of the existents crossing would create massive congestion delay and probably it would not result desirable outcome. The design of the route connecting M2 with the A13 and the M25 between junctions 29 and 30 in the river Thames demands an extensive geotechnical research and preview. The outline of the geotechnical design entails an overview of the site geology, geotechnical cross-section with an indication of the expected soil profile. In depth numerical analysis of a representative segment, highly detailed design of a representative section, appreciation and regards for the uncertainty parameters entailed, recognition and identification of the existing underground services that deals with evaluation of the ecological issues and risk valuation and assessment. The entailed practicality of building the chosen option and lastly, the Sustainability of the projected design. Fig1: route comparison of option A and C Anticipated soil profile (geotechnical cross-section) Fig2: Anticipated River Thames region soil profile River Thames Anticipated soil profile which is the geotechnical cross-section of the project basing mainly consists of layers of river alluvium, river terrace gravels, tills, Cornbrash. Great Oolite limestone, upper and lower estuarine series and upper Lias clay. The project is undertaken on the lower side of the river Thames which marks the deposition stage of the river. The river is typically mature and moves in relatively slow speed that results in depositing of the silts and other finer particles that has defined the top section of the soil profile in the area. River alluvium River alluvium is the sediments deposited a flowing river or even other groups of running water. This type of soils mainly consists of an assortment of materials that ranges from fine particles of clay and silt to huge particles mainly consisting of gravel and sand. Such deposits in most cases have traces of treasured ores called placer deposits. The deposited soil is mainly dropped by river Thames. River terrace gravels As notable from the cross-section, River terrace gravels appear on the bottom section of the river Thames valley. The gravels mainly consisted of loose small rocks that is bigger than two millimetres (mm). Standard size of gravel is normally 2mm-63 mm in terms of length. The soil profile section emanates from the active nature or erosional capability of river while at the source point. Other origins of the gravels is mainly mechanical crushing of the rocks and boulder carried by flowing water in the river. Till Till consists mainly of hard top parts in regions highland section. Historically, the land is mainly resultant of glacial erosion that the area experienced sometimes. Such sections have resisted erosion over long time thus they are exposed outside to the vagaries of nature. Stakes and rocks are visible on top section of the region. Cornbrash This is the topmost part of the Bathonian phase of the Jurassic establishment found in England. The soil section is mostly regarded as an old English agricultural term applied in Wiltshire for a group of multifaceted loose rubble soils. The soil is mainly associated with growing of corn and the name was embraced by William Smith. He christened a thin layer of shelly limestone that is notable in south portion of England. Great Oolitic limestone Between Cornbrash and upper and lower estuarine series there is a layer of Great Oolitic limestone layer. The layer has a lightly bedded and horizontally non-persistent system. The layer is typically well-cemented and exhibits a low intergranular permeability system. The layer is mostly characterised by the presence of matrix porosities and chief aquifer storage sections are normally very limited. Aquifer storage sections are normally constrained in the areas with saturated breadth of the unconstrained limestone that are notable in the higher Cotswolds. These limestone may be applied in building of the course base of the road network (Garber & Hoel, 2008, P90). Upper and lower estuarine series This is the layer notable between the Northampton sandstones ironstone and the Great Oolitic limestone. It mainly consists of the sandy mudstones, mudstones, and other soil component like the argillaceous siltstone-sandstone. The siltstone-sandstone is hugely a ferruginous type that has huge chunks of plant debris in case they are found along the river sections. The Northampton sandstones ironstone This layer falls between upper and lower estuarine series and upper lias clay.it has a hard structure framework and has been applied in building construction over a period of time. Sandstone and ironstone have been principal construction materials as many beautiful orange or brown buildings are notable in most parts of England made from it. Some areas like Oxfordshire became synonymous with fame derived from its blue or brown coloured limestone and ironstone. The same issue was notable with areas like Leicestershire and Lincolnshire. Upper lias clay This layer forms the lowest level profile layer in the project soil horizon. The Upper lias clay mainly consists of a mix of dark grey or medium fossiliferous mudstone. Some portions are normally siltstone that are laminated or even bituminous in portions. The profile has siltstone layer that presents a mudstone bed with small –grained calcareous sandstone. The structural support for civil project on top of this layer presents poor basement. Numerical analysis Equivalent accumulated 18000 lb (80km) single axle load road design analysis ESAL=fdxGrnxAADTix365xNixFEi Where ESAL=equivalent accumulated 18000 lb (80km) single axle load on an axle category i Fd=design lane factor (40%) Grn=growth factor in certain growth rate r and design period n (29.78) AADTi= first year annual average daily traffic for axle segment (16000) Ni=axle number for each side of the vehicle (1, 2, 3) FEi=load equivalency factor For passenger cars =0.00002 2 axle single unit trucks (26.7KN/axle)=0.010 3 axle single unit trucks (4.44 KN/axle) =0.088 For 2-axle single –unit trucks =0.40x29.78x45000x0.33x655x2x0.01 =1.291x106 3-axle single –unit trucks =0.40x29.78x45000x0.17x365x3x0.0877 =3.476x106 Total ESAL= (2-axle single –unit trucks) + (3-axle single –unit trucks) =5.1653x105+3.5004x106 =4.767x106 Considering the prevailing geological structure and decongestion level expected for the project Analysis period 20 years Reliability (R) High volume road (r=90%) Standard deviation (So) So=0.45 Pavement serviceability Initial serviceability index (pi=4.2 Terminal serviceability index (pt.)=2.5 Bridge truss calculations Fig3: bridge unit truss Determination of static stability 2j =m+3 J=joints M=members The bridge truss unit has 21 members and 12 joints meaning it is stable. Reaction calculation ∑y=RA+RG-200MN-200MN-200MN=0 RA+RG =600MN RA=300MN SinӨ=3/4=0.75 cosӨ=4/5=0.80 ∑y=300MN+FAI SinӨ =0 =300+FAI x0.75 =0 =FAI =300/0.75 FAI=-400MN (compression) ∑X= FAB+FAL cosӨ =0 FAB+FAL 0.80=0 FAB+-400 x 0.80=0 FAB=320 Since the members are similar in terms of angles, lengths and heights, the forces are similar to each other Members Force (MN) AB,FG 320 AI and MG 400 Design of a representative section The representation of the road section reveals a cross-sectional road area. It exhibits the profile layers of the material applied in the generation of the engineering piece or project. Fig 4: Design of a representative section According to the existing conditions in case of valleys, subcase materials will be added to lift the base levels upwards but in case of ridges underlying material will be scooped off to allow for the maintenance of the appropriate level while constructing the pavements. From fig 4, there are four main recognizable layers applied in the design and construction of the planned road. From bottom, natural formation is notable. This refers to the existing soil profile of the construction place. It will be varying according to height above the sea level and the expected level of height for the project. It can be any of the soils profile enlisted in the river Thames anticipated soil profile. On top of it is the sub-base. This region will mainly consist of small rocks and gravels (Garber & Hoel, 2008, P93). The thickness of the subbase will is expected to virtually 200mm thick in the middle but 300 mm thick on the sides as indicated. On top of the subbase there is a granular layer which majorly consists of sand. The levelling of the sand will raise the level of the road by 150 mm after machine compaction and levelling. Asphalt layer will be 150 mm thick since the road is a highway and must have standards similar to those of highways. Along the sides, there is a profile of side drain on which rainwater would be flowing. draining water is a major concern since flowing water is a major risk to travellers and can also lead to quick degeneration of the road network. Appreciation of the uncertainties of parameters and Recognition of how they can reduced Appreciation of the uncertainties of parameters emanates from recognition of various forms of uncertainties that hamper the structural design of roads, highways and bridges. In this manner, the design process of the road noted three from of failures of uncertainties that may cause havoc for the design process. The capability of the bridge has been forecasted on to about 6MN. Unexpected variations in nature might fluctuate the figure positively or negatively. While reduction of the figure might not have great impact, increase of the load might cause catastrophic damages to the bridge. Such increases might results from for case of nature like wind, storms, huge and heavy traffic jams, earthquakes and or any of the causes combined may prompt failure. Secondly, the determination of standards of strength of materials always have slight variation from the expected one. Manufactures or suppliers of the materials will intensely grilled on quality supply process since failure of the projects can emanate from any section of engineering. The strength of the metallic components for construction of the bridge truss will pass through intensive non-destructive and destructive testing to assure of extreme good quality and long lasting project. Truss analysis shall also entail well trained professional in their specified field to allow for the highest possible levels. Since mathematic calculations are always not 100 % effective use of factor of safety will be very important for the evaluation of the factor of safety of the structure Factor of safety=failure level load / actual load =Material strength/ design load From truss analysis Anticipated Material strength=12 MN Anticipated Design load =6MN =Material strength/ design load =12MN/6MN =2 The safety factor of 2 is considerably good (Garber & Hoel, 2008, P99). Normally, the safety factor of less than 1 is hugely unsafe and inconsiderable system which may prompt failure of the structural system. Application of highly skilled workers in their areas or fields of specialization will have great impact in availing the highly needed safety standards for the project. Modern quality testing and assurance systems will have great impacts in presenting the desired quality and safety standards desirable and suiting the project. Basically, the safety and quality parameter will reduced trough intensive inspections of materials, proper recruiting of workers, and proper preparation of the road cross-section and many other basic sectors of concern. Identification of existing underground services The process of identifying underground services or firms with the desirable or relevant skills in the parameter verification and risky analysis shall be advertised to the public and in international forums. The main overriding interest will be to have a strong and a road network with more than 30 years lifetime. The governmental tendering process may take an open tendering format. There other forms of tendering that include selective, negotiated, framework, serial, public procurement and single-stage or even two stage tendering process. Intensive selection process of companies will provide the best suited candidate for the implementation of the construction process. Evaluation of environmental issues and risk assessment The evaluation of environmental issues and risk assessment processes are fundamental for the entire success of the project. The project’s environmental impacts due to the road construction spatial and temporal dimensioned effects. These components have both abiotic biotic constituents and thus entails majorly the local or extensive impacts. The project would present a direct damage and loss of habitat and ecosystems that is the results of the footprint of reserve roads. There is also the impact of the spatial aspect in which there is a “road-effect zone”3 which radiates out from ever sideways of the road portions and later flows into the adjacent river channels. Such flows downstream causes the imbalance in the aquatic environments may be positioned adjacent to the road network source. The impact of the road-effect zone creates an existence of light conditions that hugely influence and disturbs soils. This condition may result in emergence of the invasive plants as opposed to the natural fauna and flora existence. The project will present a varying scenarios of cases to the ecological balance of the eco-system. This condition is due to the species habitat constituent requirements or the ecosystem distinct characteristics that are normally diverse and unrelated. River Thames has a combination of birds, mammals, amphibians and reptiles that inhabit the area. Such birds includes Charadrius hiaticula (Common ringed plover), Calidris alpina  (Dunlin), Pluvialis squatarola – (Grey plover), Limosa limosa (Black-tailed godwit) and Calidris canutus  (Red knot). These birds are mainly waders that live by looking for their food in the water by wading through. After construction of this project, less mobile wildlife types and groups or species have reduced habitats regions in comparison to wide-ranging birds or mammal. The effects on birds cannot be very lethal since bird ecological demands tend to be highly spread transversely macro-environments. In the case of the temporal dimensions there is road-related adverse effects that may occur during the construction process of the road. The construction of the road network have huge impacts on amphibian species for instance salamander that have the seasonal life-cycle cases. Amphibian species demands both terrestrial and aquatic habitats to live in their eco-system. The projected road design process will negatively affect or hamper the species, physical, habitats and chemical features at the location and thus generate disturbing landscape levels deviations (Garber & Hoel, 2008, P90). The project’s environmental impacts are notable majorly in soils, aquatic wildlife and water. Moreover, other impacts are notable on the habitat and terrestrial sectors. The aquatic wildlife adulteration or pollution by the project may result in amplified fish mortality triggered by prolonged angling pressures, management actions and poaching. The expected impacts may prompt the disruption of turtle and other amphibian relocation and migration patterns in the river Thames. There will be notable effects on animal population due to deaths by stamping in areas where roads bisect wetlands. There is a tendency of the displaced or compacted soils that frequently results from reduction in biomass productivity and there altering of such conditions create changes in the to change soil PH. There is expected reduction in plant life and population due to presence of poor water retention, reduced light levels, unexpected soil displacement, soil compaction; generation of dust and temperature variation. There is also expected reconfiguration of the land forms that would create altered hydrologic regimes. These conditions would present an altered water table location and limited or interrupted groundwater streaming into diverted superficial systems areas. The project would also result into enlarged water temperatures and subjective variation in the timing of water runoff. It may even result into the draining of the natural wetlands and creation of unintended artificial wetlands zones or even the constrained or transformed channels that prompts the outcome of the different streambed materials. Depending on the side of construction region there is a likely increase in number and extent levels of landslides and wreckages or mass flows that would highly hamper the general effects terrestrial and marine systems. There is also an expected alteration of stream flow with regards to timing and greatness of high or low flows. Presences of projects like bridges and culverts create restrictive fish passage that results in blockage of poor up-stream migration, eradicate or decrease admittance to spawning sites. Such conditions lead to fragmentation of the fish habitation patches. Maintenance of the original setting of the river is contrastingly difficult since the project would result in condensed number, depth of stream pools and size. The general results of the river impact results in moderated habitat for fish and other associated aquatic organisms. There is huge possibility of the disruption by enormous organic fragments and debris input to varying streams. This case can result in eventual variation and influence of the channel morphology and also create alteration of existent habitat. The project design also would prompt reduced bank vegetation in the areas with riparian areas and thus create highly improved erosion prompting the deposit and nutrient transfer to various streams. The project might as well result in introduction and increase of non-native fish. The staging of the road network would introduce air pollution in the area. Amplified fuels emission mainly of carbon dioxide into the ambience air shed management would highly create serious environmental backgrounds. The construction of the road network would result contaminant emission in terms of road salt, metals, oil, gasoline, other chemicals that create hazard to surrounding environment. There is expected dangers resultant from roadside vegetation from varying distances that results from alterations from original composition of the contaminated soils. Generation of the road salt may fascinates and attracts the animals that eventually results in the death of the animals as the animal creep into the pavement sections. Practicality of building the chosen option The practicality of the road design route connecting M2 with the A13 and M25 between junctions 29 and 30 is typically the best option. The project is majorly feasible in terms of cost value assessment model and repayment process. The project would reduce the long queues currently notable while crossing river Thames currently. Currently, Dartford-Thurrock crossing experiences huge delay in terms of poor strategic road network. Motorist have been experiencing huge congestion due to poor capacity issues as currently, virtually half of the motorists moving experiences delay by close to 9 minutes or even more. The congestion at the crossing point costs the English government or economy close to £15 million a year. The traffic department has anticipates an increase by close to 10-20% by 2041 in case no additional crossing is designed for the transport sector. The selection of the project A or C costs between £1.2 billion and £3.4 billion despite any option selection created. The selection of the model C may result in fulfilling of the government aspirations and other stakeholders demands in the same manner creating the expected value for money. The proposed project design is highly sustainable as it will be delivered in terms of phases. The initial phase will be assessment and eventual development for the option A and C. The provided route M2 with the A13 and M25 would create steady development of the involved areas in strategic manner. It will also create a lee-way for development of new road pavement without affecting the existing Dartford-Thurrock crossing. The proposed design highway design will highly enhance the reduction in jamming of the existent Dartford-Thurrock crossing. The option C has the ability of facilitating the conveyance of people, raw-materials, and goods, manufactured products in a speedy and effortless manner easily in the dissimilar parts of west England.  Creation of the proposed design C would result in an incremented foundation of communication in the various sectors and regions of high elevation. The design for the route M2 with the A13 and M25 would aid in expanding and growth of towns adjacent to areas of river Thames. Provision of the new route would effectively result in Transport cost or price equilibrium of commodities by increasing the mobility of the existent in the country. The location of the proposed crossing for C option is closely adjacent to the existent crossing thus it would be very helpful in releasing of the existent crossing. Fig 4: Thames map Bibliography Garber, N. J., & Hoel, L. A. (2008). Traffic And Highway Engineering. London, Cengage Learning. Read More