Element 1 – Geology for Engineers

QUETION

Geology for Engineers

Element 1 – Geology for Engineers

Q1 An excavation is required close to BH2 (Figure Q1) to construct a building with basement levels. The foundation is intended to be constructed on the sand soil layer. The groundwater level is marked on BH1 and BH3 logs as illustrated in the cross section below. The groundwater mark however is missing on BH2 log. To deliver the earthworks economically, the client has queried whether the foundation level can be reached via battering to a safe angle (without using any temporary excavation support such as sheet piles). Assume there is enough space for battered excavation and a planned exposure time of less than 6 days before foundation installation. Briefly write your advice to the client. Can the client save money, and reach the bed of foundation by battered excavation and a safe slope?

Water strike: the level at which water is first encountered
Standing water level: depth water rose to

Figure Q1 – Cross section showing the exploratory borehole logs

Q2 A construction site for a bridge over the River Orwell in Ipswich extends over an area of 200x80m, with a complete layer of drift deposits (sand with some gravel, clay and silt) on a sloped terrain, and therefore no bedrock exposure. Sixteen boreholes were excavated. A chalk rockhead (top of bedrock) was found at 5-10m depth. Boreholes are mostly positioned across lower terrains. A walk-over survey reveals a number of small valleys across the region. Available geological maps show a number of major folds – that is when a layer of rock under earth pressures has bent upwards and downwards, forming depressions and hills (Figure Q2). The geological map of the area and a cross section along the proposed bridge alignment is shown in Figure Q2. Briefly discuss the probable risk(s) that need to be taken into account in design when the data from the 16 borehole logs only are used. Underpin your answer with proper reasoning and through commenting on the landform formation mechanisms.

Figure Q2 –geological map and cross section: River Orwell crossing, Ipswich (generated by LithoFrame v2.0
Q3 The town of Bicester lies approximately 24km to the north east of Oxford and 28km to the south east of Banbury, approximately 3 km from the town centre. You are commissioned to study the ground conditions for development of the Bicester Eco-Town, which will comprise approximately 5,000 homes with supporting employment and education infrastructure. The new town will be situated on the north-western periphery of Bicester, as depicted in the OS map in Fig. Q3-1. The whole of the development site is sized appx. 350 ha and comprises Grade 3 agricultural land with a number of farmhouses and other buildings.

Figure Q3-1 – Ordnance Survey 1:25,000 map and location of the proposed new eco-town

[1] Comment on the solid and superficial geology of the east, west and middle of the project site;
[2] Comment on the strength of the topsoil layer across the project site;
[3] Comment on any possible pockets of problematic soils across the project site; briefly explain the nature of hazards (if any).
Q4 A two-storey residential building is to be constructed on a riverside plot (protected by a river wall) in South Downs, East Sussex. The ground consists of a top 0.1m dark grey spongy-like soil over 3.9m thick made ground, overlying a 5m-thick river alluvium layer (granular sand and gravel) on chalk bedrock. The alluvium layer contains a lenses of silty soils which seems to be loess. A plan view of the site and a longitudinal cross section through the site are illustrated in Figure Q4. The residential building is shown as Block H on the plan drawing. With proper reasoning, recommend a foundation solution (shallow or pile) and comment on the possible design/construction challenges.

Figure Q4 Layout of residential block H and existing defence wall and geological cross section through the site

Element 1 – Geology for Engineers

Q1   An excavation is required close to BH2 (Figure Q1) to construct a building with basement levels. The foundation is intended to be constructed on the sand soil layer. The groundwater level is marked on BH1 and BH3 logs as illustrated in the cross section below. The groundwater mark however is missing on BH2 log. To deliver the earthworks economically, the client has queried whether the foundation level can be reached via battering to a safe angle (without using any temporary excavation support such as sheet piles). Assume there is enough space for battered excavation and a planned exposure time of less than 6 days before foundation installation. Briefly write your advice to the client. Can the client save money, and reach the bed of foundation by battered excavation and a safe slope?

       Water strike: the level at which water is first encountered
          Standing water level: depth water rose to

Figure Q1 – Cross section showing the exploratory borehole logs



Q2   A construction site for a bridge over the River Orwell in Ipswich extends over an area of 200x80m, with a complete layer of drift deposits (sand with some gravel, clay and silt) on a sloped terrain, and therefore no bedrock exposure. Sixteen boreholes were excavated. A chalk rockhead (top of bedrock) was found at 5-10m depth. Boreholes are mostly positioned across lower terrains. A walk-over survey reveals a number of small valleys across the region. Available geological maps show a number of major folds – that is when a layer of rock under earth pressures has bent upwards and downwards, forming depressions and hills (Figure Q2). The geological map of the area and a cross section along the proposed bridge alignment is shown in Figure Q2. Briefly discuss the probable risk(s) that need to be taken into account in design when the data from the 16 borehole logs only are used. Underpin your answer with proper reasoning and through commenting on the landform formation mechanisms.

Project site

River crossing alignment

Figure Q2 –geological map and cross section: River Orwell crossing, Ipswich (generated by LithoFrame v2.0

Q3   The town of Bicester lies approximately 24km to the north east of Oxford and 28km to the south east of Banbury, approximately 3 km from the town centre. You are commissioned to study the ground conditions for development of the Bicester Eco-Town, which will comprise approximately 5,000 homes with supporting employment and education infrastructure. The new town will be situated on the north-western periphery of Bicester, as depicted in the OS map in Fig. Q3-1. The whole of the development site is sized appx. 350 ha and comprises Grade 3 agricultural land with a number of farmhouses and other buildings.

BH1

Figure Q3-1 – Ordnance Survey 1:25,000 map and location of the proposed new eco-town

[1] Comment on the solid and superficial geology of the east, west and middle of the project site;

[2] Comment on the strength of the topsoil layer across the project site;

[3] Comment on any possible pockets of problematic soils across the project site; briefly explain the nature of hazards (if any).

Q4   A two-storey residential building is to be constructed on a riverside plot (protected by a river wall) in South Downs, East Sussex. The ground consists of a top 0.1m dark grey spongy-like soil over 3.9m thick made ground, overlying a 5m-thick river alluvium layer (granular sand and gravel) on chalk bedrock. The alluvium layer contains a lenses of silty soils which seems to be loess. A plan view of the site and a longitudinal cross section through the site are illustrated in Figure Q4. The residential building is shown as Block H on the plan drawing. With proper reasoning, recommend a foundation solution (shallow or pile) and comment on the possible design/construction challenges.

Geological Section

Figure Q4 Layout of residential block H and existing defence wall and geological cross section through the site

Subject	Uncategorized	Pages	11	Style	APA

Answer

- Element 1 – Geology for Engineers
  
  Q.No.1
  
  Answer:
  
  We can see that the piezometric surface is above the ground for BH2. That means BH2 is potentially a flowing artesian well and the rocks surrounding it are saturated under confined pressure. Upon excavation there will be a lot of leakage from the ground. So, even though battered excavation is proposed, the site will remain an unsafe option for any long term construction. The basement rocks are saturated and the earth slippage will be more frequent even after the battering treatment. So, the client can not save money even after adoption of the above strategy and it is advised that the site should be avoided.
  
  Battering is the place the mass of a removal is slanted back to a foreordained point to guarantee soundness Battering forestalls ground breakdown by scaling the exhumed face back to a sheltered slant. All water that may amass in unearthings during the advancement of crafted by BH2 log from earth spring will be bailed, siphoned out or in any case eliminated by the temporary worker. The temporary worker will take sufficient measures for bailing as well as siphoning out water from unearthings and additionally siphoning out water from unearthings and build preoccupation channels, bunds, sumps, coffer dams and so on as might be required. Siphoning will be done legitimately from the establishments or from a sump outside the removal or some other proper strategy proposed by temporary worker ahead of time of undertaking the work.
  
  Establishment removal subterranean water table especially in sand will be made with the end goal that the pressure driven angle at the lower part of the uncovering isn’t expanded to a size that would case the establishment soils to relax because of upward progression of water. Further, balance unearthings will be made with the end goal that water powered slopes and material expulsion don’t antagonistically influence contiguous structures. Drainage powers and inclinations might be assessed by standard stream net systems. Dewatering or slice off techniques to control drainage will be utilized when essential.
  
  In the event of soil removal for pontoon establishments, the accompanying issues ought to be furthermore contemplated.
  1. Protection for the exhuming utilizing shore or sheet heaps and additionally holding framework with or without propping, secures and so on.
  2. Consideration of the extra bearing limit of the pontoon for the profundity of the dirt uncovered.
  3. Consideration of the decrease of bearing limit with regards to any upward lightness weight of water.
  The factor which may decrease soil quality are abundance water pressure in sandy soil which may cause bubbles and immerse the dirt and increment its pliancy and dryness of the dirt may lessen attachment in sandy soil and soils high in natural substance which at that point disintegrate promptly and its drawn out pressure, may cause plastic distortion (crushing or streaming), and delayed dormancy at an exhuming site. An assessment of the dirt ought to be attempted before work recommences. From this we should consider to initially eliminate the water on the layers and afterward removal continue in light of the fact that exhumed incline is sheltered when the ground is steady. That is, the incline doesn’t straighten when left for an impressive period, there is no development of material down the slant and the toe of the slant stays in a similar spot. This happen to customer to better treatment of the dirt and afterward start the establishment in any case the creation of cost more and the advantages is lesser than its perspective.
  
  Q.No.2
  
  Answer:
  
  In development the extension, the profundity of boreholes is constrained by the profundity of the dirt that is affected by bearing weight of the establishment. The prescribed borehole profundity is equivalent to one to multiple times the width of the stacked zone of 16000m3. The correct length for the site examination of the 3% of the absolute financial plan in this manner we unearth the 16 drill opening to make the underline layers and playing out the structure to help the condition necessity to improve its quality. For utilizing the 16 borehole its use must be significance on the grounds that the stream Orwell having the generally layers of alluvium store.
  
  A deficient subsurface examination may neglect to recognize risky materials which require uncommon taking care of for evacuation and removal. A temporary worker may find materials obscure to it at the assigned unearthing territory and decide they are unsafe. Since it had no earlier information on the presence of debased material, it won’t have pondered getting an extraordinary license for its removal, or the uncommon taking care of vital. Subsequently, the temporary worker’s work might be deferred while it gets endorsement of a removal site and the removal technique.
  
  There are the intertidal stored and the chalk store toward the beginning of the bedrock which are generally dissolvable in water and the scaffold are utilized to expand on the landslip of the stream or lower territory. In any case, the establishment profundity are the significant impact the heap appropriation on the soil bearing limit. A large number of the overlap happen on the subsurface which show the anticline structure on the subsurface which are powerless on tractable and break without any problem. Subsequent to considering a\ll the factor we should support the land improvement procedure to improve development plan.
  
  Q.No.3
  
  Answer:
  1. North-East Land is around 100 miles in length from east to west, and nearly 80 miles from north to south. That it is so mostly secret is because of its particular position distant from the Gulf Stream, which keeps the western shoreline of the principle island of Spitsbergen surprisingly away from icepack. Then again, North-East Land is struck by the cool Polar current which brings enormous amounts of ice from the area of Franz Josef Land. This current partitions, to pass along both the northern and the southern coasts. These components, along with practically perpetual mist, join to make North-East Land troublesome of approach, aside from late in the season or in abnormally ideal years.
  The most complete and the most fossiliferous segments of the Middle and Upper Liar are those at Bloxham, three and a half miles south-west of Banbury, and Constitution Hill, 75% of a mile west of the town.
  1. A solid soil has complex quality necessities. It needs to be a steady structure to help vegetation and a specific degree of traffic and secure the immense range of pores and gaps. And yet it needs to help development by the rancher, earthworks by soil fauna and the investigation of roots, water and gasses. It needs hearty friability. It would not like to impersonate concrete. Dirt is the upper, peripheral layer of soil, as a rule the best 5–10 inches (13–25 cm). It has the most elevated grouping of natural issue and microorganisms and is the place the greater part of the Earth’s organic soil movement happens. Dirt is made out of mineral particles, natural issue, water, and air.
  2. The dirt profiles having high ground water tables and less porous argillic skyline, disintegrated soils, sandy soils of low ripeness, beach front soils which are immersed as often as possible, and the laterites (Oxidic soils) could be considered as issue soils.
  Q.No.4
  
  Answer:
  
  Establishment is one of the vital pieces of the structure. The establishment assists with moving the absolute burdens from structure to soil, it gives solidness to structure. The profundity of the establishment is more than width having the 5 meter. Profundity of the Deep establishment is more than Shallow Foundation or more than the width of the balance. A Deep Foundation transfer on both end bearing and skin grating, with exemptions of the end-bearing heap. A Deep Foundation offers sidelong help and opposes elevate. Establishment can convey an enormous burden. The most helpful establishment for the development of the structure in alluvium store we utilized the heap establishment which greater part rely on the expense or material nature of the material.
  1. Pile Foundation
  1. Pier Foundation
  I also noticed that many of you have discussed ‘choice of suitable foundation type’. To help you tidy up your wording, I recommend flipping through following pages from the ‘Soil Mechanics’ by Graham Barnes (your Kortext read). I encourage you to sketch a cross section of ground beneath Block H and the type of foundation you recommend, showing the embedment depth (the depth at which, say your shallow foundation is going to be founded). You then can mark your sketch and refer to each feature in the text, highlighting likely challenges and solutions.
  
  Types of foundations – in graphics From ‘Soil mechanics : principles and practice ; Barnes, Graham Your Kortext book.
  
  Erosion at river bed From ‘Soil mechanics: principles and practice; Barnes, Graham Your core text book.