Immediate Settlement of Pad - Foundation Engineering - Old Exam Paper, Exams of Materials science

Download Immediate Settlement of Pad - Foundation Engineering - Old Exam Paper and more Exams Materials science in PDF only on Docsity! Page 1 of 9 CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ Semester 8 Examinations 2009/10 Module Title: Foundation Engineering Module Code: CIVL8009 School: School of Building and Civil Engineering Programme Title: Bachelor of Engineering (Honours) in Structural Engineering Programme Code: CSTRU_8_Y4 External Examiner(s): Dr. M. Richardson Mr. J. O’Mahony Internal Examiner(s): Mr. D. Cadogan Mr. G. Hayes Instructions: Answer two (2) out of three (3) questions from Section A Answer two (2) out of three (3) questions from Section B Use separate answer books for Section A and Section B Both sections carry equal marks Duration: 2 hours Sitting: Autumn 2010 Requirements for this examination: Graph paper Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt, please contact an Invigilator. Page 2 of 9 Section A QA1. (a) A square foundation is to have a load of 1925kN applied to it. With a side dimension of 2.8m, it is to be constructed in a sandy soil at a depth of 3.1m below ground level. This soil has a bulk weight  of 20.2kN/m 3 . A CPT test programme was undertaken and the average qc results for each layer are presented in Table A1 below. Calculate the immediate settlement of the pad, as well as its predicted settlement after a period of two years, assuming that the water table is well below the level of the foundation base. (10 marks) Table A1 (b) Describe the significance of the efficiency  in relation to a pile group, and explain why the efficiency varies with the density of sandy soil in the case of driven piles. (3 marks) (c) 24 concrete bored piles are to be installed as a group in a 6 x 4 configuration beneath a 11.9m by 10.1m pile cap. Each pile is designed to be of a 610mm diameter and 28.7 metres in length, with the pile group expected to support a 30.2MN working load. A clay layer with a bulk weight  of 16.7kN/m 3 is present, where the strength increases with depth according to the relationship cu = 69 + 2.6z, where z is the depth below the pile cap (in metres). Calculate the factor of safety of the pile group, as well as the efficiency factor. (8 marks) (d) In relation to the reaction of clayey and silty soils under load beneath a foundation, explain the differences between undrained and drained conditions and outline the effect of any variation in the permeability values for such a soil. (4 marks) z (m) qc ave 0.0 – 0.5 2.3 0.5 – 1.0 2.9 1.0 – 1.5 4.1 1.5 – 2.0 6.2 2.0 – 2.5 6.7 2.5 – 3.0 8.3 3.0 – 3.5 10.2 3.5 – 4.0 7.9 4.0 – 4.5 8.5 4.5 – 5.0 11.7 5.0 – 5.5 14.3 5.5 – 6.0 13.8 Page 5 of 9 Section B QB1. (a) Briefly state the two principle requirements of foundation design. (2 marks) (b) A rectangular footing 10m wide and 40m long was constructed at a depth 3m below the existing ground level. The loading on the foundation was 75kN/m 2 . The ground conditions below the foundation were such that a sandy CLAY was identified to a depth 10m below the foundation, having an undrained elastic modulus E1 of 15MN/m 2 . Below this, a layer of sandy gravelly CLAY with a modulus E2 of 40MN/m 2 was encountered and found to be 15m thick. Calculate the settlement of the foundation using the appropriate design charts provided. (14 marks) (c) Detail the advantages and disadvantages of both shallow and deep (> 6.0m) foundation construction within granular soils, making reference to foundation type and groundwater. (9 marks) QB2. (a) A 5-storey apartment complex, with two basement levels, is to be constructed on a site in an urban environment. The site had previously been used for warehousing. The adjacent buildings, two-storey office blocks with existing basement parking, were recently constructed using a buoyant raft with tension anchors and the ground conditions have been characterised in detail. Bedrock was proved to be 18m deep. Both piling and a buoyant raft foundation are being reviewed. Define an appropriate preliminary Geotechnical Category for the proposed works, outlining in detail your reasoning – make direct reference to the possible effects on the adjacent building. (5 marks) (b) In accordance with EC7 (Geotechnical Design – Part 2), detail a proposal for a ground investigation for the proposed building 40m by 60m plan area making use of a diagram, outlining the following:  zone of influence of the structure  number of exploratory locations  type of investigation techniques  depths of the proposed investigation locations (12 marks) (c) State the principles of the geotechnical design process in accordance with EC7, making use of bullet points or flow chart to outline the process expanding on the basic elements where applicable. (8 marks) Page 6 of 9 QB3. (a) Define the following terms:  allowable bearing pressure (2 marks)  ultimate bearing pressure (2 marks) (b) A square pad of dimensions 1.5m by 1.5m was constructed 3m deep in a stiff CLAY. The unit weight of the CLAY was 20kN/m 2 . An unconsolidated undrained triaxial UU test was undertaken, whereby the following data was obtained:  isotropic cell pressures of 200kPa, 400kPa and 600kPa were applied  failure at 380kPa, 580kPa and 780kPa, respectively  porewater pressures at failure of 255kPa, 455kPa and 655kPa were measured Sketch the Mohr’s Circle for the above triaxial data in terms of both total and effective stress, clearly defining the axes and stating the undrained shear strength of the CLAY being tested. (4 marks) Were the specimen to be consolidated (CU), what additional design parameters would be obtained? (2 marks) Based on the above information, and defining a suitable factor of safety, what load can be carried by the foundation? Outline the reasons for your choice. (3 marks) Making use of Skempton’s Nc design chart, what load can the pad carry? (12 marks) Page 7 of 9 Useful Formulae and Charts – Foundation Engineering Autumn 2010 1. CN = 0.77 log (2000/σv) 8. si = C1 x C2 x qn ∑([ Iz / E ] x Δz) 2. CR = 1 at depths > 10m 9. E = qc x 2.5 for square foundation = 0.95 at 6-10m = 0.85 at 4-6m 10. Iz = [0.5] + [0.1 x √(qn / σv'ave)] = 0.75 at <4m 3. qs = ∑  cu 11. C1 = [1] - [0.5][( σ'base / qn)], C2 = 1 + 0.2 log (10 t) 4. qsav =  cu 12. Nc = 5.14 x [1 + 0.2( B /L)] x [1 + (0.053 x [ D /B]) 0.5 ] 5.  = [(0.5) / (cu/v) 0.5 )] 13. i = (1 – α/) 2 6. Ic = (1.71 / N 1.4 ) 14. ic = iq = (1 – α/90°) 2 7. si = q’ x B 0.7 x Ic 15. qf = (½ B' ' N s i) + (c Nc sc ic) + (' D Nq sq iq)