Design Process - Foundation Engineering - Old Exam Paper, Exams of Materials science

Download Design Process - Foundation Engineering - Old Exam Paper and more Exams Materials science in PDF only on Docsity! Page 1 of 10 CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ Semester 8 Examinations 2010/11 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: Summer 2011 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 10 Section A Q1. (a) It is critical that an engineer, when designing for the capacity of a pile, is aware of the possible presence of filled ground or clays at the location where these piles are to be installed. Explain briefly the significance of this in regard to the design process and the possible behaviour of such piles. (3 marks) (b) A structural engineer has specified that a group of 16 concrete bored piles, of 600mm nominal diameter and 31 metres in depth, is to be installed in a 4 x 4 configuration underneath an 8.9m by 8.9m pile cap. The group is designed to support a 18MN working load – a site investigation reveals the presence of a clay layer with a bulk weight  of 17.3 kN/m 3 and whose strength is found to increase with depth as shown by cu = 69 + (2.1)(z), given that z is the depth below the pile cap. Calculate the factor of safety and the efficiency factor of the pile group. (7 marks) (c) A contract has been offered in relation to the installation of bored piles of diameter 700mm and with a shaft length of 15.9m in a clay layer whose undrained shear strength at the base level of the pile is estimated to be 152 kN/m 2 and where the average shaft capacity qs ave was found to be 129 kN/m 2 . Given that a choice of either a standard pile installation process or an under-reamed installation process can be used, where the diameter of the base is extended to 1.52m, calculate the ultimate and working load for each construction option for such a pile. (Use FoS values of FOVERALL = 2, FSKIN FRICTION = 1.5, and FEND BEARING = 3, and assume skin friction coefficient  of 0.47 and Nc of 9). (7 marks) (d) A load of 1920 kN is expected to be applied to a 2.8m square footing which is to be constructed in a sandy soil at a depth of 1.9m below ground level. The results of a CPT test programme 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 and that the soil has a bulk weight  of 18.9 kN/m 3 . (8 marks) Table A1 z (m) qc ave 0.0 – 0.5 2.6 0.5 – 1.0 2.9 1.0 – 1.5 3.6 1.5 – 2.0 6.3 2.0 – 2.5 6.9 2.5 – 3.0 7.5 3.0 – 3.5 9.8 3.5 – 4.0 7.6 4.0 – 4.5 9.1 4.5 – 5.0 12.8 5.0 – 5.5 14.9 5.5 – 6.0 15.5 Page 5 of 10 Section B Q4. (a) Define in brief the three geotechnical categories GC1, GC2 and GC3 both in terms of (i) structure types and (ii) design requirements. (6 marks) (b) It is proposed to construct a landmark building in the Cork docklands. The building will be 80m by 120m in plan and 15 storeys high, over a double basement. The site is a former industrial yard where chemical processing was historically undertaken. The site is adjacent to an existing storage silo beside the River Lee. A desk study indicated gravel deposits to depths in excess of 30m. Identify an appropriate geotechnical category for the proposed landmark building, while briefly outlining the reasoning. (2 marks) (c) Design a ground investigation as per Eurocode EC7, providing a reasonable location plan and detailing the number of locations, the depth required for expected foundation type and proposed methods of investigation. (10 marks) (d) State the principles of the geotechnical design process in accordance with EC7, making using of bullet points or a flow chart to outline the process expanding on the basic elements where applicable. (7 marks) Q5. (a) Briefly state the advantages and disadvantages of the two basic soil types, cohesive and granular, in terms of their foundation properties making specific reference to (i) bearing capacity, (ii) groundwater, (iii) settlement and (iv) excavations. (10 marks) (b) Detail the foundation design review that would be adopted for a foundation within a karst landscape, youthful karst KII, making reference to the laboratory testing requirements and the possible foundation solutions. (10 marks) (c) Using the borehole log provided on Page 9 attached, use the geomechanic system for Rock Mass Rating to determine the class of the rock. The Unconfined Compressive Strength was 85MPa – clearly identify each weighting chosen, indicating the corresponding parameter obtained from the borehole log. (5 marks) Page 6 of 10 Q6. A pad foundation 5.0m square was constructed at a depth 2.0m below existing ground level. Site investigations indicated a firm CLAY to a depth of 7.0m below existing ground level. A stiff boulder Clay was encountered below the firm CLAY, with this strata being 4.0m thick. Rock was encountered below the boulder Clay. An Unconsolidated Undrained Triaxial (UUT) test was performed on the boulder Clay and the following data was recorded: Cell pressure σ3 200kPa 400kPa 600kPa Principal stress difference 222kPa 218kPa 220kPa (a) What was the undrained shear strength for the CLAY soil? (3 marks) (b) Assuming the shear strength is uniform under the pad for both the firm Clay and boulder Clay, and using the single undrained shear strength obtained above with an appropriate FOS, what is the load that can be carried by the pad? (5 marks) Site investigations indicated a firm CLAY to a depth of 7.0m below existing ground level. A stiff boulder Clay was encountered below the firm CLAY, with this strata being 4.0m thick. Rock was encountered below the boulder Clay. (c) Calculate the settlement under the pad foundation, using the influence chart provided for the loading calculated above. (15 marks) (d) Define allowable bearing capacity in relation to the two foundation requirements reviewed above. (2 marks) Page 7 of 10 Useful Formulae and Charts – Foundation Engineering Summer 2011 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)