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Civil Engineering/basement waterproofing

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Expert: - 12/23/2008


Question

basement
One basement 10 meters beneath the ground level is being done. The raft thickness is .75 meters . The water table is high . The water has come up and flooded the place . In spite of kota stone box waterproofing being done beneath the raft. one fourth of casting has been done and work is at halt. we think to do crystalline waterproofing , but let me know how design of tor and thickness to be checked for the negative water pressure.

Answer
Hi Swadheen,

This problem has arisen possibly because proper de-watering system was not installed? Also, I would caution you about the stability of the open excavation side at the back of the picture.

In any case, the design for up-lift is very simple. If the depth of the watertable at bottom of raft is 10m, then the uplift is about 100 kN/m2. Deduct from that the self weight of the raft, which is 0.75x24= 18 kN/m2. So you need to design the raft as an upside-down  flat-slab, with columns and walls acting as supports, and then reinforce the raft accordingly. Of course you will also have the load case of gravity/wind loading, without uplift of water (maybe in the dry season), which will give you different stresses. So you need to design for the envelope load cases.

Arshad Khan

Expertise

I can answer any questions to do with civil and structural engineering consultancy and construction industry in East Africa and the Middle East, and specifically with the analysis and design of reinforced concrete structures. My particular expertise is in the aseismic design and optimisation of tall buildings.

Experience

Employment history: 36 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Zambia, Austria, Bahrain, Kuwait, Doha and the U.A.E.

Organizations
.Fellow of Institution of Structural Engineers (UK) .Fellow of Institution of Civil Engineers(UK) .Member of the Institution of Engineers, Kenya .Registered Engineer, ERB, Kenya .Member of the Architectural Association of Kenya (Engineers Chapter) .Chartered Engineer (UK)

Publications
•1984: International Conference on the Art and Practice of Structural Design, London •1994: 3rd Int. Kerensky Conference in Structural Engineering, Singapore •2008: International Conference on High-Rise Towers, Abu Dhabi

Education/Credentials
BSc, 1st Class Hons, in Building Engineering, University of Bath, UK MSc in Concrete Structures and Technology, University of London. Diploma of Imperial College, UK.

Awards and Honors
•Science Congress Special Award (for 2-seater Hovercraft - 1968) •Institution of Civil Engineers Award for outstanding performance at Bath University (1975) •Concrete Society Postgraduate study Bursary Award (1976) •Consular Representative for British High Commission, Nairobi. (1995 to 1998) •Examiner for Institution of Civil Engineers Professional Interviews, Nairobi. (1997 to 1998) •Branch Representative in Vienna for PI assessment for Inst. of Struct. Engrs. (1999 to date)

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