TECHNICAL TALK -PROBLEM STATEMENT (PUNCHING SHEAR AT BC)

1. Problem Statement (Notification of Defect)

Failure (punching shear) has happened at bottom slab of BC. BC detail as below

a. General

L = 58.65 m

W = 4.3 m

H = 2.4 m

Catchment area - 13 ha

Q from catchment 4.85 m3/s and 5.36 m3/s 50 and 100 years ARI respectively

Max Q for BC - 21.7 m3/s

Thickness of wall and slab - 400mm (Concrete G20, reinforcement T20 main bar at top and Bottom

Concrete cover 50mm accept soffit 75mm.

b. Foundation


Pile bedding (200mm x 200mm RC pile)

Horizontal 1.5 m interval , tranverse 1.7 m interval

Nos of Piles - 108 no ( 3 rows)

Pile Drive to set , 12m length at N50, 2 nos 6m pile (for info 300mmx300mm RC pile and above have 12 m length)

c. Geotechnical

N value range 0-12 at 12 meter depth. Hard stratum at 12 m depth (N50). Max allowable strucral capacity of pile was 450 KN. (PDA test carried out got 900KN).

High of embankment 6.4 m, equal to 122 Kn/m2

Traffic lLoad - 20 KN/m2

2. Solution

From BC change to 2.4 mm dia. RCP (Remove failure BC)

Foundation increase from 400mm to 600mm with craddle (total hight - 1.2 m), width of foundation 4.1 m.

Piling use 200mm x 200mm RC pile 6 m length and drive up to 12 m length - 1.42 interval for tranverse, 1 m interval horizontal.

Reinforcement at bottom slab 4 layer BRC B10 (2top +2bottom)

C0ncrete G20/20 for all
Lean Concrete GH15/20