SYNOPSIS

The intention of a transition embankment is to provide a smooth riding quality from that part of the road that is subject to long term settlement and the pile embankment leading up to the bridge or the bridge abutment. Abrupt change in settlement is also a safety hazard.

Going back 40 years, closely spaced bakau piles groups of different lengths, though imperfect were nonetheless fairly successfully used for transition embankment. Bakau piles have since been banned from use for environmental protection reasons. Transition embankments subsequently took various forms including reinforced concrete piles in groups of different lengths and at wider spacings (than bakau piles), stone columns, etc together with hinged slabs, or geosynthetics. Much of present approaches have not performed as well.

The following will be presented in this lecture:

(i) Difficulties in estimating consolidation settlement to the accuracy required for a transition design;
(ii) Difficulties in accurately estimating pile group settlement more so when fill has penetrated significantly into the soft clays;
(iii) Difficulties with estimating long term settlements of stone columns ;
(iv) Controlling weight of embankment instead of attempting to improve the soft soils offers the best approach that is also easiest to design;
(v) Methods for reducing the differential settlement in the event of failed transition design.

The lecture will also show, by case histories and numerical analyses the lesser known problem of lateral movements of the soft clay at the end of the pile
embankment affecting the adjacent piles; these effects are not reduced by increasing the extent of the pile embankments.

Specifications for design of a transition has to be realistic. The lecture will draw attention to the absurdity of present criteria commonly adopted by authorities.


BIODATA OF SPEAKER

Ir. Dr Toh Cheng Teik

Ir. Dr C.T Toh is currently a Director at Dr. Toh Associates Sdn Bhd. He has been practicing geotechnical engineering for 46 years. He graduated from Monash University in 1974 with the degree Bachelor of Civil Engineering and was subsequently awarded a Doctorate from the same university in
1979.

His experience covers foundations, soil treatment, slope stabilization, basement construction etc. in alluvial and marine deposits, peat, residual soils and rocks.

He authored the LLM Report on Trial Embankments in Muar in 1989 and was a major contributor to the CIDB Guidelines for construction of peat and Organic soils in 2015. Recently he co-authored with his colleagues several papers on a data based approach to design of bored piles; the data from more than 100 instrumented test piles.