Some Failures of the Soil Treatment Works

The foundation treatment was given to an International Company as turnkey project to treat the soil, to obtain a bearing capacity of 150KPa and a settlement not more than 50mm per year for a mixed housing development comprising of more than 500 units of mostly terrace houses and few semi-D/Detached houses. This International Company came out with the most impressive proposal, to use Dynamic Compaction in sandy area and vertical plastic drains plus 3m height fill surcharge loading for three months on the peat swamp underlaid with varying thickness of sand/marine clay (See Sketch). They claimed to have vast experience in treating such soils and the back-up of University Professor on the design.

After completion of the treatment, the settlements were found to be substantial, exceeding the predicted settlements and the rates of settlement, they requested for another three months of surcharge loading. Then they gave the green light to start building the houses, while continuing settlements monitoring. As the buildings were constructed, settlements were found to be high. By the time it was completed, this was what one of the buildings looked?

More than 100 units of the houses were pulled down after few years. Other blocks needed constant repairs. High maintenance was required for many of the houses for the rest of the life.

Why the treatment failed?

(1) Peat cannot be analysed using convention soil mechanics. Tropical Peat is not a soil, it is is more than 80%-95% water with organic matter, it contained little inorganic soils. Tropical peats are different from European peats which many had been compressed by glaciers or having more fibrous matters. Furthermore, the peat thickness varied from one location to another location resulting differential compression,

(2) the thickness of the marine soils vary from shallow at inland shore to deeper near the sea. If the link house arrangement is perpendicular to the coast, one edge will be on shallow soft soil while the other side on the thicker soil, leading to differential settlement. In fact one building block had more than 1m differential settlement! How could a structure tolerate such large difference of settlement?

(c) Consolidation theory is based on many assumptions and if these assumptions were not correct such as on homogeneity and layering thickness, then the answers would not be correct. Probably, the International Company has no experience on tropical peats/soils or they wanted to learn at the expense of others or perhaps in the first place had intention to con.

(d) the Contractor was too arrogant to admit any wrong design despite the monitoring already indicated negative results. They insisted the design was correct all the way until the building had cracked. Then they blamed the soil investigation/earthwork/ building construction were not done properly and finally they asked the client to sue them in International court at Holland. They even told the Owner that the company was left only $2. Such behaviours were shocking to us as we thought they came from advanced country, would behave in responsible way. Should they admitted incorrect design and changed the design, then many buildings could have been saved and the Client would not suffer huge loss.  The Client finally managed to obtain some compensation from professional indemnity insurance provided in the Contract but would not be able to cover all the losses. However, it could not cover the actual loss of money and time, not to mention the anger/curses/troubles created.