Flat Slab Structural System 

Although this structural system is very established for reinforced concrete system, there are very few buildings in Sarawak adopting this system. The main reason is the traditional belief of using beam-slab system being the safest, easier to design and better feng-sui. Of course, more materials, such as concrete and reinforcements, are required for the flat slab system which also discourage the engineers/owners to use the system. The layout and shape of the building will also determine the feasibility of using the system, for example, squarish and rectangular shapes favour such structural system.

This 10 storey L-shaped  Building in Bintulu with one basement, was one of the very first building to adopt flat slab system. 

It also took a lot of efforts to convince the Owner of using the system with the following advantages:

(a) Easier and faster to build
There would be less formwork and easier to lay steel reinforcements. While beam slab system would require one month to build each floor at that time, the flat slab system would require only two weeks.

(b) Easier to instal Mechanical and Electrical services
Without beams protrusion, M & E services could be laid easily.

(c) Offset cost and save time
The higher cost of more materials would be off-set by saving labour works, waiting time and overheads. Furthermore, shorter construction time will be required means faster economic return.

(d) Can build additional floor
Most building height is restricted by town planner in a particular area. Floor to floor height is also determined by the clear height requirement of the building by-law. Flat slab system reduces the space for structural system, enabling saving of 300mm space for each floor. Thus for 10 storeys, about 3m height of space could be saved and additional floor could be provided with the approval of the local authorities.

The Owner was at first sceptical and he approved only the lower four commercial floors for flat slab system while the upper floors to maintain the beam-slab system.

However, after constructing two floors, he found the speed of construction, safe indeed, cost off-set and other advantages, he requested to change all upper floors to flat slab system!

Later, the upper floors were changed from apartments to hotel with swimming pool. Such changes resulted some additional steel plate reinforcements on the flat slab which were also quite easy to construct.

The building has been there for twenty-seven years and proves that flat slab system can be a good alternative structural system.

Failed Drainage System

We always blamed Nature's exceptional high rainfall or God's action for the flood, so that no human would be blamed!

We ignored the deforestation and developments which cleared the vegetation allowing tons of soil washed into the rivers by the rain water and deposited in the rivers resulting insufficient capacities to discharge into the sea. 
We ignored our lousy habits of throwing rubbish into the drain and rivers, hampering the flow of water. 
We intruded into the water retention lands or river banks  for development resulting insufficient space for waters to store temporarily during heavy rainfall. We blocked the rivers in the name of water regulation, sea water intrusion, bridge crossings and highways in the name of providing better living conditions for humans. 
We warm up the air through indiscriminate burning, car usage  and industrial pollution, which resulted climate change and abnormal rainfall.

So, who are the culprits, Nature, God or Humans?

Failed Roadway Slope

The height of this excavated hill slope is more than 15m. There were two benches with cut off drains. Average slope was about 1: 1.5, which was quite a standard design for cut slope. Typical soil profile is shallow firm to hard residual soils at the top and sedimentary rocks (Hard black Shale) at the bottom. Why the slope failed?

The answer is the exposure of the underlying very finely laminated black Shale to the rain after excavation plus the dipping direction of the bedrock, towards the road.
The laminated Shale at this site is very thin, some as thin as paper, which allowed easy entry of water along the laminated surfaces to the whole rock, the Exposed Shale rock crumpled to fragments and small particles, slipped along the dipping planes which happened to be towards the road. Just look carefully on the failed rock conditions, you will see how these thinly bedded Shale rocks disintegrated.  
Can we detect the problematic Shale during soil investigation? Yes, rock coring requires water and if you find substantial core loss or crumbled samples, then the rock has potential problem. Dipping plane can also be detected if there are at least two boreholes across the proposed slope. Design engineers should inspect the rock samples to have a visual and feel of the soil and rock conditions.
With this kind of rock, gentler slope has to be provided and has to reduce exposure of rock to the rain/water immediately. Construction is recommended during dry season.

Deep River Bank Failure

This section of the Batang Layar is more than 1km wide and the slope is gentle with an average slope of 1:7 to 1:9. The underlying soils are predominantly river and marine deposits about 40m thickness. The clay/silt soils are very soft at top to firm/stiff at he bottom. The sensitivity is high with about 4 to 6. A wharf was supposed to be built next to this part of the river bank.

Slope Analysis using Modified Bishop Method indicated the stability was about 1.2 to 1.3. This is generally the safety of straight natural formed large river bank after years of flood, deposition, erosion, failure and stabilisation.
Thus any construction or additional filling up of river bank have to be done carefully and slowly, which has to be specified clearly. In particular, the piling method which creates vibration and may cause loss of soil strength. The filling up of the river bank have to be done in stages.

Then the slope next door failed during construction of the wharf. An excavator was seen sinking into the ground. The affected semi-circular failed zone is more than 50m and deep into the river. Why it failed?

ANSWER: Another Contractor used the river bank as his sand stockyard for another project. I requested the RE to warn him not to store the materials near the river bank and he retorted back that the land was outside our wharf project and asked us to mind our own business.
According to the RE, this Contractor used the barge to berth at the river bank during high tide and stocked up the sand to more than 4m height and within few days, the whole river bank failed. The Contractor then panicked and tried to salvage as much as possible the sand from being washed away by flowing river using the excavator. Unfortunately, he salvaged too much and his excavator sunk into the soft soil.
I did another geotechnical analysis using additional load of 40KPa, the safety factor went below 1.0, signifying the failure of the slope.
This slip failure went deep into the river and near to our wharf front, bulging out near the shipping path, which made the channel shallower, but did not affect the wharf structure. 
We have a lot of big-headed and ignorant people who knew little about engineering and yet acted as if they know better than the engineers.

Failure of a Bridge Pier

The Bridge Pier of the 36m main span and flanking 12m span bridge tilted backwards to the river bank during launching of the bridge deck steel trusses. The pier was made up of eight driven steel pipe piles and then welded with steel pipe braces to form a high supporting structure.
The Contractor reported that the Pier failed suddenly with the Resident Engineer agreeing initially. The welding of the steel joints was found to be of poor quality, but should not be the main cause of failure. The river bank showed serious slip which indicated slope failure towards the river. 
There was no earthquake, no piling, no rain and no torrential  river flow or erosion of the river bank. Then why did the Pier fail?  

If the river bank was unstable, it would have failed during pile driving which generated a lot of vibration, or when filling up the road behind the bridge abutment wall, which exerted the most load. 

Why it failed after two months of the completion of sub-structure works? The steel trusses were light and should not generate much loading to the bank!

Upon questions, queries and interviews by the design Engineer and Client on the sequence of events happening prior to failure, the frightened Resident Engineer finally admitted that he was threatened not to tell the truth. The installation Contractor actually filled up the river bank with earth from neighbouring hill, between the pier and abutment, so that he did not need to construct working platforms for the launching of the steel trusses. When the pier failed, he quickly removed all the earth and asked him to shout up. He said he did not know that filling would cause failure. He thought that this was normal way of construction practised locally. In fact, this Resident Engineer claimed that he had 15 years of working experience in Saudi Arabia, that was why the Client engaged him to supervise the construction work!

Thus, the causes were immediately determined. The additional fill, 2.5m thick at abutment to 6m thick at the pier on the river bank was a substantial load behind the pier, triggered the soft soil slope to fail and thereby pushing the pier towards the river. The poor welding of the joints caused the vertical members of the pier to break at the joints, resulting the pier falling backwards.

Solution: 
As the piles moved by more than 1.5m, they were all bent and would not be able to take the required bridge loading, the pier was abandoned. The 24m span and 12m span bridge deck was changed to 36m span bridge deck. The relevant substructures were strengthened and modified, some costs were shared between the substructure contractor (for shoddy welding) and the installation Contractor(for causing the failure using improper construction method).  The Client offered to use the fabricated 24m and 12m trusses for other bridge projects. The Design Engineer offered to re-design the rectification works. The work was finally completed in another three months time.

Slope Failure Due To Liquefaction

The slope is 1:2 with a height of 11m. The whitish soil is Sandy Silt/Clay, in fact about 25% clay, 25% Silt and the remaining is fine sand. The average natural moisture content is about 24% and the Liquid limit is about 30%. This existing Slope was stable for more than 20 years.
Then a new owner acquired the land and intended to re-build  new house and swimming pool near and on the slope. During installation of concrete piles, the slope failed and the pile driving machine fell down to the toe of the slope. The soil was seen flowing down the slope after immediate failure. There was raining in the previous night.

A sample of this soil was sent to the laboratory for testing. The moisture content was found to be about 22%, there was no obvious increase of water content in the soil.

Why did the slope fail?

Piling caused vibration. The installation of piles brought shock waves into the slope and liquefied the silty and sandy soils which actually have low liquid limits. That was why the soil flowed like lava, with little change to the moisture content, but after a few hours, it became "solid" again.

Safe Piling

These timber piles are supposed to support a house, will you feel safe to live in this house?

Some Engineers/Contractors/Owners thought that by hitting as hard as possible on the piles into the ground using heavy pile driving hammer, the piles would be able to carry more loads. They used very low set such as 1 inch or less per ten blows, in according to the design formula as their final piling criterion. The also did not protect the head using cushion and casing. 

The aftermath is the crushing of the pile heads. This also happened to concrete and steel piles. If this failure occurred on the top, it might happen at the bottom too.
Over driving, therefore should be avoided!

Fatal Landslide

When a mountain slope is cleared up by humans for farming, not only the rain water flows down the slope quickly to cause flood, it also soaks the soil below the ground, increasing the moisture content of the soil to become fluid and weakens the soil binding strength. The outcome is often disastrous. 

This landslide killed dozen of people many years ago.

It is therefore important to keep the hill slope covered with vegetation, such as grass,plants, trees, etc., which buffers the rain from eroding the soil and at the same time absorbs the water so as to keep the soil as dry as possible.

Abandoned Tilted House

Corner Double StoreyTerrace House easily costs more than RM500,000 nowadays in Kuching. If you buy a house like this, you are going to be upset for the rest of your life. Why it failed?

The housing project is located on a peat swamp with about 3m-6m peat. Some of the foundation failed when the piles, likely timber piles, buckled sideways, due to movements of earth fill supposed to cover up the swamp and to make ground above flood level. Some piles failed due to negative friction, a dragging of settling fill caused by the compression of underlying peat and soft soils.
Even, if the structure is intact, you will bothered by the sinking ground, flooded road, broken pipes and stagnant drains for the rest of your life. Just visit the Sibu houses built on the swamp, you will see that unsightly conditions.

Recommendation: Study the area carefully and DO NOT rush to buy house at the peat swamp area, which NATURE uses that as flood retention purpose. Find a better site with no peat swamp.

Road Pavement Failure

The Contractor excavated across the road, lay a water pipe, put back the soil and sealed the surface with bitumen pavement. After a while, the newly constructed pavement sank and then failed. Why?

The cause is quite obvious, the excavated materials were not put back in order and compacted. Road pavement comprises the founding soil, which in this case likely fill materials, then about 350mm thick of sub-base and base materials( 75mm to 38mm sized crushed rock materials), before sealing off with 100m thick asphalt pavement. Each layer has to be strictly compacted by mechanical Compactor from lower layer to upper layer. Thus if no compaction is done, the layers will be in loose conditions. Upon loading and water seepage, the soil/road materials will be compressed and reorientated and resulting less volume, thereby causing the pavement to sink and crack. 

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.

Failed Single Storey Houses

It was located on the coastal land, the developer filled the land with about 2m thick of soil. Then timber piles were installed to support the structure. The piles were driven down using drop hammer until "set". Single storey terrace houses were then built. 
Before anyone moved in, the houses failed miserably. Why?
If you buy a property like this, what are you going to do?

The site was underlaid with 3m-6m of peat and deep soft marine clay. By filling up with soils, loads were imposed on the underlying compressible peat and clay. Time was not given for the underlying soils to stabilise. So when piles were installed, the 2m thick fills dragged and imposed more loads to the piles. Some piles failed, in particular the edge/corner  piles. So the structures failed. 
The large settlement of the ground also caused the front approach slab to sink badly and due to edge restraints, differential settlements and cracks came in.

Sometimes, developers or engineers thought that the buildings were just one storey, light and therefore did not do any soil investigation. 

Without understanding or studying what laid beneath, caused this failure. 

Failures of Wharves

Building wharves at the river and coastal plain river banks are one of the most risky engineering works in Sarawak. The soils are generally very soft and sensitive. The safety factors for the slope stability of river banks are generally about 1.0 to 1.3 and the erosion of the bank/bank toes are often continuing. By just driving the piles, the bank may start to move. By filling up the river bank will aggravate the situation.
  
Abandoned wharves are therefore often found along the river banks. Some failed during construction and some failed after using for less than twenty years. 

Most of the failures are due to river bank movements. Some due to mis-use and overloading.

Peat Soil Seminar at Sibu - Errata

I just look back at the newspaper cutting on the Council requirements on the performance the external roads on the development projects, not to settle 200mm in two years, dated back some time 2010. 
The requirement applied only to commercial projects, NOT housing or other projects. The reason was the Council was not willing to pay for raising up the road, why should the council pay? 

Then, I cannot see the logic why this rule cannot be applied to other projects, especially the residential projects. Why the ordinary people should endure the settled roads approved by the Council? Rules should be applied for all, NOT selected projects.

Perhaps, the Council felt that the Developers and the Engineers should be responsible for the problems. Legal suits can be filed against them but the Council should know that the costs, inconvenience and time taken to do that by the buyers. Perhaps, by the time the house owners or ordinary people win the suits, the Developers or Engineers has only RM2 to pay or has migrated overseas or dead.  

PEAT SOIL SEMINAR AT SIBU