Gravels from 45m Depth below Ground Level

These gravels were extracted with great difficulty from a borehole 45m below the ground level at the upper stream of Baram River. How did they come about?
The River of the hilly area was the formerly deeply eroded valley during the ice age when sea level was low. The rise of sea level about 12,000 years ago and warming resulted in plenty of rain, brought down sands, gravels and boulders  to deposit at the upper stream of the submerged valley.
During boring,  clay,silt,sand could be easily washed out using pressured water flow but not the larger gravels. These gravels accumulated below the bottom of the borehole as the drilling got deeper. It needed some skill to get some of them out of the borehole. Sometimes, the drillers used core barrels and some times they used grouting.

But these gravels have serious impact on the Standard Penetration Tests at the test layers, very high blow counts!  So, engineers have to interpret the soil layers containing gravels,with caution. For example, N=50 blows per 300mm does not mean dense sand, it may be just medium dense sand.

Failed Road Embankment and the Probable Causes

This almost 20m high new paved road embankment at a hilly terrain in Bintulu Division failed completely after heavy rain. Why?

The road embankment is crossing a slanting, narrow and deep valley, with hill less than 5m away.

There are five main factors which affect the road embankments:

(a)   the design, the slope provided, the foundation     and the earth materials used for the filled            embankment,

(b)   the method of construction of the filled                embankment,

(c)   the rain and effective drainage,

(d)   the traffic

(e)    the breakage of water supply pipe

(f)    the maintenance.

From the photograph, it can be seen that it was a complete collapse of the filled embankment, some soil slurry was seen flowing from the right side down the slope. There seemed to be a large depression on the right hand side of the road which was part of valley, and probably formed a pond after heavy rain. No concrete drain was seen and earth drain was     presumed. No much vegetation was seen on the right hand side indicating new construction. Turfing or vegetation had not covered the bare surface     completely. Water pipe was not seen on the             embankment.

The embankment was stable for a while after construction when there was no much rain. It was the rainfall and poor drainage which resulted water infiltrated into the fill embankment and weakened the soil.  It was also the accumulated pond water which continuously supplying water into the embankment soil until the soils were saturated with a lot of free water.

Just soak a compacted soil sample in the water, you will see the immense change of moisture content, CBR and hence the strength. If you vibrate it, the whole sample would liquefy and becomes slurry. Heavy lorries and machineries cause vibration.

As there was no water pipe, it was not the water leakage that infiltrated into the embankment. In fact many filled embankments failed because the water pipe broke. This often occurred at the junction of the excavated road and filled embankment which settled due to poor foundation, compaction and erosion.

Thus, from the sudden failure of the whole embankment, it looks more like slope stability/foundation sliding failure, which means average strength of the embankment materials has gone below the design requirements. Water seepage changed the properties of the earth-fill materials.

To prevent such problem, design-wise, always provide efficient drainage for this kind of high fill embankment.  Any depression shall be filled and levelled at the road side, must indicate on the Plan. No water pond shall be allowed to form. If the soil materials are very permeable and erodible, concrete drains have to be provided to prevent water seepage into the filled embankment. It is an advantage to have a few layers of coarse grained materials in the embankment to allow water to drain through to the other side efficiently, but shall not in a way allowing erosion of these layers. The bottom layers and toe of the slope are preferably large and small crusher stones mixed with coarse sand, to allow for such drainage.

On the construction, the valley bottom in the hilly area is often weathered to reach rocks, but sometimes, there are some shallow colluvials soils, which can be easily excavated and replaced with rocky materials. Higher valley sides need to excavate 0.3-0.5 m soil and replaced with compacted soil to ensure proper anchoring and no weak contact layer. This step will form firm foundation and prevent sliding along the slanting valley. 

The choice of fill materials from the borrow pits and degree of compaction will affect the performance of the embankment. Always investigate and test the materials before use. For road project, there is always a soil laboratory specified for doing such tests. If the materials are too silty, compaction is difficult, especially during raining. Clay also cannot be compacted during raining. Just look at the Compaction Curve of the Compaction Test  and see how sensitive is the moisture content on the field density. It is difficult to achieve 90-95% optimum density due to high water content. In fact, no work shall be done during raining, unless you use gravelly or sandy materials. Gravelly materials are hard to find generally though. The excavation of borrow pits often begin at he surface which is generally firm to hard residual soils followed by highly weathered rocks. The surface soils are often used for the foundation layers of the embankments while the rocky soils are used on the top. Planning shall be in such a way that the rocky materials are used for the bottom layers. 

Sarawak is in the tropical zone, hence rainfall is a common occurrence throughout the year. The dry season may be during May-August, but can construction wait until that period? 

Another problem with the local Contractors is they like to dump-fill into the valley to build up the embankment without compaction, sometimes not even make foundation clearing and preparation. This is the easiest and fastest way to build up high embankment, especially when the Supervisors are not around. Just bore down the embankment and do SPT tests, you can detect which layers are compacted and which are not. Well compacted soil has SPTs more than 5 (depending on the materials used, compacted sands have SPT more than 10),  those less than 3 were not likely compacted although the seepage of water would also lower the SPTs. Built-up embankments do not fail easily if there is no much water seepage or erosion, but uneven settlements on the road pavement will occur.

Maintenance includes inspection, clearing, repair of the drains and turfing of any bare ground, which inhibit water to infiltrate into the filled embankment. The Authority often has insufficient fund allocated for inspection and maintenance.

Cut Slope for Shale Rock

Near to Sarikei Semangoi Mountain, the underlying bedrock is predominantly Shale bedrock. When excavating the hill to build road, studies have to be made on the Shale weathering charateristics and bedding patterns, as Shale rock is known to disintegrate easily upon exposing to weather or water instrusion.

This slope shows how the neatly cut Shale slope will become after 15 years of service. The surface is now littered with broken Shale fragments and debris. It seems to be bulking at the mid-slope too. The slope is quite gentle, probably about 1:2, gentler if including the intermediate bench. The height is about 10m. If you use slope stability analysis, the strength is only about 50N/sq.mm. During investigation, the strength can reach more than 200N/sq.mm. 

Slope analysis requires a lot forward looking and judgement, rock and soil will deteriorate with time. Ground water level changes with seasons and time too. What will be the likely strength after 50 years of exposure to weather and rainfall? What is the dipping direction and angle of the Shale bedrock?  What is the thickness of the bedding laminations? These are the factors need to be considered.

This Shale Rock is much better than the Shale rock near Roban (20km away) which has been posted earlier, as they have thicker laminations compared to the Roban Shale.

A bridge too steep

It is certainly not passable for traffic, but pedestrians still can climb through. Why the bridge failed?

It is located at a river tributary on the coastal plain of Batang Saribas. The underlying soils are soft, deep and sensitive in many areas.

The bridge has three span deck supported by two abutments on the river bank and two piers in the river.

One of the piers fell, bringing down the decks onto the river bank.

A few causes may result such failures:

(a)  river bank moves during piling. Piling generates vibration, vibration weakens soil strengths, this is particular true for senstive soils. In many areas, sensitivity can reach 4-6, thus river bank stability which has about 1.2-1.5 safety can easily drop below 1.0. When the river bank moves, the piles move too, bending the piles as well breaking/weakening the piles.
Besides piling, using heavy equipments or building temporary earth platform on the river bank for piling, earthworks and slope protection works also cause the bank to move.

(b) long piles require a number of jointings, if welding cannot be done properly, it becomes weak points, in particularly slanting piles. The joint strength must be as strong as the piles, whether under stress or bending strength, otherwise filures may occur at these points, 

(c) defective piles, whether due to manufacturing, transporting or during driving, have to be rejected and replaced.

Cause(a) was the major reason of failure, while (b) and (c) often aggravated the situations.

Prevention: River bank shall be monitored for movements, this can be done by setting up monitoring points in lines at various locations of the river bank during driving and construction. If the movements still persist after stoppage of construction activities, then the river bank has to be released of stress such as removing all the unnecessary loading or may even have to  excavate the filled ground on the river bank.
Solid RC piles and heavy dynamic piling shall be avoided.  Steel pipe piles and drop hammer driving are preferred with close monitoring.

Slope Failure Due to Erosion

This slope is located near the roadside from Bintulu to Samalaju.  The hill is low, less than 6m at the frontage and the slope provided is about average 1:1 near the road and then gently slopes towards the oil palm plantation.

The failure is localised, more of vertical collapse due to erosion than collapse through large lateral movements such as circular slippage.   Why?

The types of soils/rocks and the drainage, were the probable causes. On the top of the slope, a deep eroded channel was found, probably formed from broken shallow drain along the slope after collecting rain water. With time, due to the silty and sandy nature of the residual soil, the erosion and seepage of rainwater changed this shallow drain to deep channel, cutting into the completely weathered siltstone laminated with Mudstone, Shale and Sandstone, forming drainage holes coming out from the slope. The slope collapsed inwards as well as downwards leading the multiple cracking of slopes as well as the collapses of concrete benches and shallow drains.

Concrete drain provided must be continuous and be able to discharge effectively to the lower ground. It shall not be leaking or seeping through cracks or drain back on silty and sandy soils especially if the rainfall catchment area is large. Apparently the backgound oil palm plantation also drains towards the slope.

As the slope is far away from the road pavement, it does not seem to pose any danger to the road users.

wkm civil engineering technical world to wongkingming civil engineering technical world

Finally, all the articles in the wkm civil engineering technical world has been transferred to the wongkingming civil engineering technical world. The old sub-blog will therefore be close. Anyway, it could not be accessed since end of June due to some technical problems, I did not know why. 
Anyway, the new sub-blog is more presentable and hope the audiences would benefit from my interest and experiences.

Inadequate Retaining Wall

A Developer intended to develop a plot of land adjacent to a burial ground. They shared a common hill with boundary at the hill top. Excavation was unavoidable. The Developer attempted to cut the hill as much as possible and as close to the boundary, in order to have more land for development. The slope was almost 80 degrees to the horizontal. Then he built a rubble wall to protect the slope he had created. 
I wondered how long would the wall last as the wall was obviously not high enough to protect the excavated hill.

I did not need to wait long, the slope failed and tons of earth from the adjacent land fell into his land. It did not bury anybody, but I was not sure whether there were any buried body, corpse or skeletons  swam into the land ! 

Cantilever Beam or Balcony

I always worried about cantilever design during my professional practice, mainly because of the totally reliance on ONE support only of the structure. Many factors could go wrong, design, materials, construction, maintenance and overloading. The consequences are always abrupt and often disastrous.
Six students died in US apartment balcony failure on 17th June 2015 News report. That is a nightmare for any Engineer and related parties.

When I was working for a Consulting Firm, my senior Engineer told me, he saw one cantilever balcony collapsed during construction, overloaded with construction materials. Then my former boss also told me, this young engineer designed two 5m long cantilever beams for an Entrance roof beams, both beams failed down after removal of the form-work supports. Luckily no one was hurt. Investigation found that the young engineer used wrong inputs in the commercial computer program and grossly under-designed the beams. My boss had to pay more than RM20,000. 
When I was inspecting a 5-storey watch-tower cantilever staircase beam construction, I found that the Contractor put the top main reinforcements at the mid-depth of the beam with the so-called ten years experienced Supervisor did not know what he was supervising (later, I found that his certificate and credentials were all falsified). I immediately asked the Contractor to hack the half cast beam as well as to change the cantilever beam design to simply supported, as hacking or drilling of column was not recommended, despite Architect's unhappiness. Safety was my main concern. 
Besides strength, deflection is also a concern which needs to be checked, otherwise cracks will appear on the brickwall sitting on the beams. Higher safety factor is recommended for cantilever design, especially if you are not going down to the field to inspect.

Non-functioning Footpath

When a footpath cannot be used for walking, it is considered to be a faulty design. What happens to this footpath? 
The weep holes in the 1m high retaining wall discharge rain water onto the footpath. The footpath has no drainage discharge and level is lower near to the wall, so water accumulates there. In tropical climate, the moment water accumulates, algae flourish, making the floor slippery besides wetness. Nobody wants to walk on this kind of footpath.

One of the solutions is to provide drains near the retaining wall to drain the water away from the main footpath, a shallow one is sufficient. This drain shall connect to a discharge outlet such as manhole or to the drain beneath the footpath through uPVC pipe.

The other solution is to re-surface the floor such that it slants gently (say 1:200) towards the grass verge. As long as the water can flow away immediately and not stagnant, the floor will be walkable.

River Wharf

This wharf is more than 40 years old and is abandoned. One of the corner piles has broken and most of the structures disintegrate badly. 
Local wharf cannot last long due to four main reasons:
(a) Bank slope fails,
(b) fenders failed or being stripped away
(c) river vessels hit onto the frontage  piles,
(d) corrosion of the steel reinforcements and concrete       spalling due to salty sea water and rain water
(e) little maintenance.

River bank slope is generally natural formed slope and is subjected to erosion and change. Natural slope on flood plain has a low safety factor and if the erosion of the slope toe is severe, the banks slope may become unstable and bring down the wharf.

It is quite difficult to control the berthing of the river vessels due to river flows, tides and experience of the ship captains. Impact on the wharf creates a huge force and if the speed and angle of berth are wrong, damage to the wharf is imminent. Sometimes, huge vessels berthed onto the small wharf which was not intended to.

Concrete quality is another factor which controls the life of wharf. If the past, it was difficult even to achieve grade 30 concrete, thus allowing water to seep into the concrete and rusted the steel reinforcements. Insufficient concrete cover of steel aggravates the situation.

Maintenance is another important factor especially the fender piles which help to absorb the impact. Damaged fenders not replaced would result the river vessels hitting directly onto the structural piles, breaking the piles. Most rubber and bituminous materials cannot last more than ten years and has to be replaced after certain number of years.

The Round Worlds

It all the stars and planets are around, then there should not be any reason why Nature could not make these two round cobbles, although I was a bit perplexed initially. These round samples are rare, most of them are irregular. They were from different upper streams of Sarawak rivers. These cobbles are all sandstones, the grey one is coarser than the light grey one. 

Humans probably can also make the round samples too, by sanding or machining.

Beautiful pebble gravels

Fifteen years ago, my Contractor used unwanted river gravelly sand from Sarawak River to fill up my backyard by 1.5m high.
Today, I find these gravels lovely and beautiful.
Each of these gravels has long history to tell. Where were they from? 
What are they made up of? Why are they coloured? How old are they?
Of course, every thing on Earth is made up of star dust, including you and me. But how did they come about would need you to understand geology or even astronomical physics. If you are a civil engineer, you better know it as it is an interesting subject!

Irregular Shaped metamorhosed Mudstone

Generally, Mudstone has relatively indistinct joints and generally exist in massive bedding or interbedding with other sedimentary bedrocks.
But, these samples are hardened and irregular, as if being joined together from pieces with bonding agents. One sample looks like conglomerate with same materials. These rock samples are from a gold mine at Siniawan near Bau near Kuching.

Imagine, millions of years ago this bed of sedimentary rock was intruded by hot lava below which also brought the gold ingredients to the surface. As the sedimentary rock experienced high temperature and pressure, the soft rock got baked, shrunk and cracked, forming thousands of micro-joints. Chemical solutions then seaped in and closed all the joints.

So, there it is, our fractured metamorphosed Mudstone near the surface as humans excavated down to look for gold.

Meta-Sandstone Aggregates?

The other day I passed by an ongoing bridge construction site at Sri Aman and saw these aggregates. I was wondering what types of aggregates this Contractor used.  The stones look like Meta-sandstone. I had no one to ask at the site. 
The nearest Quarry is somewhere along Sri Aman to Betong Road, which happens to be a Meta-sandstone site. 
Meta-sandstone is a metamorphosed rock and often intruded by white quartz veins. The are just moderately good quality stones and required much tests to confirm whether they are according to the MS or BS Standard. 
I would not know whether these aggregates are suitable for use in high strength prestressed concrete structures until comprehesive tests are done. Good quality Granite aggregates are generally recommended for the high strength concrete.

Failed Column (3)

Early last month when I was in Sarikei, I saw the contractor knocked down the front part of the shophouse, two floors above the walkway plus the column. The Owner chosed to use conventional piling for the failed corner column and then to build upwards again. I was told that three months was required for the repairing works.

Last week I saw them casting the first floor.

Probably, the micro-pile system is too expensive to be adopted as the local Contractor has no such drilling machine and skills. Concern of the structures above may fail during pile and foundation installation, might also refrain Owner/Contractor to use this faster method. 

Failed Column (2)

Since it failed during the raining night, then one of the reasons must be due to water. Somehow the water entered the foundation, either the soil becomes more soggy or the water erodes the foundation. Looking at the rainwater downpipe discharge, the rainwater did not enter the covered drain, some of it seeped through the floor crevices into the soil.

Then the cover was opened and observed, the drain was eroded with holes at the base, water had been consistently entering the soil instead of discharging to the big drain and into the river.

Then you see the big vehicles stopping just nearby due to traffic light, less than 2m away. When they moved, you could feel the building trembled.

If you have played clayey soil with the water, you will know the effect. When you pour a lot of water onto soft soil, some will seep in and come out somewhere, some will enter the soil structure and increase the moisture content, some will remain on the surface to be vaporised. But when you shake it with vibration, most of water will enter the soil structure, the soil will become so soft and may become liquefied. 
After years of water entry and vibration, foundation gradually weakened and sank down. Based on the year of construction (during 1950s), the foundation was probably Bakau piles. The outer piles are the most affected, causing tilting towards outside.
As the walkway span is shorter than interior span (about 3m versus 6m), the outside column probably incurred tension when the foundation sank down, splitting the column. Loads are now transferred to interior column. It is important that this column must be able to carry the extra loads. Otherwise it will create a card type of failure.

Besides, the bars inside the cracked column and beam were quite badly rusted due to the long exposure to rain. Expanding rusting bars pressed against the concrete and aggravated cracking.  

The building really needs to be fully investigated in details by studying the original plans, revised plans, history and execute physical investigation and testing to ensure overall safety.

Failed Column (1)

Three months ago, this corner column of the 60years old 3-story Shophouses at Sarikei suddenly cracked and detached from first floor over the night after heavy raining. The first floor beam also split, putting fears to the tenants and neighbours. 
Would the building collapse? What would be the solutions as many lives could be involved? Why the failure occurred?
What will be your solutions?

Limestone Aggregates from Quarry

They look almost the same as the igneous rock aggregates, but they have more white powder on the surface and more slippery. No wonder they failed the skidding resistance tests and not recommended for road wearing course. Limestone also reacts with acid and is therefore not recommended for foundation, sub-structures and concrete surfaces that are exposed to acid or acidic rain. 
Limestone aggregates available in  Kuching are mostly from Bau or 21st Mile or 29th Mile Kuching-Serian Road Quarries. 
It costed about RM50 per ton in the retail market, delivered to my home. I bought 3 tons for my home landscaping two months back.

Poor Workmanship in Housing Construction 

(4)

The backyard retaining wall is only 1m high and is made up of 9 inch red bricks. It failed or at the brink of failure. Why? 

If you look at the failed plane and the muddy site conditions, you probably know why.
Brick retaining wall is formed by cement bonding of bricks plus brick interlocking and self gravity. Cement mortar is the chief bonding agent to bind the bricks together. The cement mortar is a mixture of one part cement to three parts sand plus the water-cement ratio of 0.45 to 0.6. The sand cannot be too fine and too coarse, somewhere in between. Lower water-cement ratio has to be used if the sand is wet (bulking during raining). Therefore obviously, the mix is in suspect, likely too wet. 
The surface has to be clean before applying cement mortar. If there is a layer of clay slurry, there is no way the cement will bind the bricks. This is likely the main cause for this failure. 
The cement has to apply uniformly throughout the surface, but looking at the photograph, you will find some bricks very clean, no cement mortar at all! The gaps between many bricks are empty, thus the surface bonding area is effectively reduced. Design normally assumed full plane surface area, 9 inch brick + 1 inch mortar x length.  If you measure the brick size, probably the length of each brick ismay not be 9 inch. Try to measure the size, you will understand!
Uncontrolled site management, poor workmanship and non-standard materials are the main culprits.

Poor Workmanship in Housing Construction 

(3)

You thought that you are designing the column base as "fixed", then you found the actual situation at site was far from your ideal assumption. What would happen to the structural performance when completed even after you had repaired? 
What caused this defect?  

If you look at the photograph closely, you will see the aggregates segregating at the base and the aggregate sizes are irregular. These aggregates are un-sieved river gravels, with some exceeding 50mm. 
The steel bars are not vertical and evenly distributed, in fact forcefully bent here and there. The starter bars from below the ground beams are not aligned with column bars above the ground floor.

So you can see many basic problems from this construction:

(a) Setting up. The survey or measurement was not done properly, therefore the vertical bars were not installed at the exact locations. (In fact, after putting up the brick wall, the rooms were found to be not rectangular or squarish),

(b) Formwork. If the formwork was not tight, leaking of cement grout could cause honeycombs,

(c) Concrete mix. Concrete was one of the most uncertain material when ready-mix was not available. Site mix was so variable that until you tested it, you wouldn't know the result. 
(Concrete is made up of cement, fine aggregates, coarse aggregates and water. The designer often specifies Grade 20, 25 or 30 for the structures, while lean concrete uses Grade 15. Grade 20 means that the concrete will achieve at least 20N/sq.mm compressive strength in 28 days. In the past, the concrete was specified with 1:2:4, 1:1.5:3 or 1:1:2 mix to achieve Grade 20, 25 or 30 respectively. 1:2:4 means one part of cement, 2 parts of fine aggregates and 4 parts of coarse aggregates. 
Is the cement fresh or properly stored? Cement deteriorates fast if it is not properly stored. 
Then the aggregates are another big uncertainties. Are they from quarries, blasted and manufactured from igneous or metamorphosed or limestone rocks? Generally, these quarry-made aggregates are more uniform and well controlled, but thiswhich also depends on quality of machineries and management control. 
But if the aggregates are river gravels, are there proper sieving procedures to obtain required sizes and cleaning to remove all the dirts, sticky silt and clay? The same applies to the fine aggregates, quarry made or river sands? Fine aggregates have generally four different zones, which zone of the fine aggregates at your site belongs to?
In buildings, the coarse aggregates specified should not exceed 20mm generally, it appeared that this construction did not comply based on the larger aggregates dug out at the problem area. When large gravels are used, they would stopped by the stirrups used as perimeter bars, then concrete would not be able to flow down to the bottom.
Finally, how much water should be added to the mix ? Water-cement ratio of 0.45 is an idealistic proportion, it will give best strength, but it is too dry for concreting work in small column. Therefore, you may need to go to 0.6 for ease of compaction and construction. Often, admixture is added to improve the workability (high slump) without sacrificing the strength. But admixture is expensive. Thus it is easier by just putting in more cement and water to achieve the same slump.
To achieve the required strength and slump, trial mix must be done much earlier before any concrete mix and materials can be approved to use at the site. It appears this site had no such trial mix,

(d) Concreting. Concrete is time dependent, the longer you wait the more difficult to work. Concrete must be poured, the best within half an hour after the mix and probably within one hour by adding chemical admixture . The moment it is hardened, it will difficult to put into place even with internal vibrators. Engine-run internal vibrators must be used to ensure that the concrete is properly compacted with no gap and holes. Otherwise, honeycombs will appear. But avoid over-compaction because it will lead to segregation of coarse aggregates at the bottom. Sometimes, you will see the workers pouring water into the concrete when they find the concrete is dry and this in fact reduce the concrete strength drastically with a higher water-cement ratio. Concrete cubes made from concrete before adding water does not reflect the actual concrete quality.

(e)  Supervision. The supervision team really has to improve the skill. Unfortunately, this supervision team who was not competent enough to do the work, was sent by the client. The Designer has to keep on reminding and writing instructions to such team,

(f)  Design has to be conservative when facing poor Contractor, incompetent supervision team and indifferent Client. Also avoid using too small columns, often requested by Architect, even though they might slander you by branding you lousy engineer if you didi not comply. The final liability is still with the Engineer.  Now the new Eurocode requires at least 200mm width for structures to reduce this kind of concreting problem.

Below is another photograph also showing slender column, probably large aggregates, conjested steel reinforcements, insufficient compaction, causing holes and honeycombs.

Poor Workmanship in Housing Construction 

(2)

Yes, just fill up, flatten the muddy soil within the ground beams, pour the concrete over it, the ground floor slab would be finished. Everything would buried under the feet. Only the new concrete surface would be seen and admired by the people!
What about the floor that sink and crack before and after being hardened?
Never mind, claim progress and money first and think about the problems later.

Often, the local Contractors are incompetent and ignorant, they cannot read Contract Specification (in English), but they can tell you that they have constructed buildings for more than twenty years. Therefore, they do not need the young Designers or Resident engineers to tell them what to do.

To prevent such situations, Site Engineers have to study what the Contractors/workers are doing at site, foresee coming problems and advise them immediately to take precautionary steps firmly when the machineries are around. For example, drainage is one of the most important temporary works in view of the frequent raining. By just building an earth drain surrounding the site and discharge to appropriate outlet will help to keep the site dry. Pumps must be available if water cannot be discharged speedily. Excavated earth shall be transported away as soon as possible if it is not required further. Outside ground level shall be lower than the designed floor level. Earthwork cannot be done on wet days, you cannot compact wet clayey soils! Sand is a better material for working in the wet season. The site Engineers have to be knowledgeable in the Specification and firm in authority before they are able to instruct the "experienced" contractors in writing, if they are not following orders.

Poor Workmanship in Housing Construction (1)

One look at this site, you already know the poor site management of the Contractor. 
Drainage was not provided, soils were littered everywhere and after raining, the slurry invaded the half finished ground floor. 
Do not expect the Contractor to clean the unfinished structures, the Contractor just continued pouring the new concrete over the soiled surfaces. What was the supervision team doing? 
No or poor supervision, many developers were not willing to spend money on supervision which also slowed down the construction. Many Contractors also cited low contract price and others were just poor in management and knowledge.
Good luck buyer, if you happen to buy one such property!

Burnt Umber/Bergundy Rock Fragment in River Gravels

This half-baked shades of brown coloured stone with distinct layers was found among the river gravels. Obviously, it had been subjected to high pressure and temperature, such that part of the fragment was fused to form very hard surface. Certainly durable, even after soaking in the water, rubbed against other gravels and rolled in the river bed for thousands of years, it still could survive. 
But if you break it apart, you will find the un-fused part of Shale and some stone fragments, which have low strengths.
That is why, if the river gravels are not screened and unsuitable materials removed, there will be localised weak spots in the concrete structure and is especially dangerous in slender columns.

Anyway, it is a beautiful natural product, but why Bergundy colour?

Various Shapes of River Gravels

They rolled tens of miles, some perhaps hundreds from the mountainous interiors to the flat plains through the help of rain, heat and water flows. Many had lived thousands of years, scoured from the bedrocks to become boulders, cobbles, and then gravels. The bedrocks in Sarawak are generally sedimentary in nature, which are easier to erode but the metamorphosed action and volcanic intrusion help to harden the rock which laid the basis for forming these hard gravels. Graywacke, sandstone, slate, phyllite, quartzite, limestone, etc. are common gravelly materials. There are many shapes and sizes too, round, oval, triangular, squarish,irregular, you name it, but most of them are smoothened and rounded at the corners. They are beautiful creatures formed by Nature.

Thirty years ago, these gravels were used for construction of concrete structures, especially in Sibu, where there was no igneous rock quarry but plentiful supply of river gravels. Concrete strengths were seldom expected to be more than Grade 30 (30 N per sq.mm). Actually, Grade 20 was most of the time adopted for design. Low strengths were due to the unpredictable strengths of gravels and often stained with a lot of silty materials. In fact, I also used the crushed boulders for some of the bridge foundation blocks in the Sarawak interiors. More cement was often required for such concrete.

Today, I collected these materials for landscaping.

Sarikei High School Classroom Block Exrension

During 1987, the Principal of the School asked me to assist designing a 2-storey extension block at the foothill of the small hill, which was the site of the old library. The new block would have six classrooms.
Being old student, it was my moral duty to help for providing me education. 
Some excavation of soil was required to bring to the same level of the old block. This excavation varies from 0m to 2m. Was piling necessary for the foundation? This would require higher cost which the School was lacked of. Of course, the safety of the students was my main concern.
A simple Soil Investigation using Mackintosh Probe Tests were carried out. It revealed shallow firm to stiff residual soils up to 4m depth across the building with some variations. A bearing capacity of 150KN per sq. meter could be used at 1.0 m below the intended ground level. Spread footings or strip footings were all viable. The recommended footing location was 1.5m below ground level to reduce the effect of water level fluctuations.
Normally, the ground floor has ground beams tie to the columns and these beams were 230 wide x 600-750mm depth, with 300mm column stumps above the footings.

I decided to use the strip footings by providing 200-300mm thick base slab combined with 750mm ground beams longitudinally thus having inverted T-shape Footings with a total depth of 1050mm below designed ground level. This would help to stiffen the structure to distribute some variations of soils and fluctuation of water levels, at the same time cut down the reinforcements of the ground beams and foundation. Shallower foundation also meaned easier construction.

Cantilever beams and expansion joints were provided to join to the old blocks. It was expected there would be a little movement between the old and new block.

The extension building was completed in 1989 and worked well in accordance to the design intention at the minimum cost.

The strip footing looks like this picture from another project, but was not flooded.

Microtonalite Stone aggregates from Quarry

Stone aggregates from quarries for making concrete are quite easily available in Kuching. They are either crushed from Igneous rocks Microtonalite, Granite, Basalt, Andesite or from sedimentary rock Limestone. Igneous rock has the best quality while Limestone is moderately good for concrete usage, but not recommended for foundation structures (acidic ground water) and structures which expose to acid such as roof slabs (acid rain).
This photo shows the commonly available Microtonalite stone aggregates from Kuching.

Central and Northern Sarawak regions such as in Sibu, Sarikei, Bintulu and Miri, do not have igneous rock quarry because of the unfavourable Geology. The stone aggregates used are therefore either the river gravels or the metamorphosed/cemented Sandstone and Limestone Quarries, which are of inferior quality compared to igneous rock quarries. Therefore, if good quality stone aggregates are to be used, they have to be bought from Kuching, which are expensive due to distance.
To determine whether the aggregates are of good quality, there are many tests to be done. These include Uni-axial compression tests for parent rocks, Sieve analysis, Crushing Value test, Impact Value test, Los Angeles Abrasion test, 10% fines test, Specific gravity, water adsorption test and sodium sulphate test, just to name a few major ones. In view of the cost and fear of failing, not many quarries or suppliers are willing to do such tests. But the local Authorities require Building structures to comply to the MS/BS standards, Engineers have to check the quality of the stone aggregates before being allowed to use. But how many of them really checked these requirements, especially the Central and Northern Regions where tests are not even available?

Failed Earth Dam

About 100m length of the 300m dam failed at the upper stream as it reached the last 0.3m stage of required 6m height during construction.   WHY?

The Dam was located on a shallow stream with less than 1m depth of water but it was also a former buried deep valley channel of about 25m deep. The soils are mainly marine deposits and the surface soils are extremely sensitive.

The design specified for the staged construction of 1m earth filling and rested for a minimum one month period  to improve the underlying soils before the next stage can continue on. In another words, a lot of standby and monitoring were required. Instrumentation included inclinometers, piezometers, settlement plates and deep gauge meters. The average slope was about 1:7. Another 4m deep excavation was required at the upper stream to increase the storage capacity of the reservoir behind the dam.

The reasons for the failures:

(a)    The Contractor did not construct the earth dam immediately due to low price of the earthworks, less than 15% of the total cost. They did not want to mobilize the earthwork equipments which cost a lot in rentals to them, such as excavators, tractors, compactors and lorries which involved a lot of standby. So they delayed until nine months later and requested for less rest periods and wanted to construct speedily towards the end of the contract period,

(b)   Many of the instruments were not installed properly and reading could not be obtained accurately or doubtful. The worst was that the results were not submitted for supervision team to evaluate immediately, but often two weeks later. In fact from the results obtained from the Contractor later, piezometers showed the sudden increase of pore water pressures and inclinometers showed increased rate of lateral movements before the failure,

(c)    The Supervision team was not experienced enough to handle incompetence yet vocal Contractor on highly technical earthworks and could not do much to enforce the original schedule. There was pressured to complete the work before the coming predicted drought and finally yielded to the Contractor’s demand. The town had been short in supply of water every year. The Contractor claimed that the slope was too gentle and even betted with his balls if the dam failed. This had psychologically influenced the supervision team and Client to doubt whether the design was too conservative,

(d)   There were some localized peaty soils in buried stream, which were not detected during investigation and properly not completely removed and  initiated the failure,

(e)   Continuous movements of heavy equipments such as compactor, excavator and lorries produced vibrations which together with the filled earth might have caused the underlying soft soils, which have an average sensitivity of more than 15, to lose some strengths.

Lessons learned:

(a)    Highly technical method of construction such as soil treatment methods or instrumentation or grouting should be used in caution as many local contractors and even the supervision teams are not skilled or experienced enough to do such works.

The main element of this earthwork design was rest period, allowing time for the underlying soils to gain strength and pore water pressure to dissipate as load was applied. But standby time costs a lot to the Contractor’s equipments and overheads. There was conflict of interests.

(b)   Use conservative design such as piling, heavy geotextiles or excavated deeper to remove the soft and sensitive soils, if there is no good Contractor in the Market, even though the cost may be two to three times more.

(c)    Firm in supervision and provide stern penalty in the Contract Clause at the beginning for failing to start work on vital works and not to be influenced easily by Contractor, whose main objective is to cut cost and earn profits. Also ignore Client or political pressures,

(d)   Site investigation shall be done more closely to detect any shallow localized buried streams/channels, perhaps 5m centre to centre using cheap Mackintosh probes (detect up to 12m depth and auger holes (extract up to 7m depth),

(e)   Instrument installations are often defective or knocked off during construction. Only really competent geotechnical sub-contractors shall be allowed to install and record readings. Alternative instrumentation proposed by Contractor shall not be allowed. Honesty pays an important part in this instrumentation (Many cheatings in installations and readings in local scene). Damaged or non-functioning instruments shall be immediately replaced.

(f)     Pay great attention to highly sensitive soils. There was doubt on the high sensitivity of soils initially whether the tests were properly done, as it was encountered first time in the local scene. The site investigation was executed some time ago and could not verify or re-test. Further investigation fund shall be allocated where doubts arise.