Different Weathering States of Mudstone

It is only one meter difference at 19m and 20m depth respectively near River Suai at northern Sarawak, but it has total different states of weathering, highly weathered and moderately weathered.

Brownish Sandstone

Sandstone rock is often stained with brown colour due to its porous nature and higher permeability to water and solution. If the solution contained iron oxides, the brown stain will be significant.

Colour Change of Phyllite

The interior is dark grey while the exterior surface is light grey and whitish, why? 
It cannot be every time you drill, it hits the quartz veins.

It is due to the exposure to water, sunlight and atmosphere which result colour change. 'Therefore, immediate examination and record should be done as soon as the sample is brought up from deep below, not after one or two months when the samples are brought back to the office.
However, to Engineers, colour change is not an important characteristics. They are more concerned with the rock sustainable structure and strength.

Road Failure

The other day, when I traveled through this stretch of Pan Borneo trunk road, it was left only one lane. A temporary steel truss bridge was built to increase the width. Half of the road embankment had disappeared.

This kind of failure is quite common during raining season and sometimes not even during the rainfall season. I looked at the sides of the road embankment, I saw one side was still retaining water and a large water pump was used to drain the water to the lower side, to be discharged to somewhere.

As I had said many times before, "WATER is one of the greatest enemies to Engineers' works!" 

Based on this picture, either the underground drain culvert was blocked or no drainage was provided. In general when this happens, water is accumulated at one side and soon seeps into the road embankment, not only weakens the soil strength but also brings some of the fine particles away, causing voids or flow channels in the road body. When the soil gets so wet ( in fact soil strength is related to moisture content of the soil) and falls below the critical value for the safe slope of the filled embankment, it simply slips and fails.

Designers sometimes fail to pick out the depressions behind road embankments due to insufficient survey data or simply do not notice the data which may be just few survey points, which are supposed to be filled flat so as water can be drained away through road side drains. Otherwise, culvert has to be provided. During construction, the site personnel are also supposed to pick up any such deficiency and rectify it immediately as they can see the site conditions more clearly. 

On the maintenance part, as the underground road culverts are often blocked by earth debris, tree branches and even rubbish, regular clearing is therefore required to prevent retention ponds being formed at the back of the road embankment. Unfortunately, we are too care free, we like to wait things to happen before actions can be taken. We cannot predict the future.

It will be of great inconvenience when the road fails, as rectification works always involves huge cost and time to the public.

Meta-Graywacke

So, this Graywacke was metamorphosed to become Meta-Graywacke.
It is found 18m below the ground near Betong Road Junction.

Graywacke

Frankly, I find difficulty to identify Graywacke. Theoretically, the rock is formed from synclinal deposits in the sea, and later uplifted and has generally three different layers of materials, the coarser at the bottom and finer at the top. It has to be grey too.

This rock sample is extracted 16m depth below ground level near Betong road junction. It appears to me more Sandstone and is light grey.

The Splitting Shale Rock

When this rock was in ground, it was so compacted that you hardly could find voids, empty spaces and cracks.

But when it was drilled, cored with water and took out from 18.2m below ground level, the rock splits at its weak planes originated from  laminated layers during deposition.  This Shale rock also cracks vertically and diagonally due to rough handling, although in nature it can crack due to weathering and geological processes.