It has been a tradition for many construction around Borneo in the past where heads are placed in foundation of gigantic structures such as this, bridges and buildings. When a new structure is to be erected, people starts to remind their children not to go out or wander far from home, fearing some headhunters will come and decapitate them. In certain culture, not only "spirit(s)" demand a head but can be specific which is conveyed through a medium. What significant was it from the lens of anthropology - culture and engineering?

It goes down in the name of development. A relic of the past that gone down and broke my heart.

Addendum: Just checked with the owner of this clip, he said there is no skull there. Mystery solved for almost 35 years.

  

Part II

Let us ponder for a while. Will bone, skull or human body able increase strength of structures? Before i go on with this discussion, i would like to put caveats to this discussion where; this discussion strictly on practice of disposing a body or bodies of human into a concrete foundation, the non-detail study on concrete behavior and changes in foundation (pad footing or pilecap) design.

1. Concrete composition change
When concrete is cast in-situ, concrete will undergo hydration process. That is the reason why we need to retain moisture within concrete (by acrylic membrane treatment or hessian damping) to ensure concrete will not (thermal) crack during this critical hours. For human body, when it undergo decomposing period, it will provide fluid and that can reduce thermal spike that ruined the concrete quality.
Another reason why body or skull perform differently is likely due to our physics. Why body or skull is preferred? From my past reading, i can recall the high content of silica from Ground Granulated Blast furnace Slag (ggbs) cement unlike normal portland cement. The key differences here is the content of silica in normal portland which quite low. 
The likelihood of the content of silica (from food) would be from gastrointestinal tract which is part of the earliest decay stage of dead human when buried in the foundation. The silica content when mixed during hydration maybe the cause to the increase of concrete quality which is similar to ggbs cement for concrete which is known to allow low cement/water content capability (which mean, the loss of water during curing process can be ignored) and high durability. It allows low strength lost in certain extreme soil condition.

Part III - "Dead body submerged from grave"

There is this post which shows a body of a dead person submerged from 6 feet down. I will not include the post with a video and photos since it is quite gory in nature. The body is buried in a swampy area. From soil taxonomy we can assume the burying area is of clay loam.

1. What is clay loam? Clay loam basically a type of soil which consist around 40-50% sand and the rest are clay and silt. The bulk density is around 1045kg/m3 while human body is around 1020kg/m3. So now, if you can recall science class back in your high school, the possibility of buoyancy taking place here is there.

2. Rotting bodies will go through 4 phases of decaying process. What i am trying to highlight here is the second phase, bloating. As we all know, dead body will float on water after hours or days going through decomposition processes. The body became more buoyant after been ingested by bacteria mainly at the intestine. Most of the time, gases such as methane, hydrogen sulfide, and carbon dioxide are filling up body which give lower density and higher buoyancy.

3. Gut is situated at the middle of our body and it is a perfect center of gravity for decomposing body and behaving like a ballast tank which provide stability (when wrapped with shroud as a whole rather being loose) through large surface area. Therefore, by logic it would float.

4. What role does clay loam soil play in this instance? Well, if you understand soil mechanics clearly and understand K coefficient of soil pressure in 3 states, you will understand how this could happened. Apart from that, the basic understanding on friction angle of the soil apart from cohesion coefficient and friction angle soil-structure will definitely explain how dead body can submerge.

5. When the swampy soil or clay loam is displaced for burial purposes, the at-rest state soil will react and K value is no longer at ka. We have passive pressure, Pp where soil tend to be displaced by the expanding or bloating body. The sandy element of soil allows infiltration of water into what was once at rest state and caused drained state of the clay loam. At critical point when the soil sheared, the only thing that is holding the body is the shroud which wrapped around the body which mean at almost critical state, the only thing that is holding the body to the around is the force from friction angle between shroud and soil. 
The sand which is much denser at 1600 kg/m3 will not allow to float, it is heavy and basically pushes the dead body down? Loose sand's friction angle in liquid state is no longer useful and it is behaving like a free particle.

6. The moment the uplift force(s) is greater than the friction angle between shroud and soil, the body will move upward due to buoyancy and gas built-up. After a while, the body is certainly above the ground.

7.Although this case have very low or extra low odd, it could happen and that causes dead body to submerge from the grave. This depends on the position of the body and the weight of the body as well.