The Megalith Movers Prehistoric Engineering
Blog 5th August 2014 The Concrete Obelisk    Yesterday we poured the concrete for our obelisk without any disasters although the weight of wet concrete pressing against the base shutter caused base it to bulge a bit. We halted the pour for a short while and strengthened the shutter, my thanks to the workman who spotted what was happening and saved us from what would have been a real disaster for this project.    During the rest of the pour I stood on the plinth nervously watching the base shutter as it creaked and groaned, luckily it held to the end but we will now have the concrete obelisk with a slightly rounded base.    As this will make the obelisk unstable we have decided to strip the shutter as soon as is prudent and scrape away the bulge while the concrete is still relatively green. Normally I would have left the shutter in place maybe seven to fourteen days but now we have decided to carefully remove the base shutter on Friday and if all goes well scrape away the bulge.    Below are a few pics of the concrete pour.    We have now almost finished the preparations for this unique experiment into how the ancient Egyptians may have raised their obelisks around 4000 years ago. On this website you will find many theories by others about how this may have been done and also a few films of experiments conducted by Archaeologists, Engineers and suchlike. Most of these theories and experiments propose that the obelisk be pulled up a temporary earth ramp and tipped or lowered into place by some means until it stands at around 70 degrees, from which angle it becomes possible to pull it to vertical with ropes. I prefer approach the problem from the completely opposite direction, that is to place the base of the obelisk in precisely the right location and then use levers from the top end to erect it. If you are reading this blog and have not read the page “raising an obelisk” then you might like to do so as things will become so much clearer.    With time on my hands while waiting for the concrete to cure I find myself thinking about all the practical problems that may await us. During the first phase of the experiment the top end will be supported by a crib of logs as it rises inch by inch, I have successfully used this method before to support a 12 ton lintel stone whilst it was being elevated to the height of the Stonehenge uprights and it worked beautifully but during this experiment the stone was lying evenly on the crib with the weight of the stone being carried vertically to the ground through the crib both during the levering and in between.      In other words the crib was trapped in a vice-like grip between the 12 ton stone and the ground. In this experiment the obelisk will actually be leaning against the crib and only during the levering will the weigh be transferred directly to the ground. In between-times the top end will be supported by and leaning against what has now become just a loose stack of logs. During the early stages of the first phase this may not be a problem as the obelisk will still be pressing down on the crib mostly from above, but as we progress towards our target of 35 degrees for the first phase this may become a serious problem which we will have to overcome.    One of the most obvious solutions that comes to mind immediately is to use a series of Spanish windlasses (one of my favourite tools) between the upper and lower layers to exert pressure on the crib so that it effectively becomes one unit held together by the windlasses. Another is to use temporary props placed under the barn doors between the crib and the plinth making sure these are inserted above the balance point of the obelisk to resist the increasing lateral force exerted on the crib by the obelisk as it continues to rise. In fact as I sit writing this blog I am now thinking that using both solutions in unison may be answer we need.    I am also now thinking of amending my original my plans to incorporate the lower barn door into the buttressing, at the end of the first phase, using carpentry techniques and squared timber. As a retired carpenter this for me was a natural thought process, but having spent some time in the region where ropes, knots and lashings are more commonly used among the farming community for temporary structures, I can now see that this may be a practical solution during the first phase. It would also be more authentic in regard to how the ancient Egyptians might have carried out this exercise if they did indeed, (as I suspect) erect the obelisks from a recumbent position.    With the aforementioned in mind I have been studying various knots and lashings, among them Square lashing, and Filipino lashing which are my favourites for the support frame with Diagonal lashing for the bracing. I have also been looking at the Lorry Drivers Hitch and various anchorages for restraining the crib during the first phase.    After this short period of studying I am now convinced that using both solutions in unison is the best method for supporting the obelisk during the first phase of the operation. I am also convinced that using lashed and braced frames of natural poles for the buttressing will provide a very stable support during all three stages of this experiment and will easily bear the weight of the obelisk, which has now risen to an estimated 10 tons with the inclusion of the steel reinforcement. Sitting thinking about this refinement I now realise that what I envisaged as temporary props can be incorporated into the buttress frames thus becoming a permanent part of the structure. In fact such a solution could be made to bear the weight of several hundred tons without increasing the diameter of the poles, but instead just increasing the number of poles used.    All being well the first stage will now proceed as follows: The top end will be levered progressively higher from its starting position on the now lashed down crib where the underside is, at the top end, due to the shape of the obelisk and the fact that the base of the obelisk sitting on a 2ft high plinth, 3ft above the ground level, until it reaches a point perhaps 1ft or more higher, when the first and smallest of the lashed together frames will be introduced. This will be inserted underneath the top end and at right angles to the lower barn door in order to resist the growing lateral force, the crib which of course is resisting the downward force during the actual levering will grow in height as the obelisk rises. As the obelisk rises a few inches at a time with each lift this frame will be moved forward until we can insert a second and bigger lashed together frame. Now both these frames will be moved forward as required, until we can introduce a third frame and so on. In all I believe four frames will be sufficient to attain our goal of 35 degrees. Cross bracing will then be introduced between the separate frames and all four frames lashed together to form one strong framework, at this point the binding between the barn doors will be cut and the frames will be lashed to the lower barn door. Further strengthening the framework. End of first phase.    At the start of the second phase with the two barn doors no longer tied together we will lever up the top barn door and insert a 4 inch diameter pole between the two barn doors using the buttressing as a resting place for the fulcrum pole and when the levering continues the 4 inch pole will roll further down between the barn doors widening the gap at the top. Eventually we will be able to insert a bigger diameter log between the barn doors. All very well in theory but in practise easier said than done. If we were still at ground level this would still be easy enough, but at this stage both the lever-men and the men handling the packing logs will be standing on scaffolding more than 10 feet above ground level, at this height man-handling heavy logs becomes not only difficult but also dangerous. A 4 inch diameter log maybe 5 foot long would be easy enough for an old man like me even standing on scaffolding. The problem is the weight of a log rises exponentially with every slight increase in diameter, therefore a 5 foot long log of 8 inches in diameter will weigh not double the weight of a 4 inch log, but perhaps 4 or 5 times the weight, impossible for one or even two men to handle at height. And 8 inches will not be the end of the story we will need logs increasing in diameter to 12, 16, 20 inches or more before we have the obelisk standing at 70 degrees.    The end of a beautiful dream you may think, another fine theory bites the dust. No Ramps. No ropes. No multitude. NO CHANCE. YOU MAY ALSO THINK. Worry not my friends, that is those of you who have read this far, every problem has a solution if you think about it long enough, and the solution to this problem occurred to me one afternoon just a few weeks ago when I was sitting outside my favourite bar enjoying my usual tipple and watching the world go by. An innocent enough pastime and very enjoyable, some of the girls over here are very pretty and you will always be rewarded with a beautiful smile whenever you smile and catch their eye. But again I digress, where was I, ah yes sitting watching the world go by when a street vendor came by pushing a handcart loaded with Kitchen chopping boards each made from a circular slice of turned log. Instant inspiration, if I was to take three chopping boards and join them together with 5 foot lathes, one board at each end and one in the middle I would have a cylinder or hollow log, weight problem solved. And even if this hollow cylinder proved too heavy to man handle into position as it probably would with bigger cylinders, the constituent parts could be assembled where needed on the scaffold. <<previous blog page next blog page >> To read & post comments click here return to top of this page

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