The pressure didn't necessarily need to be contained. All that was needed was to have water at altitude. There are numerous ways to achieve this dependent on the nature of the water pressure. With cold water geysers all that's really needed is to collect the water on top of the unfinished pyramid which is easily enough accomplished merely by siting the pyramid where the water falls. There is a massive natural fissure just to the north of the main opening to the Great Pyramid. Petrie et al, have also said that it appears there was additional structure in this area. The joints around the entrance appear to have been designed to recieve other structure. The fissure is offset from center and is aligned more closely with the queen's chamber. This would be consistent with a counterweight operating at center.

There seems little doubt that these people had a very very keen understanding of water. It was necessary to live in a land that was arid yet periodically flooded and the primary means of transportation was by water which often went through man-made canals. For further verification look at the huge number of references to water in the pyramid texts and elsewhere. Understanding the behavior of water is really very easy even with primitive views. Water seeks its level. They would certainly understand that more water or higher water equaled more pressure. There's not a great deal more understanding needed to do basic work with it and from there might spring a more thorough or even mathematic understanding. This simply means they could develope the shaduf without the calculus and could attempt basic plumbing (interesting this word derives from plumbum the Latin word for lead). It may well have been an attempt at piping the water coming from this fissure which gave birth to the Osiris legend. Osiris was induced to lie down in a box in which lead was poured.

Ultimately all that's needed is to have water at pressure. Everything else could evolve from that.

Reading the Pyramid Texts with an eye toward cold water geysers is really sobering. It simply mostly all fits. Indeed, you can virtually date the different utterances by how they refer to Rosteau, the horizon, the herb hills, the eye of Horus, Osiris, and the necropolis.

It always comes back to the evidence. It always comes back to the sand in the walls of the queens chamber, the salt encrustations, the siting, the reference to a 7 X 3 cubit eye (the grotto), the tools, artefacts, and the actuaal structures. There are the little things like Menkaure's causeway ending at Khufu's quarry (why build locks to the river when you can flood the quarry). There's the fact that scientists can't even seem to agree that the pyramid is made of stone (maybe it's more like travertine). There are the exhortations to get Osiris to stand preceeded by the command 5 pellets of natron. How better to get a geyser to erupt than adding natron? Then there are the ancient reports that stones were moved to the pyramid a bowshot (300') at a time. I can think of no other means than a counterweight falling 300' to explain such a contention. Horapollo said that the Egyptians believed that water came up out of the ground during inundation.

The geology of this area is certainly consistent with a diverse supply of caverns and caves to a very great depth. Any water flooding these would be near the surface at many points from Giza to the Fayuum. If this water were carbonated like Lake Kivu it would come up.

Yes, all the evidence is circumstantial but it does tie up all the loose ends. It would be nice to see a little investigation into this.

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Man fears the pyramid, time fears man.