<P> At the upper end of the Gallery on the right - hand side there is a hole near the roof that opens into a short tunnel by which access can be gained to the lowest of the Relieving Chambers . The other Relieving Chambers were discovered in 1837--1838 by Colonel Howard Vyse and J.S. Perring, who dug tunnels upwards using blasting powder . </P> <P> The floor of the Grand Gallery consists of a shelf or step on either side, 51 centimetres (20 in) wide, leaving a lower ramp 1.04 metres (3.4 ft) wide between them . In the shelves there are 54 slots, 27 on each side matched by vertical and horizontal slots in the walls of the Gallery . These form a cross shape that rises out of the slot in the shelf . The purpose of these slots is not known, but the central gutter in the floor of the Gallery, which is the same width as the Ascending Passage, has led to speculation that the blocking stones were stored in the Grand Gallery and the slots held wooden beams to restrain them from sliding down the passage . This, in turn, has led to the proposal that originally many more than 3 blocking stones were intended, to completely fill the Ascending Passage . </P> <P> At the top of the Grand Gallery, there is a step giving onto a horizontal passage some metres long and approximately 1.02 metres (3.3 ft) in height and width, in which can be detected four slots, three of which were probably intended to hold granite portcullises . Fragments of granite found by Petrie in the Descending Passage may have come from these now - vanished doors . </P> <P> In 2017, scientists from the ScanPyramids project discovered a large cavity above the Grand Gallery using muon radiography, which they called the "ScanPyramids Big Void". Its length is at least 30 metres (98 ft) and its cross-section is similar to that of the Grand Gallery . Its existence was confirmed by independent detection with three different technologies: nuclear emulsion films, scintillator hodoscopes, and gas detectors . The purpose of the cavity is not known and it is not accessible but according to Zahi Hawass it may have been a gap used in the construction of the Grand Gallery . The Japanese research team disputes this, however, saying that the huge void is completely different from the construction spaces previously identified . </P>

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