I don't know why those large paving stones are being laid, as not only do they look awful, they are not what permission was granted for. As Frank says, smaller paving units would be far more appropriate, integrating better with the fine grain of existing cobbles and setts.
Initially, Trinity applied for permission for the below scheme, drafted as a compromise between plans for greater and lesser numbers of pathways as discussed over the course of four years of consultation. As can be seen, the design included diagonal cross paths in Parliament Square which were considered by the case planner to be inharmonious with the rectilinear character of the enclosure, the buildings, and how they relate with each other. It was also felt that the paths were too numerous.
Otherwise considered an acceptable solution to resolving the problems of accessibility, the principal condition of granting permission was the omission of the diagonal paths and their replacement with a horizontal path connecting the Chapel and Examination Hall. A good compromise.
This proposal that was granted permission proposed the use of modern square granite setts of 100mm x 100mm, with edges and bays marked by 100mm x 200mm setts. It is difficult to understand, therefore, why large slabs of granite are being laid as test patches.
In any event, one would have to wonder why tightly knitted traditional setts, as they are supposed to be laid, cannot be used as a wheelchair surface. Why cannot pathways of the quality of the Foster Place setted surface, indeed even better, be laid? A slightly flatter stone, coupled with a vertical bonding pattern and tight laying, would surely provide a sufficiently flat surface?
A wheelchair pathway concept was successfully incorporated by the OPW into their new paving of the Upper Yard at Dublin Castle c. 1996, in this case used to architectural effect, drawing attention to the axial alignment of the entrance to the State Apartments with the Bedford Tower opposite.
A different context to Trinity though, as the roughly square-cut stones used here have a hard, structural quality, unlike the organic assemblage of cobbles in Front Square which require a softer treatment. Trinity also requires pavement widths capable of accommodating two passing chairs. In any event, the Upper Yard's paving was a grievous mistake, as not only are the 'cobbles' barely one step above hardcore - the salvaged off-casts of provincial British cities' tramlines if I recall - nastily laid in a pool of cement, and a nightmare to walk over, they also forever changed the regal character of the Yard, with its elegant compacted earth and gravel surface, which had never been cobbled in its 300 year history. A compacted surface of fawn-coloured earth and fine gravel traversed with pathways would have been fabulous. Such a crying shame.
Anyway, we'll see how Trinity pans out.