(This is for educational purposes only. I am not responsible for any damage or injury resulting from what I have described herein. If you do it anyways, please be extremely careful about yourself, other people, and expensive property being exposed to anything I have described herein)
Any object can levitate if it is given enough negative charges of the correct types. Softer negative charges can become "locked-in" the rocks as they are being processed, so they remain floating even when removed from the energy field.
With this type of construction, the engineer is faced with the problem of components floating away into the sky instead of being drawn downward. This may be overcome simply with a large net or wire screen, requiring occasional maintenance to patch the net as well as replacing smaller rocks that have dislodged and floated away upwardly. It may appear ugly, as well as having the wear proportional to usage, similar to the paved roads in that way.
A bridge would be so close to Earth's surface, the vertical gradient of gravity would be negligible. (as opposed to the situation with a floating continent, where the gradient acts as a spring holding it at a certain distance range for a certain load weight)
Over time, the charges will find their way out of the rocks, as they can't be perfectly integrated, similar in principle to a strong magnet losing some of its strength over hundreds of years. The rocks may be "recharged" by putting them through the process again.
Perhaps each rock could be engineered with its own power crystal and altimeter unit, like a scaled-down version of the floating continent system, regulating the charges to maintain position (and load-following the changing distribution of weight, for the army marching across). The smaller crystals needed would be able to react faster, having a much higher operating frequency. They would be capable of developing much more lifting force density than the "natural" type of floating rocks, so you could move many tons of army tanks, troop carriers, missile batteries, etc. across if it ever became necessary
Yet another way could be devised, using special emitters installed near the bridge, constantly beaming the levitation charges into to the rocks. Most would receive equalized charges by conduction, but larger rocks would tend to rotate in irregular patterns if the negative charges become concentrated in the downward-facing side.
The tibetans have caused huge boulders to levitate up the sides of cliffs before, using the same effect differently. Musical instruments were used to resonate the crystalline content of the stone, releasing negative charges within. Occasionally the boulders explode, because too many harder charges with nowhere to go creates more pressure than it can handle (electrostatic repulsion).
By supplying the charges externally, you don't have to use rocks with great enough crystalline content (or the sound power to "activate" them) - any rocks will do, provided they are strong enough for forces encountered in the application.
Please be very careful to make sure the correct types of charges are being put into the floating rocks, for quality of the product and safety of the process. Harder negative charges will be lost to conduction more quickly, or even cause the rocks to explode while being made. Positive charges will have the opposite effect, making the rocks heavier than normal, as well as causing bad sickness for anyone having the positive charges conducted into their body (nuclear radiation).
For more information, see Joseph Cater's book, The Ultimate Reality. It thoroughly explains the physics involved in this type of architecture.
I will demonstrate this principle very soon. Once I have made a video I will share the link here, for everyone to enjoy the demonstration.