The minimal SUSY Standard Model shows electromagnetic force coupling increasing from alpha of 1/137 to alpha of 1/25 at 10^16 GeV, and the strong force falling from 1 to 1/25 at the same energy, hence unification.
The reason why the unification superforce strength is not 137 times electromagnetism but only 137/25 or about 5.5 times electromagnetism, is heuristically explicable in terms of potential energy for the various force gauge bosons.
If you have one force (electromagnetism) increase, more energy is carried by virtual photons at the expense of something else, say gluons. So the strong nuclear force will lose strength as the electromagnetic force gains strength. Thus simple conservation of energy will explain and allow predictions to be made on the correct variation of force strengths mediated by different gauge bosons. When you do this properly, you may learn that SUSY just isn't needed or is plain wrong, or else you will get a better grip on what is real and make some testable predictions as a result.
I frankly think there is something wrong with the depiction of the variation of weak force strength with energy shown in Figure 66 of Lisa Randall's "Warped Passages". The weak strength is extremely low (alpha of 10^-10) normally, say for beta decay of a neutron into a proton plus electron and antineutrino. This force coupling factor is given by Pi2hM4/(Tc2m5), where h is Planck’s constant from Planck’s energy equation E = hf, M is the mass of the proton, T is the effective energy release ‘life’ of the radioactive decay (i.e. the familiar half-life multiplied by 1/ln2 = 1.44), c is velocity of light, and m is the mass of an electron.
The diagram seems to indicate that at low energy, the weak force is stronger than electromagnetism, which seems in error. The conventional QFT treatments show that electroweak forces increase as a weak logarithmic function of energy. See arxiv hep-th/0510040, p. 70.
'STRING THEORY' FINALLY FINDS A USE: FOR EXCUSING INFIDELITY.