  A search for Higgs boson pair production $pp \to hh$ is performed with 19.5
fb$^{-1}$ of proton--proton collision data at $\sqrt{s}=$ 8 TeV, which were
recorded by the ATLAS detector at the Large Hadron Collider in 2012. The decay
products of each Higgs boson are reconstructed as a high-momentum $b\bar{b}$
system with either a pair of small-radius jets or a single large-radius jet,
the latter exploiting jet substructure techniques and associated $b$-tagged
track-jets. No evidence for resonant or non-resonant Higgs boson pair
production is observed. The data are interpreted in the context of the
Randall--Sundrum model with a warped extra dimension as well as the
two-Higgs-doublet model. An upper limit on the cross-section for $pp \to
G^{*}_{\mathrm{KK}} \to hh \to b\bar{b} b\bar{b}$ of 3.2 (2.3) fb is set for a
Kaluza--Klein graviton $G^{*}_{\mathrm{KK}}$ mass of 1.0 (1.5) TeV, at the 95\%
confidence level. The search for non-resonant Standard Model $hh$ production
sets an observed 95\% confidence level upper limit on the production
cross-section $\sigma(pp \to hh \to b\bar{b}b\bar{b})$ of 202 fb, compared to a
SM prediction of $\sigma(pp \to hh \to b\bar{b}b\bar{b}) = 3.6 \pm 0.5$ fb.
