  A search for Higgs boson production in association with a pair of top quarks
($t\bar{t}H$) is performed, where the Higgs boson decays to $b\bar{b}$, and
both top quarks decay hadronically. The data used correspond to an integrated
luminosity of 20.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV collected
with the ATLAS detector at the Large Hadron Collider. The search selects events
with at least six energetic jets and uses a boosted decision tree algorithm to
discriminate between signal and Standard Model background. The dominant
multijet background is estimated using a dedicated data-driven technique. For a
Higgs boson mass of 125 GeV, an upper limit of 6.4 (5.4) times the Standard
Model cross section is observed (expected) at 95% confidence level. The
best-fit value for the signal strength is $\mu = 1.6 \pm 2.6$ times the
Standard Model expectation for $m_{H} = 125$ GeV. Combining all $t\bar{t}H$
searches carried out by ATLAS at $\sqrt{s}=8$ and 7 TeV, an observed (expected)
upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at
95% confidence level, with a signal strength $\mu = 1.7 \pm 0.8$.
