A search for Higgs boson production in association with a pair of top quarks ($t\bar{t}H$) is presented, 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.
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 $\mu=\frac{\sigma_\text{meas}}{\sigma_\text{SM}} = 1.6 \pm 2.6$ for $m_{H} = 125~\GeV$.
Combining all $t\bar{t}H$ searches carried out by ATLAS at $\sqrt{s}=7$ and $8~\TeV$, 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 $\mu = 1.7 \pm 0.8$.