The level of the hill was reduced by 15 m (49 ft) and the construction of two vertical tunnels was then decided.[42] On 18 January, the heavy machinery drilled to open a vertical tunnel parallel to the well and they run into a slate rock mass at 18 meters depth, which again complicates the rescue work.[43] On 23 January, the rescue team reduces the diameter of the pipe intended for vertical drilling.[7] On 25 January, the miners advance in the final search in the well.