Complex sentence: West's false wall kept slipping so he held it into place with cement, which set; when Morris and the Anglins accelerated the schedule, West desperately chipped away at the wall, but by the time he got out, his companions were gone.
Split into simpler sentences: West's false wall kept slipping so he held it into place with cement, which set. When Morris and the Anglins accelerated the schedule, West desperately chipped away at the wall, but by the time he got out, his companions were gone.