if the negative slope is small, for instance, less than 15-20 degree, soil nail+wiremesh+shotcrete+temporary prop may be tried . if the slope is large, active pressure would be very large, soil anchors prestressed (or soil tubular nail)+concrete frame+prop may be examined. !#~KSO}zW2
I remembered that long before in this forum there was a design considering the cavity excavation near the heel of the retaining structure. that may be referred to. JZ+6)R
the ground water control is more significant in this design.
