Construction tolerances are an issue. A circular secant shaft will be designed with hoop stress – if you deviate this is lost. Also secant presumably to exclude water and gain deviation can cause loss of seal. You could consider segmental casing with kelly auger to get deeper depths than achievable with CFA or CSP where you are limited by length of auger string. You need to discuss with an experienced contractor. Better to work on hoop stress (anchoring will be time consuming and costly) and perhaps better to look at a diaphragm wall.