SAP2000 Secant Bored Pile Circular Shaft with Opening

[ZackVincent]

I need to design the strengthening work around the opening of a circular shaft which is formed by secant bored pile wall (Similar to the shaft showing on this website:

http://www.zakladani.cz/en/secant-p...f-prolonged-a-line-of-prague-underground-v-a)

I have no idea how to model the secant bored pile. In my case, the pile size is 1000mm diameter and the opening is 2500mm diameter. The secondary pile is reinforced while the primary pile is a soft pile (plain concrete only). There are several ring beams to connect the piles.

Could anyone give me some advice on how to model it? Do I use frame element or shell element to model them? If frame element is used, how to connect the primary pile and secondary pile? If shell element is used, how to define the section properties and how to "release" the moment along circumferential direction (as there is no reinforced through the pile in circumferential direction)?