Select those polylines, format/modify them as surface|from profiles, multi-add them together, and format/modify the object as solid|from surface. Even if you've left one face open, ACIS will fill the shell and solidify it. (sometimes with more than one open face, depending on their relationship, sometimes even if the open face/s aren't planar. But quite often, Genie tends to snort "is this an open shell?" and refuses to solidify it.) If it's a manifold object, ie no missing faces, select all of the faces with facet editor (lasso all of the blue indicators so they turn red), and format/modify it as solid|from faces. With the facet editor version, you can build a solid (or an open shell surface, for that matter) out of composite solids and surfaces, and it also trims surfaces against each other when they intersect rather than trying to match edges exactly, they don't have to be planar or n-sided polygons, they can be curved surfaces (lofts, or spherical/cylindrical/conical/ellipsoidal). This capacity has been in TC since V9 or V10, and it's become more competent with each successive version of ACIS. It dumps history, though, so the object is what's widely called a "dumb solid", a sort of freeform primitive.