University of Missouri Law Professor Stacy Strong does a lot of good writing on international arbitration and has been especially attentive to class actions and other mass adjudication procedures. Her book, "Class, Mass, and Collective Arbitration in National and International Law", is here.
Her current paper, "Limits of Autonomy in International Investment Arbitration: Are Contractual Waivers of Mass Procedures Enforceable?" is here. It discusses such mass adjudication procedures in investment arbitration and contractual waivers of such procedures.