using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main(string[] args)

    {

        var json = @"[[{""f1"":1, ""f2"":2}]]";

        var obj = JsonConvert.DeserializeObject<List<List<InnerObject>>>(json);

        foreach (var outer in obj)

        foreach (var inner in outer)

        {

            Console.WriteLine("f1: " + inner.f1);

            Console.WriteLine("f2: " + inner.f2);

        }

    }

}

​

public class InnerObject

{

    public int f1 { get; set; }

    public int f2 { get; set; }

}