To counter-influence the massive global extent of employee disengagement (at 75%), Gallup for years has had evidence that engaged people have at least one friend at work. The proposal suggests that high engagement cultures actively nurture social connections.
I think the conversation moves forward on the consideration that friendship is a continuum from the convenience of friendliness to the durability of lifelong friendships. Social network sciences suggest that each of is capable of a finite number of people, in our life as much at work, along this continuum because each category requires available time and interpersonal chemistry often trumps extrinsic necessity.
On whatever level they occur, friendships happen naturally. They cannot be the subject of policies, incentives or training. Given this, one of the easiest ways for any organization to promote authetic friendships is to give voice to the stories of people who have already become friends at work. This legitimizes and inspires the possibilities in the most natural ways.