Could leachate recirculation promote landslides in landfill?

Generally speaking, it should not. Landfills themselves are typically at less than field capacity for weight, meaning they are less than saturated.  Even in a very wet climate, you generally don’t have enough liquid present in the landfill to cause any problem with waste stabilization or side slope stabilization. Typically, in the United States, the liquid content in waste runs somewhere between 15-25% moisture content. So, if you are just taking the leachate that is present and recirculating it back through the waste you are not increasing it. Now, if you are operating a bioreactor landfill site, you need to get above 40% moisture content, and preferably as high as 50%. In that 40-50% range, you are near the field capacity of the waste, meaning that’s about as much liquid as the waste itself can absorb. At that point, even though you have more moisture content in the waste, it still shouldn’t effect slope stabilization. The sites that have the biggest problem with slope stabilization are sites that don’t have adequate liquid removal. We see this more often outside of the United States where sites have high levels of leachate accumulation.  These are sites that don’t have an underdrain system or their underdrain system has failed.  There the liquid level in the waste mass can rise considerably.  And where there is tens of meters/feet of liquid accumulated in the waste there can be an issue where the hydrostatic pressure behind the slope is so great that it can actually cause the slide slopes to blow out and start landslides. About two or three years ago at a site in Brazil the entire landfill blew out in the middle of the night and caused a considerable mess.  So, it is possible for it to happen, but we only have a couple of instances of it occuring in the U.S. because we are required to dewater systems with leachate collection.