Backfill materials play an important role in the geotechnical engineering. Mechanical properties, rheological properties, and microscopic properties were some of the key performance for the backfill materials. In recent years, researchers have attempted to improve the performance of backfill materials with various methods. However, both natural resource shortage and climate change pose serious challenges to human survival. The focus should be on developing environmental protection technology and promoting the development of backfilling technology in the direction of clean and energy-saving.

This Special Issue intends to collect the latest developments in the development and application of backfill materials, especially the environmentally friendly high performance backfill materials. Topics addressed in this Special Issue may include but are not limited to：

(1) Environmentally friendly backfill materials

(2) New developed high performance backfill materials

(3) Environmental evaluations and performance investigations on various backfill materials

(4) Cleaner technologies for backfill engineering

(5) Applications of environmentally friendly backfill materials