There　are　two　major　challenges　for　the　use　of　enzyme-induced　carbonate　precipitation　(EICP)-based　soil　improvement　method:　cost　and　treatment　effect.　Optimizing　the　parameters　of　the　treatment　solution　is　one　way　to　enhance　the　treatment　effect　and/or　reduce　the　treatment　cost.　In　this　study,　three　key　factors:　the　initial　pH　(i.e.　pH0)　of　the　enzyme　solution　used　to　prepare　the　treatment　solution　(i.e.　the　mixture　of　enzyme　solution,　CaCl2　and　urea),　the　urease　activity　of　the　treatment　solution　and　the　concentration　of　cementation　solution　(i.e.　CaCl2　and　urea)　are　investigated.　Crude　soybean　enzyme　solution　and　the　one-phase-low-pH　injection　method　are　adopted　for　the　treatment　of　sand.　The　results　show　that　the　pH0　of　the　enzyme　solution　affects　the　urease　activity　of　enzyme　and　thus　the　urease　activity　of　the　prepared　treatment　solution.　It　is　discovered　in　this　paper　that　there　is　a　threshold　pH　value　for　the　treatment　solution.　Only　when　the　pH　of　the　treatment　solution　is　higher　than　the　threshold　pH　value,　calcium　ions　convert　completely　into　calcium　carbonate.　There　is　also　a　threshold　urease　activity　which　is　affected　by　the　concentration　of　cementation　solution,　CCS.　The　optimal　CCS　is　1.0 M.　When　the　CCS　is　higher　than　1.75 M,　the　urease　activity　of　soybean　enzyme　solution　would　be　completely　lost.　These　findings　are　important　in　guiding　the　application　of　EICP　treatment　using　the　crude　soybean　enzyme　in　real　soil　improvement　projects.　©　2024,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.