Aiming　at　the　problems　of　ground　settlement　induced　by　the　underground　pipeline　damage　in　water-rich　sand　layer,　a　set　of　visualization　experimental　device　was　designed.　For　these　cases　of　11　kinds　of　sand　samples　with　particle　size　of　skeleton　d90=1.45~8.45　mm　and　5　kinds　of　full　pipe　flow　velocity,　the　law　of　ground　settlement　induced　by　seepage　erosion　was　studied.　Research　show　that:　1)　There　are　three　modes　of　seepage　erosion　induced　by　pipeline　damage:　only　water　inrush　without　settlement,　soil　arching　formation　with　settlement　and　sand　crushing　with　settlement;　2)　The　particle　size　of　soil　skeleton,　damaged　mouth　size　and　thick-span　ratio　are　the　main　factors　to　determine　the　seepage　erosion　mode　of　soil;　3)　When　the　soil　arching　or　sand　crushing　is　formed　in　the　soil　above　the　damaged　mouth　of　pipeline,　the　relationship　between　the　particle　size　of　skeleton　d90　and　the　thick-span　ratio　r　is　that:　when　8.0≥r≥4.2,　the　d90　decreases　parabolically　with　the　increase　of　r;　when　12.5≥r≥8.0,　d90　remains　unchanged;　4)　When　the　soil　arching　or　sand　crushing　is　formed　in　the　soil　above　the　damaged　mouth　of　pipeline,　the　initial　settlement　radius　and　settlement　depth　with　the　flow　velocity　equal　to　0　are　determined　by　the　ratio　(D/d50)　of　the　damaged　mouth　diameter　D　and　the　average　particle　size　of　soil　d50;　the　settlement　radius　and　depth　increase　linearly　with　the　increase　of　full　pipe　flow　velocity;　when　the　soil　arching　is　formed,　the　expansion　velocity　(VL,　VH)　of　settlement　radius　and　settlement　depth　with　the　increase　of　flow　velocity　is　logarithmic　to　D/d50.　When　the　sand　crushing　is　formed,　the　expansion　velocity　VL　of　settlement　radius　with　the　increase　of　flow　velocity　is　that,　when　23.0≥D/d50≥6.0,　it　increases　linearly　with　the　increase　of　D/d50;　when　42.0≥D/d50≥23.0,　it　decreases　logarithmically　with　the　increase　of　D/d50.　©　2020,　Science　Press.　All　right　reserved.