Many　difficulties　are　encountered　during　EPB　tunnelling　through　the　cobble　layer　because　of　high　soil　friction　and　low　flow　characteristics.　In　order　to　solve　these　problems,　soil　conditioning　with　additives　has　become　an　indispensable　practice　to　enhance　the　properties　of　the　soil　and　make　the　soil　suit　for　the　machine.　However,　the　researches　on　soil　conditioning　are　limited　to　an　extent,　and　the　use　of　conditioning　additives　is　often　based　on　trial　and　errors　at　the　work　site　or　the　workers＇　experience.　The　soil　conditioning　for　EPB　excavation　in　the　cobble　layer　of　the　2nd-stage　project　of　Beijing　Metro　No.10　is　studied,　a　series　of　laboratory　tests　are　performed　to　investigate　and　assess　the　properties　of　additives　and　conditioned　soils.　The　optimum　injection　ratios　of　additives　(foam　injection　ratio　of　30%,　slurry　injection　ratio　of　10%,　and　the　optimum　slump　value　of　150~200　mm),　which　are　obtained　by　laboratory　tests,　are　applied　to　the　penetration　tests.　The　comparative　analysis　of　excavation　parameters　before　and　after　penetration　tests　shows　that　the　optimum　injection　ratios　of　additives　significantly　improve　the　performance　of　EPB　machine.　The　results　can　be　used　to　provide　guidelines　for　the　excavation　by　use　of　EPB　machine　under　such　soil　conditions.