Investigations　of　the　elastic　mechanical　characteristics　of　loosely　compacted　mixed　sand-clay　samples　are　essential　for　the　characterization　of　shallow　seafloor　sedimentary　reservoirs.　Here,　we　used　a　series　of　sand-clay　mixtures　(0-100%　clay　by　weight)　to　investigate　the　effects　of　pressure　load　histories　(2-50　MPa)　and　clay　fraction　on　porosity,　P-wave　velocity,　S-wave　velocity,　and　static　modulus.　The　results　indicated　that,　under　pressure　load　cycles,　the　sand-clay　mixture　samples　exhibited　high　permanent　compaction,　and　porosity　decreased　rapidly　with　increasing　clay　content.　However,　porosity　changed　differently　in　response　to　pressure　load　as　compared　to　pressure　unload.　Correspondingly,　P-wave　velocities　differed　significantly　between　pressure　load　and　unload.　The　rock　physical　models　implied　that　the　sample　frame　evolved　with　the　varying　clay　fraction.　As　the　clay　fraction　increased,　the　sample　frame　gradually　transitioned　from　primarily　sand　grains　with　dispersed　pore-filling　clay　to　primarily　clay,　ultimately　transforming　into　a　clay　frame　with　dispersed　sand　grains.　The　measured　data　generally　conformed　to　the　theoretical　model　and　falling　within　the　Voigt　and　Reuss　bounds.　Moreover,　for　all　sand-clay　mixture　samples,　although　the　static　bulk　modulus　was　consistently　lower　than　the　dynamic　bulk　modulus,　the　ratio　of　the　dynamic　modulus　to　the　static　modulus　was　highly　dependent　on　pressure　loads　and　clay　fraction.　(C)　2019　Elsevier　B.V.　All　rights　reserved.