Although　the　Rankine-based　simplified　incremental　calculation　method(SICM)　has　been　widely　applied　in　practice　for　prediction　of　nail　loads,　its　model　accuracy　has　not　yet　fully　assessed.　In　this　paper,　a　large　database　containing　a　total　of　466　measured　nail　loads　from　178　nails　reported　in　the　literature　was　established.　After　removing　questionable　data,　the　remaining　load　data　from　143　nails　were　used　to　evaluate　the　accuracy　of　the　Rankine　SICM,　which　is　characterized　by　the　model　bias　defined　as　the　ratio　of　measured　to　predicted　nail　loads,　and　the　influence　of　3　working　conditions　on　the　accuracy　of　the　SICM　was　also　investigated.　The　results　show　that,　under　typical　cases,　the　current　Rankine　SICM　underestimates　averagely　the　maximum　nail　load　by　about　10%　to　17%　with　a　high　prediction　dispersion　over　90%　while　overestimates　the　mean　nail　load　by　about　15%　with　a　moderate　prediction　dispersion　of　about　70%.　In　addition,　the　accuracy　is　statistically　correlated　to　the　magnitude　of　the　predicted　value,　which　is　undesirable.　It　was　proposed　to　estimate　the　nail　load　based　on　the　Coulomb　active　earth　pressure　theory　instead　of　the　Rankine　theory　for　accuracy　improvement.　A　calibration　constant　of　about　0.75　is　introduced　to　calibrate　the　computed　nail　load.　The　Coulomb　SICM　was　demonstrated　to　be　unbiased　on　average　with　a　medium　prediction　dispersion　from　44%　to　66%.　It　is　also　shown　that　the　accuracies　of　both　Rankine　and　Coulomb　SICMs　are　significantly　influenced　by　soil　types　whereas　the　influence　of　load　allocation　schemes,　external　loading　conditions　and　wall　types　is　marginal.　The　model　biases　of　Rankine　and　Coulomb　SICMs　respectively　follow　lognormal　and　Weibull　distributions.　Finally,　the　accuracies　of　the　two　types　of　SICM　were　discussed　complementally　from　another　four　angles.　©　2021,　Science　Press.　All　right　reserved.