Accurate　determination　of　parameters　for　an　advanced　soil　constitutive　model　highly　relies　on　laboratory　testing,　even　though　it　is　notoriously　difficult　to　obtain　undisturbed　samples　for　soft　soils.　This　study　explores　the　potential　use　of　in　situ　tests,　such　as　piezocone　penetration　tests　(CPTU)　and　seismic　dilatometer　tests　(SDMT),　to　estimate　the　constitutive　model　parameters.　Based　on　a　case　history　of　a　deep　excavation　adjacent　to　existing　tunnels　in　silt/sand-dominated　sediments,　a　calibration　approach　of　a　set　of　the　HSSmall　(Hardening　Soil　Model　with　small　strain　stiffness)　model　parameters　is　presented,　and　the　derived　parameters　are　used　to　numerically　compute　the　interactive　responses　of　tunnels　and　deep　excavations.　Several　comparisons　against　field　monitoring　data　indicate　that　the　numerical　model　with　the　CPTU/SDMT-interpreted　HSSmall　model　parameters　adequately　reproduces　observed　deformation　responses　of　deep　excavations　adjacent　to　tunnels.　However,　in　the　considered　case　study,　the　use　of　laboratory　tests　with　disturbed　samples　to　estimate　the　stiffness　parameters　of　the　HSSmall　model　results　in　an　overconservative　solution.　This　finding　supports　the　use　of　CPTU/SDMT　to　provide　representative　parameters　for　a　range　of　soil　layers,　leading　to　the　conclusion　that　tunnel　linings　may　be　beneficial　to　mitigate　ground　movements　and　wall　deflections　due　to　a　＂barrier＂　effect.