Sudden　leaks　often　occur　when　constructing　shield　tunnels　within　saturated　sandy　cobble　strata.　Therefore,　it　is　important　to　examine　the　reasons　for　water　seepage　and　understand　the　mechanisms　behind　such　problems.　This　paper　presents　a　study　that　combines　laser　scanning　technology　with　the　Python　programming　language　to　create　software　for　monitoring　tunnel　deformation.　The　software　was　employed　in　a　practical　subway　tunnel　scenario,　successfully　acquiring　deformation　data　pertaining　to　the　tunnel＇s　structural　segment　through　the　analysis　of　point　cloud　data　from　the　tunnel　lining.　Furthermore,　the　seepage-stress　coupling　theory　was　employed　to　establish　a　three-dimensional　model　of　shield　tunnel　excavation,　interlinking　groundwater　and　stratigraphic　factors　with　the　sequence　of　shield　tunnel　excavation.　The　origins　and　mechanisms　of　water　damage　resulting　from　seepage　and　leakage　are　explicated　through　an　examination　of　the　seepage　field,　displacement　field,　and　deformation　of　the　tunnel　structure　pre-　and　post-excavation.　Additionally,　on-site　monitoring　data　is　considered.　The　mechanism　of　tunnel　leakage　is　outlined　as　follows:　Tunnel　excavation　completion　induces　alterations　in　the　seepage　field,　leading　to　an　accelerated　inflow　of　groundwater　into　the　soil　beneath　the　tube　sheet　during　shield　excavation.　The　tube　sheet　of　the　shield　tunnel,　composed　of　sand　and　gravel　layers,　experiences　vertical　elliptical　deformation　that　exacerbates　shifts　in　the　displacement　field　due　to　tunnel　deformation＇s　inception　and　progression.　Excessive　tube　sheet　deformation　triggers　fracture　cracks,　ultimately　engendering　the　creation　of　seepage　channels.　These　channels,　in　turn,　foster　seepage　and　water　damage.　The　results　of　this　paper　provide　a　reference　for　preventing　and　remedying　water　infiltration　and　leakage　in　shield　tunnels　constructed　of　sandy　cobble　strata.