diff --git a/B05_Profile/B05_Profile_UI_Corridor_Station_Structure.ts b/B05_Profile/B05_Profile_UI_Corridor_Station_Structure.ts
index e0c6913f4..13b7a6c7e 100644
--- a/B05_Profile/B05_Profile_UI_Corridor_Station_Structure.ts
+++ b/B05_Profile/B05_Profile_UI_Corridor_Station_Structure.ts
@@ -211,7 +211,7 @@ export function fordSilhouettes(section: CrossSection): StructureSilhouette[] {
       points.push(floorOuter);
       patchPoints.push(floorOuter);
       const run: OffsetPoint[] = [floorOuter];
-      for (const cutPoint of [side.cutLine.from, side.cutLine.to]) {
+      for (const cutPoint of side.cutLine) {
         const at = { offset_m: cutPoint.offset, elevation_m: cutPoint.elevation };
         points.push(at);
         patchPoints.push(at);
@@ -347,8 +347,8 @@ export function culvertSilhouettes(section: CrossSection): StructureSilhouette[]
     }
     // 집수정이 원지반에 박히면 절토선까지 — 그만큼 원지반을 걷어낸다.
     if (layout.basin.cutLine) {
-      push(inletSide, [layout.basin.cutLine.from, layout.basin.cutLine.to]);
-      addRun(inletSide, [layout.basin.cutLine.from, layout.basin.cutLine.to]);
+      push(inletSide, layout.basin.cutLine);
+      addRun(inletSide, layout.basin.cutLine);
       basinCut = true;
     }
     spans[inletSide] = basinSpanOf(section);
diff --git a/B06_Section/B06_Section_UI_Cross_Box.ts b/B06_Section/B06_Section_UI_Cross_Box.ts
index c83a1a607..ab2422824 100644
--- a/B06_Section/B06_Section_UI_Cross_Box.ts
+++ b/B06_Section/B06_Section_UI_Cross_Box.ts
@@ -136,7 +136,7 @@ export function appendBoxOverlay(
     }));
     if (side.cutLine)
       lines.push({
-        points: [side.cutLine.from, side.cutLine.to],
+        points: side.cutLine,
         text: `${mark}측 끝 절토선(계획선)`,
       });
     for (const line of lines) {
diff --git a/B06_Section/B06_Section_UI_Cross_Box_Geom.ts b/B06_Section/B06_Section_UI_Cross_Box_Geom.ts
index a9ae4f1b3..247e0dae7 100644
--- a/B06_Section/B06_Section_UI_Cross_Box_Geom.ts
+++ b/B06_Section/B06_Section_UI_Cross_Box_Geom.ts
@@ -26,6 +26,7 @@ import type {
 import { buildExtrasAt } from "./B06_Section_UI_Cross_Culvert_Extra";
 import { FILL_SLOPE_RATIO_MIN } from "./B06_Section_UI_Cross_Culvert_Const";
 import { designInterpolator, groundInterpolator } from "./B06_Section_UI_Cross_Culvert_Solve";
+import { structureCutPoints, structureCutSpec } from "./B06_Section_UI_Cross_Structure_Cut";
 
 /** 구체 한쪽 끝의 조작값 — 좌·우를 따로 잡는다(2026-08-25 사용자). */
 export interface BoxSideAdjust {
@@ -135,7 +136,8 @@ export function computeBoxLayout(
   // 본체는 늘 수평(79-7) — 좌 · 우 표고 조정이 달라도(옛 저장) 평균 하나로 섬.
   const riseM = (adjust.left.riseM + adjust.right.riseM) / 2;
   const sampleOffsets = groundSamples.map((sample) => sample.offset_m ?? 0);
-  const cutSlopeRatio = section.design?.cut_slope_ratio ?? 1.0;
+  // 끝 절토 = 본선 절토 사면과 같은 복합경사(91-4)
+  const cutSpec = structureCutSpec(section.design);
 
   const sideOf = (role: BoxSideRole): BoxSideLayout => {
     const outward = role === "left" ? 1 : -1;
@@ -172,13 +174,7 @@ export function computeBoxLayout(
     let cutLine: BasinLayout["cutLine"] = null;
     let fillSegments: OutletFillSegment[] = [];
     if (groundAt(end.offset) > end.elevation + 0.05) {
-      for (let h = 0.05; h <= 20; h += 0.05) {
-        const probe = end.offset + outward * cutSlopeRatio * h;
-        if (groundAt(probe) <= end.elevation + h) {
-          cutLine = { from: end, to: { offset: probe, elevation: end.elevation + h } };
-          break;
-        }
-      }
+      cutLine = structureCutPoints(end, outward, cutSpec, groundAt);
     } else if (groundAt(end.offset) < end.elevation - 0.05) {
       fillSegments = buildExtrasAt(end, {
         startBottomElevation: bottomElevation,
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert.ts b/B06_Section/B06_Section_UI_Cross_Culvert.ts
index 245e18dd4..c05df849a 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert.ts
@@ -225,11 +225,12 @@ export function appendCulvertOverlay(
       layer.append(shape);
     }
     if (basin.cutLine) {
-      const cut = document.createElementNS(SVG_NS, "line");
-      cut.setAttribute("x1", String(x(basin.cutLine.from.offset)));
-      cut.setAttribute("y1", String(toDisplayY(basin.cutLine.from.elevation)));
-      cut.setAttribute("x2", String(x(basin.cutLine.to.offset)));
-      cut.setAttribute("y2", String(toDisplayY(basin.cutLine.to.elevation)));
+      // 점열(암 무릎 · 소단 · 91-4)
+      const cut = document.createElementNS(SVG_NS, "polyline");
+      cut.setAttribute(
+        "points",
+        basin.cutLine.map((point) => `${x(point.offset)},${toDisplayY(point.elevation)}`).join(" "),
+      );
       // 절토선은 **공사 계획선**이다 — 설계선과 같은 보라 실선으로 그린다
       // (2026-08-20 사용자 ②).
       cut.setAttribute("class", "b06-chart__design-cross");
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert_Basin.ts b/B06_Section/B06_Section_UI_Cross_Culvert_Basin.ts
index 3ef18d3fc..3d362750a 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert_Basin.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert_Basin.ts
@@ -20,7 +20,7 @@ import {
   REVET_FREEBOARD_M,
   REVET_LEAN_RATIO,
 } from "./B06_Section_UI_Cross_Culvert_Const";
-import type { CulvertSideSpec } from "./B06_Section_Api_Fetch";
+import type { CrossDesign, CulvertSideSpec } from "./B06_Section_Api_Fetch";
 import {
   minShoulderWallOffset,
   slopeLengthAlong,
@@ -34,6 +34,7 @@ import type {
   OffsetPoint,
   InletStructureChoice,
 } from "./B06_Section_UI_Cross_Culvert_Types";
+import { structureCutPoints, structureCutSpec } from "./B06_Section_UI_Cross_Structure_Cut";
 
 /** 자동(기본) 집수정 모양(54-36) — 좌측 폼 「(기본)」 표시도 이 값. */
 export const DEFAULT_BASIN_SHAPE: BasinShape = "L";
@@ -140,8 +141,10 @@ export interface BasinBuildInput {
   /** 이 측의 노견 끝 점 — 벽 상단 접점·I형 높이 성장 기준. */
   edge: { offset_m: number; elevation_m: number };
   groundAt: (offset: number) => number;
-  /** 표준단면 절토 경사(1:n) — 절토 계획선용. */
-  cutSlopeRatio: number;
+  /** 표준단면 절토 경사(1:n) — 절토 계획선용(`cutDesign` 이 없을 때 경사 하나). */
+  cutSlopeRatio?: number;
+  /** 측점 설계값 — 있으면 절토선이 본선과 같은 복합경사(암 무릎 · 소단 · 91-4). */
+  cutDesign?: Partial<CrossDesign> | null;
   adjust: BasinAdjust;
   /** 벽 두께(m). 기본 = 집수정 부재 두께. 세월교 측벽이 다른 두께를 쓸 때 넘긴다. */
   memberThicknessM?: number;
@@ -183,17 +186,8 @@ export const BASIN_INNER_WIDTH_M = 1.0;
 
 /** 집수정 단면을 만든다. 형태별 규칙은 파일 머리말 참조. */
 export function buildBasin(input: BasinBuildInput): BasinBuildResult {
-  const {
-    anchor: baseAnchor,
-    outward,
-    shape,
-    reason,
-    diameterM,
-    edge,
-    groundAt,
-    cutSlopeRatio,
-    adjust,
-  } = input;
+  const { anchor: baseAnchor, outward, shape, reason, diameterM, edge, groundAt, adjust } = input;
+  const cutSpec = structureCutSpec(input.cutDesign ?? { cut_slope_ratio: input.cutSlopeRatio });
   /** 이 부재의 기움 — 집수정 0.3, 세월교 0(수직). */
   const lean = input.leanRatio ?? REVET_LEAN_RATIO;
   const movedAnchor = {
@@ -339,13 +333,7 @@ export function buildBasin(input: BasinBuildInput): BasinBuildResult {
         : { offset: floorOuter, elevation: anchor.elevation };
     const groundHere = groundAt(refTop.offset);
     if (groundHere > refTop.elevation + 0.05) {
-      for (let h = 0.05; h <= 20; h += 0.05) {
-        const probe = refTop.offset + outward * cutSlopeRatio * h;
-        if (groundAt(probe) <= refTop.elevation + h) {
-          basinCut = { from: refTop, to: { offset: probe, elevation: refTop.elevation + h } };
-          break;
-        }
-      }
+      basinCut = structureCutPoints(refTop, outward, cutSpec, groundAt);
     } else if (groundHere < refTop.elevation - 0.05) {
       // 원지반 밖으로 나왔다 — 성토부선은 유출측과 같은 체계(1:1.2 + 5m 다단)로
       // 본체가 그린다(2026-08-22 사용자 확정). 여기서는 시작점만 넘긴다.
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert_Extra.ts b/B06_Section/B06_Section_UI_Cross_Culvert_Extra.ts
index 720b9452e..fb01894dd 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert_Extra.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert_Extra.ts
@@ -29,6 +29,8 @@ import type {
   WallAdjust,
   WallLayout,
 } from "./B06_Section_UI_Cross_Culvert_Types";
+import { structureCutPoints } from "./B06_Section_UI_Cross_Structure_Cut";
+import type { StructureCutSpec } from "./B06_Section_UI_Cross_Structure_Cut";
 import { buildRevetWallGeometry } from "./B06_Section_UI_Cross_Wall";
 
 export interface OutletExtrasInput {
@@ -48,20 +50,19 @@ export interface OutletExtrasInput {
   equalize?: boolean;
   /** 단 벽의 전면 기울기 — 형태·순수 높이로 표준경사를 고름(없으면 종전 1:0.3). */
   leanFor?: (form: string, pureHeightM: number) => number;
-  /** 끝이 원지반에 묻힐 때 수평공간 뒤 절토 경사(1:n)로 지반까지(세월교 · 박스 흙막이 · 79-7).
-   *  없으면 종전 3도 선. */
-  cutBerm?: { lengthM: number; slopeRatio: number };
+  /** 끝이 원지반에 묻힐 때 수평공간 뒤 절토(본선과 같은 복합경사 · 91-4)로 지반까지(세월교 · 박스
+   *  흙막이 · 79-7). 없으면 종전 3도 선. */
+  cutBerm?: { lengthM: number; cut: StructureCutSpec };
 }
 
-/** 수평공간(berm) 뒤 절토 경사로 원지반까지 — 공간 안에서 지반을 만나면 거기서 끝(79-7). */
+/** 수평공간(berm) 뒤 절토(복합경사 · 91-4)로 원지반까지 — 공간 안에서 지반을 만나면 거기서 끝(79-7). */
 function bermCut(
   src: OffsetPoint,
   outward: number,
-  berm: { lengthM: number; slopeRatio: number },
+  berm: { lengthM: number; cut: StructureCutSpec },
   groundAt: (offset: number) => number,
   limitOffset: number,
 ): OutletFillSegment {
-  const ratio = Math.max(berm.slopeRatio, 0.1);
   const flat = slopedCrossing(src, outward, 0, groundAt, limitOffset);
   const segment = (points: OffsetPoint[]): OutletFillSegment => ({
     points,
@@ -78,22 +79,16 @@ function bermCut(
   if (flat !== null && (flat - src.offset) * outward <= berm.lengthM + 1e-9)
     return segment([src, { offset: flat, elevation: src.elevation }]);
   const bend = { offset: src.offset + outward * berm.lengthM, elevation: src.elevation };
-  const span = (limitOffset - bend.offset) * outward;
-  let previousGap = groundAt(bend.offset) - bend.elevation;
-  for (let t = 0.25; t <= span + 1e-9; t += 0.25) {
-    const gap = groundAt(bend.offset + outward * t) - (bend.elevation + t / ratio);
-    if (gap <= 0) {
-      const fraction = previousGap > 1e-12 ? previousGap / (previousGap - gap) : 1;
-      const cross = t - 0.25 * (1 - fraction);
-      return segment([
-        src,
-        bend,
-        { offset: bend.offset + outward * cross, elevation: bend.elevation + cross / ratio },
-      ]);
-    }
-    previousGap = gap;
-  }
-  return segment([src, bend]);
+  // 소단 셈은 수평공간 끝에서 새로(91-4)
+  const cut = structureCutPoints(
+    bend,
+    outward,
+    berm.cut,
+    groundAt,
+    (limitOffset - bend.offset) * outward,
+  );
+  const head = berm.lengthM > 1e-9 ? [src, bend] : [src];
+  return segment(cut ? [...head, ...cut.slice(1)] : head.length > 1 ? head : [src, bend]);
 }
 
 export interface OutletExtrasResult {
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert_Geom.ts b/B06_Section/B06_Section_UI_Cross_Culvert_Geom.ts
index 7c3b5bbd9..ebb01bf9c 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert_Geom.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert_Geom.ts
@@ -56,6 +56,7 @@ import {
   inletChoiceAvailability,
 } from "./B06_Section_UI_Cross_Culvert_Basin";
 import { inletGroundConnector } from "./B06_Section_UI_Cross_Culvert_Extra";
+import { withBackCut } from "./B06_Section_UI_Cross_Structure_Cut";
 import {
   buildCulvertTiers,
   drawnFillPoints,
@@ -335,7 +336,7 @@ export function computeCulvertLayout(
         diameterM: diameter,
         edge: spec.role === "inlet" ? inletInfo.edge : outletInfo.edge,
         groundAt,
-        cutSlopeRatio: section.design?.cut_slope_ratio ?? 1.0,
+        cutDesign: section.design,
         adjust: basinAdjust,
         heightM: basinHeightM,
       });
@@ -615,7 +616,7 @@ export function computeCulvertLayout(
   const slopeOf = (wall: WallLayout): FillSlopeSegment =>
     fillSlopeOf(wall, wall.role === "inlet" ? inletInfo.edge : outletInfo.edge);
   for (const wall of walls) {
-    const slope = slopeOf(wall);
+    const slope = withBackCut(slopeOf(wall), wall, section.design, groundAt, !culvert.hidden_pipe);
     // 사면선은 노견부터 우리가 그린다 — 트림 경계를 노견까지 당겨 백엔드 설계선의
     // 성토 구간을 통째로 덮는다(설계선은 1:1.2 고정이라 그대로 두면 다시 어긋난다).
     if (wall.outward > 0) {
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert_Tiers.ts b/B06_Section/B06_Section_UI_Cross_Culvert_Tiers.ts
index 6396cc06f..37815717a 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert_Tiers.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert_Tiers.ts
@@ -16,6 +16,7 @@ import { buildExtrasAt } from "./B06_Section_UI_Cross_Culvert_Extra";
 import { fillWallBaseWidth } from "./B06_Section_UI_Cross_Culvert_Solve";
 import type { OffsetPoint, WallAdjust, WallLayout } from "./B06_Section_UI_Cross_Culvert_Types";
 import { outlineLeanOf } from "./B06_Section_UI_Cross_Lean";
+import { structureCutSpec } from "./B06_Section_UI_Cross_Structure_Cut";
 
 // d의 0점 = **성토선 길이 0 지점**(벽 상단 = 노견 — 2026-08-23 사용자 확정).
 // 그 자리(하단선 중점)는 이음선 상단점이 노견 끝에 오는 offset이고, 기본 자리는
@@ -89,7 +90,7 @@ export function buildCulvertTiers(input: {
     culvert?.body
       ? {
           lengthM: Math.max(spec?.revet_berm_m ?? GUARD_CUT_BERM_M, 0),
-          slopeRatio: section.design?.cut_slope_ratio ?? 1.0,
+          cut: structureCutSpec(section.design),
         }
       : undefined;
   // 성토부선 + 다단 기슭막이(2026-08-22 — 보호공 삭제, 윗면 선만 성토부선으로).
diff --git a/B06_Section/B06_Section_UI_Cross_Culvert_Types.ts b/B06_Section/B06_Section_UI_Cross_Culvert_Types.ts
index 322748453..98bd07199 100644
--- a/B06_Section/B06_Section_UI_Cross_Culvert_Types.ts
+++ b/B06_Section/B06_Section_UI_Cross_Culvert_Types.ts
@@ -112,8 +112,8 @@ export interface BasinLayout {
    *  "cut" = 절토측 유입(성토사면 없음), "short" = 성토사면 3m 이하,
    *  "manual" = 규칙상 기슭막이 자리지만 사용자가 집수정을 선택. */
   reason: "cut" | "short" | "manual";
-  /** 집수정이 원지반 안으로 들어갈 때의 절토선(구조물 바깥 끝 → 지반 교차점). */
-  cutLine: { from: OffsetPoint; to: OffsetPoint } | null;
+  /** 집수정이 원지반 안으로 들어갈 때의 절토선 점열(구조물 바깥 끝 → 복합경사 → 지반 교차점 · 91-4). */
+  cutLine: OffsetPoint[] | null;
   /** 구조물이 원지반 밖으로 나올 때의 성토(되메움)선 — 경사 5도(임시), 지반 교차점까지. */
   fillLine: { from: OffsetPoint; to: OffsetPoint } | null;
 }
diff --git a/B06_Section/B06_Section_UI_Cross_Ford.ts b/B06_Section/B06_Section_UI_Cross_Ford.ts
index f21cc38ca..6ea9ed38d 100644
--- a/B06_Section/B06_Section_UI_Cross_Ford.ts
+++ b/B06_Section/B06_Section_UI_Cross_Ford.ts
@@ -138,7 +138,7 @@ export function appendFordOverlay(
       );
     }
     if (side.cutLine) {
-      planLine([side.cutLine.from, side.cutLine.to], `${role} 측벽 절토선(계획선)`);
+      planLine(side.cutLine, `${role} 측벽 절토선(계획선)`);
     }
   }
 
diff --git a/B06_Section/B06_Section_UI_Cross_Ford_Geom.ts b/B06_Section/B06_Section_UI_Cross_Ford_Geom.ts
index d40326c05..c33ac5554 100644
--- a/B06_Section/B06_Section_UI_Cross_Ford_Geom.ts
+++ b/B06_Section/B06_Section_UI_Cross_Ford_Geom.ts
@@ -148,7 +148,6 @@ export function computeFordLayout(
   const uphill = section.uphill_side ?? "left";
   const inletOnLeft = uphill === "left";
   const roadTopAt = roadTopFactory(section, edges.left, edges.right);
-  const cutSlopeRatio = section.design?.cut_slope_ratio ?? 1.0;
 
   // 바닥판이 놓일 계류 하상 — 두 노견 사이 원지반 최저점.
   const bedElevation = (() => {
@@ -182,7 +181,8 @@ export function computeFordLayout(
       diameterM: ford.diameter_m,
       edge: { offset_m: edge.offset_m, elevation_m: roadTopAt(edge.offset_m) },
       groundAt,
-      cutSlopeRatio,
+      // 측벽 끝 절토 = 본선 절토 사면과 같은 복합경사(91-4)
+      cutDesign: section.design,
       // 내공 폭 자리에 날개벽 투영 연장을 넣는다 — 바닥판이 그만큼 계류측으로 뻗는다.
       adjust: {
         innerWidthM: Math.max(wing.slab_extend_m, 0),
diff --git a/B06_Section/B06_Section_UI_Cross_Structure_Cut.ts b/B06_Section/B06_Section_UI_Cross_Structure_Cut.ts
new file mode 100644
index 000000000..d24ec6819
--- /dev/null
+++ b/B06_Section/B06_Section_UI_Cross_Structure_Cut.ts
@@ -0,0 +1,107 @@
+/* =============================================================================
+ * B06_Section_UI_Cross_Structure_Cut.ts
+ * 구조물 끝 → 원지반 **절토선 점열**(91-4) — 본선 절토 사면과 같은 복합경사.
+ *
+ * 꼭짓점은 `common_util_cross_berm.cutProfilePoints` 그대로(암 → 토사 무릎 · 소단) · 경계 = 원지반 +
+ * `rock_boundary_offset_m` · 켬 = 암 프리셋 + `two_stage_slope` · 소단 = `design.berm` · 소단 셈은
+ * 구조물 끝에서 새로 · 원지반 교점에서 자름.
+ * 쓰는 곳 = 흙막이 수평공간 뒤 · 박스 끝 · 세월교 측벽 끝 · ㄴ·ㄷ 집수정 끝 · 절토 쪽 배관 유출 벽 뒤.
+ * ========================================================================== */
+
+import { bermSpec, cutProfilePoints } from "../common_util/common_util_cross_berm";
+import type { BermSpec } from "../common_util/common_util_cross_berm";
+import type { CrossDesign } from "./B06_Section_Api_Fetch";
+import type { OffsetPoint } from "./B06_Section_UI_Cross_Culvert_Types";
+
+/** 절토 제원 — 암(또는 단일) 경사 · 토사 경사 · 암 경계 오프셋(없으면 경사 하나) · 소단. */
+export interface StructureCutSpec {
+  cutRatio: number;
+  soilRatio: number;
+  rockOffsetM: number | null;
+  berm: BermSpec | null;
+}
+
+/** 측점 설계값에서 절토 제원 — 본선 `computeCrossDesign` 과 같은 켬 조건. */
+export function structureCutSpec(design?: Partial<CrossDesign> | null): StructureCutSpec {
+  const cutRatio = Math.max(design?.cut_slope_ratio ?? 1.0, 0.1);
+  const offset = design?.rock_boundary_offset_m;
+  const twoStage =
+    design?.geometry_preset === "rock" && design.two_stage_slope === true && offset != null;
+  const berm = design?.berm;
+  return {
+    cutRatio,
+    soilRatio: Math.max(design?.soil_cut_slope_ratio ?? cutRatio, 0.1),
+    rockOffsetM: twoStage ? offset : null,
+    berm: berm ? bermSpec(berm.width_m, berm.interval_m, berm.slope_deg) : null,
+  };
+}
+
+/** 원지반 교점 찾는 걸음(m). */
+const STEP_M = 0.05;
+
+/**
+ * `from`(원지반 아래) → 바깥(`outward`)으로 절토 꼭짓점 · 마지막 점 = 원지반 교점.
+ * `reachM` 안에서 못 만나면 null.
+ */
+export function structureCutPoints(
+  from: OffsetPoint,
+  outward: number,
+  spec: StructureCutSpec,
+  groundAt: (offset: number) => number,
+  reachM = 50,
+): OffsetPoint[] | null {
+  const at = (dist: number): number => from.offset + outward * dist;
+  const rockOffsetM = spec.rockOffsetM;
+  const boundary = rockOffsetM === null ? null : (dist: number) => groundAt(at(dist)) + rockOffsetM;
+  const profile = cutProfilePoints(
+    0,
+    from.elevation,
+    spec.cutRatio,
+    spec.soilRatio,
+    boundary,
+    spec.berm,
+    Math.max(reachM, STEP_M),
+    // 소단이 있으면 경계를 오갈 때마다 꺾음 — 본선 `cutPoints` 와 같음.
+    spec.berm !== null,
+  );
+  const points: OffsetPoint[] = [from];
+  for (let i = 1; i < profile.length; i += 1) {
+    const [d0, z0] = profile[i - 1];
+    const [d1, z1] = profile[i];
+    const steps = Math.max(1, Math.ceil((d1 - d0) / STEP_M));
+    let previousGap = groundAt(at(d0)) - z0;
+    for (let k = 1; k <= steps; k += 1) {
+      const t = k / steps;
+      const gap = groundAt(at(d0 + (d1 - d0) * t)) - (z0 + (z1 - z0) * t);
+      if (gap <= 0) {
+        // 걸음 사이 교점 보간 — 선이 지반을 넘지 않게
+        const share = previousGap > 1e-12 ? previousGap / (previousGap - gap) : 1;
+        const tc = (k - 1 + share) / steps;
+        points.push({ offset: at(d0 + (d1 - d0) * tc), elevation: z0 + (z1 - z0) * tc });
+        return points;
+      }
+      previousGap = gap;
+    }
+    points.push({ offset: at(d1), elevation: z1 });
+  }
+  return null;
+}
+
+/**
+ * 배관 유출 벽이 절토 쪽(벽 바깥 윗모서리가 원지반 아래)이면 그 모서리부터 절토선을 사면 점열 뒤에
+ * 이음 — 트림이 노견부터 설계선을 지워 절토사면이 사라지던 자리(91-4). 관 숨김(세월교 · 박스 흙막이 ·
+ * 독립 기슭막이)은 `enabled` 거짓.
+ */
+export function withBackCut<T extends { points: OffsetPoint[] }>(
+  slope: T,
+  wall: { role: string; outward: number; points: OffsetPoint[] },
+  design: Partial<CrossDesign> | null | undefined,
+  groundAt: (offset: number) => number,
+  enabled: boolean,
+): T {
+  const corner = wall.points[2];
+  if (!enabled || wall.role !== "outlet" || !corner) return slope;
+  if (groundAt(corner.offset) <= corner.elevation + 0.05) return slope;
+  const cut = structureCutPoints(corner, wall.outward, structureCutSpec(design), groundAt);
+  return cut ? { ...slope, points: [...slope.points, ...cut] } : slope;
+}
diff --git a/resources/tester/helper_91_ground_free.cjs b/resources/tester/helper_91_ground_free.cjs
index 5aed020f1..47eb605a6 100644
--- a/resources/tester/helper_91_ground_free.cjs
+++ b/resources/tester/helper_91_ground_free.cjs
@@ -127,4 +127,65 @@ out.lean = ["left_cut", "right_cut", "both_fill", "both_cut"].map((mode) => [
   leanOf({ form: "돌쌓기(찰)", height_m: 1.5, section_mode: mode, side: "좌" }),
   leanOf({ form: "돌쌓기(찰)", height_m: 1.5, section_mode: mode, side: "좌", face_role: "절토" }),
 ]);
+// ③ 91-4 유출측 절토 복합경사 — 꼭짓점 사이 경사(수평/수직) · 사면 길이 · 끝 = 원지반 교점
+const { groundInterpolator } = loadTs(B06("B06_Section_UI_Cross_Culvert_Solve.ts"));
+function profile(points, samples) {
+  const groundAt = groundInterpolator(samples);
+  const legs = points.slice(1).map((p, i) => {
+    const dx = Math.abs(p.offset - points[i].offset);
+    const dz = p.elevation - points[i].elevation;
+    return { ratio: dz > 1e-9 ? r3(dx / dz) : null, slant: r3(Math.hypot(dx, dz)), run: r3(dx) };
+  });
+  const end = points[points.length - 1];
+  return { legs, endGap: r3(Math.abs(groundAt(end.offset) - end.elevation)) };
+}
+const withBerm = (s) => {
+  s.design.berm = { width_m: 0.5, interval_m: 3, slope_deg: 0 };
+};
+// 흙막이 수평공간 뒤(박스 352.14 · 세월교 173.09)
+function guardTails(base, edit = () => undefined) {
+  const s = clone(base);
+  edit(s);
+  const { culvert } = layoutsOf(s, base);
+  return [...culvert.outletFill.segments, ...culvert.basinFill.segments]
+    .filter((g) => g.kind === "cut")
+    .map((g) => profile(g.points, s.samples));
+}
+out.guardTails = [...guardTails(at(352.14)), ...guardTails(FORD)];
+// 박스 끝 · 세월교 측벽 끝(흙막이 없음)
+const { computeBoxLayout } = loadTs(B06("B06_Section_UI_Cross_Box_Geom.ts"));
+const { computeFordLayout } = loadTs(B06("B06_Section_UI_Cross_Ford_Geom.ts"));
+function endCuts(base, compute) {
+  const s = clone(base);
+  delete s.culvert;
+  s.uphill_side = "left"; // 절토 쪽(우측)을 유출로
+  return compute(s, s.samples)
+    .sides.filter((side) => side.cutLine)
+    .map((side) => profile(side.cutLine, s.samples));
+}
+out.boxEnd = endCuts(at(352.14), computeBoxLayout);
+out.fordEnd = endCuts(FORD, computeFordLayout);
+// 절토 쪽 배관 유출 벽 뒤(관 340 · 유출 = 우측 절토) · 소단 있음/없음
+function cutOutlet(edit = () => undefined) {
+  const s = clone(at(340));
+  s.uphill_side = "left";
+  s.culvert = {
+    type: "pipe",
+    chainage_m: 340,
+    pipe_kind: "흄관",
+    diameter_m: 1.0,
+    min_cover_m: 0.5,
+    inlet: { role: "inlet", structure: "기슭막이", revet_form: "돌쌓기(찰)" },
+    outlet: { role: "outlet", structure: "기슭막이", revet_form: "돌쌓기(찰)" },
+  };
+  s.design.inlet_structure = "revet";
+  edit(s);
+  const layout = computeCulvertLayout(s, s.samples, undefined, "revet");
+  const wall = layout.walls.find((w) => w.role === "outlet");
+  const pts = layout.designTrim.minSlope.points;
+  const from = pts.findIndex((p) => Math.abs(p.offset - wall.points[2].offset) < 1e-9);
+  return profile(pts.slice(from), s.samples);
+}
+out.cutOutlet = cutOutlet();
+out.cutOutletBerm = cutOutlet(withBerm);
 process.stdout.write(JSON.stringify(out));
diff --git a/resources/tester/test_79_guard_shape.py b/resources/tester/test_79_guard_shape.py
index f33cbcafe..22607986f 100644
--- a/resources/tester/test_79_guard_shape.py
+++ b/resources/tester/test_79_guard_shape.py
@@ -80,7 +80,8 @@ def test_흙막이_끝_절토는_수평공간_뒤(shape: dict) -> None:
     tails = [tail for group in shape["cutDefault"] for tail in group]
     assert tails, "절토 끝선이 없음"
     for tail in tails:
-        assert tail["points"] == 3
+        # 시작 · 수평공간 끝 · (암 무릎 · 소단) · 원지반 교점 — 본선 절토와 같은 복합경사(91-4)
+        assert tail["points"] >= 3
         assert tail["flat"] == pytest.approx(0, abs=1e-6)
         assert tail["berm"] == pytest.approx(1.0, abs=1e-3)
     for tail in shape["cutBerm2"]:
diff --git a/resources/tester/test_91_ground_free.py b/resources/tester/test_91_ground_free.py
index 7fc4cdf36..09e1c5de4 100644
--- a/resources/tester/test_91_ground_free.py
+++ b/resources/tester/test_91_ground_free.py
@@ -83,3 +83,34 @@ def test_지형에_막힘_잔재_없음() -> None:
         source = (ROOT / "B06_Section" / name).read_text(encoding="utf-8")
         assert "shiftBlockedM" not in source and "지형에 막힘" not in source, name
         assert "noticeExtraLimit" not in source and "noticeShortfall" not in source, name
+
+
+def _knee(cut: dict) -> bool:
+    """암(1:0.4) 뒤 토사(1:1.0) 무릎이 있음 — 픽스처 = 리핑암 · 2단계 · 경계 −0.5 m."""
+    ratios = [leg["ratio"] for leg in cut["legs"] if leg["ratio"] is not None]
+    return any(a == 0.4 and b == 1.0 for a, b in zip(ratios, ratios[1:]))
+
+
+def test_흙막이_수평공간_뒤_절토_복합경사(fit: dict) -> None:
+    tails = fit["guardTails"]
+    assert tails and all(cut["endGap"] < 0.01 for cut in tails)
+    assert all(cut["legs"][0]["ratio"] is None for cut in tails)  # 수평공간 먼저
+    assert sum(_knee(cut) for cut in tails) >= 2
+
+
+def test_박스_끝_세월교_측벽_끝_절토_복합경사(fit: dict) -> None:
+    for cuts in (fit["boxEnd"], fit["fordEnd"]):
+        assert cuts and all(_knee(cut) and cut["endGap"] < 0.01 for cut in cuts)
+
+
+def test_절토_쪽_배관_유출_벽_뒤_절토사면_살아남(fit: dict) -> None:
+    cut = fit["cutOutlet"]
+    assert _knee(cut) and cut["endGap"] < 0.01
+
+
+def test_소단은_구조물_끝에서_새로_셈(fit: dict) -> None:
+    legs = fit["cutOutletBerm"]["legs"]
+    flat = next(i for i, leg in enumerate(legs) if leg["ratio"] is None)
+    assert sum(leg["slant"] for leg in legs[:flat]) == pytest.approx(3.0, abs=1e-3)
+    assert legs[flat]["run"] == pytest.approx(0.5, abs=1e-3)
+    assert fit["cutOutletBerm"]["endGap"] < 0.01