diff --git a/B06_Section/B06_Section_Api_Types.ts b/B06_Section/B06_Section_Api_Types.ts
index 45a42aa34..d74e1ce27 100644
--- a/B06_Section/B06_Section_Api_Types.ts
+++ b/B06_Section/B06_Section_Api_Types.ts
@@ -61,6 +61,7 @@ export type {
 import type { FordPavementSpec } from "./B06_Section_UI_Cross_Ford_Pavement";
 import type { RevetmentSpec } from "./B06_Section_UI_Cross_Revetment";
 import type { PavementEntry } from "@util/common_util_structure_pavement";
+import type { UnderdrainSpec } from "@util/common_util_structure_underdrain";
 export type { FordPavementSpec, RevetmentSpec };
 
 export interface SectionContextResponse {
@@ -336,6 +337,8 @@ export interface CrossSection extends SectionStation {
   revetment?: RevetmentSpec;
   /** 노면공(G군) 포장 — 범위 안 측점마다(88). 두께 · 무늬 · 확폭 켬. */
   pavement?: PavementEntry[];
+  /** 맹암거 — 기준 측점(288-1). 높이 · 경사 · 측구 없음 · 노면 기울임 · 돌 무늬 형상. */
+  underdrain?: UnderdrainSpec;
 }
 
 export interface SectionDetailResponse {
diff --git a/B06_Section/B06_Section_Cross_Refresh.ts b/B06_Section/B06_Section_Cross_Refresh.ts
index d4fd143f2..95b11ad4d 100644
--- a/B06_Section/B06_Section_Cross_Refresh.ts
+++ b/B06_Section/B06_Section_Cross_Refresh.ts
@@ -360,8 +360,8 @@ function refreshLocally(input: CrossRefreshInput): number[] | null {
             (typeof design.ditch_type === "string" ? design.ditch_type : "standard"),
           paved: pavedBySpecs(section),
           // 물넘이 자리 = 측구 없음 · 지대 낮은 쪽 한 경사(286-2 · 287-4 · 서버 `tilt_ranges` 짝 = 얹힌 제원)
-          tilted: Boolean(section.ford_pavement),
-          tiltPct: section.ford_pavement?.slope_pct ?? null,
+          tilted: Boolean(section.ford_pavement || section.underdrain),
+          tiltPct: section.ford_pavement?.slope_pct ?? section.underdrain?.slope_pct ?? null,
           standard,
           berm: bermAt(section.chainage_m, design),
           rockBoundaryOffsetM,
diff --git a/B06_Section/B06_Section_Engine_Tilt.py b/B06_Section/B06_Section_Engine_Tilt.py
new file mode 100644
index 000000000..3fa30b969
--- /dev/null
+++ b/B06_Section/B06_Section_Engine_Tilt.py
@@ -0,0 +1,100 @@
+"""구조물 자리 기울기 — 물넘이포장 · 맹암거 측점의 노면(287-4 · 288-1).
+
+그 자리 횡단 설계 = 측구 없음 · 노면 = 한 경사로 지대 낮은 쪽(`compute_cross_design(tilted=…,
+tilt_pct=…)`). 경사 = 물넘이 경사각도(%) · 맹암거 암거 경사(%) · 비면 표준 횡단경사.
+  · 물넘이포장 = 관 지점 정본(pipe_points) 범위(기준 ± 월류 폭/2).
+  · 맹암거 = 구조물 정본(structures.json) A군 점형 · 기준 측점 한 곳 — 횡단 dict 에
+    `underdrain`(높이 · 경사)을 얹어 횡단도가 돌 무늬 형상을 그림(TS 짝
+    `common_util_structure_underdrain.ts`).
+판정 폭 = 포장 범위와 같은 0.02 m(`paved_at`).
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+from typing import Any
+
+from B05_Profile.B05_Profile_Structures_Repository import load_structures
+from B06_Section.B06_Section_Engine_Culvert import load_culvert_sets
+
+logger = logging.getLogger(__name__)
+
+UNDERDRAIN_TYPE_ID = "cross_underdrain"
+_EDGE_TOLERANCE_M = 0.02
+
+TiltRange = tuple[float, float, float | None]
+
+
+def _number(value: Any) -> float | None:
+    try:
+        parsed = float(value)
+    except (TypeError, ValueError):
+        return None
+    return parsed if parsed == parsed else None
+
+
+def load_underdrains(project_root: Path) -> list[dict[str, Any]]:
+    """구조물 정본의 맹암거 — `{structure_id, chainage_m, height_m, slope_pct}` ·
+    실패하면 빈 목록."""
+    try:
+        structures = load_structures(str(project_root))[1]
+    except Exception:  # noqa: BLE001 — 정본을 못 읽어도 설계 계산은 이어 간다
+        logger.exception("B06 맹암거를 읽지 못했습니다 (없음으로 본다)")
+        return []
+    found: list[dict[str, Any]] = []
+    for structure in structures:
+        if structure.type_id != UNDERDRAIN_TYPE_ID:
+            continue
+        options = structure.options or {}
+        height = _number(options.get("culvert_height_m"))
+        slope = _number(options.get("culvert_slope_pct"))
+        found.append(
+            {
+                "structure_id": structure.structure_id,
+                "chainage_m": float(structure.anchor_m()),
+                "height_m": height if height and height > 0 else None,
+                "slope_pct": slope if slope and slope > 0 else None,
+            }
+        )
+    return found
+
+
+def tilt_ranges(project_root: Path | None) -> list[TiltRange]:
+    """측구 없이 노면을 지대 낮은 쪽 한 경사로 기울이는 자리 — (시작, 끝, 경사 %)."""
+    if project_root is None:
+        return []
+    out: list[TiltRange] = []
+    for at, spec in load_culvert_sets(project_root).items():
+        if spec.get("type") == "ford_pavement":
+            half = float(spec.get("span_m") or 0.0) / 2.0
+            out.append((at - half, at + half, spec.get("slope_pct")))
+    for drain in load_underdrains(project_root):
+        out.append((drain["chainage_m"], drain["chainage_m"], drain["slope_pct"]))
+    return out
+
+
+def tilt_args(chainage_m: float, ranges: list[TiltRange]) -> dict[str, Any]:
+    """그 측점의 구조물 자리 기울기 — `compute_cross_design(**...)` 로 넘김 ·
+    저장분 짝 `stored_tilt`."""
+    tol = _EDGE_TOLERANCE_M
+    hit = next((r for r in ranges if r[0] - tol <= chainage_m <= r[1] + tol), None)
+    pct = hit[2] if hit else None
+    return {"tilted": hit is not None, "tilt_pct": float(pct) if pct is not None else None}
+
+
+def attach_underdrains(project_root: Path, cross_sections: list[dict[str, Any]]) -> int:
+    """맹암거 기준 측점의 횡단 dict 에 `underdrain` 을 얹는다. 얹은 개수를 돌려준다."""
+    drains = load_underdrains(project_root)
+    attached = 0
+    for section in cross_sections:
+        chainage = _number(section.get("chainage_m"))
+        if chainage is None:
+            continue
+        hit = next(
+            (d for d in drains if abs(d["chainage_m"] - chainage) <= _EDGE_TOLERANCE_M), None
+        )
+        if hit:
+            section["underdrain"] = dict(hit)
+            attached += 1
+    return attached
diff --git a/B06_Section/B06_Section_Router.py b/B06_Section/B06_Section_Router.py
index d640c495b..7c9256058 100644
--- a/B06_Section/B06_Section_Router.py
+++ b/B06_Section/B06_Section_Router.py
@@ -26,6 +26,7 @@ from B06_Section.B06_Section_Engine_Design import (
     stored_shoulder_extend,
 )
 from B06_Section.B06_Section_Engine_Structures_Wall import attach_wall_structures
+from B06_Section.B06_Section_Engine_Tilt import attach_underdrains, tilt_args, tilt_ranges
 from B06_Section.B06_Section_Repository import (
     count_cross_sections,
     create_longitudinal_section,
@@ -51,8 +52,6 @@ from B06_Section.B06_Section_Router_Design import (
     pavement_ranges,
     stored_berm,
     stored_cut_slope,
-    tilt_args,
-    tilt_ranges,
 )
 from B06_Section.B06_Section_Router_Design import (
     attach_default_designs as _attach_default_designs,
@@ -287,6 +286,7 @@ def _read_section_detail(project_root: Path, longitudinal_file_path: str) -> dic
     # 그래야 횡단도·설계선 트림·폐회로 면적이 그 벽을 본다(2026-09-06 사용자 확정).
     attach_wall_structures(root, cross_sections)
     attach_pavement_structures(root, cross_sections)  # 노면공 형상(88)
+    attach_underdrains(root, cross_sections)  # 맹암거 형상(288-1)
     return {"longitudinal": longitudinal, "cross_sections": cross_sections}
 
 
@@ -450,6 +450,7 @@ async def regenerate_sections(
         attach_culvert_sets(project_root, result["cross_sections"])
         attach_wall_structures(project_root, result["cross_sections"])
         attach_pavement_structures(project_root, result["cross_sections"])
+        attach_underdrains(project_root, result["cross_sections"])
         return SectionDetailResponse(
             longitudinal=result["longitudinal"], cross_sections=result["cross_sections"]
         )
diff --git a/B06_Section/B06_Section_Router_Design.py b/B06_Section/B06_Section_Router_Design.py
index 878399892..035ec26ff 100644
--- a/B06_Section/B06_Section_Router_Design.py
+++ b/B06_Section/B06_Section_Router_Design.py
@@ -15,6 +15,7 @@ from B06_Section.B06_Section_Engine_Design import (
     stored_shoulder_extend,
     stored_tilt,
 )
+from B06_Section.B06_Section_Engine_Tilt import tilt_args, tilt_ranges
 from common_util.common_util_cross_berm import (
     BERM_DEFAULT_DEPTH_M,
     BERM_DEFAULT_INTERVAL_M,
@@ -94,27 +95,6 @@ def ford_pavement_ranges(project_root: Path | None) -> list[tuple[float, float]]
     return [(at - half, at + half) for at, half in halves]
 
 
-def tilt_ranges(project_root: Path | None) -> list[tuple[float, float, float | None]]:
-    """측구 없이 노면을 지대 낮은 쪽 한 경사로 기울이는 자리(287-4) — 물넘이포장 범위 ·
-    경사 = 경사각도(%)."""
-    if project_root is None:
-        return []
-    out: list[tuple[float, float, float | None]] = []
-    for at, spec in load_culvert_sets(project_root).items():
-        if spec.get("type") == "ford_pavement":
-            half = float(spec.get("span_m") or 0.0) / 2.0
-            out.append((at - half, at + half, spec.get("slope_pct")))
-    return out
-
-
-def tilt_args(chainage_m: float, ranges: list[tuple[float, float, float | None]]) -> dict[str, Any]:
-    """그 측점의 구조물 자리 기울기 — `compute_cross_design(**...)` 로 넘김 ·
-    저장분 짝 `stored_tilt`."""
-    hit = next((r for r in ranges if paved_at(chainage_m, [(r[0], r[1])])), None)
-    pct = hit[2] if hit else None
-    return {"tilted": hit is not None, "tilt_pct": float(pct) if pct is not None else None}
-
-
 def ford_surface_drops(project_root: Path | None) -> list[tuple[float, float]]:
     """세월교가 앉은 측점의 노면 하강량 — [(누가거리, 월류 높이 m)].
 
diff --git a/B06_Section/B06_Section_Section_Store.ts b/B06_Section/B06_Section_Section_Store.ts
index 67465f56d..38b9ddbf6 100644
--- a/B06_Section/B06_Section_Section_Store.ts
+++ b/B06_Section/B06_Section_Section_Store.ts
@@ -40,6 +40,11 @@ import {
   type PavementStructureInput,
 } from "@util/common_util_structure_pavement";
 import { setGeneralStations } from "../common_util/common_util_structure_station";
+import {
+  attachUnderdrainSpecs,
+  underdrainSpecsFrom,
+  type UnderdrainInput,
+} from "../common_util/common_util_structure_underdrain";
 import { forgetDraftStations, withDraftStations } from "./B06_Section_Section_Drafts";
 import { applyStructureAreaRows, structureAreaRows } from "./B06_Section_Structure_Layouts";
 import type { CrossSectionPatch, SectionDetailResponse } from "./B06_Section_Api_Fetch";
@@ -74,6 +79,11 @@ async function withDraftWalls(
   // 횡단도에 아무것도 안 보이던 결함의 원인이다(창 둘에서 같은 증상, 실측 확인).
   await withDraftPipeKinds(detail, projectId);
   if (!drafts || !drafts.length) return withStructureAreas(detail);
+  // 맹암거(288-1) — 초안 기준 측점으로 제원을 다시 얹음(짝 `common_util_structure_underdrain`)
+  attachUnderdrainSpecs(
+    detail.cross_sections as unknown as Array<Record<string, unknown>>,
+    underdrainSpecsFrom(drafts as unknown as UnderdrainInput[]),
+  );
   const types = await fetchStructureTypes().catch(() => []);
   // 노면공(88) — 초안 범위로 포장 제원을 다시 얹음(짝 `common_util_structure_pavement`)
   const paveTypes = new Set(types.filter((type) => type.group === "G").map((type) => type.type_id));
diff --git a/B06_Section/B06_Section_UI_Cross_Underdrain.ts b/B06_Section/B06_Section_UI_Cross_Underdrain.ts
new file mode 100644
index 000000000..e3bba0f0e
--- /dev/null
+++ b/B06_Section/B06_Section_UI_Cross_Underdrain.ts
@@ -0,0 +1,136 @@
+/* =============================================================================
+ * B06_Section_UI_Cross_Underdrain.ts
+ * 맹암거 횡단 형상(288-1 · 요구 183-3).
+ *
+ *   · 노면 = 설계 노면 — 서버 · TS 짝이 암거 경사로 지대 낮은 쪽 한 경사로 기울여 냄 · 측구 없음.
+ *   · 옵셋선 = 노면을 암거 높이만큼 아래로 같은 각도.
+ *   · 성토 쪽 = 옵셋선을 성토 사면과 만날 때까지 · 절토 쪽 = 절토 사면을 아래로 늘여 옵셋선과 만남.
+ *   · 노면 · 양쪽 선 · 옵셋선이 둘러싼 안 = 돌 무늬(흙막이 돌 그리기 `drawStones`).
+ * 높이가 비면 그리지 않음(수치를 지어내지 않음).
+ * ========================================================================== */
+
+import type { CrossDesign } from "./B06_Section_Api_Fetch";
+import type { OffsetPoint } from "./B06_Section_UI_Cross_Culvert_Types";
+import { drawStones } from "./B06_Section_UI_Cross_Wall_Hatch";
+import type { UnderdrainSpec } from "@util/common_util_structure_underdrain";
+
+const SVG_NS = "http://www.w3.org/2000/svg";
+let clipSeq = 0;
+
+type Edge = { offset_m: number; elevation_m: number };
+
+/** 한쪽 둘레(노면 끝 → 옵셋선과 만나는 자리) — `outward` = 바깥 부호(+1 좌 · −1 우). */
+function sidePath(
+  edge: Edge,
+  outward: 1 | -1,
+  line: readonly Edge[],
+  roadGrade: number,
+  heightM: number,
+): OffsetPoint[] {
+  const start = { offset: edge.offset_m, elevation: edge.elevation_m };
+  const offZ = (o: number) => edge.elevation_m + roadGrade * (o - edge.offset_m) - heightM;
+  const outside = line
+    .filter((p) => (p.offset_m - edge.offset_m) * outward > 1e-6)
+    .sort((a, b) => (a.offset_m - b.offset_m) * outward);
+  const first = outside[0];
+  if (!first) return [start, { offset: start.offset, elevation: offZ(start.offset) }];
+  if (first.elevation_m >= edge.elevation_m) {
+    // 절토 — 사면을 안쪽 아래로 늘여 옵셋선과 만남
+    const k = (first.elevation_m - edge.elevation_m) / (first.offset_m - edge.offset_m);
+    const d = Math.abs(k - roadGrade) < 1e-9 ? 0 : -heightM / (k - roadGrade);
+    const offset = edge.offset_m + d;
+    return [start, { offset, elevation: offZ(offset) }];
+  }
+  // 성토 — 사면을 따라 내려가다 옵셋선을 만나는 자리
+  const path: OffsetPoint[] = [start];
+  let prev = edge;
+  for (const point of outside) {
+    const fa = prev.elevation_m - offZ(prev.offset_m);
+    const fb = point.elevation_m - offZ(point.offset_m);
+    if (fb <= 0) {
+      const t = fa / (fa - fb);
+      const offset = prev.offset_m + (point.offset_m - prev.offset_m) * t;
+      path.push({ offset, elevation: offZ(offset) });
+      return path;
+    }
+    path.push({ offset: point.offset_m, elevation: point.elevation_m });
+    prev = point;
+  }
+  path.push({ offset: prev.offset_m, elevation: offZ(prev.offset_m) });
+  return path;
+}
+
+/** 맹암거 형상 둘레 — 좌 노면 끝 → 우 노면 끝 → 우 둘레 → 옵셋선 → 좌 둘레(위로). 높이 없으면 null. */
+export function underdrainOutline(
+  design: CrossDesign,
+  heightM: number | null,
+): OffsetPoint[] | null {
+  const edges = design.road_edges;
+  if (!edges || !(heightM && heightM > 0)) return null;
+  const { left, right } = edges;
+  const span = left.offset_m - right.offset_m;
+  if (!(Math.abs(span) > 1e-9)) return null;
+  const grade = (left.elevation_m - right.elevation_m) / span;
+  const line = design.design_line ?? [];
+  const leftPath = sidePath(left, 1, line, grade, heightM);
+  const rightPath = sidePath(right, -1, line, grade, heightM);
+  return [
+    { offset: left.offset_m, elevation: left.elevation_m },
+    ...rightPath,
+    ...leftPath.slice(1).reverse(),
+  ];
+}
+
+/** 맹암거 형상을 그린다(돌 무늬 · 둘레 클립). 그렸으면 그 무리 — 둘레에 고름 표식(`data-structure-id` · 288-2). */
+export function appendUnderdrainOverlay(
+  svg: SVGElement,
+  spec: UnderdrainSpec | undefined,
+  design: CrossDesign,
+  x: (offset: number) => number,
+  y: (elevation: number) => number,
+): SVGGElement | null {
+  const outline = spec ? underdrainOutline(design, spec.height_m) : null;
+  if (!spec || !outline) return null;
+  const px = (p: OffsetPoint): [number, number] => [x(p.offset), y(p.elevation)];
+  const points = outline.map((p) => px(p).join(",")).join(" ");
+  const group = document.createElementNS(SVG_NS, "g") as SVGGElement;
+  group.setAttribute("class", "b06-chart__underdrain");
+  const body = document.createElementNS(SVG_NS, "polygon");
+  body.setAttribute("points", points);
+  body.setAttribute("class", "b06-chart__underdrain-body");
+  clipSeq += 1;
+  const clipId = `b06-underdrain-clip-${clipSeq}`;
+  const clip = document.createElementNS(SVG_NS, "clipPath");
+  clip.setAttribute("id", clipId);
+  const clipShape = document.createElementNS(SVG_NS, "polygon");
+  clipShape.setAttribute("points", points);
+  clip.append(clipShape);
+  const stones = document.createElementNS(SVG_NS, "g");
+  stones.setAttribute("clip-path", `url(#${clipId})`);
+  const height = spec.height_m!;
+  const offsets = outline.map((p) => p.offset);
+  const [lo, hi] = [Math.min(...offsets), Math.max(...offsets)];
+  const { left, right } = design.road_edges;
+  const grade = (left.elevation_m - right.elevation_m) / (left.offset_m - right.offset_m);
+  const roadZ = (o: number) => left.elevation_m + grade * (o - left.offset_m);
+  const at = (u: number, v: number): OffsetPoint => {
+    const offset = lo + (hi - lo) * u;
+    return { offset, elevation: roadZ(offset) - height * (v + 0.5) };
+  };
+  const [ax, ay] = px(at(0, 0));
+  const [bx, by] = px(at(1, 0));
+  drawStones(
+    stones,
+    {
+      spanM: Math.hypot(hi - lo, grade * (hi - lo)),
+      pixelsPerMeter: Math.abs(x(1) - x(0)) || 1,
+      point: (u, v) => px(at(u, v)),
+      leanDegrees: (Math.atan2(bx - ax, -(by - ay)) * 180) / Math.PI,
+    },
+    false,
+    height,
+  );
+  group.append(body, clip, stones);
+  svg.append(group);
+  return group;
+}
diff --git a/B06_Section/B06_Section_UI_Cross_View.ts b/B06_Section/B06_Section_UI_Cross_View.ts
index e8178a2a2..d21aac8a6 100644
--- a/B06_Section/B06_Section_UI_Cross_View.ts
+++ b/B06_Section/B06_Section_UI_Cross_View.ts
@@ -21,6 +21,7 @@ import {
 } from "./B06_Section_UI_Cross_Ford_Pavement";
 import { ownWallsDrawAt } from "./B06_Section_UI_Cross_Culvert_Wire";
 import { attachShapePick } from "./B06_Section_UI_Cross_Shape_Pick";
+import { appendUnderdrainOverlay } from "./B06_Section_UI_Cross_Underdrain";
 import { raiseWalls } from "./B06_Section_UI_Cross_Wall";
 import { attachChuteBandPick } from "./B06_Section_UI_Cross_Wall_Hatch";
 import { appendSpoilFillOverlay } from "./B06_Section_UI_Cross_SpoilFill";
@@ -454,6 +455,8 @@ export function createCrossSectionCard(
       );
       if (!fordPaved)
         appendPavementOverlay(plotLayer, section.design, x, toDisplayY, section.pavement);
+      // 맹암거(288-1) — 노면 아래 암거 높이만큼 돌 무늬 형상
+      appendUnderdrainOverlay(plotLayer, section.underdrain, section.design, x, toDisplayY);
       // 세월교 측점 — 계획고는 이미 월류 높이만큼 내려와 있다. "월류가 없었다면"
       // 노면을 점선으로 남겨 얼마나 내려앉았는지 읽히게 한다(2026-08-30 사용자).
       appendFordSurfaceDropPlan(plotLayer, section.design, x, toDisplayY, fordLayout);
diff --git a/B06_Section/B06_Section_UI_Style_Cross_Areas.css b/B06_Section/B06_Section_UI_Style_Cross_Areas.css
index b970a0463..d875d8a78 100644
--- a/B06_Section/B06_Section_UI_Style_Cross_Areas.css
+++ b/B06_Section/B06_Section_UI_Style_Cross_Areas.css
@@ -267,6 +267,18 @@
   stroke-width: 1;
 }
 
+/* 맹암거(288-1): 노면 아래 돌 무늬 형상 */
+.b06-chart__underdrain-body {
+  fill: color-mix(in srgb, #3aa0a8 16%, transparent);
+  stroke: #3aa0a8;
+  stroke-width: 1.2;
+}
+
+.b06-chart__underdrain-body.is-active {
+  fill: color-mix(in srgb, #3aa0a8 34%, transparent);
+  stroke-width: 2.2;
+}
+
 /* 배수관 세트(2026-08-19): 배관·기슭막이·돌붙임 — 분리 도형 3종 + 집수정 라벨 */
 /* 관은 실무 도면처럼 점선 윤곽 2줄 느낌 — 채움은 식별용으로만 아주 옅게. */
 .b06-chart__culvert-pipe {
diff --git a/B07_DesignDetail/B07_DesignDetail_Cross_Overlay.ts b/B07_DesignDetail/B07_DesignDetail_Cross_Overlay.ts
index 81a1400e1..6af40280b 100644
--- a/B07_DesignDetail/B07_DesignDetail_Cross_Overlay.ts
+++ b/B07_DesignDetail/B07_DesignDetail_Cross_Overlay.ts
@@ -17,6 +17,7 @@ import { appendBoxOverlay } from "../B06_Section/B06_Section_UI_Cross_Box";
 import { appendCulvertOverlay } from "../B06_Section/B06_Section_UI_Cross_Culvert";
 import { appendFordOverlay } from "../B06_Section/B06_Section_UI_Cross_Ford";
 import { appendFordPavementOverlay } from "../B06_Section/B06_Section_UI_Cross_Ford_Pavement";
+import { appendUnderdrainOverlay } from "../B06_Section/B06_Section_UI_Cross_Underdrain";
 import {
   appendCrossDesignOverlay,
   appendPavementOverlay,
@@ -487,6 +488,7 @@ function drawDesign(
   const { design, culvert, box, ford, own } = layouts;
   const paved = appendFordPavementOverlay(svg, section.ford_pavement, design, x, y);
   if (!paved) appendPavementOverlay(svg, design, x, y, section.pavement);
+  appendUnderdrainOverlay(svg, section.underdrain, design, x, y); // 맹암거(288-1)
   appendCrossDesignOverlay(
     svg,
     design,
diff --git a/common_util/common_util_structure_underdrain.ts b/common_util/common_util_structure_underdrain.ts
new file mode 100644
index 000000000..ca2a91d44
--- /dev/null
+++ b/common_util/common_util_structure_underdrain.ts
@@ -0,0 +1,66 @@
+/* =============================================================================
+ * common_util/common_util_structure_underdrain.ts
+ * 맹암거(cross_underdrain · A군 점형) 제원을 횡단 측점에 얹는다(288-1).
+ *
+ * 기준 측점(0.02 m 안) 횡단 dict 에 `underdrain` = 높이 · 경사 — 횡단도가 돌 무늬 형상을 그리고,
+ * 설계 계산은 그 측점을 측구 없이 지대 낮은 쪽 한 경사로 기울임(`tilted`).
+ * 파이썬 짝 = `B06_Section/B06_Section_Engine_Tilt.py`(`load_underdrains` · `attach_underdrains`).
+ * ========================================================================== */
+
+export const UNDERDRAIN_TYPE_ID = "cross_underdrain";
+const EDGE_TOLERANCE_M = 0.02;
+
+/** 맹암거 제원 — 높이 · 경사가 비면 null(높이 없으면 형상 없음 · 경사 없으면 표준 횡단경사). */
+export interface UnderdrainSpec {
+  structure_id: string | null;
+  chainage_m: number;
+  height_m: number | null;
+  slope_pct: number | null;
+}
+
+export interface UnderdrainInput {
+  structure_id?: string | null;
+  type_id: string;
+  chainage_m?: number | null;
+  start_m?: number | null;
+  options?: Record<string, unknown> | null;
+}
+
+const positive = (value: unknown): number | null => {
+  const parsed = value === "" || value === null || value === undefined ? NaN : Number(value);
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : null;
+};
+
+/** 구조물 목록의 맹암거 제원(파이썬 `load_underdrains` 짝). */
+export function underdrainSpecsFrom(structures: readonly UnderdrainInput[]): UnderdrainSpec[] {
+  return structures.flatMap((structure) => {
+    const at = structure.chainage_m ?? structure.start_m;
+    if (structure.type_id !== UNDERDRAIN_TYPE_ID || typeof at !== "number") return [];
+    const options = structure.options ?? {};
+    return [
+      {
+        structure_id: structure.structure_id ?? null,
+        chainage_m: at,
+        height_m: positive(options.culvert_height_m),
+        slope_pct: positive(options.culvert_slope_pct),
+      },
+    ];
+  });
+}
+
+/** 기준 측점 횡단 dict 에 `underdrain` 을 얹는다(옛 값은 걷음) — 얹은 개수(파이썬 `attach_underdrains` 짝). */
+export function attachUnderdrainSpecs(
+  sections: Array<Record<string, unknown>>,
+  specs: readonly UnderdrainSpec[],
+): number {
+  let attached = 0;
+  for (const section of sections) {
+    delete section.underdrain;
+    const chainage = Number(section.chainage_m);
+    const hit = specs.find((spec) => Math.abs(spec.chainage_m - chainage) <= EDGE_TOLERANCE_M);
+    if (!hit) continue;
+    section.underdrain = { ...hit };
+    attached += 1;
+  }
+  return attached;
+}
diff --git a/resources/tester/helper_288_underdrain.cjs b/resources/tester/helper_288_underdrain.cjs
new file mode 100644
index 000000000..5611079cc
--- /dev/null
+++ b/resources/tester/helper_288_underdrain.cjs
@@ -0,0 +1,87 @@
+/* 288 맹암거 횡단 헬퍼 — 진짜 TS 를 Node 로 돌려 표준출력 JSON 한 벌로.
+ * 입력 = argv[2] JSON 파일 { structures, sections }.
+ */
+const fs = require("fs");
+const path = require("path");
+const ts = require(path.join(__dirname, "..", "..", "config", "node_modules", "typescript"));
+
+const ROOT = path.join(__dirname, "..", "..");
+const cache = new Map();
+const load = (file) => {
+  if (cache.has(file)) return cache.get(file);
+  const js = ts.transpileModule(fs.readFileSync(file, "utf8"), {
+    compilerOptions: { module: ts.ModuleKind.CommonJS, target: ts.ScriptTarget.ES2020 },
+  }).outputText;
+  const box = { exports: {} };
+  cache.set(file, box.exports);
+  const near = (m) => {
+    if (m.startsWith("@config/")) return load(path.join(ROOT, "config", `${m.slice(8)}.ts`));
+    if (m.startsWith("@util/")) return load(path.join(ROOT, "common_util", `${m.slice(6)}.ts`));
+    if (m.startsWith(".")) return load(path.join(path.dirname(file), `${m}.ts`));
+    return new Proxy({}, { get: () => () => {} });
+  };
+  new Function("exports", "module", "require", js)(box.exports, box, near);
+  return box.exports;
+};
+
+class Node {
+  constructor(tag) {
+    this.tag = tag;
+    this.attrs = {};
+    this.children = [];
+  }
+  setAttribute(k, v) {
+    this.attrs[k] = String(v);
+  }
+  getAttribute(k) {
+    return this.attrs[k] ?? null;
+  }
+  append(...kids) {
+    this.children.push(...kids);
+  }
+}
+globalThis.document = { createElementNS: (_ns, tag) => new Node(tag) };
+
+const input = JSON.parse(fs.readFileSync(process.argv[2], "utf8"));
+const util = load(path.join(ROOT, "common_util", "common_util_structure_underdrain.ts"));
+const draw = load(path.join(ROOT, "B06_Section", "B06_Section_UI_Cross_Underdrain.ts"));
+
+const specs = util.underdrainSpecsFrom(input.structures);
+const sections = input.sections.map((s) => ({ ...s }));
+const attached = util.attachUnderdrainSpecs(sections, specs);
+
+// 지대 낮은 쪽(우)으로 5 % 기울인 노면 · 좌 = 절토(오름) · 우 = 성토(내림) · 암거 높이 1 m
+const design = {
+  road_edges: {
+    left: { offset_m: 3, elevation_m: 100.15 },
+    right: { offset_m: -3, elevation_m: 99.85 },
+  },
+  design_line: [
+    { offset_m: 6, elevation_m: 102.9 },
+    { offset_m: 3, elevation_m: 100.15 },
+    { offset_m: -3, elevation_m: 99.85 },
+    { offset_m: -7, elevation_m: 97.2 },
+  ],
+};
+const svg = new Node("g");
+const group = draw.appendUnderdrainOverlay(
+  svg,
+  { structure_id: "ud-1", chainage_m: 40, height_m: 1, slope_pct: 5 },
+  design,
+  (o) => o,
+  (e) => e,
+);
+const body = group?.children.find((k) => k.attrs.class === "b06-chart__underdrain-body");
+
+process.stdout.write(
+  JSON.stringify({
+    specs,
+    attached,
+    sections: sections.map((s) => s.underdrain ?? null),
+    outline: draw.underdrainOutline(design, 1),
+    noHeight: draw.underdrainOutline(design, null),
+    drew: !!group,
+    bodyId: body?.attrs["data-structure-id"] ?? null,
+    stones: group?.children.filter((k) => k.tag === "g").flatMap((g) => g.children).length ?? 0,
+  }),
+);
diff --git a/resources/tester/test_286_1_ford_pavement_design.py b/resources/tester/test_286_1_ford_pavement_design.py
index 68c52322a..da373f8af 100644
--- a/resources/tester/test_286_1_ford_pavement_design.py
+++ b/resources/tester/test_286_1_ford_pavement_design.py
@@ -138,7 +138,7 @@ def test_저장_뒤_서버가_물넘이_측구를_맞춤():
     router = _read("B06_Section", "B06_Section_Router_Design.py")
     assert "stored_tilt(design) == tilt" in router
     refresh = _read("B06_Section", "B06_Section_Cross_Refresh.ts")
-    assert "tilted: Boolean(section.ford_pavement)," in refresh
+    assert "tilted: Boolean(section.ford_pavement || section.underdrain)," in refresh
 
 
 CHUTE = {"ford_chute_1_structure": "돌붙임", "ford_chute_1_thickness": 30}
diff --git a/resources/tester/test_288_underdrain_cross.py b/resources/tester/test_288_underdrain_cross.py
new file mode 100644
index 000000000..b78011f18
--- /dev/null
+++ b/resources/tester/test_288_underdrain_cross.py
@@ -0,0 +1,143 @@
+"""288 맹암거 횡단 형상(요구 183-3 · 9).
+
+못박는 것
+  - 288-1 맹암거 기준 측점 = 측구 없음 · 노면 = 암거 경사로 지대 낮은 쪽 한 경사(물넘이 286 · 287 길 —
+    서버 `tilt_ranges` · `tilt_args` · TS 짝 `tilted`) · 제원 얹기 서버 `attach_underdrains` ↔ TS
+    `attachUnderdrainSpecs` 같은 값 · 형상 = 노면을 암거 높이만큼 아래로 옵셋 → 성토 쪽은 성토 사면과
+    만남 · 절토 쪽은 절토 사면을 늘여 만남 · 그 안 돌 무늬 · 높이 비면 안 그림.
+
+진짜 TS 는 `helper_288_underdrain.cjs` 가 Node 로 돌림. 화면은 사용자 확인.
+"""
+
+from __future__ import annotations
+
+import json
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+HERE = Path(__file__).resolve().parent
+ROOT = HERE.parents[1]
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+import B06_Section.B06_Section_Engine_Tilt as tilt  # noqa: E402
+from B05_Profile.B05_Profile_Structures_Schema import StructureInstance  # noqa: E402
+from B06_Section.B06_Section_Engine_Design import compute_cross_design  # noqa: E402
+
+STRUCTURES = [
+    {
+        "structure_id": "ud-1",
+        "type_id": "cross_underdrain",
+        "placement": "point",
+        "chainage_m": 40.0,
+        "options": {"culvert_height_m": 0.8, "culvert_slope_pct": 4},
+    },
+    {  # 경사 · 높이 빈 맹암거 — 표준 횡단경사 · 형상 없음
+        "structure_id": "ud-2",
+        "type_id": "cross_underdrain",
+        "placement": "point",
+        "chainage_m": 80.0,
+        "options": {},
+    },
+    {
+        "structure_id": "x-1",
+        "type_id": "cross_drain_exposed",
+        "placement": "point",
+        "chainage_m": 60.0,
+    },
+]
+SECTIONS = [{"chainage_m": c} for c in (20.0, 40.0, 60.0, 80.0)]
+
+pytestmark = pytest.mark.skipif(
+    not (ROOT / "config" / "node_modules" / "typescript").is_dir(),
+    reason="프론트엔드 의존성 미설치",
+)
+
+
+@pytest.fixture()
+def project(monkeypatch, tmp_path) -> Path:
+    items = [StructureInstance(**s) for s in STRUCTURES]
+    monkeypatch.setattr(tilt, "load_structures", lambda _root: (1, items))
+    monkeypatch.setattr(tilt, "load_culvert_sets", lambda _root: {})
+    return tmp_path
+
+
+@pytest.fixture(scope="module")
+def ts(tmp_path_factory) -> dict:
+    source = tmp_path_factory.mktemp("s288") / "in.json"
+    source.write_text(
+        json.dumps({"structures": STRUCTURES, "sections": SECTIONS}), encoding="utf-8"
+    )
+    proc = subprocess.run(
+        ["node", str(HERE / "helper_288_underdrain.cjs"), str(source)],
+        capture_output=True,
+        text=True,
+        encoding="utf-8",
+        timeout=60,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout)
+
+
+def test_맹암거_자리_기울기_서버(project):
+    ranges = tilt.tilt_ranges(project)
+    assert ranges == [(40.0, 40.0, 4.0), (80.0, 80.0, None)]
+    assert tilt.tilt_args(40.0, ranges) == {"tilted": True, "tilt_pct": 4.0}
+    assert tilt.tilt_args(80.01, ranges) == {"tilted": True, "tilt_pct": None}
+    assert tilt.tilt_args(60.0, ranges) == {"tilted": False, "tilt_pct": None}
+
+
+def test_제원_얹기_서버_TS_같은_값(project, ts):
+    sections = [dict(s) for s in SECTIONS]
+    assert tilt.attach_underdrains(project, sections) == 2 == ts["attached"]
+    assert [s.get("underdrain") for s in sections] == ts["sections"]
+    assert ts["sections"][1] == {
+        "structure_id": "ud-1",
+        "chainage_m": 40.0,
+        "height_m": 0.8,
+        "slope_pct": 4.0,
+    }
+
+
+def test_맹암거_측점_설계_측구_없음_낮은_쪽_기울기():
+    samples = [
+        {"offset_m": o / 2, "elevation_m": round(100.0 + 0.35 * o / 2, 4), "valid": True}
+        for o in range(-24, 25)
+    ]
+    kwargs = {"ground_type": "soil", "section_mode": "left_cut", "ditch_side": "left"}
+    got = compute_cross_design(samples, 100.4, tilted=True, tilt_pct=4.0, **kwargs)
+    assert got["ditch_enabled"] is False and got["cross_slope_pct"] == 4.0
+    left, right = (got["road_edges"][k]["elevation_m"] for k in ("left", "right"))
+    assert left > right  # 지반이 좌로 오름 = 우가 낮음
+
+
+def test_형상_옵셋선_성토_절토와_만남(ts):
+    outline = [(p["offset"], p["elevation"]) for p in ts["outline"]]
+    expected = [
+        (3, 100.15),  # 좌 노면 끝
+        (-3, 99.85),  # 우 노면 끝
+        (-4.632653, 98.768367),  # 우 성토 사면 ∩ 옵셋선
+        (1.846154, 99.092308),  # 좌 절토 사면을 늘인 선 ∩ 옵셋선
+    ]
+    assert len(outline) == len(expected)
+    for got, want in zip(outline, expected):
+        assert got == pytest.approx(want, abs=1e-5)
+    assert ts["noHeight"] is None
+    assert ts["drew"] is True and ts["stones"] > 0
+
+
+def test_횡단도_B07_이_맹암거를_그림():
+    view = (ROOT / "B06_Section" / "B06_Section_UI_Cross_View.ts").read_text(encoding="utf-8")
+    assert (
+        "appendUnderdrainOverlay(plotLayer, section.underdrain, section.design, x, toDisplayY);"
+        in view
+    )
+    b07 = (ROOT / "B07_DesignDetail" / "B07_DesignDetail_Cross_Overlay.ts").read_text(
+        encoding="utf-8"
+    )
+    assert "appendUnderdrainOverlay(svg, section.underdrain, design, x, y);" in b07
+    refresh = (ROOT / "B06_Section" / "B06_Section_Cross_Refresh.ts").read_text(encoding="utf-8")
+    assert "tilted: Boolean(section.ford_pavement || section.underdrain)," in refresh