Domain: Engineering — Geotechnical Engineering
Target concept: Sandbox Model: Pile Spacing Effect Using Closely Spaced and Widely Spaced Circular Piles

Video generation prompt: Two transparent sandbox models are placed side by side, each containing four vertical cylindrical supports holding a square plate. The spacing between the supports is smaller on the left and larger on the right. Identical loads are added to both simultaneously and progressively increased.

Evaluation guide:
(i) Target concept: Group efficiency reduction due to decreased (closer) center-to-center pile spacing in shallow foundations on granular soil: piles spaced closely enough that their zones of stress influence in the sand overlap, lowering the group's combined bearing capacity relative to the same piles spaced farther apart.
Minimum mechanism: Piles must be embedded in cohesionless granular medium (sand), laterally unconstrained, and loaded axially; failure must arise from soil bearing-capacity exhaustion beneath the closely spaced group (not pile buckling or material failure); the spacing difference between the two sandboxes must drive the differential response.
(ii)Storyline: Frame 0–2: Static shot showing two side-by-side transparent sandboxes, each with four vertical cylindrical supports and one square plate resting fully on them; supports in left sandbox are visibly closer together than in right. Frame 3–5: Identical loads descend synchronously and contact both plates at the same visual instant, then continue increasing. Frame 6–9: Left-side plate progressively deflects downward and/or tilts; sand beneath it develops a central depression with radial outward heave; right-side plate remains motionless and level; sand beneath it shows no deformation. Perspective: Fixed frontal orthographic view, full sandbox height visible, no obstructions, consistent lighting from upper front-left.

Manual:
Experimental Procedure
1. Place two identical transparent sandbox models side-by-side.
2. Install four identical vertical cylindrical supports inside each sandbox: closely spaced under the left plate, more widely spaced under the right plate.
3. Set a rigid square plate on all supports in both models.
4. Apply identical loads simultaneously to both plates, and increase the load progressively.
5. Observe until failure occurs in one model only.
Observation of Experimental Phenomena
- Left model (closely spaced piles): plate sags, tilts, or collapses; sand shows localized depression and outward bulging.
- Right model (widely spaced piles): plate remains fully supported and level; sand surface stays flat and undisturbed.
Summary of Experimental Principles
Closer pile spacing causes the piles' stress zones in the sand to overlap, reducing the group's combined bearing capacity and load-sharing efficiency; this concentrates stress and triggers earlier failure than in the widely spaced group, which behaves closer to individual, non-interacting piles — demonstrating the pile spacing effect in foundation design.

Prompt Grounding rubric:
level_1: No side-by-side transparent sandbox models are visible; cylindrical supports are absent or clearly not four per sandbox; no square plate rests on either sandbox; no load application is shown; the two sandboxes show no spacing difference between their supports.
level_2: Two containers are present but are not both transparent or not placed side by side; the number of visible cylindrical supports in at least one sandbox is not four; a square plate is missing or not resting on the supports in one sandbox; loads are not applied to both plates in a synchronized way.
level_3: Two transparent sandbox models are placed side by side; each contains exactly four vertical cylindrical supports; a square plate rests on all four supports in both models; the supports in the left sandbox are visibly closer together (smaller spacing) than the supports in the right sandbox; identical-looking loads are applied to both plates at the same time.
level_4: Building on the 3-point description, the two sandboxes match in size and sand fill level, the cylindrical supports within each sandbox are identical to each other in height and diameter, the square plates on both sides are the same size and shape, and the loads applied to each side are visually identical in size, shape, and the frame at which they first touch their respective plates.
level_5: Beyond the 4-point description, the spacing contrast between the left (closer) and right (wider) support groups is unambiguous and clearly readable against the sandbox width; the plate on each side makes flush, gapless contact with all four of its supports before loading begins; and the transparent sandbox walls clearly reveal the sand and support positions on both sides with no obstruction or glare hiding either group.

Scientific and Causal Correctness rubric:
level_1: The outcome contradicts the pile-spacing principle: the widely spaced (right) model fails while the closely spaced (left) model remains intact; both models fail identically; neither model shows any failure despite the load having clearly increased; or the sand appears to flow like a liquid rather than settle as a granular deposit.
level_2: A difference between the two models appears, but the causal chain is broken: a support visibly buckles or fractures before the load ever touches its plate, the plate lifts away from its supports without any load being removed, or the sand under both models deforms by visibly the same amount despite the difference in support spacing.
level_3: Failure occurs only in the closely spaced (left) model: its plate visibly sags, tilts, or drops; the sand beneath it develops a noticeably deeper or more spread-out depression than the sand beneath the widely spaced (right) model; the right-side plate stays level and its sand surface shows little to no visible change; but the load-then-failure sequence is not clearly shown (e.g., the plate already looks tilted at first load contact, or the deformation isn't clearly shown following the load's arrival).
level_4: Building on the 3-point description, the load is clearly shown contacting both plates before any deformation begins, the left-side failure (sag/tilt/collapse) visibly follows the load contact rather than preceding or coinciding with it, and the sand beneath the right-side (widely spaced) model stays essentially flat and undisturbed for the entire sequence; but one secondary detail looks off (e.g., the sand grains under the left plate look uniformly wet/cohesive rather than dry and granular, or the two sides' supports appear to bend by visibly similar amounts despite the difference in outcome).
level_5: Beyond the 4-point description, the left (closely spaced) plate's downward sag/tilt/collapse and the localized sand depression with outward heave beneath it develop progressively and only on the left; the right (widely spaced) side's plate and sand remain visibly unchanged from the first frame to the last; the increasing load visibly precedes and drives the left-side failure, consistent with closely spaced piles' overlapping stress zones in the sand reducing their combined bearing capacity relative to the more widely spaced group.

Spatiotemporal Consistency rubric:
level_1: A sandbox, a support, the plate, or a load object vanishes and reappears, or jumps to a new position, between consecutive frames; the sand's surface height or texture resets abruptly with no visible cause; the lighting on the scene changes drastically from one frame to the next with no apparent source for the change; the plate visibly cracks into fragments and then reassembles whole, or a support bends and warps as though flexible before any real failure has occurred.
level_2: One sandbox visibly shifts position relative to the other between frames; a support's height or tilt changes suddenly without any load acting on it; the sand surface shows a sudden jump in height or texture rather than a gradual change; a load object disappears mid-descent and reappears elsewhere; a shadow points in a new direction with no change in the implied light source.
level_3: Both sandboxes stay in the same place relative to each other and to the background throughout; the four supports in each sandbox keep their vertical orientation and their spacing from one another; each plate stays connected to its supports until the moment of failure, without gaps appearing and disappearing; the sand deforms gradually rather than snapping to a new shape; the descending loads move continuously rather than jumping between positions.
level_4: Building on the 3-point description, the sandbox walls stay rigid and stationary against the room behind them, the four supports in each sandbox keep the same spacing relative to each other before failure begins, the plates remain fully flat and fully seated on their supports until deformation starts, and the sand's deformation on the left spreads outward gradually from the point of highest stress rather than appearing all at once.
level_5: Beyond the 4-point description, no sandbox, support, plate, or load object stretches, bends, or warps out of its normal proportions in any frame; the depth relationship between the two sandboxes and the background stays consistent, with neither appearing to shift toward or away from the camera unnaturally; and the camera's framing of the full scene does not pan, tilt, zoom, or dolly at any point during the sequence.