Lythos SPWA

Retaining structures

Sheet pile wall analysis

Free-earth support limit equilibrium and staged Winkler beam-spring analysis side by side; Mononobe-Okabe seismic pressures, tension-only anchors and reliability studies.

$ pip install lythosspwa

Run

lythos-spwa

Default port

8779

Python

3.10+

Version

0.1.1

Licence

AGPL-3.0

See the examples →ReferenceSource ↗

A cantilever or multi-anchored sheet pile wall is analysed two ways and the two are put side by side:

1. Limit equilibrium — the free-earth support method with Coulomb / Mononobe-Okabe earth pressures gives the embedment depth, the anchor forces and the internal-force diagrams.
2. Beam-spring (Winkler) — the wall as a beam on elastoplastic soil springs, built in stages, gives the deflections and moments the sequence of construction actually produces, with tension-only inclined anchors.

On top of either, a parametric or reliability study reports sensitivities, the probability of failure with a 95 % confidence interval, and the reliability index β.

What it computes

Limit equilibrium (free-earth support)

• Coulomb (static) and Mononobe-Okabe (seismic) earth pressures for a vertical wall, with the cohesion term 2c√K and a tension cut-off on the active side.
• Embedment: moment equilibrium about the toe (cantilever, simplified method) or about the lowest anchor (free-earth), by root-finding. D_design = round-up(1.2·D_req).
• Horizontal and axial force per anchor, and the vertical component.
• Net pressure, earth and water pressures, shear, moment, rotation and deflection diagrams.
• Checks: bending stress against f_y/FS, deflection against H/120, H/100 or H/240, and an indicative vertical equilibrium check.

Beam-spring (Winkler)

• Euler-Bernoulli beam on elastoplastic springs bounded by the active and passive limits, starting from at-rest (K₀ = 1 − sin φ).
• Staged construction, worked out automatically: excavate to the anchor level plus the overdig, install the anchor, carry on to the final level; the springs keep their state between stages.
• Anchors as tension-only springs, k_h = EA/(L_free·s)·cos²α, with a lock-off load.
• Subgrade modulus k_s entered directly, or from Ménard-Bourdon or Schmitt (1995).

Seismic — Mononobe-Okabe K_AE / K_PE; below the water table the inertia angle from γ_sat/γ′ (restrained pore water); the Westergaard hydrodynamic pressure of the free water in front of the wall, 7/8·k_h·γ_w·√(H_w·y).

Screenshots

Results summary: limit equilibrium and beam-spring side by side

Bending moment — dark theme

Beam-spring (Winkler), stage by stage

Reliability study

Quick start

pip install lythosspwa
lythos-spwa                                    # interface: http://127.0.0.1:8779/

lythos-spwa example -o quay.spwa
lythos-spwa run quay.spwa -o report.pdf
lythos-spwa study quay.spwa -o samples.csv

Background

Lythos SPWA is the desktop program SPWA (PyQt6 + Matplotlib) rebuilt as a web application. The analysis cores are the same code; the Qt interface has been replaced by a local server and a browser page, and the Qt-based PDF writer by ReportLab. Files written by SPWA v0.1 load with the defaults filled in.

Next steps

• Examples — a two-anchor quay wall, the effect of earthquake, limit equilibrium against beam-spring.
• Reference — method notes, inputs, modules.
• For the continuum and overall stability see LythosFEA.