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Lythos SPWA

Sheet pile wall analysis, driven from your browser. A cantilever or multi-anchored 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 sweeps any input — a range, or a distribution — and reports sensitivities, the probability of failure with a confidence interval, and the reliability index β.

The whole program — every label, result text, figure and report — is bilingual in English and Turkish, switchable while it runs.

The interface is a small HTTP server on your own machine, driven from a browser. That keeps the program usable over a remote session or inside a container, where a desktop toolkit would need a display it does not have, and it costs no dependency beyond the standard library.

This is the sibling of LythosFEA and Lythos Kinematic, and follows the same architecture. It began life as the desktop program SPWA; see Background.

Screenshots

Results summary	Bending moment, dark theme

Beam-spring (Winkler)	Reliability study

Install & run

pip install lythosspwa
lythos-spwa                      # opens the interface in your browser

From a clone, with nothing installed but the scientific stack:

pip install numpy scipy matplotlib reportlab
python main.py

Python 3.10+ is required. Word reports need python-docx and the spreadsheet export of a study needs openpyxl; both are extras (pip install "lythosspwa[docx,xlsx]"), and the interface offers those formats only when they are installed.

Command line

lythos-spwa                                # web interface (the default)
lythos-spwa web --port 9000 --lang tr --no-browser
lythos-spwa example -o project.spwa        # a starter project file
lythos-spwa run project.spwa -o report.pdf # analyse, print the results, write a report
lythos-spwa study project.spwa -o samples.csv

run and study read the same .spwa file the interface saves, so a case set up in the browser can be re-run unattended.

What it computes

Limit equilibrium (free-earth support)

• Earth pressures: Coulomb (static) and Mononobe-Okabe (seismic) 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); solved by root-finding, D_design = round-up(1.2·D_req)
• Anchors: horizontal and axial force per anchor, and the vertical component
• Diagrams: net pressure, earth and water pressures, shear, moment, rotation, deflection
• 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 kₛ entered directly, or from Ménard-Bourdon or Schmitt (1995)
• Water in the excavation either as given (underwater dredging) or dewatered until the final stage

Seismic

• Mononobe-Okabe K_AE / K_PE, with the inertia angle θ computed from γsat/γ′ below the water table (restrained pore water)
• Westergaard hydrodynamic pressure of the free water in front of the wall, 7/8·kh·γw·√(H_w·y), as a driving load

Both corrections can be switched off.

Parametric and reliability studies

• Variables: any soil, anchor, geometry, load, seismic or factor input, as a range or as a distribution (normal, lognormal, uniform; mean and CoV)
• Sampling: one-at-a-time sweep, full grid, Latin hypercube, Monte Carlo; correlated inputs through the API (Study(..., correlation={(a, b): rho}))
• Results: Spearman rank and standardised regression sensitivities, failure probability with a 95 % confidence interval and the reliability index β, tornado charts
• Runs in parallel with progress and cancellation; exports to CSV / XLSX and becomes section 7 of the report

Reports

Choose PDF, self-contained HTML or Word in the header and press Export report…. The report carries the inputs (geometry, soil, anchors, section, options), the limit-equilibrium results, the beam-spring results (kₛ table, stages, anchor forces, checks, comparison with the LE analysis), the figures, the warnings and the method notes — in whichever language the interface is in. All three formats are assembled from one place, so they say the same thing.

Project files (.spwa)

JSON. Save writes the inputs and the study definition; Open… reads them back. Files written by SPWA v0.1 (anchor depths only, no kₛ fields) load with the defaults filled in.

Modules

file	content
lythosspwa/analysis_engine.py	Free-earth support analysis: Coulomb / Mononobe-Okabe pressures, embedment (brentq), anchor forces, diagrams at D_req, stress / deflection / vertical checks
lythosspwa/beam_spring.py	Winkler beam on elastoplastic springs with staged construction, tension-only inclined anchors, kₛ from Ménard-Bourdon or Schmitt
lythosspwa/study.py, study_plots.py	Parametric (OAT / grid) and reliability (LHS / Monte Carlo) studies: sampling with optional Gaussian-copula correlation, parallel runner, sensitivities, P_f with 95 % CI and β, CSV / XLSX export, figures
lythosspwa/plotting.py, plot_style.py	Matplotlib figures (schematic + diagrams, beam-spring 4-panel), theme-aware
lythosspwa/report.py, pdf.py	Calculation report: one HTML assembly, exported as PDF (reportlab), self-contained HTML or DOCX
lythosspwa/forms.py	Input schema and readers; converts between the interface's flat values and the engine's configuration
lythosspwa/summary.py	The results as summary cards and as text, for the browser and the command line alike
lythosspwa/render.py	Figures to PNG, off-screen (Agg)
lythosspwa/web/	The local HTTP server, the session that runs the analyses, and the browser interface
lythosspwa/config.py	Defaults, theme, plot palette, translations, section database
lythosspwa/section_database.json	I [m⁴/m] and W [m³/m] of sheet pile sections

Method notes

• LE: moment equilibrium about the toe (cantilever, simplified method) or the lowest anchor (free-earth). Internal forces are evaluated at the theoretical depth D_req; D_design = round-up(1.2·D_req) is the constructed length. For more than one anchor the LE distribution is approximate — the beam-spring results should govern.
• Seismic: Mononobe-Okabe with K_AE / K_PE (vertical wall); below the water table θ uses γsat/γ′ (restrained pore water); Westergaard hydrodynamic pressure of the free water in front of the wall is applied as a driving load.
• Beam-spring: p = clip(p_ref ± kₛ·Δw, p_a, p_p) per node, at-rest start; anchors T = max(0, P₀·cosα/s + k_h·Δw); moment from the element curvature (EI·w″).
• Vertical check (indicative): ΣT_h·tanα against the skin friction ∫(p_a + p_p)·tanδ over the embedded length; no end bearing.

Development

pip install -e ".[dev]"
pytest -q                 # 99 tests: engine, beam-spring, report, study, forms, web, packaging
ruff check .

The tests cover the analysis cores against closed-form and published cases, the report in all three formats, the input schema and its file round-trips, and the interface itself — the session and the HTTP layer both, so the browser is exercised without a browser.

Releasing to PyPI is described in docs/releasing.md; tools/upload_to_pypi.py does it from an editor, without a terminal.

Background

Lythos SPWA is the desktop program SPWA (PyQt6 + Matplotlib) rebuilt as a web application: the analysis cores are the same code, while the Qt interface has been replaced by a local server and a browser page, and the Qt-based PDF writer by reportlab. Nothing in the program needs a display any more, it installs from PyPI in one command, and the original desktop version remains at hdaltuntas/spwa.

License

MIT © 2025 Hasan Deniz Altuntaş

Author

Hasan Deniz Altuntaş