Which tool, when?

The Lythos family deliberately contains tools that answer the same question two ways: a slope can be solved by limit equilibrium (LE) or by finite elements (FEA); a sheet pile wall by limit equilibrium or by beam-spring. The table below maps typical engineering questions to the right tool.

By question

Your question	Tool	Why
What is this slope's factor of safety, and where is the critical slip surface?	Lythos LE	Eight methods and thousands of surfaces in seconds; the standard route for reports and comparisons.
What if the slip surface isn't circular, or there is soil-structure interaction?	LythosFEA	Under strength reduction the mechanism falls out of the deviatoric strain field.
How far does the wall move during excavation, and what happens to the anchor loads?	LythosFEA or Lythos SPWA	FEA solves the continuum; SPWA is faster and makes the sheet pile design checks.
Is the sheet pile's embedment and section enough?	Lythos SPWA	Free-earth support + staged Winkler, stress and deflection checks, a section database.
Which failure do the joints in this rock slope allow?	Lythos Kinematic	Markland test, stereonet, Monte Carlo probability.
How many bolts, how long, for the critical rock wedge?	Lythos Kinematic	Wedge/planar/toppling limit equilibrium and a bolt spacing × length matrix.
Can this footing carry this load, and how wide must it be?	Lythos Bearing	Six factor sets side by side, EN 1997-1 design approaches, the width required.
How much, and how fast, will the raft / fill settle?	Lythos Settle	Immediate + consolidation + secondary, t50/t90, angular distortion.
How long must the pile be, what does the group carry, how much does it settle?	Lythos Pile	α/β/λ, four group efficiencies, block failure, required length, equivalent raft.
How long must the rock socket be?	Lythos Pile	Twelve published correlations and a design length.
Is the reinforcement of this MSE wall enough?	Lythos MSEW	FHWA/AASHTO external and internal stability, ASD or LRFD, the required length.

Shared code between siblings

The family shares code, too:

• MSEW's bearing capacity factors are Lythos Bearing's. The bearing capacity of the wall's base is computed with the same factors.py and capacity.py.
• Kinematic's two modules plot on one stereonet. Screening and limit equilibrium use the same projection, and the most critical component found in screening goes to limit equilibrium in one click.
• LE and FEA check each other. FEA's 2:1 slope test is made against an independently written Bishop search (1.377 against 1.381).

By analysis type

	FEA	LE	Kinematic	Bearing	Settle	Pile	SPWA	MSEW
Limit equilibrium		●	●	●		●	●	●
Finite elements / springs	●						●
Deformation / settlement	●				●	●	●
Staged construction	●						●
Earthquake (pseudo-static)		●	●	●			●	●
Groundwater	●	●	●	●	●	●	●	●
Reliability / probability			●	●	●	●	●
PDF / HTML report	HTML	JSON/CSV/SVG	PDF	●	●	●	●	●
Turkish interface			●	●	●	●	●	●
DXF import	●

A calculation program does not replace engineering judgement

Read the limitations on each program's Reference page. LythosFEA, for example, has no consolidation and no hardening soil model; Lythos MSEW does not check global and compound stability — use Lythos LE for that.