| Tip | Reason | |-----|--------| | Pre‑define multiple possible crack lines | If you are unsure where the crack will open, place several candidate joints and assign a low normal stiffness (e.g., 10 kN/m³). The one experiencing the highest tensile stress will open first. | | Use a “soft” normal stiffness instead of exactly zero when the solver struggles with convergence. | A tiny residual stiffness (1–10 kN/m³) stabilises the linear system while still allowing realistic opening (> mm). | | Check element aspect ratios – Keep the height/width ratio of elements adjacent to the crack ≤ 5. | Poor aspect ratios amplify numerical artefacts near the discontinuity. | | Validate against a simple analytical solution (e.g., a cantilever beam with a crack). | Guarantees that your joint properties are correctly defined before tackling complex geometry. | | Leverage the Phase‑Field module for verification – Run a quick phase‑field simulation of the same geometry. | If both approaches predict a similar crack path, you have confidence in the line‑element model. | | Document the joint parameters – Keep a small table (in your report) of kn, ks, φ, c, and cut‑off for every joint. | Makes model review and future updates straightforward. | | Avoid “over‑refining” – Excessive mesh density can cause extremely small time steps and long run times. Use adaptive refinement only where needed. | | Use the “Joint Slip” result type to evaluate whether the crack is sliding or just opening. | Helps decide if you need to increase φ or add cohesion. |
| Step | Action |
|------|--------|
| 1 | Define the bulk material (e.g., Concrete, Rock Mass) using a suitable model (Mohr‑Coulomb, Hardening Soil, etc.). |
| 2 | Create a new Joint (type = J2):
– Normal stiffness kn = 0 (or 1 kN/m³ if you want a tiny residual).
– Shear stiffness ks = E/(2(1+ν)) × thickness (or simply set a high value). |
| 3 | Set Tension cut‑off = ON; define the Cut‑off stress = 0 kPa (pure tension). |
| 4 | Assign Friction angle φ according to the material (e.g., 0° for a pure crack, 20°–30° for a joint). |
| 5 | (Optional) Add a Cohesion value if the crack is partially cohesive (e.g., 5 kPa). |
| 6 | Link the joint to the line elements: Assign → Joint → J2 → select the line(s). |
Software like Plaxis 2D, developed by Bentley Systems, is widely used for geotechnical analysis. It's a powerful tool for engineers and professionals in the field of civil engineering, offering advanced features for modeling and simulating the behavior of soil and rock. Plaxis 2d V21 Full Crack BETTER
Below is a concise guide you can follow for a typical tunnel‑lining or slab‑on‑grade problem.
| Symptom | Likely Cause | Remedy |
|---------|--------------|--------|
| Solver diverges after the crack opens | Normal stiffness set exactly to zero → singular stiffness matrix. | Use a tiny kn (1–10 kN/m³) or enable Automatic Damping. |
| Crack opening appears “stiff” (very small) | Shear stiffness too high combined with a non‑zero kn. | Reduce kn further, or check that the Tension cut‑off is turned ON. |
| Unexpected crack path (e.g., diagonal instead of horizontal) | Mesh anisotropy or poorly aligned line elements. | Refine mesh, align line elements with expected crack direction, or add additional candidate joints. |
| Large oscillations in joint forces | Load step too large for the sudden stiffness drop. | Decrease load increment (max % per step) or use Load Control instead of Displacement Control. |
| No crack opens even though tensile stress > 0 | Cut‑off stress set > 0 (default sometimes 0.01 kPa). | Set cut_off = 0 explicitly. |
| Crack slides excessively | Friction angle φ too low or shear stiffness too high. | Increase φ or add a small cohesion to resist shear. | | Tip | Reason | |-----|--------| | Pre‑define
Given the risks associated with using cracked software, here are some alternatives:
Below is a concise example script (Plaxis 2D Script language) that builds a simple tunnel lining with a pre‑defined full crack at the crown. You can paste it into the Console or save as a .txt file and run it. | Step | Action | |------|--------| | 1
*-------------------------------------------------
* Plaxis 2D V21 – Full Crack Example
*-------------------------------------------------
* Geometry
new
material 1 Concrete
model = "Mohr-Coulomb"
e = 30e9
nu = 0.2
phi = 30
c = 5e3
end
material 2 Soil
model = "Hardening Soil"
e = 25e6
nu = 0.35
phi = 20
c = 2e3
end
* Tunnel
point 1 0 0
point 2 0 -10
point 3 5 -10
point 4 5 0
line 1 1 4
line 2 4 3
line 3 3 2
line 4 2 1
block 1 1 2 3 4 material=1
block 2 1 2 3 4 material=2
* Full crack at crown (line 1)
joint 1 type=J2
kn = 0
ks = 1e10 ! high shear stiffness
phi = 0 ! pure tensile crack
cohesion = 0
cut_off = 0
end
assign joint=1 to line 1
* Mesh
mesh 1 1 2 3 4 size=0.2
refine line 1 size=0.05 ! fine mesh along crack
* Boundary conditions
fix point 1 ux uy
fix point 2 ux uy
fix point 3 ux uy
fix point 4 ux uy
* Loading – increase internal pressure
stage 1
pressure line 2 -100 kPa ! ground load
end
stage 2
pressure line 3 -200 kPa ! simulate overburden increase
end
* Solver
set newton_raphson on
set max_iterations 30
set convergence tolerance=0.001
set damping automatic
* Run
calculate
* Post‑process (optional)
plot joint normal displacement joint=1
export joint forces joint=1 to "joint1_forces.csv"
What the script does