Can the ground take it?
The pick works. Does the support?
Your job: support a crawler through three picks. Assess two candidate ground locations for the same lift. Choose bare tracks, one mat layer, or two layers, then run the same swing at each location. The crane and picks stay fixed in the diagram so you can isolate the support and soil effects. This exercise checks assumed pressure where the support meets the soil; it does not check a buried weak layer.
Blue + ✓ within game limit · Gold + ! above game limit
Each tile shows modeled surface pressure / assumed soil limit in PSF. More effective mat area can carry a greater reaction at the same soil limit, provided the mats actually distribute that load.
The support has to work through the whole pick.
A short radius is only part of the decision. Compare the same three hoisting locations and swing with different support beneath the tracks. Watch for the highest pressure through the swing, not just at the final position.
Run a plan to see which support zone controls.
What this picture cannot see: a firm crust over soft soil. Equal pressure at the surface can produce very different pressure at depth when the loads and footprints differ. A real ground assessment must consider the soil profile below the support, too.
Related Field Note: Use 4D to test the erection plan → discusses adding detail where it changes the decision.
Back to the erection plan →Assumptions, limits and references
What the game shows. Four invented support zones make the reaction shift visible as the crawler swings through the picks. For each zone, modeled pressure at the soil-contact surface = zone reaction (kips) × 1,000 ÷ assumed effective bearing area (ft²). A zone passes when that pressure is at or below its assigned PSF limit. The game samples the displayed swing, including returns to the common hoisting location; reach is a separate geometry check.
Teaching numbers. Total supported load stays at 400 kips, starting at 100 kips per zone before a fictional reaction shift. The four reactions always add to 400 kips, and their path does not change when the mat option changes. Assumed effective areas per zone are 22 ft² for bare tracks, 50 ft² for one mat layer and 62 ft² for two cross-laid layers. These are effective contact assumptions, not mat dimensions or values from a crane chart. The normal game limit is 3,000 PSF, matching the Mobile Crane Support Handbook table’s presumptive value for loose sand. Location 2 assigns the east-side zones of the same fixed setup a 1,000 PSF soft-clay limit, matching the table’s soft clay or silt category. Soil-controlled reaction in kips = PSF limit × effective area ÷ 1,000. These categories are examples, not a soil classification for this fictional site.
What mat layers mean. With the same reaction and a larger effective contact area, modeled surface pressure falls. At the same soil PSF limit, the supported reaction can rise. The soil’s allowable PSF does not rise because another layer is stacked. Actual effective area depends on mat layout, bending stiffness, load transfer and contact; a second layer does not automatically engage all its area. Mat capacity and settlement are separate checks.
What the diagram omits. It treats the soft-clay strip as a lower limit at the contact surface, not as a buried layer. Duerr’s handbook example gives two supports the same 4,000 PSF surface pressure: 4,000 lb on a 1 × 1 ft plate and 64,000 lb on a 4 × 4 ft mat. Using its approximate 60° load-spread method at a depth of 3 ft, the calculated average pressures at the top of a soft layer are about 201 and 1,149 PSF, respectively. The loads differ: this comparison illustrates why a matching surface PSF does not establish matching stress at depth. This game does not perform that depth calculation, a subsurface investigation or a settlement analysis. It also omits machine-specific reactions, mat bending and shear, ground water, buried services, slopes, lift capacity and crane stability. A pass here is only a pass in this exercise.
References: David Duerr, Mobile Crane Support Handbook, 2nd ed., pp. 43 and 48 (user-provided excerpts); Lawrence Sapirio, Cranes and Derricks, 4th ed. (future reference; no figures or ratings from it are used here). Further reading: OSHA ground conditions ↗ · DICA on effective bearing area ↗ · Duerr on effective bearing length ↗.