Motorized CBR Loading Machine
Applies constant penetration rate of 1.27 mm/min (0.05 in/min) with electronic load cell up to 50 kN.
Civil Engineering / California Bearing Ratio (CBR)
FREE TO EXPLORELABORATORY 27 · CIVIL ENGINEERING
California Bearing Ratio (CBR) of Compacted Pavement Subgrade & Base Soils
Determine the California Bearing Ratio (CBR) of compacted subgrade soil under soaked and unsoaked conditions, evaluate penetration resistance force (P), and determine pavement design thickness according to ASTM D1883 / AASHTO T193. Explore interactive structural mechanics, materials simulation, and civil engineering telemetry.
STRUCTURAL MATERIALS · MECHANICS · GEOTECHNICAL · HYDRAULICS · HIGHWAYS · SURVEYING
Your virtual civil engineering laboratory.
PENETRATION RESISTANCE FORCE P—
CIVIL INFRASTRUCTURE TELEMETRY
Ready to sample with Penetration d = 2.5 mm.
Adjust Penetration d, then execute civil engineering measurement.
Civil engineering telemetry is evaluated rigorously using 64-bit IEEE 754 precision. Residuals reflect ordinary least-squares regression across successive observations. Continuous data structures support high-fidelity structural mechanics and geotechnical continuum modeling.
Civil engineering assumptions and boundary condition limits
The civil engineering physical models apply within the specified calibrated operational window (1.5 to 5.0 mm). Compacted crushed aggregate base course soil tested in soaked state. Standard California reference loads: P_std(2.5 mm) = 13.34 kN, P_std(5.0 mm) = 20.00 kN. Linearized penetration force relates directly to penetration depth d with stiffness slope 2.4000 kN/mm. At d = 2.50 mm: P = 6.00 kN, yielding CBR = (6.00 / 13.34) · 100% = 45.0%.
Laboratory apparatus & testing equipment.
Hardened Cylindrical Steel Penetration Piston
Machined piston with 49.63 ± 0.13 mm diameter (1935 mm² / 3.0 in² area) conforming to ASTM D1883.
Heavy-Duty Steel CBR Compaction Molds
152.4 mm internal diameter by 177.8 mm height molds with perforated baseplates and collar.
Annular & Slotted Steel Surcharge Weights
2.27 kg paired split weights simulating pavement pavement overburden stresses (4.54 kg total).
Soaking Water Bath & Swell Dial Indicator
4-day soaking tank with tripod dial indicator measuring vertical soil swell to 0.01 mm.
Digital Linear Displacement Transducer (LVDT)
Monitors piston penetration depth d into soil with 0.001 mm resolution.
FOLLOW THE METHOD
A reason behind every step.
Determine the California Bearing Ratio (CBR) of compacted subgrade soil under soaked and unsoaked conditions, evaluate penetration resistance force (P), and determine pavement design thickness according to ASTM D1883 / AASHTO T193. Standardized parameter settings: 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 mm.
01
Soil Moisture Dosing & Compaction
Mix 6.0 kg of base course soil at Optimum Moisture Content (OMC); compact into 152.4 mm CBR mold in five layers with 56 blows per layer of 4.54 kg rammer; trim surface flush.
02
Surcharge Placement & 96-Hour Soaking
Place perforated swell plate and 4.54 kg surcharge weights on soil; mount swell dial gauge; submerge mold in water bath for 96 hours (4 days); record daily swell percentage.
03
Post-Soak Draining & Surface Drying
Remove mold from bath; allow water to drain freely through baseplate for 15 minutes; remove surcharge weights; wipe excess surface water.
04
CBR Machine Mounting & Seating
Place mold on machine platen; reposition 4.54 kg surcharge weights; seat penetration piston centrally with a small seating load of 45 N; zero load and displacement channels.
05
Constant-Rate Piston Penetration
Engage machine at constant rate of 1.27 mm/min (0.05 in/min); log penetration force P at depths of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 mm.
06
CBR Calculation & Pavement Sizing
Plot force versus penetration depth; apply initial concave-upward zero correction if necessary; evaluate CBR at 2.5 mm and 5.0 mm; determine governing design CBR%.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into civil engineering insight.
Points are your recorded observations. The solid regression line validates California Bearing Ratio (CBR) mathematical scaling.
LINEAR REGRESSION FIT · y = mx + b
P = 2.4000 · d
| # | Piston Penetration Depth d (mm) | Penetration Resistance Force P (kN) | Piston penetration depth d (mm) | Penetration resistance force P (kN) | Remove |
|---|
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CHECK YOUR UNDERSTANDING
Explain what the civil engineering metrics mean.
The standard penetration rate of the CBR piston in ASTM D1883 is:
The standard reference force for 2.54 mm (0.1 in) penetration on standard crushed stone is:
The standard soaking duration to simulate worst-case groundwater saturation is:
If a soil requires a penetration force of 3.34 kN at 2.54 mm, its California Bearing Ratio (CBR) is:
THEORY AND STRUCTURAL CONTEXT
Civil engineering background & physical principles.
The California Bearing Ratio (CBR) is the universal empirical design parameter used worldwide in AASHTO, FAA, and Asphalt Institute methodologies for determining the structural thickness of flexible asphalt pavements and airport runways. Conceived by the California Division of Highways in the late 1920s, the CBR test (ASTM D1883) evaluates the mechanical shearing resistance of compacted subgrade, subbase, and base course soils relative to a standard crushed limestone base material. Soil prepared at Optimum Moisture Content (OMC) is compacted into a heavy cylindrical steel mold (152.4 mm diameter, 177.8 mm height) in five layers using a 4.54 kg rammer. To simulate the worst-case moisture scenario during seasonal spring thaws and monsoon floods, specimens are subjected to a 96-hour (4-day) soaking period in a water bath under surcharge weights simulating pavement overburden (minimum 4.54 kg), while swell dial gauges monitor vertical volumetric swelling. The soaked mold is then mounted in a motorized compression frame, and a hardened steel piston (49.63 mm diameter, cross-sectional area 1935 mm² / 3.0 in²) penetrates the soil at a standardized constant rate of 1.27 mm/min (0.05 in/min). Penetration force P is recorded at standard depths, notably 2.54 mm (0.1 in) and 5.08 mm (0.2 in). The CBR percentage is calculated by dividing measured piston resistance by the standard penetration resistance of high-grade crushed California stone (13.34 kN at 2.54 mm, and 20.00 kN at 5.08 mm): CBR% = (P / P_std) x 100%. In this laboratory, penetration force is logged across penetration depths from 1.5 to 5.0 mm to calibrate the penetration stiffness slope and extract the design CBR.
P = 2.4000 · d
Compacted crushed aggregate base course soil tested in soaked state. Standard California reference loads: P_std(2.5 mm) = 13.34 kN, P_std(5.0 mm) = 20.00 kN. Linearized penetration force relates directly to penetration depth d with stiffness slope 2.4000 kN/mm. At d = 2.50 mm: P = 6.00 kN, yielding CBR = (6.00 / 13.34) · 100% = 45.0%.