Chapter 8 — Soil and Rock Classification — Railway Ground Hazard Risk Management

Primary Reference: USACE EM 1110-1-1804, Geotechnical Investigations (2001), Sections 3-1 through 3-8; ASTM D2487, D3282, D4318, D422, D1140, D2938; AREMA MRE Chapter 1, Sections 1.3–1.4; AASHTO M 145.

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Executive Summary

Consistent, reproducible classification of soil and rock is the common language shared between field personnel, laboratory technicians, design engineers, and railroad client reviewers. Every boring log, lab report, and geotechnical analysis submitted to CSXT, NSR, UPRR, BNSF, CPKC, Amtrak, CN, and G&W subsidiaries relies on a classification framework that is traceable to recognized standards — principally the Unified Soil Classification System (USCS, ASTM D2487) for soils, AASHTO M 145 for pavement subgrade classification, and quantitative rock quality indices (RQD, Rock Mass Rating, and Geological Strength Index) for rock. AREMA MRE Chapter 1 references both USCS and AASHTO M 145 as acceptable classification standards for railroad earthwork design. This chapter presents the full classification methodology for soils and rock in railroad project contexts, including Atterberg limit interpretation, gradation analysis, RQD (Chapter 6 cross-reference), RMR, and GSI. Three worked examples drawn from CSXT, NSR, and BNSF projects illustrate the classification process end-to-end. A representative data table, figure placeholders, practical recommendations, a field and lab checklist, and five practice questions with complete answers follow.

8.1 Background — Why Classification Matters for Railroad Clients

Railroad embankment fills, subgrade soils, and foundation materials are evaluated using classification results at every project phase. Specifically:

CSXT Engineering Standards require USCS classification for all boring samples and specify that fill materials placed within 3 ft of the top of subgrade must be non-plastic or low-plasticity (PI ≤ 6%) to limit swelling potential and differential track settlement.
NSR's Engineering Standards Manual references AASHTO M 145 classification for subgrade evaluation on reconstruction projects, with Group A-7-6 soils triggering mandatory ground improvement assessment.
UPRR Engineering Instruction Manual specifies that subgrade soils classified as A-6 or A-7 require CBR testing (Chapter 18) before design proceeds.
BNSF Engineering Instructions require that all soil sample descriptions on boring logs include the USCS group symbol, group name, color, moisture condition, and estimated consistency — deviations result in data package rejection.
CPKC Track Standards require USCS classification supplemented by frost susceptibility rating for all subgrade soils in Canadian operations, where freeze-thaw cycles drive differential heave on the prairie mainline.
Amtrak Engineering Standards specify that laboratory-verified USCS classification (not field-estimated) is required for all samples used in NEC settlement and stability analyses.
CN Engineering Standards add a requirement for frost susceptibility classification (FS-0 through FS-4, per the Corps of Engineers criterion) on all Canadian projects north of 45°N latitude.
G&W Engineering Bulletins accept field USCS classification for reconnaissance-level assessments but require lab verification for final design on projects involving embankment heights exceeding 10 ft.

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Soil Mechanics — Origin, Formation, Profile and Application

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Classification systems used by railways, side by side

European railways have not used a single system. The United Kingdom, France, Germany, Switzerland and others use the Unified Soil Classification System (Casagrande); Scandinavian railways rely mainly on grain size; Italy, Greece and others use the AASHO (now AASHTO) system. Profillidis calls the USCS the most generally applicable. ASTM D2487 is based on it but requires laboratory classification tests and subdivides further, whereas USCS allows a tentative visual classification. BS 5930 also derives from Casagrande but draws the sand and gravel boundaries differently, and DIN 4022 subdivides silt, sand and clay into fine, medium and coarse.

Figure 8-10 compares the grain-size boundaries of the main systems. They do not coincide (the silt–sand boundary, for example, falls between 0.02 mm and 0.074 mm), so check which system a historic log used before carrying its descriptions into a UIC or AREMA subgrade assessment.

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Figure 8-10. Grain-size boundaries for clay, silt, sand and gravel in the Bureau of Soils, Atterberg, MIT, AASHO, Unified/ASTM and DIN 4022 systems. Profillidis Fig. 9.2. — **Figure 8-10.** Grain-size boundaries for clay, silt, sand and gravel in the Bureau of Soils, Atterberg, MIT, AASHO, Unified/ASTM and DIN 4022 systems. Profillidis Fig. 9.2.

After Profillidis (2014), §9.3, Fig. 9.2. Full reference under Supplemental Sources.

8.2 Grain-Size Analysis

8.2.1 Sieve Analysis (ASTM D422 / D6913)

Sieve analysis separates soil particles by mechanical sieving through a standardized stack of sieves. Key sieves and particle size boundaries:

Sieve	Opening (in.)	Particle Class Boundary
3 in.	3.00	Coarse gravel / cobble
¾ in.	0.75	Fine gravel / coarse gravel
No. 4	0.187	Gravel / sand boundary
No. 10	0.079	Coarse / medium sand
No. 40	0.0165	Medium / fine sand
No. 200	0.0029	Sand / fines boundary

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Equation 8-1 — Percent Passing (by mass):

P_i (%) = [Mass passing sieve i / Total dry mass of specimen] × 100

Equation 8-2 — Coefficient of Uniformity:

C_u = D_60 / D_10

Equation 8-3 — Coefficient of Curvature:

C_c = (D_30)² / (D_10 × D_60)

Where D_10, D_30, D_60 = grain diameter (mm or in.) at which 10%, 30%, and 60% of the soil mass is finer, respectively.

Gravel classification: Well-graded gravel (GW) requires C_u ≥ 4 and 1 ≤ C_c ≤ 3. Poorly graded gravel (GP) fails either criterion. Sand classification: Well-graded sand (SW) requires C_u ≥ 6 and 1 ≤ C_c ≤ 3. Poorly graded sand (SP) fails either criterion.

8.2.2 Hydrometer Analysis (ASTM D422)

For the fines fraction (passing No. 200 sieve), hydrometer analysis determines the silt/clay boundary at 0.002 mm (2 µm). The hydrometer reading at elapsed time t is converted to equivalent particle diameter using Stokes' Law:

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Equation 8-4 — Equivalent Particle Diameter (Stokes' Law):

D = √(18 × η × L / (G_s − 1) × γ_w × t)

Where:

D = equivalent particle diameter (mm)
η = viscosity of water at test temperature (g/cm·s); at 68°F, η = 0.01002 g/cm·s
L = effective hydrometer depth (cm); varies with reading
G_s = specific gravity of solids (typically 2.65–2.72 for mineral soils; use measured value per ASTM D854)
γ_w = unit weight of water (g/cm³) = 1.0
t = elapsed time (minutes × 60 = seconds)

Note: In English practice, hydrometer results are still reported in mm for particle size; the USCS boundary between silt and clay remains at 0.002 mm regardless of unit system.

Supplemental figures · LEVI Library

**Supplemental Figure 8-S3.** Grain shape descriptors for coarse-grained soil: (a) rounded, (b) subrounded (continued on following sheet in source with subangular and angular). *Source: U.S. Army Corps of Engineers (2001). *Geotechnical Investigations*. EM 1110-1-1804.*

Case study: 8.14.1 Gradings before and after compaction: the oversize that was never tested (Look 2023), in §8.14 Case Studies.

Case study: 8.14.2 Representative sampling from a weathered-rock stockpile (Look 2023), in §8.14 Case Studies.

8.3 Atterberg Limits (ASTM D4318)

Atterberg limits define the moisture content boundaries between soil behavioral states for fine-grained soils. They are measured on the fraction passing the No. 40 sieve.

8.3.1 Liquid Limit (LL), Plastic Limit (PL), and Plasticity Index (PI)

No additional content.

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Equation 8-5 — Plasticity Index:

PI = LL − PL

Equation 8-6 — Liquidity Index (LI) — measure of in-situ consistency:

LI = (w_n − PL) / PI

Where w_n = natural (field) water content (%). Interpretation:

LI	Consistency State
< 0	Stiff / desiccated
0–0.25	Very stiff
0.25–0.50	Stiff
0.50–0.75	Medium
0.75–1.00	Soft
> 1.00	Very soft / approaching liquid state

Activity (A) — clay mineralogy indicator:

Equation 8-7 — Activity:

A = PI / (% clay fraction)

Where % clay fraction = % finer than 0.002 mm from hydrometer analysis.

A	Clay Mineral Type
< 0.75	Inactive (kaolinite dominant)
0.75–1.25	Normal (illite dominant)
> 1.25	Active (montmorillonite / smectite)

Activity > 1.25 is a critical flag on all railroad projects: highly active clays exhibit significant swell potential when wetted after desiccation — a chronic track geometry problem along CSXT's Carolina division, BNSF's Texas Panhandle routes, and UPRR's expansive clay zones in Wyoming and Colorado. CN Engineering Standards require swell testing (ASTM D4546) whenever A > 1.0.

8.3.2 Shrinkage Limit (SL)

The shrinkage limit (ASTM D4943) is the water content below which further drying causes no volume change. For railroad embankments in seasonally dry climates (BNSF Great Plains, UPRR Southwest, CN Prairie), SL data inform desiccation crack depth estimates used in slope stability models (Chapter 13).

Supplemental reference · LEVI Library

Reading clay mineralogy and swell potential from the limits

Table 8-S3. Typical Atterberg limits for clay minerals (Carter & Bentley, Table 8.2)

Mineral	PL (Ca⁺⁺)	LL (Ca⁺⁺)	PL (Na⁺)	LL (Na⁺)	Typical activity
Montmorillonite	65–79	123–177	86–97	280–700	Ca 1.5; Na 7.2
Illite	36–42	69–100	34–41	61–75	0.9
Kaolinite	26–36	34–73	26–28	29–52	0.33–0.46

Table 8-S4. Swelling potential from plasticity index (Carter & Bentley, Table 8.4)

Swelling potential	PI (Seed et al., 1962)	PI (Krebs & Walker, 1971)
Low	0–15	0–15
Medium	10–30	15–24
High	20–55	25–46
Very high	> 40	> 46

Table 8-S5. Expansion potential from shrinkage limit and linear shrinkage (after Altmeyer, 1955)

Potential	Shrinkage limit (%)	Linear shrinkage (%)
Critical	< 10	> 8
Marginal	10–12	5–8
Non-critical	> 12	< 5

Swelling potential here is the percent swell of a laterally confined specimen compacted at optimum moisture (standard Proctor) and soaked under a 1 psi surcharge: 0–1.5% low, 1.5–5% medium, 5–25% high, > 25% very high. Seed et al. (1962) related it to plasticity as S = 60K·PI^2.44 with K = 3.6 × 10⁻⁵, valid for clay contents of 8–65% and accurate to about ±33% of lab values. Because each index is uncertain, Holtz and Gibbs (adopted by USBR) recommend judging expansion potential from colloid content, PI and shrinkage limit together, then confirming with an ASTM D4546 swell test where the result matters for track geometry.

Source: Carter, M. and Bentley, S. P. (2016). Soil Properties and their Correlations, 2nd ed. Wiley

Supplemental reference · LEVI Library

One-point liquid limit for production testing

For large corridor programs, NYSDOT’s GTM-7 (based on AASHTO T89) allows a one-point liquid limit: accept a trial that closes the groove in 15–30 drops, with at least two consistent consecutive closures, then LL = w (N/25)^0.12. The factor ranges from 0.941 at 15 drops to 1.022 at 30 drops. Reserve multi-point flow curves for design-critical samples and borderline A-line soils.

Source: New York State DOT Geotechnical Engineering Bureau (2015). Test Method for Liquid Limit, Plastic Limit, and Plasticity Index, GTM-7 Rev. 2

8.4 Unified Soil Classification System (USCS — ASTM D2487)

8.4.1 Classification Flowchart Logic

Step 1 — Coarse or Fine?

If ≥ 50% retained on No. 200 sieve → Coarse-grained (G or S prefix)
If > 50% passing No. 200 sieve → Fine-grained (M, C, or O prefix) or Highly Organic (Pt)

Step 2 — For Coarse-grained soils:

If ≥ 50% of coarse fraction retained on No. 4 → Gravel (G); else → Sand (S)
If fines < 5%: classify as W (well-graded) or P (poorly graded) using C_u and C_c
If fines 5–12%: dual symbol (e.g., GW-GM)
If fines > 12%: classify fines as M (non-plastic) or C (plastic) using Atterberg limits

Step 3 — For Fine-grained soils (plot on Casagrande Plasticity Chart):

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Equation 8-8 — A-line (boundary between clay and silt/organic):

PI = 0.73 × (LL − 20)

Equation 8-9 — U-line (upper bound of natural soils):

PI = 0.9 × (LL − 8)

Classification matrix:

Position on Chart	LL < 50 (Low Plasticity)	LL ≥ 50 (High Plasticity)
Above A-line	CL (lean clay)	CH (fat clay)
Below A-line or PI < 4	ML (silt)	MH (elastic silt)
Organic (LL_oven < 0.75 × LL_wet)	OL	OH
Fibrous, very high water content	Pt (peat)	Pt

Borderline classifications (e.g., CL-ML for soils plotting near the A-line with 4 ≤ PI ≤ 7) must be noted on boring logs submitted to BNSF, Amtrak, and CN — these clients explicitly require dual symbols in this zone.

Supplemental reference · LEVI Library

Field identification of fines before lab results arrive

Field logs use the visual-manual procedure (ASTM D2488). The USACE field tests, run on the minus No. 40 fraction:

Test	Procedure	Interpretation
Dilatancy	Shake a 1-in. pat of moist soil in the palm, then squeeze it	Very fine clean sand: quick, distinct water and gloss. Inorganic silt: moderately quick. Plastic clay: no reaction.
Dry strength	Dry a putty-consistency pat and crumble it between the fingers	Strength increases with plasticity; high for fat clay. Silts and silty sands are slight — sand feels gritty, silt feels like flour. Break on a fresh surface, not a shrinkage crack.
Toughness	Roll a 1/8-in. thread repeatedly until it crumbles at the plastic limit, then knead the pieces	Stiffer threads and tougher lumps at the PL indicate higher clay content.
Ribbon	Flatten a 1/2–3/4 in. roll to 1/8–1/4 in. thick	High-plasticity clay: 8–10 in. ribbon; shorter for lower plasticity; non-plastic soil will not ribbon.

USACE also lists quick checks for organic matter (odor), calcium carbonate cementation (dilute HCl), and whether a “rock-like” material is shale (slaking in water). Record color with Munsell soil color charts — color reflects mineralogy, drainage, and organic content.

Source: U.S. Army Corps of Engineers (2001). Geotechnical Investigations. EM 1110-1-1804

Supplemental figures · LEVI Library

**Supplemental Figure 8-S1.** Dilatancy test: squeezing the shaken pat — water and gloss disappear and the soil stiffens and cracks. *Source: U.S. Army Corps of Engineers (2001). *Geotechnical Investigations*. EM 1110-1-1804.*

**Supplemental Figure 8-S2.** Ribbon test: moist soil flattened to a 1/8–1/4 in. ribbon; high-plasticity clays form ribbons 8–10 in. long. *Source: U.S. Army Corps of Engineers (2001). *Geotechnical Investigations*. EM 1110-1-1804.*

Field identification of fine-grained soil

Coarse vs. fine follows the 50-50 rule: more than 50% passing the No. 200 sieve is fine-grained, and in coarse soils the No. 4 sieve separates sand from gravel. In a name like “silty sand,” the second word is the predominant material. Clay particles carry a charge that gives cohesion and plasticity; silt does not. Dry silt blows away as dust, wet silt feels slippery and wet clay feels sticky. The distinction matters operationally, because silts and fine sands can fail very rapidly while deep clay embankments tend to creep.

Table 8-3. Field tests for fine-grained soil
Test	Silt	Low-plasticity clay	High-plasticity clay
Dilatancy (shake a wet pat)	Water appears quickly; pat loses shape	Water appears slowly; holds shape	No change
Toughness (roll a 1/8-in. thread)	Difficult to roll any thread	Easy, moderately plastic thread	Possible but difficult; very stiff
Dry strength (crush a dry 1/8-in. piece)	Crumbles with little pressure	Moderate	Cannot be broken with fingers

Plasticity index guide used in the course: 0 non-plastic, 1–5 slightly plastic, 5–10 low, 10–20 medium, 20–40 high, and 40+ very high. Organic soils (topsoil, peat) are identified by fiber, color and odor and should be avoided as subgrade.

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Figure 8-11. Relative particle sizes of gravel, sand, silt and clay. — **Figure 8-11.** Relative particle sizes of gravel, sand, silt and clay.

Figure 8-12. The dilatancy (shaking) test. — **Figure 8-12.** The dilatancy (shaking) test.

Figure 8-13. The toughness test: rolling a 1/8-in. thread. — **Figure 8-13.** The toughness test: rolling a 1/8-in. thread.

Figure 8-14. Field decision flow for classifying an unknown soil. — **Figure 8-14.** Field decision flow for classifying an unknown soil.

After Geotechnology for Railroaders Program, Module 2; §08, §10. Full reference under Supplemental Sources.

Classification cautions for track subgrade

The majority component does not always control behavior. A soil that is 60% gravel with clay-filled voids behaves like clay. AASHTO’s 35% fines cutoff between granular and silt-clay materials reflects this better than the 50% boundary in USCS.
c and φ depend on drainage and saturation, not on soil name. “Sand: c = 0” holds only for drained (or dry) conditions. “Clay: φ = 0” holds only for saturated undrained loading. Partially saturated subgrade usually has to be analyzed in total stress with both c and φ non-zero. Treating these as fixed soil constants is a common source of analysis error.
Classification tests use disturbed samples. They say nothing about in-place moisture, strength or stiffness. Pair them with in situ testing or undisturbed samples.
Be consistent. Use the ASTM D2488 visual-manual flow charts and modifiers consistently: “with sand” at 15–25% coarse material, and a “sandy” prefix at 30% or more. Soil naming is often done poorly in practice.
Ballast sources. For rock being assessed as a ballast source, classify by petrographic thin section (ground to 0.03 mm, with carbonate and feldspar staining) as well as by hand specimen (Chapter 2, §2.3.2).

After Selig & Waters (1994), ch. 3. Full reference under Supplemental Sources.

8.5 AASHTO M 145 Classification

The AASHTO classification (AASHTO M 145) is used specifically for pavement subgrade evaluation and is the primary soil classification system referenced by NSR and UPRR for track subgrade rehabilitation projects. It classifies soils into Groups A-1 through A-7 based on gradation and Atterberg limits.

Table 8-1. AASHTO M 145 Classification Summary (Abbreviated)
Group	% Pass No. 200	LL	PI	Typical USCS	Subgrade Rating
A-1-a	≤ 15	—	≤ 6	GW, GP	Excellent
A-1-b	≤ 25	—	≤ 6	SW, SP, GM	Excellent
A-2-4	≤ 35	≤ 40	≤ 10	GM, GC, SM	Good
A-2-6	≤ 35	≤ 40	> 10	GC, SC	Good-Fair
A-3	≤ 10	NP	NP	SP	Good
A-4	> 36	≤ 40	≤ 10	ML, OL	Fair
A-5	> 36	> 40	≤ 10	MH, OH	Fair-Poor
A-6	> 36	≤ 40	> 10	CL	Poor
A-7-5	> 36	> 40	≤ LL − 30	MH, CH	Poor
A-7-6	> 36	> 40	> LL − 30	CH	Very Poor

Group Index (GI) — quantifies subgrade quality within a group:

Reference graphics

AASHTO Soil Classification for Pavement Design

TxDOT Soil Classes C1–C4 for Embankment and Subgrade

Equation 8-10 — Group Index:

GI = (F − 35) × [0.2 + 0.005(LL − 40)] + 0.01(F − 15)(PI − 10)

Where:

F = percent passing No. 200 sieve (%)
LL = liquid limit (%)
PI = plasticity index (%)
GI is rounded to the nearest whole number; GI = 0 for A-1, A-2, A-3

GI = 0 indicates excellent subgrade; GI = 20 (maximum) indicates very poor subgrade. NSR's Engineering Standards Manual specifies ground improvement (Chapter 17) when GI ≥ 12 in track subgrade applications.

8.6 Rock Classification

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8.6.1 Rock Quality Designation (RQD)

RQD is calculated from rock core runs per the procedure established in Chapter 6 (Equation 2-4). To summarize:

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Equation 8-11 — RQD:

RQD (%) = [Σ length of intact core pieces ≥ 2 in.] / [Total core run length] × 100

RQD (%)	Rock Quality
0–25	Very Poor
25–50	Poor
50–75	Fair
75–90	Good
90–100	Excellent

NSR requires RQD to be calculated and recorded on every core run for Appalachian tunnel and rock cut projects. CPKC applies RQD as the primary acceptance criterion for rock riprap material on Rocky Mountain slope stabilization projects.

8.6.2 Rock Mass Rating (RMR — Bieniawski 1989)

RMR classifies the overall rock mass quality using six parameters, each assigned a rating:

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RMR Parameters and Tunnel Support by RMR Class

Equation 8-12 — Rock Mass Rating:

RMR = R₁ + R₂ + R₃ + R₄ + R₅ + R₆

Parameter	Rating Range	Description
R₁ — UCS (psi)	0–15	UCS < 36 psi → 0; UCS > 29,000 psi → 15
R₂ — RQD (%)	3–20	RQD 0–25% → 3; RQD 90–100% → 20
R₃ — Spacing of discontinuities	5–20	< 2 in. → 5; > 6.6 ft → 20
R₄ — Condition of discontinuities	0–30	Soft infill > 0.2 in. → 0; very rough, unweathered → 30
R₅ — Groundwater	0–15	Flowing water → 0; dry → 15
R₆ — Discontinuity orientation	−12 to 0	Adjustment for orientation relative to structure

RMR	Rock Class	Description
81–100	I	Very good rock
61–80	II	Good rock
41–60	III	Fair rock
21–40	IV	Poor rock
0–20	V	Very poor rock

RMR is used on NSR tunnel feasibility studies and on CPKC bridge pier excavation designs in the Canadian Shield. CN Engineering Standards reference RMR for classification of rock cut stability in their Geotechnical Engineering Manual, which we adapt for CN project deliverables.

8.6.3 Geological Strength Index (GSI — Hoek & Brown 1997)

GSI provides a rock mass characterization input for the Hoek-Brown failure criterion, used in rock slope stability analyses (Chapter 13) for NSR and CPKC projects. GSI is estimated from field observation of structure and surface condition of discontinuities:

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Equation 8-13 — Hoek-Brown Rock Mass Strength:

σ'₁ = σ'₃ + UCS × (m_b × σ'₃/UCS + s)^a

Where:

σ'₁, σ'₃ = major and minor principal effective stresses (psi or ksf)
UCS = uniaxial compressive strength of intact rock (psi)
m_b = reduced Hoek-Brown constant = m_i × exp((GSI − 100)/(28 − 14D))
s = exp((GSI − 100)/(9 − 3D))
a = 0.5 + (1/6)(exp(−GSI/15) − exp(−20/3))
D = disturbance factor (0 = undisturbed; 1 = heavily blasted)
m_i = intact rock constant (from Hoek-Brown tables; e.g., granite = 32, sandstone = 17, shale = 6)

GSI estimation charts (Marinos & Hoek 2000) are included in NSR project deliverables as a figure in the geotechnical data report (Appendix E).

8.6.4 Q-System (Barton et al. 1974)

The Q-system (Tunneling Quality Index) is used when NSR, CPKC, or Amtrak projects involve tunnel or large underground excavation design:

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Rock Classification vs Ground Behaviour (Q / RMR)

Rock Mass Classification — Beyond the Number

Equation 8-14 — Q Index:

Q = (RQD / J_n) × (J_r / J_a) × (J_w / SRF)

Where:

J_n = joint set number (3 for one set; up to 20 for crushed rock)
J_r = joint roughness number (1 = smooth planar; 4 = rough undulating)
J_a = joint alteration number (1 = unaltered; 12 = thick clay infill)
J_w = joint water reduction factor (1 = dry; 0.05 = high inflow)
SRF = stress reduction factor (1 = low stress; up to 400 for squeezing ground)

Q	Rock Class	Support Category
> 40	Exceptionally good	Spot bolting
10–40	Very good	Systematic bolting
1–10	Good to fair	Shotcrete + bolts
0.1–1	Poor	Multiple passes
< 0.1	Extremely poor	Heavy support

Supplemental reference · LEVI Library

Correction: RQD piece length is 4 in.

Equation 8-11 above uses a 2-in. threshold. ASTM D6032, FHWA GEC 5 and the USBR field manual all define RQD using sound core pieces 4 in. or longer, measured along the core centerline, as Chapter 6 (Section 6.5.2) states. GEC 5 adds two rules often missed: pieces that are not hard and sound are excluded even if longer than 4 in. (so weathered rock is downgraded), and RQD is not appropriate for BQ/BX core — NQ/NX is optimal. Recommend revising Equation 8-11 to 4 in..

Field estimates of intact strength and weathering

Table 8-S1. Rock material strength grades (GEC 5, Table 37)

Grade	Description	Field identification	UCS range (psi)
R0	Extremely weak	Indented by thumbnail	36–145
R1	Very weak	Crumbles under firm blows of hammer point; peeled by pocket knife	145–725
R2	Weak	Peeled by knife with difficulty; shallow indentations with firm hammer blow	725–3,600
R3	Medium strong	Cannot be scraped or peeled with knife; fractured with single firm blow	3,600–7,250
R4	Strong	More than one blow needed to fracture	7,250–14,500
R5	Very strong	Many blows needed to fracture	14,500–36,000
R6	Extremely strong	Can only be chipped	> 36,000

Table 8-S2. Weathering grades (GEC 5, Table 38)

Grade	Term	Description
I	Fresh	No visible weathering; slight discoloration on major discontinuities possible
II	Slightly weathered	Discoloration of rock material and discontinuity surfaces; surface may be somewhat weaker
III	Moderately weathered	Less than half decomposed/disintegrated to soil; fresh or discolored rock as framework or corestones
IV	Highly weathered	More than half decomposed/disintegrated to soil; rock as framework or corestones
V	Completely weathered	All decomposed to soil; original mass structure largely intact
VI	Residual soil	All converted to soil; structure and fabric destroyed; not significantly transported

A complete rock description strings these together in a set order, e.g. “slightly weathered, crystalline, gray, fine-grained, medium strong (R3) basalt,” followed by a rock-mass description of joint sets, spacing, persistence, infilling, roughness and seepage (GEC 5, after Wyllie). The strength grade gives the R₁ input to RMR when no UCS test is available.

Source: Sabatini, P. J. et al. (2002). Evaluation of Soil and Rock Properties. Geotechnical Engineering Circular No. 5, FHWA-IF-02-034 · U.S. Bureau of Reclamation (1998). Engineering Geology Field Manual, 2nd ed., Vol. I

Rock families and ballast suitability

If an excavator can dig it, treat it as soil; once rock breaks apart, it behaves like soil. Igneous extrusive rock cooled quickly (basalt) is fine-grained and dark, and it is the preferred ballast family: the darker and finer, the better. Slowly cooled granite is coarser and less suitable. Sedimentary rock (sandstone, limestone) and metamorphic rock are generally not recommended for ballast; soft rock can grind into a mud spot within a few years.

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Figure 8-15. Angular, dark, extrusive ballast rock. — **Figure 8-15.** Angular, dark, extrusive ballast rock.

After Geotechnology for Railroaders Program, Module 2, Module 3; Module 2 §07; Module 3 §05. Full reference under Supplemental Sources.

8.7 Frost Susceptibility Classification

For CPKC prairie mainline and CN Canadian operations, frost susceptibility is a primary classification criterion. The U.S. Army Corps of Engineers frost susceptibility classification:

FS Class	Description	Frost Heave Risk
FS-0	Non-frost-susceptible	Negligible
FS-1	Slightly frost-susceptible	Slight
FS-2	Moderately frost-susceptible	Moderate
FS-3	Moderately to highly frost-susceptible	High
FS-4	Very highly frost-susceptible	Very High

Key criteria: GW, GP, SW, SP with < 3% fines = FS-0. ML, MH, and fine-grained silts with > 10% finer than 0.02 mm = FS-3 to FS-4. CH clays with high activity = FS-2 (heave dominated by water absorption, not ice lens formation). CN Engineering Standards require FS classification for all subgrade materials north of 45°N; CPKC Track Standards require frost index analysis (freezing degree-days) combined with FS class to determine minimum non-frost-susceptible ballast/subballast thickness.

Supplemental reference · LEVI Library

USACE frost groups by percent finer than 0.02 mm

The standard USACE groups (1965), which the FS classes above correspond to, are defined by the percent finer than 0.02 mm (20 μm), not the No. 200 sieve:

Group	Soils
NFS	All soils with < 3% finer than 0.02 mm
F1	Gravelly soils with 3–20% finer than 0.02 mm
F2	Sands with 3–15% finer than 0.02 mm
F3	Gravelly soils > 20% finer; sands (except silty fine sands) > 15% finer; clays with PI > 12; uniformly varved clays
F4	Silts and sandy silts; fine silty sands > 15% finer; lean clays with PI < 12; non-uniform varved clays

Susceptibility increases from F1 to F4. Carter and Bentley note that kaolinitic clays tend to heave more than montmorillonitic clays because water is more mobile in non-expanding clay structures — a counter-intuitive point when CH subgrade is assumed to be low frost risk. A quick screen (TRRL, 1970): granular soil with < 10% passing No. 200 is not susceptible; granular soil with > 10% fines or cohesive soil with PI < 20 is susceptible; cohesive soil with PI > 20 is not.

Confirm the frost-susceptibility classification with a hydrometer test, because the percent finer than 0.02 mm cannot be read from a sieve analysis.

Source: Carter, M. and Bentley, S. P. (2016). Soil Properties and their Correlations, 2nd ed. Wiley

Frost susceptibility in the UIC framework

Profillidis ranks silt as very frost-susceptible, clay as susceptible, and sand and gravel as not susceptible. Frost susceptibility is the third subgrade parameter, after soil class and hydrogeology, in climates where freezing is frequent. Protection is sized with the frost index (Chapter 2, §2.5).

After Profillidis (2014), §9.4, §9.11.1. Full reference under Supplemental Sources.

8.8 Representative Classification Data Table

Table 8-2. Representative Soil Classification Data — G&W Gulf Coast Subsidiary Track Rehabilitation
Sample ID	Depth (ft)	% Pass No. 200	LL (%)	PL (%)	PI (%)	USCS	AASHTO	GI	LI	Notes
B-1, S-2	3–5	68	52	22	30	CH	A-7-6	16	0.83	Fat clay; soft consistency; swell concern
B-1, S-4	8–10	44	38	19	19	CL	A-6	8	0.47	Lean clay; medium stiff
B-2, S-1	1–3	22	28	14	14	SC	A-2-6	0	0.21	Clayey sand; fill material suspected
B-2, S-3	6–8	78	61	27	34	CH	A-7-6	18	1.05	Fat clay; LI > 1.0 indicates near-liquid state
B-3, S-2	4–6	12	NP	NP	NP	SP	A-3	0	—	Fine sand; non-plastic
B-3, S-5	14–16	55	44	21	23	CL-ML	A-6	9	0.63	Borderline; dual symbol required

B-2, S-3 at 6–8 ft: LI = 1.05 and GI = 18 indicate very poor subgrade. G&W Engineering Bulletin EB-14 triggers mandatory ground improvement review (Chapter 17) for GI ≥ 15 under new track construction.

8.9 Worked Examples

Example 8-1 — USCS Classification, NSR Appalachian Corridor

Context: A sample from B-4 at 12–14 ft depth on an NSR bridge approach along the Pocahontas Division (Virginia) has the following lab results:

% passing No. 200 sieve: 62%
LL = 48%, PL = 21%
Natural water content w_n = 33%

Step 1 — Coarse or fine-grained? 62% passing No. 200 → Fine-grained.

Step 2 — Plasticity Index:

PI = LL − PL = 48 − 21 = 27%

Step 3 — A-line check (Eq. 8-8):

PI_A-line = 0.73 × (LL − 20) = 0.73 × (48 − 20) = 0.73 × 28 = 20.4%

PI = 27% > 20.4% → Above A-line

Step 4 — LL classification: LL = 48% < 50% → Low plasticity → CL (Lean Clay)

Step 5 — Liquidity Index (Eq. 8-6):

LI = (33 − 21) / 27 = 12 / 27 = 0.44

LI = 0.44 → Stiff to medium consistency.

USCS Classification: CL — Lean Clay

Step 6 — AASHTO Check: 62% passing No. 200 > 36%; LL = 48% > 40% → A-5 or A-7; PI = 27% > 10%; PI vs. (LL − 30) = 18% → PI > LL − 30 → A-7-6

Equation 8-10 — GI:

GI = (62 − 35) × [0.2 + 0.005(48 − 40)] + 0.01(62 − 15)(27 − 10)

= 27 × [0.2 + 0.040] + 0.01 × 47 × 17

= 27 × 0.240 + 7.99

= 6.48 + 7.99 = 14.47 → GI = 14

Conclusion: CL / A-7-6, GI = 14. NSR Engineering Standards Manual requires ground improvement assessment for GI ≥ 12. This sample drives a Chapter 18 CBR evaluation and Chapter 17 ground improvement scope on the NSR bridge approach.

Example 8-2 — USCS Classification from Sieve Data, BNSF Intermodal Facility

Context: Subgrade fill investigation for a new BNSF intermodal yard near Kansas City. Lab sieve results:

Sieve	% Passing
1 in.	100
No. 4	88
No. 10	74
No. 40	42
No. 200	7

D_10 = 0.006 in.; D_30 = 0.028 in.; D_60 = 0.10 in. LL = NP; PL = NP

Step 1 — Coarse or fine? 7% passing No. 200 → Coarse-grained.

Step 2 — Gravel or sand? 12% retained on No. 4 (= 100 − 88); 81% of coarse fraction is sand. → Sand (S)

Step 3 — Fines classification: 7% fines — borderline 5–12% → dual symbol required. Fines are NP → M suffix.

Step 4 — C_u and C_c (Eqs. 4-2, 4-3):

C_u = D_60 / D_10 = 2.5 / 0.15 = 16.7 ≥ 6 ✓

C_c = (D_30)² / (D_10 × D_60) = (0.71)² / (0.15 × 2.5)

= 0.504 / 0.375 = 1.34; 1 ≤ 1.34 ≤ 3 ✓

Meets SW criteria → SW-SM (Well-Graded Sand with Silt)

AASHTO: 7% pass No. 200 ≤ 35%; NP → A-1-b, GI = 0

Conclusion: SW-SM / A-1-b, GI = 0. Excellent subgrade material. BNSF Engineering Instructions rate this as acceptable for intermodal yard subgrade without ground improvement, subject to proof-roll acceptance during construction (Chapter 15).

Example 8-3 — Rock Mass Rating Calculation, CPKC Rocky Mountain Cut

Context: We are evaluating a rock cut on CPKC's Mountain Subdivision in British Columbia. NQ core (1.875-in. diameter) was recovered from a 10-ft run. Core log data:

UCS = 14,500 psi (tested at lab, Chapter 10)
RQD = 68% (from core log, Chapter 6)
Discontinuity spacing: average 6 in. (0.5 ft)
Discontinuity condition: slightly rough surfaces; separation < 0.04 in.; slightly weathered walls
Groundwater: damp, no free water
Discontinuity orientation: moderately unfavorable relative to cut slope

Step 1 — R₁ (UCS = 14,500 psi): UCS = 14,500 psi → Rating = 7 Step 2 — R₂ (RQD = 68%): → Rating = 13 Step 3 — R₃ (spacing = 6 in. = 0.5 ft): 2–8 in. spacing → Rating = 10 Step 4 — R₄ (slightly rough, < 0.04-in. separation, slightly weathered): → Rating = 20 Step 5 — R₅ (damp, no free water): → Rating = 10 Step 6 — R₆ (moderately unfavorable): → Adjustment = −5

Equation 8-12:

RMR = 7 + 13 + 10 + 20 + 10 + (−5) = 55

Rock Class III — Fair Rock. Per CPKC Engineering Track Standards and CN Engineering Standards (which CPKC inherited from the CN/KCS merger integration), Class III rock in a cut slope requires a kinematic stability analysis (Chapter 13) and pattern rock bolting consideration. Blasting disturbance factor D = 0.7 for production blasting; this reduces effective RMR and should be considered in the Hoek-Brown analysis.

8.10 Figure Placeholders

Figure 8-1: USCS classification flowchart — coarse-grained branch with C_u and C_c criteria.
Figure 8-2: USCS classification flowchart — fine-grained branch with Casagrande plasticity chart.
Figure 8-3: Casagrande Plasticity Chart with A-line, U-line, and classification zone labels; sample data points from Table 8-2 plotted.
Figure 8-4: AASHTO M 145 group classification decision tree — gradation and Atterberg limit paths.
Figure 8-5: Grain-size distribution curves — example set from G&W Gulf Coast project showing clay-rich subgrade vs. acceptable fill gradation.
Figure 8-6: RMR rating chart — all six parameters with numerical rating scales.
Figure 8-7: GSI estimation chart (Marinos & Hoek 2000) — structure vs. surface quality matrix.
Figure 8-8: Q-system parameter selection chart — J_n, J_r, J_a ranges from Barton et al. (1974).
Figure 8-9: Activity chart — PI vs. clay fraction for soils from CSXT Atlantic Coastal Plain and BNSF Texas Panhandle projects.

Reference graphics

Flexible Pavement Layers — Subgrade to Asphalt

8.11 Practical Recommendations

Require lab-verified USCS classification for all design samples on Amtrak and CN projects. Field-estimated classifications are acceptable for preliminary boring logs but must be superseded by lab results before any analysis. Amtrak ES and CN Engineering Standards explicitly require this; submit revised boring logs with lab USCS symbols within 30 days of lab completion.
Use dual USCS symbols for borderline coarse-grained soils (5–12% fines) and borderline fine-grained soils (PI between 4 and 7, near A-line). BNSF and UPRR data reviewers flag boring logs with single symbols in these zones as non-conforming. The dual symbol (e.g., CL-ML, SW-SM) is required, not optional.
Flag A-7-6 soils and GI ≥ 12 immediately upon receipt of lab results on NSR and G&W projects. These triggers activate ground improvement evaluation requirements under NSR's Engineering Standards Manual and G&W Engineering Bulletins, respectively. Early flagging allows the project team to add CBR testing (Chapter 18) to the lab program before samples are discarded.
Record Activity for all CH soils encountered on CSXT, BNSF, and UPRR projects. Activity > 1.25 requires swell testing per ASTM D4546, and the swell pressure must be documented in the geotechnical data report (Appendix E). Neglecting swell characterization on active clay subgrades is a leading cause of track geometry exceptions on CSXT's Carolina and Piedmont divisions.
Include frost susceptibility classification on all CPKC and CN projects north of 45°N latitude. Determine FS class from grain-size data (% finer than 0.02 mm) and report alongside the USCS symbol in boring logs. CPKC Track Standards specify a minimum 24-in. non-frost-susceptible subballast layer for FS-3 and FS-4 soils.
Provide RMR, GSI, and Q values in tabular format in the geotechnical data report for all NSR and CPKC rock projects. These values must be cross-referenced to the core run depth and boring ID and supported by photographs of the core box. NSR reviewers require that RMR ratings be accompanied by individual parameter justification, not just the final summed score.
Recalibrate hydrometer analysis for local specific gravity on G&W Gulf Coast projects. Gulf Coast soils frequently contain shell fragments and organic matter with G_s values outside the standard 2.65–2.72 range. Use measured G_s (ASTM D854) to correct hydrometer data; failure to do so can shift silt/clay boundary by up to 5% and affect USCS classification.

8.12 Field and Laboratory Checklist — Soil and Rock Classification

Plain text version

Field (During Drilling and Sampling)

[ ] Visual field USCS classification recorded on boring log at time of sampling (color, moisture, consistency, texture)
[ ] Borderline cases flagged with tentative dual symbol pending lab verification
[ ] Core box photographs taken per client requirements (CSXT: 300 dpi minimum; Amtrak: 600 dpi; NSR: include scale bar and core box ID tag)
[ ] RQD measured and recorded per ASTM D6032 on every core run (Chapter 6)
[ ] Discontinuity spacing, orientation, roughness, and infill noted in rock core log
[ ] Smear test and dry strength estimated in field for fine-grained soils

Laboratory

[ ] Moisture content (ASTM D2216) — all split-spoon and Shelby tube samples
[ ] Atterberg limits (ASTM D4318) — all fine-grained samples and samples with > 10% passing No. 200
[ ] Sieve analysis (ASTM D422/D6913) — all coarse-grained and mixed samples
[ ] Hydrometer (ASTM D422) — all samples with significant fines (> 30% passing No. 200)
[ ] USCS classification assigned and verified against Casagrande chart
[ ] AASHTO M 145 classification and GI calculated for all subgrade samples
[ ] Activity calculated for all CH and MH soils; flag A > 1.25
[ ] Frost susceptibility class assigned for CPKC and CN samples (% finer than 0.02 mm from hydrometer)
[ ] All lab results entered into gINT per client template (CSXT, NSR, UPRR, BNSF, Amtrak) or Log*Plot (G&W)
[ ] Lab test result table formatted per Appendix B template before submission

8.13 Practice Questions

Question 4-1 A soil sample from a CSXT embankment foundation has LL = 56%, PL = 24%, and 71% passing the No. 200 sieve. Natural water content is 41%. Classify the soil by (a) USCS, (b) AASHTO with GI, and (c) calculate the Liquidity Index and interpret the consistency.

Answer 4-1: (a) > 50% pass No. 200 → fine-grained. PI = 56 − 24 = 32%. A-line at LL = 56: PI_A = 0.73 × (56 − 20) = 26.3%. PI = 32% > 26.3% and LL > 50 → CH (Fat Clay). (b) F = 71% > 36%; LL = 56% > 40%; PI = 32% > 10%; PI vs. LL − 30 = 26% → PI > LL − 30 → A-7-6. GI = (71 − 35) × [0.2 + 0.005(56 − 40)] + 0.01(71 − 15)(32 − 10) = 36 × [0.2 + 0.080] + 0.01 × 56 × 22 = 36 × 0.280 + 12.32 = 10.08 + 12.32 = GI = 22 → report as 20 (maximum value) (c) LI = (41 − 24)/32 = 17/32 = 0.53 — Medium consistency (stiff to medium). Despite being CH (high plasticity), the soil is not in an unstable state; however, GI = 20 triggers mandatory ground improvement assessment per CSXT Engineering Standards for any embankment load exceeding 3 ft of fill.

Question 4-2 Sieve analysis on an UPRR subgrade sample yields: D_10 = 0.003 in., D_30 = 0.019 in., D_60 = 0.090 in. Fines content = 9%. LL = NP. Calculate C_u and C_c and assign the USCS dual symbol.

Answer 4-2: C_u = 0.090 / 0.003 = 30.0 ≥ 6 ✓ C_c = (0.019)² / (0.003 × 0.090) = 0.000361 / 0.000270 = 1.34; 1 ≤ 1.34 ≤ 3 ✓ Meets SW criteria; fines 5–12% → dual symbol required; fines NP → M suffix → SW-SM (Well-Graded Sand with Silt). UPRR Engineering Instruction Manual accepts SW-SM as a suitable subgrade material provided density is verified during construction (Chapter 15).

Question 4-3 A VST and Atterberg limit test on a BNSF soft-ground sample yield s_u = 0.22 tsf and PI = 48%. (a) Compute the Bjerrum-corrected s_u and (b) determine the Activity if the clay fraction (< 0.002 mm) = 35%.

Answer 4-3: (a) At PI = 48%, interpolate Bjerrum μ: between 40% (μ = 0.85) and 60% (μ = 0.75) → μ = 0.75 + (60 − 48)/(60 − 40) × (0.85 − 0.75) = 0.75 + 0.60 × 0.10 = 0.75 + 0.06 = μ = 0.81 s_u (design) = 0.81 × 0.22 = 0.178 tsf = 356 psf (b) A = PI / clay fraction = 48 / 35 = 1.37 → Active clay (montmorillonite/smectite dominant). A > 1.25 triggers swell testing per BNSF Engineering Instructions. Both the corrected s_u and swell data must be included in the Appendix E geotechnical report.

Question 4-4 A 10-ft rock core run from an Amtrak NEC tunnel feasibility study in Baltimore yields: RQD = 74%; UCS = 22,000 psi; average joint spacing = 1.5 ft; slightly rough surfaces, no infill, unweathered; dry borehole; favorable orientation. Calculate RMR and classify the rock mass.

Answer 4-4: R₁: UCS = 22,000 psi → 12 R₂: RQD = 74% → 13 R₃: Spacing = 1.5 ft (18 in.; 8–24 in. range) → 15 R₄: Slightly rough, no infill, unweathered → 25 R₅: Dry → 15 R₆: Favorable orientation → 0

RMR = 12 + 13 + 15 + 25 + 15 + 0 = 80 — Class II, Good Rock. Amtrak Engineering Standards require RMR ≥ 60 for unsupported spans in tunnel design; this rock marginally satisfies the criterion and warrants a Q-system check before finalizing tunnel support recommendations.

Question 4-5 A CN subgrade sample in Manitoba (latitude 50°N) has 18% of particles finer than 0.02 mm and USCS classification ML. What frost susceptibility class applies and what is the practical implication for CN track design?

Answer 4-5: ML soils with 18% finer than 0.02 mm → FS-3 (Moderately to Highly Frost-Susceptible). CN Engineering Standards for projects north of 45°N require: (1) frost susceptibility documented in the geotechnical data report; (2) freezing degree-day analysis for the site; (3) design of subballast layer thickness sufficient to prevent frost heave in the track structure. For FS-3 soils, CN Engineering Standards typically require a minimum 30 in. of non-frost-susceptible (FS-0) granular subballast above the natural subgrade, but the required thickness must be confirmed by a site-specific freeze-depth calculation using the modified Berggren equation (beyond this chapter's scope). Track geometry monitoring (Chapter 15) is required through the first three freeze-thaw cycles after construction.

Cross-References

Chapter 6 — Borings and Sampling: RQD measurement procedure; core recovery; sampling requirements by soil type
Chapter 7 — In Situ Testing: CPT SBT chart as supplementary classification tool; DMT I_D for field soil type screening
Chapter 11 — Bearing Capacity: USCS and consistency input to bearing capacity factor selection
Chapter 12 — Settlement Analysis: Compression index C_c correlated to LL; preconsolidation from LI and OCR
Chapter 13 — Slope Stability: RMR and GSI for rock slope; s_u from LI correlation for embankment stability
Chapter 18 — Pavement Subgrade: AASHTO M 145 GI feeds directly into CBR estimation and subgrade design
Chapter 17 — Ground Improvement: GI ≥ 12 and CH/A-7-6 classification trigger ground improvement
Appendix E — Report Preparation: Classification tables, plasticity charts, and grain-size curves required in GDR

8.14 Case Studies

Field case studies by Burt G. Look, from Earthworks: Theory to Practice – Design and Construction (CRC Press/Balkema, 2023), chosen for this chapter’s topics. Each is summarized from the book with its key figures and a closing note on railroad application added by the authors of this manual. Credit for the case material belongs to Look; see item S13 under Supplemental Sources.

Case Study 8.14.1 — Gradings before and after compaction: the oversize that was never tested

Case study · Look (2023) §4.6

Related section: 8.2 Grain-Size Analysis

On a cut-to-fill earthworks job, rocks up to 24 in were visible and many particles exceeded 10 in, yet four of five grading certificates gave 6 in as the maximum size. Look calls this survivorship bias: the large pieces are left behind when the sample is taken, so they never appear in the result. Visual observation should always be part of the assessment.

Averaged gradings before and after compaction with two 19-ton vibrating rollers were similar to each other but clearly different from the pre-compaction gradings, because rolling breaks the material down. A specification limiting fines to 7% passing the No. 200 sieve would pass this material before compaction and fail it after. Since performance depends on the compacted state there is a case for post-compaction testing; since roller type and size change the result there is a case for pre-compaction testing. Either way, the specification has to say which.

For railroad work: the same question arises for subballast and granular fill acceptance. State in the special provision whether gradation is tested at the source, on the stockpile, or after placement and compaction.

**Figure 8-LK1.** Stockpile on a cut-to-fill job with a 24 in. rock; most gradings reported 6 in. as the largest size. *Source: Look (2023), Figure 4.7-1, p. 115.*

Source: Look, B. G. (2023). Earthworks: Theory to Practice – Design and Construction. CRC Press/Balkema. Case study §4.6, pp. 114. Summarized and paraphrased; figures reproduced for internal reference. Full reference under Supplemental Sources.

Case Study 8.14.2 — Representative sampling from a weathered-rock stockpile

Case study · Look (2023) §5.9

Related section: 8.2 Grain-Size Analysis

Four stockpile samples of extremely to slightly weathered sandstone/siltstone all reported 100% passing 1½ in., yet rocks up to 12 in were visible in the pile. After rolling, 24 post-compaction gradings gave a maximum particle size under 3 in for both roller types, while the embankment surface still showed 12 in. pieces. The “increase” in coarse fraction after compaction is an artefact of the biased pre-compaction samples. Fines rose only slightly, from 10% to about 11%, although rolling visibly broke down the large weathered particles.

Look’s conclusion is that the industry places misplaced confidence in test certificates as proof that a material specification has been met.

Table 8-LK1. Average gradings of XW–SW sandstone/siltstone, % passing (after Look 2023, Table 5.7)

Sieve	Pre-compaction (n = 4)	Smooth drum (n = 12)	Padfoot (n = 12)
3 in.	100.0	100.0	100.0
1½ in.	100.0	82.8	80.3
¾ in.	75.5	65.4	61.8
No. 8	33.0	25.0	23.9
No. 40	27.0	21.6	20.4
No. 200	10.0	11.1	10.8

**Figure 8-LK2.** Oversize (> 12 in.) extremely to slightly weathered interbedded rock in the stockpile, absent from the test samples. *Source: Look (2023), Figure 5.9-2, p. 145.*

Source: Look, B. G. (2023). Earthworks: Theory to Practice – Design and Construction. CRC Press/Balkema. Case study §5.9, pp. 142–144. Summarized and paraphrased; figures reproduced for internal reference. Full reference under Supplemental Sources.

Author and Sources

Authors: Daniel P. Colwell and Mario Ruel. This chapter was written and compiled by Daniel P. Colwell and Mario Ruel for Railway Ground Hazard Risk Management.

Technical content is drawn from the published sources below, and credit for that material belongs to their authors and publishers. Tables, equations and figures taken from a specific source are also cited where they appear.

Primary sources

USACE EM 1110-1-1804, Geotechnical Investigations (2001), Sections 3-1 through 3-8
ASTM D2487, D3282, D4318, D422, D1140, D2938
AASHTO M 145
AREMA MRE Chapter 1, Sections 1.3–1.4

Supplemental sources (LEVI Library)

Sabatini, P. J. et al. (2002). Evaluation of Soil and Rock Properties. Geotechnical Engineering Circular No. 5, FHWA-IF-02-034
Carter, M. and Bentley, S. P. (2016). Soil Properties and their Correlations, 2nd ed. Wiley
New York State DOT Geotechnical Engineering Bureau (2015). Test Method for Liquid Limit, Plastic Limit, and Plasticity Index, GTM-7 Rev. 2
U.S. Bureau of Reclamation (1998). Engineering Geology Field Manual, 2nd ed., Vol. I
U.S. Army Corps of Engineers (2001). Geotechnical Investigations. EM 1110-1-1804
Look, B. G. (2023). Earthworks: Theory to Practice – Design and Construction. CRC Press/Balkema. Case studies §4.6, §5.9

File locations for these documents are listed under Supplemental Sources — LEVI Library.

Supplemental Sources — LEVI Library

Material in the green “Supplemental reference” boxes throughout this chapter was added from the following documents in the LEVI geotechnical library. Text is summarized or paraphrased; tables are reproduced with their original source noted; figures are reproduced from the cited document for internal reference use. Consult the original document before relying on a value for design. Blocks marked “After Selig & Waters (1994)” summarize item S12 for railroad clients; tables are condensed from the book and its figures are not reproduced. The Case Studies section summarizes case studies from item S13 by Burt G. Look; its figures are reproduced from the book for internal reference use, and the closing “For railroad work” note in each case study is added by the authors of this manual.

Sabatini, P. J. et al. (2002). Evaluation of Soil and Rock Properties. Geotechnical Engineering Circular No. 5, FHWA-IF-02-034
Carter, M. and Bentley, S. P. (2016). Soil Properties and their Correlations, 2nd ed. Wiley
New York State DOT Geotechnical Engineering Bureau (2015). Test Method for Liquid Limit, Plastic Limit, and Plasticity Index, GTM-7 Rev. 2
U.S. Bureau of Reclamation (1998). Engineering Geology Field Manual, 2nd ed., Vol. I
U.S. Army Corps of Engineers (2001). Geotechnical Investigations. EM 1110-1-1804
Profillidis, V. A. (2014). Railway Management and Engineering, 4th ed. Farnham, UK: Ashgate. Chapters 7–9, 11–13, 16–17, 20 and 22 (track system, mechanical behavior of track, subgrade, sleepers, ballast, transverse effects, maintenance, slab track, electrification foundations, safety)
Benesch. Geotechnology for Railroaders Program, Modules 1–8 (two-day training course reference: risk management, geology and soils, ballast and sub ballast, drainage, slides, slope and subgrade stabilization, scour, rock falls, beaver dams, winter problems, spring thaw, extreme weather, earthquakes). Field photographs and figures from the course; slope stabilization process slides adapted from material by D. Colwell
Selig, E. T. and Waters, J. M. (1994). Track Geotechnology and Substructure Management. London: Thomas Telford. Used on this page: ch. 3
Look, B. G. (2023). Earthworks: Theory to Practice – Design and Construction. Leiden: CRC Press/Balkema (Taylor & Francis). ISBN 978-1-032-10470-6. Case studies used on this page: §4.6, §5.9