Section 4 of the outline, Subsurface, Surface, and Elevated Piping Work, is the largest on the exam at 21%. CSLB lists six topics: shoring and sloping excavations; preventing erosion; tunneling, drilling and boring; installing pipelines; connecting and testing systems; and connecting dry utilities.[1] Because it is more than a fifth of the exam, this book splits it in two. This chapter covers the ground work — keeping the trench open safely, keeping the soil on site, and going under things instead of through them. Chapter 5 covers the pipe itself.
Expect several questions built on the numbers in Cal/OSHA's excavation article (Title 8, Article 6).
4.1 Shoring and sloping excavations
Definitions that decide questions
- A trench is "a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet."[2]
- A protective system protects workers from cave-ins; the options are "support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection."[2]
- A shield (trench box) is "a structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure."[2] A shield does not hold the walls up; it protects the people inside when the walls come down.
- A competent person is "capable of identifying existing and predictable hazards ... and who has authorization to take prompt corrective measures to eliminate them."[3] Both halves matter: knowledge and authority. A foreman who can see the problem but is not allowed to stop the work is not a competent person.
When protection is required
Every employee in an excavation must be protected from cave-ins by an adequate protective system, with two exceptions: excavations made entirely in stable rock[4], and excavations "less than 5 feet in depth and examination of the ground by a competent person provides no indication of a potential cave-in."[4] Note what the second exception does not say: a 4-foot trench in running sand with water seeping in is not automatically exempt. The 5-foot line is where protection becomes mandatory regardless; below it, the competent person decides.
Five feet is also where the Cal/OSHA permit starts (Chapter 1): trenches 5 feet or deeper that someone must enter.[5]
Classifying the soil
Cal/OSHA's system, in Appendix A to section 1541.1, ranks deposits "in a hierarchy of Stable Rock, Type A, Type B, and Type C, in decreasing order of stability."[6] A competent person classifies each deposit from at least one visual and one manual analysis.[6]
- Type A — cohesive soil with an unconfined compressive strength of 1.5 tsf or more.[6] But "no soil is Type A if" it is fissured, subject to vibration from heavy traffic or pile driving, or previously disturbed.[6] In practice, very little soil next to a street is Type A.
- Type B — cohesive soil between 0.5 and 1.5 tsf, and certain granular soils such as angular gravel and silt, and most previously disturbed soils.[6]
- Type C — cohesive soil of 0.5 tsf or less; granular soils including gravel, sand and loamy sand; submerged soil or soil from which water is freely seeping.[6]
In a layered system, classify by the weakest layer.[6] And classification is not a one-time act: if conditions change — rain, seepage, new vibration — the competent person re-evaluates and reclassifies.[6]
Sloping and benching
Appendix B gives the maximum allowable slopes, written as horizontal to vertical, for excavations less than 20 feet deep[7]:
| Soil or rock type | Maximum slope (H:V) | Angle from horizontal |
|---|---|---|
| Stable rock | Vertical | 90° |
| Type A | ¾:1 | 53° |
| Type B | 1:1 | 45° |
| Type C | 1½:1 | 34° |
Other rules around the table:
- If you do not classify the soil at all, the default (Option 1) is to slope "not steeper than one and one-half horizontal to one vertical" — the Type C slope.[4]
- Type A excavations open 24 hours or less and 12 feet or less deep may use a short-term slope of ½:1.[7]
- In Type A, an excavation 8 feet deep or less may have an unsupported vertical lower portion no taller than 3½ feet.[7] In Type C, any vertical lower portion must be shielded or supported to at least 18 inches above the top of the vertical side.[7]
- Signs of distress — cracks, bulging, spalling, raveling — require cutting the slope back at least ½H:1V flatter than the maximum.[7] Surcharge loads from spoil, equipment or traffic require the competent person to flatten the slope further.[7]
- Sloping or benching deeper than 20 feet must be designed by a registered professional engineer.[7]
Worked example: how wide is a sloped trench at the top?
A trench for a sewer is 10 feet deep and 4 feet wide at the bottom, in Type B soil, sloped on both sides. How wide is it at the top?
Type B is 1:1, so each side lays back 10 × 1 = 10 feet. Top width = 4 + 10 + 10 = 24 feet. In Type C (1½:1) each side lays back 15 feet and the top is 34 feet wide; in Type A (¾:1) each side lays back 7.5 feet and the top is 19 feet wide.
The mistakes the exam plants: using one side only (14 feet in Type B), and reading 1½:1 as vertical-to-horizontal, which gives a slope steeper than Type A. The first number is always horizontal.
That width is why shoring or shields are often cheaper than sloping in streets: 34 feet of open cut through Type C soil next to traffic and utilities is usually impossible.
Support systems and shields
The alternatives to sloping are support systems (timber, hydraulic or pneumatic shoring) and shields. Designs come from one of four routes: Cal/OSHA's own appendices, the manufacturer's tabulated data, other tabulated data approved by a registered engineer, or a registered engineer's design.[2] Whatever the route, "at least one copy of the design shall be maintained at the jobsite during construction of the protective system."[4]
Timber shoring (Appendix C) applies to trenches not exceeding 20 feet in depth.[8] Its members are the crossbraces, the uprights and, where required, the wales.[8] The tables use actual, not nominal, timber dimensions[8], and they are not adequate where adjacent loads exceed a two-foot soil surcharge.[8] Uprights extend to the top of the trench with the lower end no more than 2 feet from the bottom.[4]
Installation and removal rules that the exam likes:
- Excavating up to 2 feet below the bottom of a support system is allowed only if it is designed for the full trench depth and there is no sign of soil loss behind or below it.[4]
- Removal starts at the bottom and progresses upward.[4] Backfill goes in as the supports come out.[4]
- Damaged shoring or shield components are examined by a competent person before further use.[4]
Shields:
- No one may be inside a shield while it is being installed, removed or moved vertically.[4]
- In a trench with sloped upper walls above a vertical lower portion, the shield must extend at least 18 inches above the vertical walls.[4]
- Workers must be protected while entering and leaving the shield — a ladder inside the box, not a climb down the open wall.
Everything else in Article 6 that protects the crew
These rules from section 1541 appear on the exam as often as the slopes do:
- Ladders. Trenches 4 feet or deeper need a stairway, ladder, ramp or other safe means of egress so that no employee travels more than 25 feet laterally to reach it.[9]
- Spoil. Keep excavated material and equipment at least 2 feet from the edge, or use retaining devices.[9]
- Atmosphere. Where oxygen deficiency (less than 19.5% oxygen) or a hazardous atmosphere could exist — landfills, near stored hazardous substances — test before entry into excavations more than 4 feet deep.[9] Prevent exposure to flammable gas above 20% of the lower flammable limit.[9]
- Water. No work in excavations with accumulated or accumulating water unless adequate precautions are taken.[9]
- Inspections. A competent person inspects daily, before the start of work and as needed during the shift, and after every rainstorm or other hazard-increasing occurrence.[9] If there is evidence of a possible cave-in, exposed employees are removed until precautions are taken.[9]
- Crossings. Where employees or equipment cross excavations over 6 feet deep and wider than 30 inches, provide walkways or bridges with standard guardrails.[9]
- Loads and equipment. No one under loads handled by lifting or digging equipment[9]; a warning system (barricades, signals, stop logs) where mobile equipment approaches an edge the operator cannot see.[9]
- Adjacent structures. Do not undermine sidewalks or pavement without support[9]; do not excavate below adjacent footings without underpinning, stable rock or an engineer's approval.[9]
- Utilities. Determine the approximate location of subsurface installations before opening an excavation, and protect, support or remove them while it is open.[9]
4.2 Preventing erosion
The permit and the plan
A site disturbing one acre or more needs coverage under the State Water Board's Construction Stormwater General Permit, currently Order 2022-0057-DWQ, effective September 1, 2023.[10] Coverage brings a Stormwater Pollution Prevention Plan (SWPPP) prepared and implemented by qualified people — the Caltrans specifications use the abbreviation QSP for a "qualified SWPPP practitioner."[11] On Caltrans work, the contractor's water pollution control program includes "developing and implementing the WPCP, providing a WPC manager, conducting WPC training, and monitoring, inspecting and correcting WPC practices."[11]
Erosion control versus sediment control
These are different jobs, and the exam checks that you know which is which:
- Erosion control keeps soil where it is: temporary soil stabilization such as hydroseed, mulch, tackifiers, erosion control blankets and covers on stockpiles. It is the first line of defense because soil that never moves never needs catching.
- Sediment control catches soil that has already moved: fiber rolls, silt fences, check dams, sediment traps and drain inlet protection.
Caltrans treats them in separate sections — temporary soil stabilization and temporary sediment control[11] — and they are maintained differently. Remove sediment from the surface of an erosion control blanket when it exceeds 1 inch deep[11], and from a Type 2 inlet sediment trap when its volume is reduced by about half.[11] Where a check dam and a blanket share an area, install the blanket first.[11] Fiber rolls are staked so that the stake notch is even with the top of the roll.[11]
Site housekeeping that keeps sediment off the street
- Stockpiles. Cover active and inactive soil stockpiles with stabilization material or a temporary cover and surround them with a linear sediment barrier[11]; active stockpiles get this before a forecasted storm.[11]
- Tracking. Sediment tracked onto pavement must not reach storm drains, and Caltrans requires tracked material removed within 6 hours.[11] Stabilized construction entrances and street sweeping are the tools.
- Concrete washout. Washout water is highly alkaline and may not go to a drain. Caltrans allows a temporary washout facility, a portable washout or a washout bin.[11] Rinse water from cleaning sediment control devices may not enter an inlet or waterway either.[11]
- Natural drainage. Where excavation interrupts natural drainage, use diversion ditches, dikes or similar means to keep surface water out of the excavation.[9]
4.3 Tunneling, drilling and boring
When the Tunnel Safety Orders apply
Cal/OSHA's Tunnel Safety Orders cover tunnels, shafts and underground chambers, and specifically "boring and pipejacking operations 30 inches in diameter or greater in size"[12] and "all shaft excavations intended to exceed 20 feet in depth where employees may enter the shaft."[12] A jack-and-bore crossing with a 36-inch casing is therefore tunnel work, with its own rules — even though it looks like pipeline work from the street.
Gas classification
Before bidding, and in all cases before underground construction, the owner obtains a gas classification from the Division.[13] Tunnels are classified as nongassy, potentially gassy, gassy or extrahazardous.[13] A tunnel is gassy where gas is likely or where flammable gas above 5% of the lower explosive limit has been detected 12 inches or more from any surface under normal ventilation[13]; 20% of the LEL at that distance is one of the triggers for extrahazardous.[13] The classification is posted at the site and every worker is told[13]; if readings exceed the limits, "no underground works shall advance until reclassification has been made."[13]
Trenchless methods
- Horizontal directional drilling (HDD). A steerable drill head bores a pilot hole along a planned path, which is reamed and the pipe pulled back. Caltrans requires the bore equipment to have "directional control of the boring tool and ... an electronic boring tool location detection system"[11], the boring tool to be "only as large as necessary to install the conduit"[11], and any drilling fluid — "mineral slurry or wetting solution" to lubricate the tool and stabilize the hole — to be water based.[11]
- Jack and bore (auger boring) and jack and drill. A steel casing is jacked from a pit while an auger or drill removes spoil inside it. Caltrans places jacking or drilling pits no closer than 2 feet to the pavement edge whenever possible[11] and prohibits "excessive water that will soften the subgrade or undermine the pavement."[11]
- Pipe jacking and microtunneling push the product pipe itself behind a boring machine; at 30 inches and above they fall under the Tunnel Safety Orders.[12]
Every trenchless method is still an excavation under the 811 law, which names "drilling, augering, tunneling ... cable or pipe plowing and driving."[14] The bore path must be located and potholed where it crosses marked facilities (Chapter 5).
Sources cited in this excerpt
- License Examination Study Guide: General Engineering (A), form 13E-A (03-2026). Contractors State License Board, 2026-03 (for examinations scheduled on or after February 1, 2025); read 2026-09-24. https://www.cslb.ca.gov/Resources/StudyGuides/AStudyGuide.pdf
- Cal. Code Regs. tit. 8, section 1540. Excavations. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1540.html
- Cal. Code Regs. tit. 8, section 1504. Definitions. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1504.html
- Cal. Code Regs. tit. 8, section 1541.1. Requirements for Protective Systems. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1541_1.html
- Cal. Code Regs. tit. 8, section 341. Permit Requirements. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/341.html
- Cal. Code Regs. tit. 8, section 1541.1a. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1541_1a.html
- Cal. Code Regs. tit. 8, section 1541.1b. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1541_1b.html
- Cal. Code Regs. tit. 8, section 1541.1c. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1541_1c.html
- Cal. Code Regs. tit. 8, section 1541. General Requirements. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/1541.html
- Construction Stormwater Program. California State Water Resources Control Board, accessed 2026-09-24. https://www.waterboards.ca.gov/water_issues/programs/stormwater/construction.html
- Standard Specifications, 2025 Edition. California Department of Transportation, 2025. https://dot.ca.gov/-/media/dot-media/programs/design/documents/2025_stdspecs.pdf
- Cal. Code Regs. tit. 8, section 8403. Scope and Application. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/8403.html
- Cal. Code Regs. tit. 8, section 8422. Tunnel Classifications. California Department of Industrial Relations (Title 8 text), accessed 2026-09-24. https://www.dir.ca.gov/title8/8422.html
- California Government Code section 4216. California Legislative Information, accessed 2026-09-24. https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=4216