, New Mexico GF-9 Utility Lines EXAM with
Questions and Answers/Plus a Rationale
Updated 2026 A+/Instant
Download PDF
EXAM COVERAGE - 1. Excavation and Trenching Safety
Standards - 2. Utility Line Installation and Backfilling
Procedures - 3. Soil Classification and Shoring Requirements -
4. Underground Utility Locating and Damage Prevention - 5.
Environmental Protection and Erosion Control - 6. Regulatory
Compliance and Permitting
1. When performing excavation work near existing underground utilities in New Mexico, what is
the mandatory minimum horizontal clearance required by state statute before mechanized
equipment may be operated within the tolerance zone?
A. 12 inches
B. 24 inches
C. 36 inches
D. 48 inches
CORRECT ANSWER : B
Rationale: State utility damage prevention regulations mandate a minimum 24-inch horizontal
tolerance zone on each side of marked underground facilities to prevent strikes from heavy
machinery. Options A, C, and D are incorrect because 12 inches provides insufficient clearance
for safe mechanized excavation, while 36 and 48 inches exceed the statutory baseline
requirement.
,2. A contractor is installing a pressurized high-density polyethylene (HDPE) utility line that crosses
beneath a major drainage ditch. Which backfill methodology ensures the highest structural
integrity and prevents differential settlement under dynamic hydraulic loads?
A. Unselected native trench spoils compacted to 85% Standard Proctor density
B. Loose uncompacted granular material placed up to the springline only
C. Controlled Low Strength Material (CLSM) flowable fill placed to the subgrade level
D. Untreated clay clods tamped manually using light pneumatic compactors
CORRECT ANSWER : C
Rationale: Controlled Low Strength Material (CLSM) or flowable fill provides self-leveling
structural support that completely surrounds and encapsulates utility lines beneath drainage
crossings without requiring mechanical compaction. Options A, B, and D fail to achieve
adequate structural support and are prone to settlement and erosion under hydraulic flow
conditions.
3. According to standard trench safety specifications, at what specific unsupported trench depth
does OSHA and state construction compliance mandate the implementation of a protective
system such as sloping, shoring, or shielding?
A. 3 feet
B. 5 feet
C. 7 feet
D. 10 feet
CORRECT ANSWER : B
Rationale: Federal and state safety standards require protective systems in all excavations that
reach or exceed 5 feet in depth unless the excavation is made entirely in stable rock. Options A,
C, and D are incorrect because 3 feet is below the regulatory threshold, while 7 and 10 feet
delay protective measures past the legally mandated limit.
4. When evaluating soil classification for utility trench stability under OSHA guidelines, Type C
soil is characterized by which of the following physical properties?
, A. Cohesive soil with an unconfined compressive strength of 1.5 tsf or greater
B. Granular soils including gravel, sand, and loamy sand with high cohesive stability
C. Cohesive soil with an unconfined compressive strength of 0.5 tsf or less, or submerged
soil
D. Previously disturbed stable rock formations with continuous fracture planes
CORRECT ANSWER : C
Rationale: Type C soil represents the least stable classification, defined by an unconfined
compressive strength of 0.5 tons per square foot (tsf) or less, or soil that is vibratory-loaded or
completely submerged. Options A and B describe higher-strength Type A and Type B soils, while
Option D describes stable rock rather than soil.
5. In utility construction projects involving asphalt or concrete surface restoration, what is the
primary purpose of saw-cutting the existing pavement prior to trench excavation?
A. To reduce overall project material purchasing costs
B. To create a clean, vertical shear plane that prevents edge spalling and uncontrolled
fracturing
C. To accelerate the natural curing process of newly poured utility backfill
D. To eliminate the need for traffic control plates during overnight operations
CORRECT ANSWER : B
Rationale: Saw-cutting establishes a neat, vertical boundary line that protects the surrounding
pavement structure from cracking and spalling during mechanical bucket extraction. Options A,
C, and D are incorrect as saw-cutting increases preparation thoroughness rather than cutting
costs, curing time, or traffic plate requirements.
6. Which of the following non-destructive excavation techniques is specifically required when
exposing critical utility crossings identified during the initial design phase?
A. High-impact drop hammers
B. Heavy-duty hydraulic multi-rippers
Questions and Answers/Plus a Rationale
Updated 2026 A+/Instant
Download PDF
EXAM COVERAGE - 1. Excavation and Trenching Safety
Standards - 2. Utility Line Installation and Backfilling
Procedures - 3. Soil Classification and Shoring Requirements -
4. Underground Utility Locating and Damage Prevention - 5.
Environmental Protection and Erosion Control - 6. Regulatory
Compliance and Permitting
1. When performing excavation work near existing underground utilities in New Mexico, what is
the mandatory minimum horizontal clearance required by state statute before mechanized
equipment may be operated within the tolerance zone?
A. 12 inches
B. 24 inches
C. 36 inches
D. 48 inches
CORRECT ANSWER : B
Rationale: State utility damage prevention regulations mandate a minimum 24-inch horizontal
tolerance zone on each side of marked underground facilities to prevent strikes from heavy
machinery. Options A, C, and D are incorrect because 12 inches provides insufficient clearance
for safe mechanized excavation, while 36 and 48 inches exceed the statutory baseline
requirement.
,2. A contractor is installing a pressurized high-density polyethylene (HDPE) utility line that crosses
beneath a major drainage ditch. Which backfill methodology ensures the highest structural
integrity and prevents differential settlement under dynamic hydraulic loads?
A. Unselected native trench spoils compacted to 85% Standard Proctor density
B. Loose uncompacted granular material placed up to the springline only
C. Controlled Low Strength Material (CLSM) flowable fill placed to the subgrade level
D. Untreated clay clods tamped manually using light pneumatic compactors
CORRECT ANSWER : C
Rationale: Controlled Low Strength Material (CLSM) or flowable fill provides self-leveling
structural support that completely surrounds and encapsulates utility lines beneath drainage
crossings without requiring mechanical compaction. Options A, B, and D fail to achieve
adequate structural support and are prone to settlement and erosion under hydraulic flow
conditions.
3. According to standard trench safety specifications, at what specific unsupported trench depth
does OSHA and state construction compliance mandate the implementation of a protective
system such as sloping, shoring, or shielding?
A. 3 feet
B. 5 feet
C. 7 feet
D. 10 feet
CORRECT ANSWER : B
Rationale: Federal and state safety standards require protective systems in all excavations that
reach or exceed 5 feet in depth unless the excavation is made entirely in stable rock. Options A,
C, and D are incorrect because 3 feet is below the regulatory threshold, while 7 and 10 feet
delay protective measures past the legally mandated limit.
4. When evaluating soil classification for utility trench stability under OSHA guidelines, Type C
soil is characterized by which of the following physical properties?
, A. Cohesive soil with an unconfined compressive strength of 1.5 tsf or greater
B. Granular soils including gravel, sand, and loamy sand with high cohesive stability
C. Cohesive soil with an unconfined compressive strength of 0.5 tsf or less, or submerged
soil
D. Previously disturbed stable rock formations with continuous fracture planes
CORRECT ANSWER : C
Rationale: Type C soil represents the least stable classification, defined by an unconfined
compressive strength of 0.5 tons per square foot (tsf) or less, or soil that is vibratory-loaded or
completely submerged. Options A and B describe higher-strength Type A and Type B soils, while
Option D describes stable rock rather than soil.
5. In utility construction projects involving asphalt or concrete surface restoration, what is the
primary purpose of saw-cutting the existing pavement prior to trench excavation?
A. To reduce overall project material purchasing costs
B. To create a clean, vertical shear plane that prevents edge spalling and uncontrolled
fracturing
C. To accelerate the natural curing process of newly poured utility backfill
D. To eliminate the need for traffic control plates during overnight operations
CORRECT ANSWER : B
Rationale: Saw-cutting establishes a neat, vertical boundary line that protects the surrounding
pavement structure from cracking and spalling during mechanical bucket extraction. Options A,
C, and D are incorrect as saw-cutting increases preparation thoroughness rather than cutting
costs, curing time, or traffic plate requirements.
6. Which of the following non-destructive excavation techniques is specifically required when
exposing critical utility crossings identified during the initial design phase?
A. High-impact drop hammers
B. Heavy-duty hydraulic multi-rippers
