6.30 EXCAVATION

The importance of being able to identify soil types cannot be overemphasized. Some soil types have to be placed in the proper location. For example, Standard Road Plan RL-1 illustrates where unsuitable soils are allowed to be placed in the roadway. The inspector must be sure that the work is performed according to the plans.

The inspector should be familiar with all the "Standard Road Plans" listed, in particular RA standards for sewer construction, RB standards for incidental construction, RC standards for erosion control, RE standards for guardrail, RF standards for drainage, and RL standards for excavation and embankment.

Grading plans show cut equals fill plus/or minus shrink or swell respectively. Shrink is the change in quantity from cut to fill and includes subsidence, change from in situ density to compacted density, incidental loss, and all other factors changing density. Swell is the increase in class 12 excavation from ledge rock to broken rock in the fills. The swell factor will include other losses or increases.

Roadway and Borrow Excavation is divided into the following classifications:

Class 10
Includes all normal earth materials, such as loam, silt, gumbo, peat, clay, soft shale, sand, and gravel. Class 10 is subdivided into Unsuitable Soil and Suitable Soil.

UNSUITABLE SOIL - Use Standard Road Plan RL-1

Slope Dressing Only

• Peat or muck
• Soils with Plasticity Index (P.I.) 35 or greater
• A-7-5 or A-5 having less than 1.35 Mg/m³ (85 pcf) AASHTO T-99 proctor density

Type C Disposal - Placed 1 m (3 feet) below top of subgrade in Fills

• All soils other than A-7-5 or A-5 having a AASHTO T-99 proctor density of 1.5 Mg/m³ (95 pcf) or less
• All soils other than A-7-5 or A-5 containing 3.0% or more carbon

Type B Disposal - 1.5 m (5 ft) below top of subgrade in fills

• A-7-6 (30 or greater)
• Residual clays (overlaying bedrock) regardless of classification

Type A Disposal in Fills – 1.5 m (5 ft) below top of subgrade in fills but placed in alternate layers with Type C Unsuitable or Suitable Soil

• Shale
• A-7-5 or A-5 soils having a AASHTO T-99 proctor density greater than 1.35 Mg/m³ (86 pcf) but less than 1.5 Mg/m³ (95 pcf).

SUITABLE SOIL

• AASHTO T-99 Proctor Density of 1.5 Mg/m³ (95 pcf) or greater, and
• AASHTO M 145-91 Group index less than 30

Class 12
Includes granite, quartzite, chert, limestone, sandstone, hard shale and slate. Includes estimated or measured volumes of boulders.

Class 13
Commonly referred as "Unclassified Excavation." The contract documents will specify the limits for Class 13.

Select Soils
Must meet all criteria, except proctor, if proctor was not taken.

Cohesive Soil

• Must have 45% or less silt content
• Must have a proctor AASHTO (T-99) density of 1.75 Mg/m³ (110 pcf) or greater
• A-6 or A-7-6 soils of glacial origin
• Must have a plasticity index (PI) of 10 or greater

Granular Soil

• Must have a proctor density of 1.75 Mg/m³ (110 pcf) or greater
• Must have a combined silt and clay content of 15% or less (finer than 0.074 mm or #200 sieve)
• PI = 3 or less
• A-1, A-2, or A-3(0)

These are desired select soil criteria, but may be overridden by Office of Design (Soils Section) if soils meeting these requirements are not found within the project.

6.31 PEAT EXCAVATION

Office of Design uses two methods for peat removal. In both methods, it is required to de-water the excavated area during the placement of the granular blanket and the embankment.

Total Removal of Peat
In this method, the peat is removed entirely down to an identifiable soil layer. Soil sheets in the plans will identify the soil type found below the peat. If problems in identifying this soil class are encountered, the Office of Design (Soils Section) or the Office of Construction should be contacted for assistance.

Partial Removal of Peat
In areas where the peat is very deep, partial removal is designed with an overload specified to remove most of the settlement which will occur due to the remaining peat.  The Office of Design (Soils Section) has calculated the stability of the area under the plan requirements; therefore, the plan should be explicitly followed to prevent possible failure.

To fill the excavated area below water, material with 85% or more sand may be placed without de-watering. Placement of material with less than 85% sand requires de-watering and Type A compaction.

6.32 ROCK EXCAVATION

Rock excavation is defined as excavation which cannot be made with equipment normally used for Class 10. Any excavation requiring ripping or blasting is considered rock excavation (Class 12). The soil sheets of the road plans are useful in determining the depth at which Class 12 excavation begins.

Because Class 12 excavation requires field judgment, overburden removal should begin near the centerline so the backslope can be adjusted to meet the design template in case the rock elevation is not uniform.

The backslope on rock excavation is usually 1/2:1 except where presplitting is indicated on the plans.

Presplitting is a multiphase blasting operation:
Phase 1: Drill holes into rock ledge
Phase 2: Detonate a "light" explosive charge to prefracture the ledge
Phase 3: Production blasting to remove material and develop a uniform rock face

Presplitting is a part of the Class 12 excavation quantity with the locations shown on the soil cross sections by the 1/4:1 slope. This work may also be tabulated on the "C" plan sheets.

Since Class 12 excavation is a measured item, elevations are required before and after rock excavation.

The “Blasters' Handbook”, a good source of information about explosives, is available from:


International Society of Explosive Engineers
29100 Aurora Road
Cleveland, OH  44139
(Telephone 440-349-4004)

Shale is classified as Class 12 excavation and in many cases can be moved in a manner normal to Class 10. Where shale can be handled in a manner normal to Class 10, the shale should be measured and paid for as Class 10. Shale cuts are usually benched and covered with topsoil in accordance with the plans. If unexpected shale is found, the shale should be covered with topsoil if possible.

Payment for "rock pick-up" during stabilizing crop seeding and fertilizing should be measured and paid for as Class 12. If Class 12 is not included as an item in the contract documents, the quantity should be paid for at 10 times the contract price of Class 10 excavation or embankment-in-place item.

6.33 USE OF AND PAYMENT FOR WATER USED FOR EXCAVATION AND EMBANKMENT

The placement of select backfill and special backfill both have moisture limit requirements.  When either type of backfill is moisture deficient, water should be added

and mixed into the backfill material prior to compaction. If water is added, and there is no contract item for water, then it should be paid for as extra work if in accordance with Specification 2102.14E.

For fugitive dust control, see Construction Manual 2.12.

6.34 CONTRACTOR FURNISHED BORROW AREAS

On some projects, the contract documents will require a "contractor borrow." In these cases, the contractor is responsible for:
• Providing approved fill material by selecting a site (or sites) for each plan required soil type
• Obtaining all state and federal permits and clearances including but not limited to:
A) Archaeological (Refer to Construction Manual 6.35)
B)  Historical (Refer to Construction Manual 6.35)
C)  Environmental
D)  Storm Water Discharge (Refer to Construction Manual Chapter 10)
E) Wetlands (Refer to Construction Manual Chapter 10)

Approval for soil type may be obtained by:

• The contractor obtaining and providing soil samples to the project engineer. The project engineer will forward the samples to the Office of Materials for test evaluations.
• The contractor requesting a representative of the Office of Design (Soils Section) to visit the site to observe the soil profile. In this case, the contractor must provide excavated test pits (or trenches) profiling the proposed borrow site.
• Contractor submittal of subsurface information to Soils Design. The information should be plotted similarly to borrow “R” plan sheets used for design borrows and include surface elevation, thickness of layers, soil sample locations and soil classifications.

Assuming that the proposed alternate borrow site meets the design criteria for the intended soil type, that all archaeological/historical clearances have been obtained and that the plan site is not a mandatory borrow, an alternate borrow site may be approved as follows:

• If use of the alternate borrow site results in no change in quantities, the change may be executed as a mutual benefit change and plan quantity agreement.
• If the alternate borrow site results in significant savings, such as decreased amount of overhaul, this is to be executed as a Value Engineering Incentive Proposal.

6.35 PRESERVATION OF CULTURAL RESOURCES