00_31_32.13_Geotechnical_Baseline_Report.pdf

McCook Reservoir Groundwater Monitoring Wells

00 31 32.13_Geotechnical_Baseline_Report

Chicagoland Underflow Plan (CUP) McCook Reservoir Main Tunnel System (MTS) Geotechnical Baseline Report (GBR)

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Chicagoland Underflow Plan (CUP) McCook Reservoir Main Tunnel System (MTS)

Table of Contents

List of Acronyms ............................................................................................................................. i

1.0 Introduction and Background .......................................................................................... 1-1

1.1 Introduction ................................................................................................................... 1-1

1.2 Purpose .......................................................................................................................... 1-1

1.3 Relation to the Contract Documents ............................................................................. 1-2

1.4 Organization of this Report ........................................................................................... 1-2

2.0 Project Description ........................................................................................................... 2-1

2.1 Main Tunnel System Components Summary ................................................................ 2-1

2.2 Shafts ............................................................................................................................. 2-2

2.3 Tunnel ............................................................................................................................ 2-2

3.0 Summary of Geological Data ........................................................................................... 3-1

3.1 Sources of Information .................................................................................................. 3-1

3.1.1 Design Phase Subsurface Exploration and Laboratory

Testing Program (AECOM 2008) .......................................................................... 3-1

3.1.2 Subsurface Investigations by Others (1970 – 2000) .............................................. 3-1

3.1.3 Criteria for Data Inclusion ..................................................................................... 3-1

3.1.4 Previous Underground Experience ........................................................................ 3-2

3.2 Regional Geology .......................................................................................................... 3-2

3.3 General Site Geology .................................................................................................... 3-2

3.3.1 Soil ......................................................................................................................... 3-2

3.3.2 Rock ....................................................................................................................... 3-2

3.3.3 Structure ................................................................................................................. 3-3

3.3.4 Groundwater Levels ............................................................................................... 3-4

3.4 Soil Unit Properties ....................................................................................................... 3-4

3.4.1 General ................................................................................................................... 3-4

3.4.2 Fill .......................................................................................................................... 3-4

3.4.3 Alluvium and Glacial Deposits .............................................................................. 3-4

3.5 Rock Unit Properties ..................................................................................................... 3-4

3.5.1 General ................................................................................................................... 3-4

3.5.2 Rock Weathering ................................................................................................... 3-5

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3.5.3 Equivalent Hydraulic Conductivity ....................................................................... 3-5

4.0 Characterization and Behavior of Engineering Geological Units .................................... 4-1

4.1 Properties and Behavior of Engineering Units – Soil ................................................... 4-1

4.1.1 Soil Classification .................................................................................................. 4-1

4.2 Properties and Behavior of Engineering Units – Rock ................................................. 4-2

4.2.1 Engineering Rock Unit .......................................................................................... 4-3

4.2.2 Discontinuity Orientation....................................................................................... 4-3

4.2.3 Joint Spacing .......................................................................................................... 4-4

4.2.4 Excavation and Support Classes ............................................................................ 4-4

5.0 Construction Considerations for Construction Shaft (Contractor Option) ...................... 5-1

5.1 Construction Shaft ......................................................................................................... 5-1

5.1.1 Drill and Blast for Shaft Excavation ...................................................................... 5-1

5.1.2 Ground Support ...................................................................................................... 5-1

5.2 Groundwater .................................................................................................................. 5-2

6.0 Construction Considerations for Tunneling ..................................................................... 6-1

6.1 Anticipated Tunneling Conditions ................................................................................ 6-1

6.1.1 Drill and Blast Tunneling ....................................................................................... 6-1

6.2 Ground Support ............................................................................................................. 6-1

6.3 Estimated Groundwater Inflows .................................................................................... 6-1

6.4 Grouting ........................................................................................................................ 6-2

7.0 References ........................................................................................................................ 7-1

Tables

Table 4-1 Soil Engineering Unit Baselines ................................................................................ 4-2

Table 4-2 Engineering Rock Unit – Baseline Intact Rock Properties ....................................... 4-3

Table 4-3 Summary of Joint Set Baselines ................................................................................ 4-3

Table 4-4 Summary of Joint Spacing Classes ............................................................................ 4-4

Table 4-5 Summary of Joint Set Spacing Observations ............................................................ 4-4

Table 4-6 Relationship between E&S Classes and RMR .......................................................... 4-4

Table 6-1 Estimated Support Class Quantities .......................................................................... 6-1

Attachments

Attachment A Construction Shaft – Contractor Option – Ground Profile i

List of Acronyms

B&V Black & Veatch

BTS Brazilian tensile strength

CCD Chicago City Datum

CUP Chicagoland Underflow Plan

DSC differing site conditions

E&S Excavation and Support

GBR Geotechnical Baseline Report

GDR Geotechnical Data Report

HPU hydraulic power unit

ID inside diameter

LASMA Lawndale Avenue Solids Management Area

MGS Main Gate/Access Shaft

MTS Main Tunnel System

MWRDGC Metropolitan Water Reclamation District of Greater Chicago

RMR Rock Mass Rating

RQD Rock Quality Designation

SWRP Stickney Water Reclamation Plant

TARP Tunnel and Reservoir Plan

UCS unconfined compressive strength

USACE United States Army Corps of Engineers

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1.0 Introduction and Background

1.1 Introduction

This Geotechnical Baseline Report (GBR) describes geotechnical conditions that can be assumed during construction of the new Chicagoland Underflow Plan (CUP) 33 ft internal diameter (ID)

McCook Main Tunnel System (MTS), approximately 1,600 ft in length, located in Chicago, Illinois. The project is being designed by Black & Veatch Corporation (B&V) on behalf of the

USACE, Chicago District.

Refer to the project Geotechnical Data Report (GDR) prepared by B&V for the McCook

Reservoir Main Tunnel System for the project location, tunnel alignment and shaft location figures.

1.2 Purpose

This GBR provides information relevant to subsurface conditions, referred to as the baseline conditions. The purpose of the GBR is to:

• Set baselines for geotechnical conditions and material behavior assumed to be encountered during construction shaft excavation and tunnel excavation.

• Identify important construction considerations, key project constraints, and selected requirements to be addressed by the Contractors during bid preparation and construction.

The contractual baselines do not represent warranties by the Government of the actual subsurface conditions that will be encountered by the Contractor. Rather, the purpose of the baselines is to translate the results of geotechnical investigations into clear descriptions of subsurface conditions. Nothing in this GBR limits the rights of the Government should a claim arise for differing site conditions (DSC).

The GBR is based upon several assumptions regarding the sequence of construction, the means and methods, and workmanship to be employed by the Contractor. The anticipated behavior of subsurface materials as described herein will be influenced by the means and methods selected and used during construction by the Contractor; and therefore, behavior may vary from that described in this report. The Contractor must evaluate the soil and groundwater conditions described herein as they relate to, and interact with, the means and methods selected by the

Contractor for construction.

Any means and methods proposed by the Contractor where the Contractor believes the baseline becomes invalid or requires modification must be raised and discussed during the bid phase prior to bid opening. The Contractor has a duty to inform the Government of the baselines the

Contractor believes are invalid, or require modification during the bid phase.

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1.3 Relation to the Contract Documents

This GBR references the GDR prepared by B&V for the McCook Reservoir MTS. The GDR presents details of the project field investigation completed in 2008 by AECOM and results of twenty previous investigations completed between 1970 and 2000 at or near the McCook

Reservoir site. Also included as part of the GDR are the results of the laboratory testing performed on soil and rock samples collected during the investigation(s), including detailed descriptions of the field and laboratory testing data, methods, and procedures. Boring logs and a summary table of laboratory test results and histograms depicting the distribution of various laboratory testing data are presented in the GDR. This GBR and the GDR are provided as information for the Contractor and are included in the Contract Documents. If there are any inconsistencies between the GBR and the GDR, the GBR shall take precedence.

This GBR is not intended to present the minimum required design and standards of construction contained in the Plans and Specifications. Nothing in this GBR should be construed as amending or altering the Plans and Specifications or applicable FAR clauses, or relaxing the standards of construction

The technical concepts, terms, and descriptions in this report follow standards commonly used in geotechnical engineering/engineering geology which have specific meaning pertaining to the work. Bidders should have a qualified geotechnical engineer or qualified engineering geologist carefully review this GBR so that a complete understanding of the information presented in this report is developed prior to submitting a bid.

1.4 Organization of this Report

This GBR broadly follows the principles contained in the ASCE document entitled

“Geotechnical Baseline Reports for Construction”, dated 2007 and is comprised of an

Introduction and Background (Section 1.0) and the following six sections (Section 2.0 to Section

7.0) as detailed below:

• Section 2.0 (Project Description) presents detailed descriptions about the project location, purpose, components, and requirements.

• Section 3.0 (Summary of Geological Data) describes the project setting including geological considerations and a summary of the available data from the GDR.

• Section 4.0 (Characterization and Behavior of Engineering Units) presents the characterization and behavior of material types present along the project alignment, including behavior of the different engineering units classified on the project.

• Section 5.0 (Construction Considerations for Shafts) presents the optional shaft construction considerations.

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• Section 6.0 (Construction Considerations for Tunneling) presents the tunnel construction considerations.

• Section 7.0 (References).

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2.0 Project Description

The purpose of the McCook Reservoir project is to reduce flood damages in the greater Chicago combined sewer system area. The McCook Reservoir is part of the larger CUP, which includes tunnels for storm water storage and conveyance, and reservoirs for storm water storage. The

CUP is also known as the Tunnel and Reservoir Plan (TARP).

McCook Reservoir will be located in a limestone/dolomite quarry, with nearly vertical pre-split perimeter walls. The reservoir will have two stages (Stage 1 invert at El. -284 CCD, Stage 2 invert at El. -279 CCD), separated by a weir (top El. -200 CCD). Minor storm events will be contained in the tunnel system (Mainstream and Des Plaines Tunnels).

The existing Mainstream Tunnel (1982) is 33 ft ID circular tunnel with 1 ft thick unreinforced concrete lining. The Main Tunnel which will be constructed under this project contract is a 33 ft

ID tunnel with reinforced concrete lining and will connect the McCook Reservoir to the existing

Mainstream Tunnel. Controlling gates will be installed in the MGS at the midpoint between the reservoir and Mainstream Tunnel to regulate the inflow of storm water.

The McCook Reservoir main gates will comprise of three 14.5 ft by 29.5 ft (opening size) wheel gates on each of the bifurcations within the MTS located in the MGS. The gates will control flow from the existing TARP tunnel into the reservoir. The main gates (center gates) will be designed to seal in either direction. The upstream guard gates (located on the mainstream tunnel side) will be designed to seal against hydrostatic head on the upstream side. The downstream guard gates

(located on the reservoir side) will be designed to seal against hydrostatic head on the downstream side. Additional gates and valves in the Distribution Tunnel System direct the flow to and from the reservoir and to the Stickney Water Reclamation Plant (SWRP) through the existing conveyance tunnels.

2.1 Main Tunnel System Components Summary

The purpose of the McCook Reservoir Main Tunnel System (MTS) is to connect the Mainstream

Tunnel to the McCook Reservoir. The MTS includes the following components:

Main Tunnel – An approximately 1,600 ft long, 33 ft ID tunnel connecting the Mainstream Tunnel and the McCook Reservoir, bifurcated for approximately 290 ft through the MGS.

Main Gate/Access Shaft (MGS) – An 88 ft ID, approximately 295 ft below grade circular shaft located near the midpoint of the Main Tunnel. The MGS is currently under construction under a separate contract (W912P6-09-C-0026).

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Construction Shaft – Contractor Option – An optional, 25 ft ID, approximately 285 ft below grade shaft located approximately 300 ft downstream of the Main Tunnel/Mainstream Tunnel Connection.

Gates – Six rectangular steel wheel gates and the associated gate control structures located in the MGS. Each bifurcation of the Main Tunnel contains one main gate and two guard gates - one upstream and one downstream of the main gate. The gates and associated gate control structures are currently being manufactured under a separate contract (W912P6-08-C-0023)

Main Tunnel/Mainstream Tunnel Connection – Live connection of the Main Tunnel to the existing Mainstream Tunnel.

Main Tunnel/McCook Reservoir Connection – Portal connection of the Main Tunnel to the McCook Reservoir, including construction of an Energy Dissipation Structure.

Control Building – A surface facility located at the MGS that houses the gate operating controls, hydraulic power units (HPUs) and provides limited storage.

2.2 Shafts

The MGS, located at STA 0+00, is being constructed under a separate contract (W912P6-09-C-

0026) which will be completed prior to execution of the MTS contract. Site access, working parking, and construction offices will be located at the MGS.

An optional 25 ft ID, approximately 285 ft deep Construction Shaft located at STA. 5+41E to help complete the tunnel and aid with construction of the live connection to the Mainstream

Tunnel may be utilized by the Contractor depending on the means and methods elected in his technical approach.

The optional Construction Shaft is anticipated to be excavated using a combination of mechanical equipment above the top of rock and blasting methods below the top of rock.

2.3 Tunnel

The approximately 1,600 ft tunnel shall be excavated from the MGS. The Construction Shaft

(Contractor Option) may be used for construction purposes if elected by the Contractor.

For the purposes of this GBR, the tunnel is assumed to be excavated by drill and blast methods at a grade of approximately 0.18 percent sloping from the Mainstream Tunnel (highest invert elevation) to the McCook Reservoir (lowest invert elevation).

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3.0 Summary of Geological Data

Twenty subsurface investigations from 1970 to 2000 have been conducted within or near the

McCook Reservoir. A summary of the data including the design subsurface investigation conducted specifically for the MTS (AECOM 2008) is included below.

3.1 Sources of Information

3.1.1 Design Phase Subsurface Exploration and Laboratory Testing Program

(AECOM 2008)

The design phase subsurface exploration program was completed in July 2008 and consisted of three test borings designated LB-121-08, LB-122-08, and LB-123-08. The design phase subsurface exploration program consisted of drilling conventional test borings, performing downhole geophysical (acoustic and optical televiewer) logging, field conductivity tests, and installing groundwater monitoring wells and piezometers. Locations of test borings completed during the design phase exploration program are included in the project GDR and are shown on the Contract Drawings. For the results of the design phase subsurface exploration and laboratory testing program, refer to the project GDR.

3.1.2 Subsurface Investigations by Others (1970 – 2000)

Twenty subsurface investigations in the general vicinity of the proposed MTS have been completed since 1970 to aid in the design and construction of the McCook Reservoir and MTS.

Refer to the project GDR for a complete listing of the previous subsurface explorations and laboratory testing programs.

3.1.3 Criteria for Data Inclusion

Roughly 419 borings and numerous reports for various geotechnical/geological investigations have been completed to gather subsurface information in the general vicinity of the McCook

Reservoir. For purposes of this report, the data has been culled and analyzed, as follows.

All 419 borings were utilized for soil and rock unit properties.

Eight borings; (as described in the project GDR) LB 121-08, LB 122-08, LB-123-08, 156-

B1, LB 101-98, LB 106-98, MW-1-99, and OW-1 and their associated in situ and laboratory test data were utilized for lithology, groundwater, engineering unit baselines, RMR, and

RQD. The eight borings were chosen based on their proximity (within 650 ft) to the MTS project site and their penetration into rock.

The McCook Haul Tunnels Design Project Report dated September, 2001 and prepared by

URS Corporation was utilized for purposes of defining and baselining structural and discontinuity data.

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Refer to the project GDR for the individual borings logs and in situ, laboratory and structural data referenced above.

3.1.4 Previous Underground Experience

Refer to the McCook MTS GDR for a listing of previous underground construction experience near the McCook Reservoir project site.

3.2 Regional Geology

The project site lies on the eastern flank of the northwestward trending Kankakee Arch and is covered by a sequence of glacial drift deposits underlain by approximately 4,000 ft of Cambrian-to Silurian-aged sedimentary rock which in turn is underlain by Precambrian-aged crystalline rock.

The Cambrian- to Silurian-aged sedimentary rock of the Kankakee Arch consist of various dolomite, shale and sandstone formations underlain by Precambrian-aged crystalline rock which is located significantly below the floor of the quarry/reservoir.

The rock in the project vicinity is generally overlain by a sequence of fill, alluvial deposits, and glacial drift deposits (youngest to oldest).

3.3 General Site Geology

3.3.1 Soil

In general, the soil stratigraphy in the project area consists of Fill, Alluvium, and Glacial deposits. Fill has been placed overlying the native materials as a result of channelization, dredging, and construction of the Metropolitan Water District of Greater Chicago’s (MWRDGC)

Lawndale Avenue Solids Management Area (LASMA), and other local construction.

The rock surface in the vicinity of the project site is generally classified as “slightly weathered” to “fresh”.

Detailed descriptions of the Fill, Alluvium, and Glacial deposits (including glacial till) are presented in Section 3.4.

3.3.2 Rock

3.3.2.1 Lithology

The rock underlying the project alignment consists of lithologies belonging to the Racine, Sugar

Run, Joliet, Kankakee, Elwood, and Wilhelmi Formations. A detailed description of the formations is presented in the McCook Main Tunnel System GDR.

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Racine Formation – the primary lithology of the Racine Formation as seen from the borings is a moderately hard to hard, slightly weathered, fine-grained, light gray-to-gray dolomite. This formation contains stylolites and stylolitic joints, chert bands and nodules, vugs, and pits.

Sugar Run Formation – The primary lithology of the Sugar Run Formation as seen from the borings is a hard, fresh, fine-grained, massive, light gray dolomite with stylolites, clay partings, and few to trace vugs and chert nodules.

Joliet Formation – The primary lithology of the Joliet Formation as seen from the borings is a medium hard, fresh, very fine-grained, thickly-bedded, gray to dark gray dolomite, with vugs and occasional stylolites.

Kankakee Formation – The primary lithology of the Kankakee Formation as seen from the borings is a medium hard to hard, slightly weathered, fine-to-medium grained, dark brown to gray dolomite with clay partings, vugs, chert nodules and bands, and fossils.

Elwood Formation – The primary lithology of the Elwood Formation as seen from the borings is a moderately hard, fresh, fine to medium grained, thinly-banded, gray to brownish-gray dolomite with black clay partings, fossils and occasional chert nodules.

Wilhelmi Formation – The primary lithology of the Wilhelmi Formation as seen from the borings is a moderately hard, fresh, very fine-grained, thinly bedded, argillaceous, dark gray to black dolomite.

3.3.3 Structure

Structure of the rock in the project area is defined by bedding and jointing discontinuities with bedding being the more prominent of the two (URS, 2001).

For purposes of this report, bedding is defined by a change in formation type through the stratigraphic sequence. Formations are presented in Section 3.3.2.1 and are generally defined by similar characteristics (mineralogy, depositional environment, fossil type). Bedding changes are frequently gradational rather than distinct and commonly occur within the same vertical elevation (approximately 10 to 20 ft) across the project site.

Since 1991 two major joint sets have been extensively mapped and recorded in the project area.

For purposes of this report the two joint sets will be labeled J1 and J2 and their orientation, dip and spacing is presented in Section 4. Refer to the project GDR for more detailed description of the joints.

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3.3.4 Groundwater Levels

Groundwater levels, from the eight borings (Section 3.1.3), near the optional Construction Shaft and proposed tunnel alignment ranged from El. -1.5 to -42.1 CCD and were generally obtained at the start of the drilling operations each day.

Groundwater level fluctuations occur with time and seasonal change due to variations in precipitation, evaporation, surface water runoff, and local dewatering.

3.4 Soil Unit Properties

3.4.1 General

A general description of the various soil units and their engineering properties is provided in this section. Anticipated behavior of the various soil units relative to optional Construction Shaft is described in Section 4. Soil sampling was conducted on the eight borings (Section 3.1.3) near the project site.

3.4.2 Fill

Man-made Fill near the project site is generally associated with dredging neighboring water bodies and previous construction or paving activities. Onsite Fill generally consists of asphalt, limestone base course, silty clay, silty sand, sand and trace gravel, roots and organics.

3.4.3 Alluvium and Glacial Deposits

Alluvium and Glacial deposits are present below the Fill and were seen in all the design phase borings. These deposits generally consist of organic clay, silty clay, fine to coarse sand and gravel, silt, sandy silt, silty sand, sandy clay, gravel, sandy gravel, cobbles and boulders.

Differentiating between the Alluvium and Glacial deposits in the borings was not always possible and for purposes of the GBR they are grouped together. Deposits generally varied in thickness from 21 ft (LB-122-08) to 36 ft (LB-101-98).

3.5 Rock Unit Properties

3.5.1 General

Data from laboratory tests conducted on samples of intact rock from design phase borings, and from previous laboratory testing on past borings, are presented in the project GDR. The purpose of this testing was to obtain information on the unconfined compressive strength (UCS) and the

Brazilian tensile strength (BTS) tests. All the laboratory data is summarized in tabular form in the project GDR. Also presented in the GDR are a series of scatter plots for the various laboratory tests, including RQD. Analysis of these histograms shows intact rock properties do not vary significantly by formation or by location within the project area. Baseline values for the intact rock properties are presented in Section 4.

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3.5.2 Rock Weathering

In general, the weathering profile of the top of rock shows slight weathering grading to fresh with depth.

For purposes of this report, the top of rock is defined as the elevation or depth at which continuous rock mass is encountered. Rock and top of rock for construction purposes are defined in Section 31 00 00 – Earthwork.

3.5.3 Equivalent Hydraulic Conductivity

Equivalent rock mass hydraulic conductivity (k) was evaluated based on the results of 66 water pressure tests conducted in the design phase test borings as summarized in the project GDR.

Review of k values relative to geologic formation, depth below top of rock, and location along the tunnel alignment was undertaken to determine if correlations existed to facilitate predictions of water inflow during construction. Evaluation shows no clear correlations between geologic formation and equivalent hydraulic conductivity, or depth below top of rock and equivalent hydraulic conductivity. No tests showed a k value greater than 10-3 cm/sec and twelve tests

(18%) measured k values greater than 10-4 cm/sec.

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4.0 Characterization and Behavior of Engineering Geological Units

4.1 Properties and Behavior of Engineering Units – Soil

The material descriptions of the soil units designated for this project, which include Fill, Alluvium, and Glacial deposits, are the same as presented in Section 3.4.

Behavior of soils during optional Construction Shaft construction shall impact the Contractor’s selection of means and methods for temporary shaft support construction. Ground behavior depends upon several factors including: gradation and texture of soil materials (e.g. the percentage and plasticity of fine materials), groundwater conditions, soil formation, depositional environment and structure, and the construction means and methods employed. The anticipated ground behavior for the soil units encountered during project construction has been classified in accordance with the Tunnelman’s Ground Classification. Ground classification based on the behavior of soft ground tunnels was first proposed by Terzaghi in 1950 and has been modified by several authors, most notably by Heuer in 1974. The Tunnelman’s Ground Classification system is used in this GBR to describe the anticipated behavior of the soil units present.

For purposes of defining characteristics and behaviors of the soil profile, the materials present along the alignment have been classified into the following two Engineering Units for ground classification purposes:

Coarse-Grained Soils - Includes fine to coarse sand and gravel, silty sand, and boulders in varying proportions

Fine-Grained Soils – Includes silt, sandy silt, clay, silty clay, sandy clay, silty sandy clay, and organic clay in varying proportions

Both Engineering Units contain Fill, Alluvium, and Glacial materials as described in Section 3.

The following sections describe the behavioral characteristics of engineering soil units at the project site.

4.1.1 Soil Classification

No soil will be encountered during tunnel excavation. Soil will only be encountered during excavation of the optional Construction Shaft. Soil behavior at a particular location will depend upon the type of material being excavated and whether the material is above or below groundwater. The material behavior will vary depending on the magnitude of the hydraulic gradient providing the acting driving force. The types of ground behavior to be expected when excavating though soil materials comprising cohesive soils (lean clay, fat clay, silt, elastic silt) and granular soils (clayey sand and silty sand) shall include the following:

Fine-Grained Soil materials above groundwater level – Slow Raveling

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Fine-Grained Soil materials below groundwater water level – Slow to Fast Raveling

Coarse-Grained Soil materials above groundwater level – Running

Coarse-Grained Soil materials below groundwater level – Flowing

For baseline purposes the soil material shall be expected to contain rock fragments, cobbles, and boulders within 40 ft of the soil rock interface, derived from the weathering of the underlying rock. The Contractor should consider these rock fragments as having intact rock properties the same as the native rock and use the baseline material parameters considered in Section 4.2 for bid purposes.

The soil properties for the optional Construction Shaft are defined in Section 5. The baseline properties for design of temporary support and for excavation of each soil type to be encountered during excavation are presented in Table 4-1 below.

Table 4-1 Soil Engineering Unit Baselines

Parameter Unit Soil

Fine-Grained Coarse-Grained

Unit Weight (In Situ) pcf 145 145

Cohesion psf 2,000 0

Friction Angle degrees 0 35

Permeability cm/sec 1x10-7 1x10-4

4.2 Properties and Behavior of Engineering Units – Rock

Based upon the available data for each rock type presented in Section 3.3.2 it has been determined that the intact rock properties show no significant variation along the project alignment. For this reason we have designated the rock along the entire length of the tunnel alignment as a single engineering unit, herein referred to as the Engineering Rock Unit.

The Engineering Rock Unit has been divided based upon Rock Mass Rating (RMR) into a series of three Excavation and Support (E&S) Classes for drill and blast excavations.

E&S Class I = RMR > 60;

E&S Class II = RMR 40 – RMR 60; and

E&S Class III = RMR < 40.

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4.2.1 Engineering Rock Unit

The baseline intact rock properties are presented in Table 4-2. Rock material baselines are presented using arithmetic average and a value that 90% of the rock does not exceed. It should be noted that the UCS baseline value determination includes only direct UCS testing.

The impact of rock structure and discontinuities on tunneling is considered in Section 4.2.3.

Table 4-2 Engineering Rock Unit – Baseline Intact Rock Properties

Parameter Unit Engineering Unit

Average 90%

Unconfined Compressive Strength (UCS) psi 15,000 25,000

Brazilian Tensile Strength (BTS) psi 1,500 2,300

4.2.2 Discontinuity Orientation

The predominant discontinuity within the shafts and along the tunnel profile will be bedding. For baseline purposes the bedding dip angles will range from 0 to 5 degrees, generally in a southerly direction

The baseline ranges in orientation of the two joint sets (J-1 and J-2) are summarized in Table 4-3.

Table 4-3 Summary of Joint Set Baselines

Feature Dip Angle

Range (degrees)

Dip Direction

Range

(azimuth)

Mean Plane Dip

Angle (degrees)

Mean Plane Dip

Direction

(azimuth)

J-1 80-90 315-325

135-145 140

J-2 80-90 35-45

215-225 220

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4.2.3 Joint Spacing

The joint spacing classification used for the project is summarized in Table 4-4 (Brown, 1981).

Table 4-4 Summary of Joint Spacing Classes

Feature Joint Spacing Range

From (in.) To (in.)

Extremely Close 0.0 0.75

Very Close 0.75 2.5

Close 2.5 8

Moderately Wide 8 24

Wide 24 60

Very Wide 60 >60

The baseline ranges for joint spacing of the two joint sets are summarized in Table 4-5.

Table 4-5 Summary of Joint Set Spacing Observations

Feature Joint Spacing Range (in.) Typical Joint Spacing

J-1 12 to >60 Moderately wide to very wide

J-2 12 to >60 Moderately wide to very wide

4.2.4 Excavation and Support Classes

The Engineering Rock Unit is divided based upon Rock Mass Rating (RMR) into a series of three E&S Classes for drill and blast mined tunnel support. Ratings for six parameters (UCS, RQD, joint spacing, joint condition, groundwater condition, and joint orientation) were used to classify the rock mass using the RMR system in accordance with Bieniawski (Bieniawski 1989).

The ratings for each of the six parameters are summed to provide a value of RMR between 0 and

100. A summary of the project E&S Classes assigned based upon RMR’s for the engineering units is presented in Table 4-6 and baselined in Section 6.

Table 4-6 Relationship between E&S Classes and RMR

E&S Class RMR RMR Rock Description

E&S Class I > 60 Good to Very Good

E&S Class II 40 to 60 Fair

E&S Class III < 40 Poor to Very Poor

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5.0 Construction Considerations for Construction Shaft (Contractor Option)

This section presents the baselines for subsurface conditions anticipated at the optional

Construction Shaft. The location, surface elevation, shaft invert elevation, and depth below ground surface for the optional Construction Shaft are shown on the Contract Drawings.

5.1 Construction Shaft

The Contractor shall be responsible for the design of temporary ground support in the soil materials and rock at the optional Construction Shaft.

5.1.1 Drill and Blast for Shaft Excavation

The drill and blast sections of the project will include excavation of rock within the optional

Construction Shaft. Ground vibration and air blast limits are stated in the Contract Documents.

5.1.2 Ground Support

For bidding purposes at the optional Construction Shaft the Contractor shall assume that the following conditions apply:

The ground surface elevation at the center of the optional Construction Shaft is El. 21.5

CCD.

The top of rock elevation (soil/rock interface) shall be sloping and shall vary between El.

-7.0 CCD and El. -12.0 CCD within the shaft footprint area.

The Contractor shall encounter a zone of loose and blocky ground for a depth of 10 ft below the top of rock.

No contaminated soil or groundwater will be encountered during excavation of the shafts.

Temporary ground support systems in the soil shall be designed and constructed to maintain ground surface settlement to within the limits provided in the Contract

Documents and shall actively control inflow of water into the shaft to a volume that does not impact construction for the duration of the contract.

The Contractor will not encounter any obstructions greater than defined in the Project

Specifications.

Hard rock ground support systems shall be designed and constructed to maintain support of excavation in accordance with the Contract Documents.

Refer to Attachment A for the baseline ground profile at the site of the optional Construction

Shaft.

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5.2 Groundwater

For baseline purposes the Contractor will assume that measurable groundwater will be encountered in the subsurface and that dewatering will be required. The groundwater infiltration will be concentrated in intervals associated with the overburden-bedrock contact if the optional construction shaft is excavated and with portions of the underground work within the Elwood

Formation.

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6.0 Construction Considerations for Tunneling

The characterization of the ground behavior presented in this GBR is based upon the assumption that the tunnel, or any starter and tail tunnels, will be constructed using drill and blast techniques.

6.1 Anticipated Tunneling Conditions

The tunnel shall pass through the Engineering Rock Unit which has been classified based upon rock types with similar intact rock properties (see Section 4.0 for detailed description). The

Engineering Rock Unit is subdivided based upon rock mass behavior for this project correlated with the RMR into a series of three E&S Classes as described in Section 4.0 (E&S Class I, E&S

Class II, and E&S Class III) and as presented in the Contract Documents.

6.1.1 Drill and Blast Tunneling

The drill and blast sections of the project will include rock excavation for the tunnel. Ground vibration and air blast limits are stated in the Contract Documents.

6.2 Ground Support

Tunnel lining shall consist of a two pass system. This includes initial support of the tunnel during excavation, and the permanent lining as defined on the Contract Drawings.

The initial support requirements for each E&S class will be designed by the Contractor. The estimated total length of each E&S Class required during construction of the tunnel is presented in Table 6-1.

Table 6-1 Estimated Support Class Quantities

E&S

Class RMR Rock Conditions

Total Length

(ft)

Percent of Total

Tunnel Length

I > 60 Good to very good rock, massive 1,398 90

II 40 – 60 Fair rock, blocky 77.5 5

III < 40 Poor to very poor rock, very blocky to blocky/disturbed

77.5 5

For baseline purposes no additional payment shall be made for transitioning between E&S

Classes.

6.3 Estimated Groundwater Inflows

Groundwater inflow estimates have been undertaken using equivalent rock mass hydraulic conductivity derived from in situ water pressure testing and the Heuer Method (Heuer, 1995 &

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6-2

2005) to provide baseline estimates of initial heading inflow (Qh) and steady state inflow (Qs) for the total tunnel length (1,600 ft).

For baseline purposes the maximum initial heading (Qh) inflow (initial flush flow) shall be 275 gpm per heading (duration = 36 hrs) and the maximum steady state inflow experienced over the length of the tunnel (Qs) shall be 110 gpm. In the event that two headings are being worked at the same time the maximum initial heading (Qh) inflow (initial flush flow) shall be 550 gpm

(duration = 36 hrs).

6.4 Grouting

Routine pre-excavation grouting is not required and has not been considered in the groundwater inflow estimates presented in Section 6.3, Estimated Groundwater Inflows.

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7.0 References

Bieniawski, Z.T., Engineering Rock Mass Classifications, 1989, Wiley, New York.

Brown, E.T., Rock Characterization Testing and Monitoring, 1981, Pergamon Press, Oxford, England.

Heuer, R., Estimating Rock Tunnel Water Inflow, 1995 RETC Proc., June 1995, San

Francisco, CA.

Heuer, R., Estimating Rock Tunnel Water Inflow – II, 2005 RETC Proc., June 2005, Seattle, WA.

Heuer, R., Important Ground Parameters in Soft Ground Tunnels", Proceedings of Eng.

Found. Conf. on "Subsurface Exploration for Underground Excavation and Heavy

Construction", August, 1974, Henniker, New Hampshire, ASCE.

Attachment A Construction Shaft – Contractor Option

Ground Profile