HomeMy WebLinkAboutSDP 2021-0029; IONIS LOTS 21 AND 22; SOIL NAIL WALL AND CONCRETE PAVERS; 2023-01-18Project No. 06442-32-31A
January 18, 2023
Ionis Pharmaceuticals, Inc.
2855 Gazelle Court
Carlsbad, California 92010
Attention: Mr. Wayne Sanders
Subject: GEOTECHNICAL RECOMMENDATIONS:
SOIL NAIL RETAINING WALL AND
PRELIMINARY CONCRETE PAVER PAVEMENT
IONIS PHARMACEUTICALS LOTS 21 AND 22
(CARLSBAD OAKS NORTH BUSINESS PARK)
CARLSBAD, CALIFORNIA
References: 1. Update Geotechnical Report, Ionis Lots 21 and 22 (Carlsbad Oaks North Business
Park), Carlsbad, California, dated October 19, 2021, prepared by Geocon
Incorporated (Project No. 06442-32-31A).
2. Precise Grading Plans for: Ionis Pharmaceuticals Lots 21 & 22, City of Carlsbad,
California, prepared by Pasco Laret Suiter & Associates, undated.
Dear Mr. Sanders:
In accordance with Mr. Jon Olhson with DGA Planning/Architecture/Interiors, we are providing
geotechnical recommendations for use in design of the planned soil nail retaining wall and preliminary
concrete paver section for the subject project. The recommendations presented herein should be used in
conjunction with the information presented in Reference No. 1.
Summarized below are the geotechnical recommendations:
1.0 Soil Nail Retaining Wall
1.1 We understand that a permanent soil nail retaining wall is planned adjacent to the north and
east margins of the parking garage. In general, ground conditions are moderately suited to soil
nail wall construction techniques. The wall will be excavated in compacted fill and granitic
rock. Moderate to heavy effort should be expected when drilling into the granitic rock.
Localized zones of rock up to 12 inches in diameter and occasionally larger rock could be
encountered in the existing fill materials that could be difficult to drill.
GEOCON
INCORPORATED
G E OT E CHN I CAL ■E NV I RONMENTA L ■ MA T ER I A L S
6960 Flanders Drive ■ Son Diego, California 92121-297 4 ■ Telephone 858.558.6900 ■ Fax 858.558.6159
Geocon Project No. 06442-32-31A - 2 - January 18, 2023
1.2 Soil nail walls consist of installing closely spaced steel bars (nails) into a slope or excavation
in a top-down construction sequence. Following installation of a horizontal row of nails,
drains, water-proofing and wall reinforcing steel are placed and shotcrete applied to create a
final wall.
1.3 The wall should be designed by an engineer familiar with the design of soil nail walls.
1.4 Corrosion protection should be provided for the nails considering the wall is a permanent
structure.
1.5 Testing of the soil nails should be performed in accordance with the latest version of
guidelines provided by the Federal Highway Administration (FHWA) or similar guidelines.
At least two verification tests should be performed on non-production (sacrificial) nails to
confirm design assumptions for each soil/rock type encountered prior to start of construction.
The bond length of the verification nails should be adjusted to allow for pullout testing to
evaluate the ultimate bond stress. In addition, verification testing (additional sacrificial test
nails) may be required during production to check capacities for different in-situ conditions
encountered during construction and/or installation methods. A minimum of 5 percent of the
production nails should also be proof tested.
1.6 Geocon Incorporated should observe the wall construction operations and testing of the soil
nails.
1.7 The soil strength parameters listed in Table A can be used in design of the soil nails. The bond
stress is dependent on drilling method, diameter, and construction method. Therefore, the
designer should evaluate the bond stress based on the existing soil conditions and the
construction method.
TABLE A
SOIL STRENGTH PARAMETERS FOR SOIL NAIL WALLS
Description Cohesion (psf) Friction Angle
(degrees)
Estimated
Ultimate Bond
Stress (psi)*
Compacted Fill 200 30 15
Weathered Granitic Rock 300 38 35
*Assuming gravity fed, open hole drilling techniques.
1.8 A drain system should be incorporated into the design of the soil nail wall as shown herein.
Geocon Project No. 06442-32-31A - 3 - January 18, 2023
1.9 Geocon Incorporated should review the wall plans prior to final design submittal to check
whether additional analyses and/or recommendations are required.
2.0 Preliminary Concrete Paver Pavement Recommendations
2.1 We understand that non-permeable pavers consisting of high strength brick pavers are planned
for the project. The preliminary section presented herein is for budgetary estimating purposes
only and are not for construction. The final paver pavement section will be provided after the
grading operations are completed, subgrade soils are sampled, and laboratory resistance value
(R-Value) testing is performed on the soil samples collected.
2.2 We calculated the paver pavement section in general conformance with the Interlocking
Concrete Pavement Institute Technical guidelines (ICPI Tech Spec Number 4, Structural
Design of Interlocking Concrete Pavement for Roads and Parking Lots) and Caltrans
Highway Design Manual (Topic 633). We used a traffic index (TI) of 6.5 for design of the
pavement section based on information provided by Pasco Laret Suiter & Associates (PLSA).
We used an estimated R-Value of 30 and 78 for soil and aggregate base, respectively, in the
pavement calculations. Table B presents the preliminary concrete paver section.
EX ;,.vATION Ft
SOIL NAI~
AND GROUT
3'MIN.
WHERE
REQUIRED
PERFORATED COLLECTOR DRAIN
SCHEDULE 40 PVC PIPE (OR OTHER)
UNIFORMLY SLOPED LEADING TD
POSITIVE GRAVITY OUTLET OR
CONTROLLED DRAINAGE DEVICE
FINISH
SURFACE
Geocon Project No. 06442-32-31A - 4 - January 18, 2023
TABLE B
PRELIMINARY CONCRETE PAVER SECTIONS
Drive Isle Traffic Index Design R-Value
Minimum Concrete Paver Thickness, inches [mm]
Bedding (inches)
Class 2 Aggregate Base (inches)
Heavy Truck & Fire
Lane 6.5 30 3.15 [80] 1.0 10.0
*Paver sections are for project ultimate traffic loading only and not for support of construction traffic.
Provided below are general recommendations for construction of the paver pavement section:
1. Concrete paver installation should be performed in accordance with ICPI Tech Spec 2,
Construction of Interlocking Concrete Pavement.
2. Contractor should refer to project landscaping architect for type of paver to use.
3. The pavers should be placed on bedding sand that meets ASTM C33 gradation as indicated in
ICPI Tech 17 (see paver manufacture specifications for actual bedding sand gradation). The
pavers and sand bedding should be constructed over Class 2 aggregate base materials
conforming to Section 26-1.02B of the Standard Specifications of Caltrans with a ¾-inch
maximum size aggregate.
4. Prior to placing the pavers, sand bedding and aggregate base materials, the subgrade soil should
be scarified, moisture conditioned as necessary, mixed and compacted to a dry density of at least
95 percent of the laboratory maximum dry density near to slightly above optimum moisture
content per ASTM D 1557. The depth of compaction should be at least 12 inches. Class 2 base
materials should also be compacted to at least 95 percent of the laboratory maximum dry density
near to slightly above optimum moisture content per ASTM D 1557.
5. Stable edge restraints such as Portland cement concrete (PCC) curbs are essential to maintain
horizontal interlock while the paver units are subjected to repeated vehicular loads. Edge
restraints should be constructed in accordance with ICPI Tech Spec Number 3, Edge Restraints
for Interlocking Concrete Pavements. Where pavers will be subject to vehicular loads and where
not restrained by PCC curbs, a concrete beam at least 8 inches wide should be provided to hold
the pavers together. The beam should extend at least 6 inches below the aggregate base material.
The edge restraints (beam) should be provided with two No. 3 steel reinforcing bars, placed top
and bottom.
6. Interlocking pavers should be placed directly adjacent to one another to minimize areas where
water can percolate down into the base and subgrade. In addition, a sealant to bind the sand
between the pavers should be used.
7. A maintenance schedule consisting of inspecting the pavement sections should be established
and periodic removal, replacement, and re-leveling of individual pavers may be required.
8. Consideration should be given to placing Mirafi HP570 or equivalent subgrade stabilizing
materials on the compacted subgrade soil prior to placing the aggregate base and installing the
pavers. The use of subgrade stabilizing materials reduces the potential for paver movement due
Geocon Project No. 06442-32-31A - 5 - January 18, 2023
to saturated subgrade soils that typically result with time. Also, the frequency of removing and
replacing individual pavers may be reduced potentially resulting in lower maintenance cost.
9. The performance of pavement, aggregate base, and subgrade materials are highly dependent on
providing surface drainage. Ponding of water on or adjacent to the structural surface may result
in saturation of the subgrade materials and subsequent distress. To reduce the occurrence for
such situations, a surface drainage gradient should be maintained across the pavement surface.
Drainage from landscaped areas should be directed to controlled drainage structures.
10. Where landscaping or landscape planters are planned adjacent to pavements supporting
vehicular loading, an impermeable liner should be placed at the edges to prevent landscape
irrigation from migrating into the adjacent pavement base and subgrade soils. The liner should
extend at least 6 inches below the bottom of the aggregate base. In-lieu of providing an
impermeable liner, edge restraints (band and/or concrete curbs) may be extended at least
6 inches below the bottom of the base section.
Should you have questions regarding this letter, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Emilio Alvarado
RCE 66915
EA:am
(e-mail) Addressee