SUBJECT: GEOTECHNICAL REVIEW OF MSE WALL PLANS … Report...Aug 28, 2017 · and Calculations for Poinsettia 61, SRD Project No. 1704-003, August 21. Mr. Nakaya: In accordance with

August 28, 2017

Lennar Homes 25 Enterprise, Suite 300 Aliso Viejo, California 92656

Attention: Mr. Jamison Nakaya

SUBJECT: GEOTECHNICAL REVIEW OF MSE WALL PLANS Poinsettia 61 Development Carlsbad, California

References: Group Delta (2014). Report of Geotechnical Investigation, Poinsettia 61 Development, Carlsbad, California, Document No. 14-0188, November 20.

Group Delta (2017). Supplemental MSE Retaining Wall Recommendations, Poinsettia 61 Development, Carlsbad, California, Document No. 17-0081, July 12.

O’Day Consultants (2017). Rough Grading, Storm Drain and Retaining Wall Plans and Details for Poinsettia 61, Sheets 1 through 38, August 21.

Soil Retention Designs Inc. (2017A). Verdura Retaining Wall Plans for Poinsettia 61, Sheets 21 through 38, August 18.

Soil Retention Designs Inc. (2017B). Verdura Retaining Wall Design Summary and Calculations for Poinsettia 61, SRD Project No. 1704-003, August 21.

Mr. Nakaya:

In accordance with your request, we have reviewed the geotechnical aspects of the referenced Mechanically Stabilized Earth (MSE) retaining wall plans for the Poinsettia 61 Development in Carlsbad, California. We have also conducted global stability analyses for eight cross sections of the planned MSE walls and associated slopes, as shown in the attached figures. In general, our review indicates that the geotechnical aspects of the referenced MSE wall plans conform to the intent of the geotechnical recommendations provided in our supplemental report (GDC, 2017). Specific aspects of the MSE wall plan review and slope stability analyses are discussed below.

Geotechnical Review of MSE Wall Plans GDC Project No. SD412B Poinsettia 61 Development August 28, 2017 Lennar Homes Page 2

N:\Projects\SD\SD412B Lennar - Poinsettia 61, T&O of Earthwork Construction\5. Reports\17-0100\17-0100.doc

PLAN REVIEW COMMENTS

Group Delta Consultants provided geotechnical recommendations to aid in design of the MSE walls in the referenced letter (GDC, 2017). In summary, we recommended that the existing fill soil in both the retained and foundation influence zones for the new MSE wall be assumed to have a friction angle of 32º with 100 lb/ft2 cohesion, and a total unit weight of about 125 lb/ft3. Note that the MSE wall design neglected the cohesion component. We also recommended that the soil used in the reinforced zone have a minimum friction angle of 32º with a total unit weight of about 120 lb/ft3. The MSE wall backfill should also be a granular, free draining material with an Expansion Index of 20 or less, and should be compacted to at least 90 percent of the maximum dry unit weight based on ASTM D1557.

Our review of Table 3 on Sheet 21 of the MSE wall plans indicates that the MSE wall designer assumed a friction angle of 32º for both the retained and foundation zones, with a unit weight of 125 lb/ft3 for the retained soil, and a unit weight of 120 lb/ft3 for the reinforced zone. These values conform to our recommended soil parameters. Note that the proposed MSE wall backfill should be sampled and tested by Group Delta Consultants prior to placement in order to confirm that these criteria are satisfied. The compacted fill in the reinforced zone should have a friction angle of 32º or more when tested using ASTM D3080 with the test specimens remolded to approximately 90 percent relative compaction per ASTM D1557. The test specimens should be remolded at near optimum moisture content, and then saturated prior to testing.

Section 2.05 on Sheet 21 of the MSE wall plans indicates that the soil used in the retained zone should be less than ¾-inch in maximum dimension, and have no more than 35 percent fines per ASTM D6913. The plans also indicate that the reinforced soil should also have a Plasticity Index (PI) less than 20 per ASTM D4318, and an Expansion Index less than 20 per ASTM D4829 per our recommendations. Again, soil samples should be tested prior to placement to confirm that the material placed in the reinforced zone meet these criteria. Note that although much of the on-site soil will meet these criteria, the clayey, fine grained soils will not (CL, ML and CH).

Table 3 on Sheet 21 of the referenced plans also indicates that a peak ground acceleration (PGA) of 0.30g was applied to the MSE wall design (taken as two-thirds of the PGAM value from the California Building Code). We have no objection to the PGA used for the MSE wall design.

GLOBAL STABILITY ANALYSIS

The remainder of this document presents the results of our global stability analyses for the planned MSE walls. The general geotechnical conditions throughout the site were described in the referenced investigation report (GDC, 2014). Plan views of the proposed MSE walls and associated slopes are shown in the attached Figures A-1 through H-1 for Cross Sections A-A’ through H-H’, respectively (O’Day, 2017). The existing and proposed topography at each cross section location correspond to that shown on the grading plans in Figures A-1 through H-1.



The proposed MSE wall configuration, geogrid type, and geogrid length at each cross section location correspond to that shown on the Verdura Retaining Wall Plans (Soil Retention, 2017A). The geogrid parameters used for our analyses were summarized in Table 4 on Sheet 21 of the wall plans, and were also summarized in the associated calculations (Soil Retention, 2017B).

The planned MSE walls will be located in relatively close proximity to several of the borings and/or test pits conducted for the geotechnical investigation (GDC, 2014). The geologic conditions at each cross section location were estimated based on the conditions encountered in those nearby explorations. Based on the planned depths of excavation, we anticipate that the proposed MSE walls along the northern edge of the site will generally be underlain directly by dense sandstone of the Santiago Formation. However, along the remainder the site (where fills are proposed), the MSE walls will generally be underlain by alluvium that will first need to be excavated and replaced with compacted fill prior to building the planned MSE walls. Maximum temporary cut slope inclinations of 1:1 were recommended for the remedial excavations. However, the saturated alluvium will need to be dewatered prior to excavation.

Samples of the various soils encountered in the subsurface explorations were tested as part of the geotechnical investigation, as described in Appendix B of that report (GDC, 2014). Based on those shear tests, we anticipate that compacted fill soils derived from the on-site materials will typically have a drained shear strength exceeding 32º with 100 lb/ft2 cohesion. By comparison, the lower bound of the peak shear strength of the sandstone of the Santiago Formation was estimated as 35º with 150 lb/ft2 cohesion. The shear tests also suggest a lower bound peak strength of 23º with 200 lb/ft2 cohesion for the intact claystone beds, and 19º with zero cohesion for the highly fissured claystone beds encountered in some of the explorations.

The referenced MSE wall plans and associated structural calculations included detailed design parameters such as the exposed wall height, wall embedment, wall batter, geogrid type, geogrid length and geogrid locations (Soil Retention, 2017AB). The planned MSE walls will typically have a 1:4 (horizontal to vertical) batter, and will generally use a uniform length of Miragrid 8XT, 10XT or 20XT geogrid. The Verdura 40 blocks will typically be about 18-inches wide, 12-inches deep, and 8-inches high. The excavation along the base of each wall will be sloped back beneath the reinforced zone at a minimum 2-percent gradient to a collector subdrain, that will need to outlet to the storm drain system or other approved gravity outlet.

The stability of the proposed MSE wall system was evaluated using the program SLOPE/W, incorporating the various soil and geogrid parameters described above. The stability analyses were conducted using Spencer's Method of Slices, which satisfies both force and moment equilibrium. All of the critical failure surfaces were optimized. The analyses focused on the worst-case conditions, including the highest sections of the walls in close proximity to the highest sections of slope. Our stability analyses are presented in the figures immediately following each plan view (i.e. A-2 to A-3 through H-1 to H-4).



For each cross section, we evaluated the long-term static stability of the planned MSE wall configuration. Out analyses indicate that the proposed MSE wall sections we analyzed had a long-term Factor of Safety (FS) in excess of the minimum required of 1.5 (FS ≥ 1.5). In some cases, we also evaluated the temporary stability of the 1:1 forecuts that will be needed to remove the existing compressible alluvium beneath the development. These analyses indicated that the temporary stability of the 1:1 cut slopes up to 20-feet in height would exceed the minimum required of 1.2 (FS ≥ 1.2), provided that the alluvium is first dewatered.

For the seismic analyses, we varied the applied pseudo-static horizontal load (Kh) on the wall until the Facor of Safety of the critical failure surface was approximately equal to 1.0 (FS = 1.0). The Yield Acceleration (Ky) determined in this manner was then compared to the Design level

Peak Ground Acceleration (PGA) of 0.31g in order to estimate the lateral deformation () that the MSE wall and slope may experience during an earthquake. For most of the sections, the Yield Acceleration exceeded the Design level seismic demand, indicating that no seismic displacement would occur. For the remaining sections, the estimated seismic deformation was less than one inch, which would typically be deemed tolerable per the standards of practice.

In summary, our global stability analyses indicate that the planned MSE walls and slopes will have an adequate safety factor against deep seated failure, provided that they are constructed in general accordance with our geotechnical recommendations. The worst-case cross section we analyzed had a long-term safety factor of 1.5, which is typically deemed adequate. Our seismic stability analyses also indicate the MSE walls will experience less than about one inch of lateral deformation due to the Design level earthquake, which is also deemed acceptable.

LIMITATIONS

Our services were performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable soils engineers and geologists practicing in this or similar localities. No warranty, express or implied, is made as to the conclusions and professional advice included in this report. We appreciate this opportunity to be of professional service. Feel free to contact the office with any questions or comments, or if you need anything else.

GROUP DELTA CONSULTANTS

Matthew A. Fagan, G.E. 2569 Senior Geotechnical Engineer

Distribution: (1) Addressee, Mr. Mr. Jamison Nakaya ([email protected]) (1) Addressee, Mr. Mr. Andrew Han ([email protected])

mailto:[email protected]

mailto:[email protected]

mattf

Typewritten Text

12-31-17

FIGURES

A-1

CROSS SECTION A-A’

17-0100

9245 ACTIVITY ROAD, SUITE 103SAN DIEGO, CA 92126 (858) 536-1000

SD412B

Poinsettia 61 DevelopmentLenna Homes

A

A’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER

GROUP DELTA CONSULTANTS, INC.ENGINEERS AND GEOLOGISTS

A-2


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section A-A’ does meet the minimum required FS of 1.5 (F.S~2.17).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


A-3


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section A-A’ is approximately 0.43g, which exceeds the Design level PGA of 0.31g.

The estimated slope deformation under the Design level seismic demand is negligible (less than 1 inch).

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


B-1

CROSS SECTION B-B’

17-0100


SD412B


B

B’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


B-2


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section B-B’ does meet the minimum required FS of 1.5 (F.S~1.50).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


B-3


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section B-B’ is approximately 0.30g.

The slope deformation under the Design level seismic demand of 0.31g is estimated at less than 1 inch.

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


C-1

CROSS SECTION C-C’

17-0100


SD412B


C

C’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


C-2


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section C-C’ does meet the minimum required FS of 1.5 (F.S~1.50).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


C-3


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section C-C’ is approximately 0.31g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


D-1

CROSS SECTION D-D’

17-0100


SD412B


DD’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


D-2


17-0100


SD412B


NOTES:

Test Pit TP-7 and Boring B-14 indicate that there is a considerable amount of loose saturated alluvium in this portion of the site (GDC, 2014).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


D-3


17-0100


SD412B


NOTES:

The alluvium is considered compressible and liquefiable, and should be excavated to expose dense formational materials throughout the site.

The safety factor of the proposed temporary 1:1 cut slope will exceed 1.2, provided that the alluvium is dewatered as necessary.

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


D-4


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section D-D’ does meet the minimum required FS of 1.5 (F.S~2.12).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


D-5


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section D-D’ is approximately 0.40g, which exceeds the Design level PGA of 0.31g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


E-1

CROSS SECTION E-E’

17-0100


SD412B


E

E’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


E-2


17-0100


SD412B


NOTES:

Borings B-13 and B-14 indicate that there is a considerable amount of loose saturated alluvium in this portion of the site (GDC, 2014).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


E-3


17-0100


SD412B


NOTES:

The alluvium is considered compressible and liquefiable, and should be excavated to expose dense formational materials throughout the site.

The safety factor of the proposed temporary 1:1 cut slope will exceed 1.2, provided that the alluvium is dewatered as necessary.

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


E-4


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section E-E’ does meet the minimum required FS of 1.5 (F.S~1.88).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


E-5


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section E-E’ is approximately 0.34g, which exceeds the Design level PGA of 0.31g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


F-1

CROSS SECTION F-F’

17-0100


SD412B

Poinsettia 61 DevelopmentLenna HomesF

F’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


F-2


17-0100


SD412B


NOTES:

Previous explorations indicate that there is a considerable amount of loose saturated alluvium in this portion of the site (GDC, 2014).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


F-2


17-0100


SD412B


NOTES:

Previous explorations indicate that there is a considerable amount of loose saturated alluvium in this portion of the site (GDC, 2014).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


F-3


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section F-F’ does meet the minimum required FS of 1.5 (F.S~1.98).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


F-4


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section F-F’ is approximately 0.40g, which exceeds the Design level PGA of 0.31g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


G-1

CROSS SECTION G-G’

17-0100


SD412B


G

G’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


G-2


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section G-G’ does meet the minimum required FS of 1.5 (F.S~2.14).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


G-3


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section G-G’ is approximately 0.49g, which exceeds the Design level PGA of 0.31g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


H-1

CROSS SECTION H-H’

17-0100


SD412B


H H’

SCALE:1” ~ 20’(11x17)

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


H-2


17-0100


SD412B


NOTES:

Boring B-9 indicates that there is about 8 to 10 feet of existing undocumented fill in this portion of the site (GDC, 2014).

Compressible undocumented fill should be excavated and compacted as discussed in Seciton 6.3.2 of the geotechical investigation report (GDC, 2014).

PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


H-3


17-0100


SD412B


NOTES:

The static safety factor for the proposed MSE wall at Section H-H’ does meet the minimum required FS of 1.5 (F.S~1.71).PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


H-4


17-0100


SD412B


NOTES:

The Yield Acceleration (Ky) for the proposed MSE wall at Section H-H’ is approximately 0.34g.


PROJECT NAME

PROJECT NUMBER

DOCUMENT NUMBER

FIGURE NUMBER


Documents

SUBJECT: GEOTECHNICAL REVIEW OF MSE WALL PLANS … Report...Aug 28, 2017 · and Calculations for Poinsettia 61, SRD Project No. 1704-003, August 21. Mr. Nakaya: In accordance with