Geotechnical memo.pdf

F:\P2005\1040\B38\Soil Characterization\dcl-Characterization_Memo-20100422.doc

M E M O R A N D U M

TO: Jade Neild, NRCS

FROM: Amy Hunt, P.E. – F&O Dean Audet, P.E. – F&O

DATE: May 13, 2010

RE: Soil Characterization, Janet Drive Site

This memorandum is provided to summarize the results of investigations conducted to evaluate soil conditions within the proposed stream channel for the proposed floodplain modifications at Janet Drive in West Warwick, Rhode Island (the site).

The findings presented herein were based on a series of seven soil borings advanced by hand utilizing a hand auger and/or a hand-driven Geoprobe® sampler to depths of approximately three to four feet below grade (fbg) at the site on April 16, 2010, and the resulting sieve analyses of four samples, including one composite sample and three discrete grab samples collected throughout the site. The locations of the borings are depicted on Figure 1, attached. During the field investigation, portions of the site where excavation is proposed were flooded, which prevented access and effective observation of those portions of the site. Subsurface conditions are inferred between these and other boring locations near the boundary of this low area.

To the extent possible, borings were advanced around this area from higher ground, and were advanced to approximately 4 feet in order to infer conditions within the flooded area. Due to the on-site flooding, groundwater was observed in the borings at depths of less than two feet below grade (fbg), and the depths of the borings were limited by collapsing boreholes.

Primary observations across the site are as follows:

• The majority of the site was overlain by a layer of organic material, consisting of decomposed leaves and roots, approximately two to three inches thick. This material was generally underlain by a lens of fine to medium sand, with greater or lesser amounts of coarser sand, silt and clay as noted in the attached boring logs.

• Soil within the site was generally devoid of coarse materials (rocks or gravel) to depths of up to four feet.

• Initially, the borings were planned for depths of up to five fbg, coinciding with the depth of the proposed stream channel. However, boring advancement was impeded at depths of approximately 3-4 feet, primarily by collapse associated with shallow groundwater.

• In several locations, tree roots were observed at depths of between one to three fbg, causing shallow refusals. Where these conditions were encountered, soil lithology was inferred from other borings advanced at the site. Generally, the site-wide lithology was

Memo – Jade Neild, NRCS Geotechnical Investigation – Janet Drive May 13, 2010 largely uniform, and these shallow refusals are not anticipated to prevent the characterization of site-wide soil.

• Clayey soil was observed in the central and northern portions of the proposed stream channel.

• Clay was not observed within the area of the proposed berm at the southeastern edge of the site. Soil in these areas consisted of fine to medium sands with limited amounts of silt. Discrete lenses of coarser sand were observed along the area of the proposed berm at the southeastern edge of the site.

• Groundwater was generally encountered at a depth of approximately two fbg, and was observed to drain into the borehole over a matter of several minutes.

Four samples of representative media were collected and submitted to Thielsh Engineering for sieve analysis in order to determine the suitability of on-site soil for reuse in the berm structures proposed for the site. These sample locations are shown on Figure 1.

• The first sample (referenced herein as the composite sample) was an aggregate sample of soil encountered in the top three to four feet site wide, and represents the loamy sand material observed in the majority of the borings at depths of up to four feet.

• The remaining three samples were collected from discrete intervals at locations SS-2 (along the northeastern edge of the proposed stream channel), SS-3 (in approximately the center of the proposed stream channel), and SS-7 (at the eastern edge of the proposed stream channel within the proposed berm area.

o The sample collected from SS-2 consisted of a poorly sorted sand mixture observed from depths of approximately 2-4 feet below grade.

o The sample collected from SS-3 consisted of a finer mixture of material from the center of the site at depths of up to 4 feet below grade, which included higher proportions of silt and clay than elsewhere at the site.

o The sample collected from SS-7 consisted of a lens of moderately coarse sand observed at depths of 1-2.5 feet below grade at the northeastern corner of the site within the proposed berm.

Each of the soil samples was reported to contain a predominantly sandy mixture containing between approximately 10% and 25% fines by weight. Hydrometer readings were not collected to determine the relative proportions of silt and clay within the samples. The table below summarizes the relative proportions of coarse material (3/8” diameter gravel or larger), sand, and fine material (silt and clay), as well as the Unified Soil Classification System (USCS) designations and median grain sizes of the soil samples.

Memo – Jade Neild, NRCS Geotechnical Investigation – Janet Drive May 13, 2010

Location % Coarse % Sand % Fines Median Grain Size

(mm) USCS Designation Composite 6.0 82.2 11.8 0.3 Silty sand SS-2 12.7 74.9 12.4 0.6 Silty sand SS-3 0 78.3 21.7 0.2 Silty sand SS-7 27.5 56.2 16.3 1.15 Poorly graded sand

The fluvial geomorphology study in March 2010 recommended that the stream bed material consist of material with a minimum mean grain size of 0.9 mm. However, after review of the sieve analyses, the project fluvial geomorphologist concluded that the mean grain size at this site would also be appropriate for reuse in the stream channel proposed for this site.

Soils at the site generally meet the textural profile of a loamy or silty sand. No suspect fill materials (i.e. construction materials, broken glass, or other evidence of solid waste) were observed in soil on site, nor was any evidence of improper disposal of petroleum or hazardous material observed. Therefore, no regulatory disposal requirements (solid waste disposal requirements, hazardous materials regulation, etc.) are anticipated for site soil.

Attachments: Figure 1 – Soil Boring Location Plan Boring Logs

SHORTWAY DRIVE

UNDEVELOPED - 40' WIDE PUBLIC

PERPETUAL EASEMENT AREA

SHORTWAY DRIVE

UNDEVELOPED - 40' WIDE PUBLIC

PERPETUAL EASEMENT AREA

1.

M S

V

IE

W

U C

S : DATENo. BY

REVISIONS

DESCRIPTION

DATE

CHIEF DESIGNER:

REVIEWED BY:

PROJ. MANAGER:

LM

A

N

C

TB

VERT.:

HORZ.:

VERT.:

HORZ.:

SCALE:

DATUM:

DATE:

PROJ. No.:

Fi le

P at h:

J

:\D W

G \P

\1

0\ B

\C iv il\

P la n\

B

_E

W D

.d w g, L ay ou t:

x1

7- L_

R I7

2- S

M -M

O N

O

Th u, A pr

2,

- 4

:2

P M

U se r:

dl af ra nc e

NATURAL RESOURCES CONSERVATION SERVICE

SOIL SAMPLE LOCATIONS

JANET DRIVE FLOODPLAIN RESTORATION

WEST WARWICK RHODE ISLAND

20051040.B38

APRIL 2010

FIGURE 1

1" = 30'

FUSS & O'NEILL

Disciplines to Deliver