Environmental Engineering Reference
In-Depth Information
Rensselaer Polytechnic
Institute, Troy, New York
(El. 233 ft, MSL)
Hartford,
Connecticut
Cleveland,
Ohio
mft
N
N
N
17
Brown silty clayey
sand
Soft gray varved
silty clay
Fill - brown silty
sand
Stiff brown varved
clay and silt
11
2
14
6
Stiff gray clayey
silt
2
Firm gray varved clay
and silt
9
20
Soft red-brown
varved silt and
clay
4
LL = 58 (CL)
PL = 33
w
n
= 52
11
Stiff gray varved
clay and silt
2
2
LL = 67 (CL)
PL = 39
w
n
= 57
12
10
γ
d
= 72 pcf
2
2
9
- with seams c - f
sand
40
Till - red-brown
silty, clayey,
sandy, gravel
70
Stiff gray clay,
occasional silt varves
11
LL = 33
PL = 9
w
n
= 25
Medium compacted gray
silty fine sand,
occasional clay seams
15
20
60
13
20
10
15
- becoming firm
80
6
74/6 in
Weathered black
shale (shale fragments
in clayey silt matrix)
5
42
Hardpan
100%
Hard black shale
30
100
(a)
(b)
(c)
120
FIGURE 7.96
Logs of typical test borings in glaciolacustrine deposits. Legend: N, standard penetration test values;
—
,
groundwater level; %, percent core recovery; LL, liquid limit (on clay varves) (%); PI, plasticity index;
w
n
,
natural water content (%);
γ
d, unit dry weight. (Courtesy of Joseph S. Ward and Associates.)
long piles or surcharging. Because of the rootmat and other organic soils, proper floor sup-
port is always a major concern in the area when deep foundations are required.
New York City, Glacial Lake Flushing:
A geologic section across upper mid-Manhattan at
113th Street is given in
Figure 7.98.
It shows the irregular bedrock surface excavated by the
glacier, the variable thickness of the varved clays, and overlying strata of sand, organic silt,
and miscellaneous fill. The sand is stratified and probably represents late glacial outwash,
whereas the organic silt, common to the New York City area, is a recent estuarine deposit.
In studies of varved clays where an accurate knowledge of their properties is required, it is
necessary to count the various varves of sand, silt, and clay, to measure their cumulative thick-
ness, and, if possible, to perform laboratory tests on representative samples of the silt and clay
varves, since their characteristics are distinctly different. Testing a mixture of varves will pro-
duce nonrepresentative results. Where varves are very thin, discriminating testing is not fea-
sible. Parsons (1976) has summarized the principal properties of the New York City varved
clays as given in
Table 7.13.
A plasticity chart for silt and clay varves is given in
Figure 7.99.
Parsons (1976) notes that buildings ranging from 7 to 21 floors in height have been sup-
ported on a number of foundation types, including spread footings, mats, and shallow
tapered piles, with all types apparently bearing in the upper sand stratum. Settlement
observations have been carried out on 70 representative buildings through the construction
