The table below summarizes the results of subsurface exploration. Determine the site class.

Question

Layer number	Depth below ground surface (m)	Description	Undrained Shear Strength	USCS Group Symbol & Plasticity index
1	0–5	Desiccated clay, highly over-consolidated	150 kPa	CH PI = 60
2	5–15	Slightly over-consolidated clay	100 kPa	CH PI = 65
3	15–20	Normally consolidated clay	60 kPa	CH PI = 35
4	20–30	Till and rock	N/A	N/A

Accepted Answer

The procedure is as follows:
Step 1: Check site class F, which must have one or more of the following characteristics:
a. Soils vulnerable to potential failure or collapse under seismic loading such as liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented soils.
b. Peats and/or highly organic clays (H > 10 feet of peat and/or highly organic clay where H = thickness of soil).
c. Very high plasticity clays (H > 25 feet with plasticity index PI > 75).
d. Very thick soft/medium stiff clays (H > 120 feet) with [latex]s_{u}[/latex] < 1000 psf.
None of these requirements are met; hence, it is not a site class F.

Step 2: Check site class E, which must have more than 10 feet of soil having the following characteristics: plasticity index PI > 20, moisture content w ≥ 40%, and undrained shear strength [latex]s_{u}[/latex] < 500 psf. All three layers exceed [latex]s_{u}[/latex] of 500 psf (24 kPa), so this condition is not met.
Step 3: Site class will be C, D, or E, depending on the undrained shear strength. Using Eq. (14.1):

[latex]s_{u}=d_{c} /\left[\Sigma\left(d_{i} / s_{u i} ight) ight]=(20) /(5 / 150+10 / 100+5 / 60)=92 kPa ext { or } 1900 psf[/latex]

From Table 14.11 the answer is site class D—stiff soil profile.

TABLE 14.11 Site Class Definitions
Site class	Soil profile name	Average properties in top 100 ft[latex] {}^{a}[/latex]
Site class	Soil profile name	Standard Shear wave velocity, [latex]v _{s}[/latex], (ft/s)	Soil undrained penetration resistance, [latex]\left(N_{1} ight)_{60}[/latex]	shear strength, [latex]s_{u}[/latex], (psf)
A	Hard rock	[latex]v _{s}[/latex] > 5000	N/A	N/A
B	Rock	2500 < [latex]v _{s}[/latex] ≤5000	N/A	N/A
C	Very dense soil and soft rock	1200 < [latex]v _{s}[/latex] ≤ 2500	[latex]\left(N_{1} ight)_{60}[/latex] > 50	[latex]s_{u}[/latex] > 2000
D	Stiff soil	600 ≤ [latex]v _{s}[/latex] ≤ 1200	15 ≤ [latex]\left(N_{1} ight)_{60}[/latex] ≤ 50	1000 ≤ [latex]s_{u}[/latex] ≤ 2000
E	Soft soil	[latex]v _{s}[/latex] < 600	[latex]\left(N_{1} ight)_{60}[/latex] < 15	[latex]s_{u}[/latex] < 1000
E	Any profile with more than 10 feet of soil having the following characteristics: plasticity index PI > 20, moisture content w ≥ 40%, and undrained shear strength [latex]s_{u}[/latex] < 500 psf
F	Any profile containing soils having one or more of the following characteristics: 1. Soils vulnerable to potential failure or collapse under seismic loading such as liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented soils. 2. Peats and/or highly organic clays (H > 10 feet of peat and/or highly organic clay where H = thickness of soil). 3. Very high plasticity clays (H > 25 feet with plasticity index PI > 75). 4. Very thick soft/medium stiff clays (H > 120 feet) with [latex]s_{u}[/latex] < 1000 psf.
Notes: a – see Chap. 20 of ASCE Standard 7-10 (2010) for further details. For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m², 1 pound per square foot = 0.0479 kPa. N/A = Not applicable. ASCE Standard 7-10 recommends use of uncorrected N-values instead of [latex]\left(N_{1} ight)_{60}[/latex]. Sources: Table 20.3-1 and Chap. 20 of ASCE Standard 7-10 Minimum Design Loads for Buildings and Other Structures (2010).

Question 14.4: The table below summarizes the results of subsurface explora...

Related Answered Questions

The results of subsurface exploration and laboratory testing indicate a site class C. The structural engineer has reported that the preliminary category for the proposed structure is Seismic Design Category D. The engineering geologist has determined that the probabilistic MCEG peak ground ...

Verified Answer:

Determine the site class for the subsoil profile shown in Fig. 11.21. Assume the site will be subjected to strong ground shaking during the design earthquake. ...

Verified Answer:

Solve Prob. 14.4 for the condition of Layer Nos. 3 and 4 being sand with a (N1)60 = 12 for Layer 3 and (N1)60 = 8 for Layer 4. ...

Verified Answer:

Solve Prob. 14.4 for the condition of Layer No. 4 being sand with (N1)60 = 55. ...

Verified Answer:

For Prob. 6.12, which includes Fig. 6.13, determine the site class. ...

Verified Answer:

Solve Prob. 14.1 assuming the retaining wall is restrained. Compare this answer to the value based on the equation ko = 1 – sin Φ. ...

Verified Answer:

Verified Answer:

For the retaining wall shown in Fig. 10.5 (i.e., the 20-ft-high gravity retaining wall), determine the values of PH and PV using the active earth pressure listed in Table 14.10. Compare these answers with those from Fig. 10.5. ...

Verified Answer: