Determination of Seismic Elastic Response Spectrum
1. Input of the soil parameter:
Note: The site period is determined based on input of either the standard penetration test (NSPT{blows/300mm}) or the shear wave velocity (Vs,30) or the undrained shear strength (cu) in the upper 30m soil depth. Please, select the preferred input parameter from the option below:
D1, D2 ..D20 refer to column nos. 1-20 for inputting the thicknesses (m) of the soil layers of each borehole.
P1, P2 ..P20 refer to column nos. 1-20 for inputting the soil parameter which is either NSPT{blows/300mm} or Vs,30 or cu.
Table can be filled manually or by performing copy (CTRL+C) and paste (CTRL+V) of data from Excel spreadsheet.
If all entries to a particular “thickness” column have been left blank, the program will automatically fill in a default thickness of 1.5 m.
SPT-N values that have been taken from the testing of very stiff materials have to be corrected to the penetration depth of 300 mm. For example, an SPT-N value of 50 for the penetration depth of 100 mm should be corrected to 150.
Avoid including borelogs taken from a very large area featuring systematic spatial variation in geology within the area. The maximum number of borelogs to be included into one analysis is capped at 20.
A borelog indicating exceptional conditions compared to other borelogs taken from the same site is a call for undertaking further investigations to determine the spatial extent of the anomalies. More borelogs need to be taken to map out the site geology to determine the subsoil profile.
SPT-N Values and Soil Description
Sand (BS5930: 1999)
Clay (Terzaghi et al., 1996)
Description
SPT-N Value (blows/300 mm)
Description
SPT-N Value (blows/300 mm)
Very Loose
0-4
Very Soft
0-2
Loose
4-10
Soft
2-4
Medium
10-30
Firm
4-8
Dense
30-50
Stiff
8-15
Very Dense
>50
Very Stiff
15-30
-
-
Hard
>30
Type of soil parameter (P):
Borehole 1
Borehole 2
Borehole 3
Borehole 4
Borehole 5
Borehole 6
Borehole 7
Borehole 8
Borehole 9
Borehole 10
Borehole 11
Borehole 12
Borehole 13
Borehole 14
Borehole 15
Borehole 16
Borehole 17
Borehole 18
Borehole 19
Borehole 20
D1
P1
D2
P2
D3
P3
D4
P4
D5
P5
D6
P6
D7
P7
D8
P8
D9
P9
D10
P10
D11
P11
D12
P12
D13
P13
D14
P14
D15
P15
D16
P16
D17
P17
D18
P18
D19
P19
D20
P20
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
P-value for the remaining depth:
2. Results: Soil Characteristics and Elastic Response Spectrum
I. Soil Profile:
Figure 1: Soil Profile
Table 1: Thickness (m) and Soil Parameter (P) of Soil Layers of Different Boreholes Note: D1, D2.. and P1, P2.. columns in the table are thickness and selected soil parameter of soil layers of the respective boreholes.
II. Most Onerous Groundtype:
The average soil parameter (P) for each borehole, and the average site period is calculated using Eqs (1) and (2), respectively. The soil parameter and period for the whole site is the values calculated for the most onerous borehole.
$$ {P = \frac{\sum^n_{i=1} {d_i}}{ \sum^n_{i=1} \dfrac{d_i}{P_{i}} }}\tag{1}$$
$$ {T_{site} = 4 \sum^n_{i=1} \frac{ {d_i}}{ {V_{s,i}} }}\tag{2}$$
Where:
di = thickness of each layer 'i',
n = number of soil layers,
Pi = soil parameter of soil layer 'i' Vs,i = shear wave velocity of soil layer 'i' (which is calculated by correlating the input soil parameter to shear wave velocity as provided in Table 1 of the BC-3:2013).
Table 2: Average soil parameter for each borehole and Ground Type (based on most onerous borehole).
Borehole No.
Site Classification (most onerous)
III. Seismic Elastic Response Spectrum:
a. Response Spectral Acceleration (RSA) Diagram:
Figure 2: RSA Diagram
b. Acceleration Displacement Response Spectrum (ADRS) Diagram:
Figure 3: ADRS Diagram
Table 3: Response Spectral Acceleration (RSA) and Response Spectral Displacement (RSD) of soil.
T (sec)
RSA-soil (g)
RSD-soil (mm)
3. References:
1.Building and Construction Standards Committee (2013). Guidebook for Design of Buildings in Singapore to Requirements in SS EN 1998-1.Building and Construction Standards Committee, Singapore.
2. European Commitee for Standardization (2004). EN 1998-1:2004 Eurocode 8: Design of structures for earthquake resistance - Part 1 : General rules, seismic actions and rules for buildings.
3. BS 5930 (1999).Code of Practice for Site Investigations. British Standards Institution.
4. Terzaghi, K., Peck, R. B., & Mesri, G. (1996). Soil mechanics in engineering practice. John Wiley & Sons.
Disclaimer
The authors assume no responsibility for any injury, damage, liability, negligence and/or otherwise to any individual or property from the use or application of any of the methods, products, instructions, or ideas contained in the material herein.