Program AU1c – AS1170.4 response spectrum generator (Imai-Tonouchi)

QUAKE ADVICE_Seismic Design Response Spectrum Report

Determination of Seismic Design Response Spectrum Based on Imai & Tonouchi Model

1. Input Parameters:

'Imai & Tonouchi Model' requires information of the thickness, SPT-N and soil type, and soil age for soil layers in each Borehole.

I. Hazard Design Factor (Z) in term of 'g':
II. Annual Probability of Exceedance and Probability Factor (k_p):

III. Thickness, SPT-N, Soil Type, and Soil Age of Soil Layers in each Borehole:

Note:

Table can be filled manually or by performing copy (CTRL+C) and paste (CTRL+V) of data from Excel spreadsheet.
D1, D2 ..D20 refer to column nos. 1-20 for inputting the thicknesses (m) of the soil layers whereas N1, N2 ..N20 refer to the input of the SPT-N (blows/300 mm) values.
Please enter soil types as specified in AS 1726: 'GP', 'GW', 'GM', 'GC', 'SP', 'SW', 'SM', 'SC', 'ML', 'MH', 'CL', 'CI', 'CH', correctly for each layer of soil in the 'Soil Type' column of each borehole.
Please enter the soil ages in the form of initials 'Q' for Quaternary, 'H' for Holocene, and 'P' for Plesitocene for each layer of soil correctly in the 'Soil Age' column of each borehole. If soil age is not known, specify it as 'Q'.
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 too many borelogs from too closely spaced boreholes into one analysis as doing this would not necessarily result in obtaining an accurate estimate of the site period.
Must also 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.
This program which is based on making use of blow counts taken from standard penetration tests (SPT) as input information cannot be used to identify Class Ae (hard rock) sites nor Class Be (rock) sites both of which have much higher shear wave velocity than is measurable by SPT. Sites class Ae, Be and Ce are taken to be site class Ce by default when this program is used.
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. There is an option to employ geophones to take site natural period on a few locations to help understand the subsoil conditions better. Alternatively, take the more onerous site class for design purposes. With the construction of an important structure in onerous soil conditions, it is worth considering the option of undertaking a more detailed investigation to generate a site-specific response spectrum to override the code specified response spectrum model.

SPT-N Values and Soil Description
Very Loose	less than 6	Very Soft	0-2
Loose Dry	6-10	Soft	2-5
Medium Dense	10-30	Firm	5-10
Dense	30-50	Stiff	10-20
Very Dense	>50	Very Stiff	20-40
Gravel	>30	Hard	>40
¹AS1170.4:2007. ²BG Look, 2014.

	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	N1	Soil Type	Soil Age	D2	N2	Soil Type	Soil Age	D3	N3	Soil Type	Soil Age	D4	N4	Soil Type	Soil Age	D5	N5	Soil Type	Soil Age	D6	N6	Soil Type	Soil Age	D7	N7	Soil Type	Soil Age	D8	N8	Soil Type	Soil Age	D9	N9	Soil Type	Soil Age	D10	N10	Soil Type	Soil Age	D11	N11	Soil Type	Soil Age	D12	N12	Soil Type	Soil Age	D13	N13	Soil Type	Soil Age	D14	N14	Soil Type	Soil Age	D15	N15	Soil Type	Soil Age	D16	N16	Soil Type	Soil Age	D17	N17	Soil Type	Soil Age	D18	N18	Soil Type	Soil Age	D19	N19	Soil Type	Soil Age	D20	N20	Soil Type	Soil Age
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

IV. Energy Ratio (N₆₀/N_measured):

Note: Energy ratio is the conversion factor for converting the measured N values to corrected N values corresponding to 60% energy efficiency. A value of 1 is suggested for the case of Australia (Sabatini et al., 2002).

2. Results: Soil Characteristics and Design Response Spectrum

I. Soil Profile with SPT-N Value:

Figure 1: SPT-N Profile

II. Average Shear Wave Velocity (V_s) and Natural Time Period (T_s) of Soil:

The following equations given by 'Imai & Tonouchi Model' are used to calculate shear wave velocity of each soil layer 'i'.

For gravel (GP, GW, GM, GC) $$ {Holocene: SWV_i = 72.5 \times N_{60_i}^{0.35}}\tag{1a}$$ $$ {Plesitocene: SWV_i = 132.4 \times N_{60_i}^{0.25}}\tag{1b}$$ For sand (SP, SW, SM, SC) $$ {Holocene: SWV_i = 85.0 \times N_{60_i}^{0.29}}\tag{1c}$$ $$ {Plesitocene: SWV_i = 106.6 \times N_{60_i}^{0.29}}\tag{1d}$$ For silt and clay (ML, MH, CL, CI, CH) $$ {Holocene: SWV_i = 103.8 \times N_{60_i}^{0.27}}\tag{1e}$$ $$ {Plesitocene: SWV_i = 124.4 \times N_{60_i}^{0.26}}\tag{1f}$$
$$ {V_s = \frac{H_s}{ \sum^n_{i=1} \dfrac{d_i}{SWV_{i}} }}\tag{2}$$ $$ {T_s = \frac{4 \times H_s}{V_s}}\tag{3}$$ Where:
H_s = total depth of soil,
n = number of soil layers,
d_i = thickness of soil layer 'i',
N_{60_i} = corrected SPT-N value (corresponding to 60% energy efficiency) of soil layer 'i'

Borehole No.	Average Shear Wave Velocity (m/sec)	Site Period (sec)

III. Seismic Design Response Spectrum:

a. Response Spectral Acceleration (RSA) and Acceleration Displacement Response Spectrum (ADRS) Diagram:

Figure 2: RSA Diagram

Figure 3: ADRS Diagram

T (sec)	RSA-soil (g)	RSD-soil (mm)

3. References:

Standard, A. (2007). AS 1170.4-2007 (Amdt 2018).Structural Design Actions, Part 4: Earthquake Actions in Australia..

Look, B. G. (2014). Handbook of geotechnical investigation and design tables. CRC Press.

Sabatini, P.J., Bachus, R. C., Mayne, P. W., Schneider, James A., Zettler, T. E. (2002). Geotechnical Engineering Circular No. 5: Evaluation of Soil and Rock Properties, Report no: FHWA IF-02-034. Federal Highway Administration, Washington, DC United States.

Wair, B. R., DeJong, J. T., & Shantz, T. (2012). Guidelines for estimation of shear wave velocity profiles. Pacific Earthquake Engineering Research Center.

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.

SPT-N Values and Soil Description
Sand¹		Clay²
Description	SPT-N Value (blows/300 mm)	Description	SPT-N Value (blows/300 mm)
Very Loose	less than 6	Very Soft	0-2
Loose Dry	6-10	Soft	2-5
Medium Dense	10-30	Firm	5-10
Dense	30-50	Stiff	10-20
Very Dense	>50	Very Stiff	20-40
Gravel	>30	Hard	>40
¹AS1170.4:2007. ²BG Look, 2014.

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Program AU1c – AS1170.4 response spectrum generator (Imai-Tonouchi)