ACTIVE METHOD FOR HILLSIDE CONSTRUCTION OF 1996

M. Falamaki (Dr.)

B Sc, M Sc, Ph D, MIEAust, CPEng – NPER (Structural Engineer), MASCE, Certifying Engineer in NT,

Registered Professional Engineer (R.P.E.Q) in QLD, Builder’s License Number: 79637C,

Building Consultancy Licence Number: BC926

ABSTRACT In 1985 the Australian Geomechanics Society (AGS) in its publication: Australian Geomechanics News No. 10 on 1985, in

an article prepared by Walker et al method of 1985 introduced the concept of risk into hillside residential development

through a method called passive method for hillside construction of 1985 that was basically a weather related approach.

The endorsement of this method by AGS was their first serious mistake.

This was the beginning of the introduction of the concept of risk into the residential development (through the building

approval process) within Australia. It was then rapidly accepted and adopted by Local Governments within critical

metropolitan areas of Wollongong, Sydney and Melbourne.

The Active Method for Hillside Construction that is not a weather related approach and is based on engineering

principals was developed in 1996; while prior to 1996, practitioners were using passive method for hillside construction

of 1985

It was four long years after the introduction of the Active Method for Hillside Construction of 1996 that on March 2000

AGS published an article in condemnation of the passive method of hillside construction of 1985 and requested the

practitioners to cease using that method, a method that was endorsed by AGS for about 15 years.

The second serious mistake of AGS is the presentation of the so called Good Hillside Practice Method in its 2007

publication.

For the reasons that were listed in this article the Good Hillside Practice Method presented by AGS in its 2007

publication is not only potentially unsafe but also does not even comply with basic engineering principals.

It is therefore recommended that the practitioners cease using the so called Good Hillside Practice Method and adopt the

Active Method for Hillside Construction of 1996 for their day to day practice.

The Active Method for Hillside Construction of 1996 which is based on engineering principals could be utilised for the

construction on sites with steep slopes as well as in most properties with the alleged risk of landslide.

This approach will also considerably reduce the adverse effects of Councils involvements on the affairs of the land

owners of properties located on steep slopes.

The houses constructed using the Active Method not only are stable but they also stabilise their surrounding areas by not

allowing the soil to mobilise under adverse conditions.

1 BACKGROUND

1.1 THE FIRST SERIOUS MISTAKE OF AGS

In or about 1985 the Australian Geomechanics Society (AGS) in an article prepared by Walker et al method of 1985

introduced the concept of risk into hillside residential development. The endorsement of this method was the first serious

mistake of AGS.

This was the introduction of the concept of risk into the residential development (through the building approval process)

within Australia. It was then rapidly accepted and adopted by Local Governments within critical metropolitan areas of

Wollongong, Sydney and Melbourne.

Regarding the instability issue, much instability is rainfall related, and landslide activity has increased through clearing of

vegetation.

On the other hand, short intense rainfall events tend to produce surface erosion and debris flow (the land wash issue), as

occurred in a number locations in Wollongong during the heavy rainfall of the 17th

of August 1998.

In terms of awareness, most of the Australian populace would be familiar with the landslide in the Kosciuzko ski resort

village of Thredbo in 1997 which demolished two accommodation lodges and resulted in the death of 18 people. The

landslide involved the rapid collapse of a fill embankment that had previously supported the Alpine Way above the

village.

Walker et al method of 1985 introduced the passive method for hillside construction of 1985 which was basically a

weather related approach. The serious problem with this approach was that this system would not be safe if the site is

exposed to excessive rainfall.

It is common practice to keep water away from the building; and this could be achieved by designing a proper

drainage system around the building (for one in 100 years rainfall) to stop the penetration of water to underneath the

building the consequence of which would be that the shale or the clay type materials below the building becomes

liquefied and consequently slippery allowing the building slips over the bedrock and downhill.

It is now in public records that the green house effect causes rainfalls much heavier than one in 100 years to take place

(such as one in 300 years that took place in Wollongong on the 17th

of August 1998). The heavy rainfall causes that

the drainage system that was designed for one in 100 rainfall becomes useless; allowing for the penetration of water

under the building, then allowing for the liquefaction of the soil bellow the building and consequently the slipping of

building downhill.

It might be the case that if practitioners were following a method similar to the Active Method for Hillside

Construction of 1996 disasters such as the Thredbo landslide of 1997 would not take place. It might also be the case

that some of the Thredbo structures were

even built prior to 1985, and their construction probably did not comply even with the passive method for hillside

construction of 1985.

In short, the Thredbo disaster of 1997 in which 18 people died might be a consequence of the above-mentioned

endorsement of AGS; and it was shortly after this disaster that AGS in its publication of March 2000 abandoned the

above-mentioned Walker et al method of 1985 and recommended the practitioners to cease using the same approach

that it endorsed for 15 years.

1.2 THE SECOND SERIOUS MISTAKE OF AGS

The Active Method for Hillside Construction is not weather related approach and is based on engineering principals

was developed in 1996. Prior to 1996, practitioners were using passive method for hillside construction of 1985

It was four years after the introduction of the Active Method for Hillside Construction of 1996 that on March 2000

AGS published an article in condemnation of the passive method of hillside construction of 1985 and requested the

practitioners to cease using that method, a method that was endorsed by AGS for about 15 years.

The second serious mistake of AGS that has not yet acknowledged by them is their endorsement of the so called Good

Hillside Practice Method in their 2007 publication.

For the reasons that were listed in the following paragraphs the so called Good Hillside Practice Method presented by

AGS in its 2007 publication is not only potentially unsafe but also does not even comply with basic engineering

principals.

It is therefore recommended that the practitioners cease using the above-mentioned Good Hillside Practice Method

and adopt the Active Method for Hillside Construction of 1996 for their day to day practice.

2 DETAILS OF THE GOOD HILLSIDE PRACTICE METHOD

AGS in its publication of 2007 put a number of recommendations under the heading Good Hillside Practice Method.

These unsafe recommendations were summarized in Figure 1.

An example of the above-mentioned unsafe recommendations of AGS that were summarized in their Figure 1 is

explained in the following lines:

Figure 1 that was extracted from the AGS publication of 2007 shows a building sitting on a number of piles over the

hillside; while all these piles were socketed into the bedrock only over a short length (see Figure 1).

If the soil mobilises and starts to slide downhill the huge lateral load imposed on the building caused by the movement

of the soil would then be transferred (through the floor diaphragm of the building) to the slender piles bellow, causing

them to rotate and (as there is nothing to stop their rotation) causes them to collapse and then the destabilisation of the

dwelling is a likely outcome.

Also, in terms of engineering principals, the building should be designed in such a way that under any loading

condition all the actions and reactions on the building remain in equilibrium, while as illustrated in Figure 1, there is

no resistance to the overturning moment that is caused by the soil movement. This means that the equilibrium of

moments is not satisfied and consequently, the use of Good Hillside Practice Method is in fact a violation of

engineering principals.

In other words, the Good Hillside Practice Method presented by AGS in its 2007 publication not only is potentially

unsafe but also does not even comply with basic engineering principals.

Fig

ure

1 -

Th

e G

oo

d H

ills

ide

Pra

ctic

e M

eth

od

pre

sen

ted

by

AG

S i

n i

ts 2

00

7

3 DETAILS OF THE ACTIVE METHOD FOR HILLSIDE

CONSTRUCTION OF 1996

As was mentioned previously, for the reasons that were listed in this technical paper the Good Hillside

Practice Method presented by AGS in its 2007 publication is not only potentially unsafe but also does

not comply with basic engineering principals.

It is therefore recommended that the practitioners cease using the so called Good Hillside Practice

Method and adopt the Active Method for Hillside Construction of 1996 for their day to day practice.

The Active Method for Hillside Construction of 1996 which is based on engineering principals could be

utilised for the construction on sites with steep slopes as well as in most properties with the alleged risk

of landslide.

This approach will also considerably reduce the adverse effects of Council’s involvements on the affairs

of the land owners of properties located on steep slopes.

In Active Method for Hillside Construction of 1996 the structural system that is developed is a workable

and economic system in which both the lateral and vertical loads are transferred down to the intact

bedrock below the building by means of various structural building elements such as walls, floor

diaphragms, retaining walls, bracing members, beams and columns. The structure itself acts in such a

way that the overturning moment that is caused by the lateral loads is resisted by the walls and bracing

structure built within the building while the uplift forces that are caused by the overturning is restrained

by anchorage of the footings in the rock. This is illustrated in Figure 2.

Because of the nature of the design of the houses built on the basis of the Active Method for Hillside

Construction of 1996 those houses are not only stable but they also stabilise their surrounding areas by

not allowing the soil to mobilise under adverse conditions.

The Active Method for Hillside Construction of 1996 is in line with all the relevant Australian standards,

as well as the building code of Australia.

Prior to 1996, practitioners were using passive method for hillside construction of 1985 that was a

weather related approach; while contrary to this the Active Method for Hillside Construction of 1996 is

independent of weather related issues.

Since 1985 and up to 2000, slope instability analysis was based on the passive method for hillside

construction of 1985 that was endorsed by AGS; then three years after the Thredbo landslide of 1997

that is on March 2000 AGS officially announced that the passive method for hillside construction of 1985

was deficient, and recommended that practitioners and regulators cease using that method.

In other words, it was four long years after the introduction of the Active Method for Hillside

Construction of 1996 that AGS requested the practitioners to cease using the passive method for hillside

construction of 1985, a method that was endorsed by AGS for about 15 years.

It is important to note that the passive method for hillside construction of 1985 relies on the amount of

rainfall that is now very hard to predict especially when we are now exposed to the side effects of the

green house effects; and this by itself makes the passive method unsafe.

The links listed below are the links to two DVD that provide some general details of a typical excavation

at 12 Arter Avenue Figtree, construction of footings of the building, socketing the foundations of the

building down into intact tightly jointed rock as well as part of the building works performed:

http://www.youtube.com/watch?v=56fhKaixruM,

http://www.youtube.com/watch?v=Ldhv4p8RI7c

Dec

kin

g t

o b

e p

lace

d o

ver

Vo

id f

or

safe

ty a

nd

uti

liza

tion

.

Fig

ure

2:

A t

yp

ical

cro

ss s

ecti

on

of

the

stee

l fr

ame

of

a re

sid

enti

al b

uil

din

g e

rect

ed

on

th

e b

asis

of

Act

ive

Met

ho

d f

or

Hil

lsid

e C

on

stru

ctio

n.

4 CONCLUSIONS

The existing evidence suggest that Active Method for Hillside Construction of 1996 which is based on

engineering principals is a state of the art, to the effect that the design method that was employed by this

approach could be applied with confidence.

The unique structural system presented in this method is a workable and economic system in which both

the lateral and vertical loads transfer down to the intact bedrock below the building through various

building elements such as walls, floor diaphragms, retaining walls, bracings, beams and columns.

It was four years after the introduction of the Active Method for Hillside Construction of 1996 that on

March 2000 AGS (that is, after realising the dangers of its uneducated endorsement of the very unsafe

passive method of hillside construction of 1985 for a period of 15 years) it requested the practitioners to

cease using the previously endorsed passive method.

This was a serious mistake of AGS; however, its mistakes did not stop in 2000. That is, in year 2007 it

committed a second serious mistake. The second mistake of AGS that has not yet been acknowledged by

them is their endorsement of the so called Good Hillside Practice Method in their 2007 publication.

For the reasons listed in this technical paper it is requested (by the author of this paper) that practitioner

urgently cease using the very unsafe Good Hillside Practice Method presented by AGS in its 2007 and

adopt the Active Method for Hillside Construction of 1996 for their day to day practice.

The Active Method for Hillside Construction of 1996 could be utilised for the construction on sites with

steep slopes and in most properties with the alleged risk of landslide.

This approach will also considerably reduce the adverse effects of Councils involvements on the affairs of

the land owners of properties located on steep slopes.

The houses constructed using the Active Method not only are stable but they also stabilize their

surrounding areas, not giving the soil an opportunity to mobilize under adverse conditions.

M. Falamaki (Dr.) B Sc, M Sc, Ph D, MIEAust, CPEng – NPER (Structural Engineer), MASCE, Certifying Engineer in NT, Registered Professional

Engineer (R.P.E.Q) in QLD, Builder’s License Number: 79637C, Building Consultancy Licence Number: BC926

drfalamaki@gmail.com

M: 0423 294 999