Contents
ABBREVIATIONS ... IV GLOSSARY ... V 1 INTRODUCTION ... 1-1
1.1 GEOHAZARDS IN THE PHILIPPINES ... 1-1 1.2 THE NEED FOR A PRELIMINARY GEOHAZARD ASSESSMENT ... 1-1 1.3 MITIGATION OF GEOHAZARDS ... 1-2
2 GEOHAZARDS IN THE PHILIPPINES ... 2-1
2.1 INTRODUCTION ... 2-1 2.2 SEISMICITY ... 2-1 2.2.1 The Nature of Seismicity ... 2-1 2.2.2 Faulting ... 2-4 2.2.3 The Preliminary GeoHazard Assessment ... 2-4 2.3 LIQUEFIABLE SOILS ... 2-5
2.3.1 The Nature of Liquefaction ... 2-5 2.3.2 Preliminary GeoHazard Assessment ... 2-6 2.4 VOLCANIC ACTIVITY ... 2-8
2.4.1 The Nature of the GeoHazard ... 2-8 2.4.2 Preliminary GeoHazard Assessment ... 2-8 2.5 UNSTABLE SLOPES ... 2-10
2.5.1 Introduction ... 2-10 2.5.2 Preliminary GeoHazard Assessment ... 2-11 2.6 KARST ... 2-12
2.6.1 Preliminary GeoHazard Assessment ... 2-13 2.7 MINING ACTIVITIES ... 2-13
2.7.1 Preliminary GeoHazard Assessment ... 2-13 2.8 PROBLEM SOILS ... 2-14
2.8.1 Expansive soils ... 2-14 2.8.2 Fills... 2-16 2.8.3 High Compressibility Soils ... 2-17 2.8.4 Contaminated Soils ... 2-18 2.9 GROUNDWATER ... 2-20 2.10 FLOODING,SCOUR AND EROSION ... 2-21 2.10.1 Preliminary GeoHazard Assessment ... 2-21 2.11 TSUNAMIS, SEICHES, STORM SURGES ... 2-22
2.11.1 Preliminary GeoHazard Assessment ... 2-22 2.12 GEOTHERMAL ACTIVITY ... 2-22
2.12.1 Preliminary GeoHazard Assessment ... 2-23 2.13 EFFECTS OF CLIMATE CHANGE ... 2-24
3 PRELIMINARY GEOHAZARD ASSESSMENT ... 3-1
3.1 REQUIRED EXPERTISE ... 3-1 3.2 SCOPE OF PRELIMINARY GEOHAZARD ASSESSMENT ... 3-1 3.2.1 Desk Study ... 3-1 3.2.2 Reconnaissance ... 3-2 3.3 PRELIMINARY GEOHAZARD ASSESSMENT REPORT ... 3-2 3.4 FURTHER ACTION... 3-3
Volumes
Volume 1 Introduction and Overview
Volume 2A GeoHazard Assessment
Volume 2B Engineering Surveys
Volume 2C Geological and Geotechnical Investigations
Volume 3 Water Engineering Projects
Volume 4 Highway Design
Volume 5 Bridge Design
Volume 6 Public Buildings and Other Related Structures
Annexes
Annex A Seismicity
Annex B Liquefiable Soils
Annex C Volcanic Activity
Annex D Unstable Slopes and Landslides
Annex E Problem Soils: Expansive Soils
Annex F Fumaroles and Hydrothermal Explosion
Annex G Sources of GeoHazard Assessment Data
Tables and Figures
Table 2-1 Landslide Hazard (after PTCPD, 2012) ... 2-11 Table 2-2 Properties of Clay Minerals ... 2-14 Table 2-3 Main Contaminative Industries (Environment Agency) ... 2-19 Table 2-4 Contaminated Ground Risk to Infrastructure ... 2-20 Table 2-5 Relation of Climate Change to GeoHazard ... 2-25 Figure 2-1 A Collapsed Building during the July 16, 1990 Northern Luzon Earthquake ... 2-2 Figure 2-2 Structural Map of the Philippines ... 2-3 Figure 2-3 Map showing Peak Horizontal Acceleration Values for Rock... 2-5 Figure 2-4 Cyclic Mobility Resulting in Spreading of Bridge Foundations, Niigata 1964 ... 2-6 Figure 2-5 Liquefaction Map ... 2-7 Figure 2-6 Active and Potentially Active Volcanoes ... 2-9 Figure 2-7 PHIVOLCS Description of Volcanoes ... 2-10 Figure 2-8 Landslide Hazard Map ... 2-11 Figure 2-9 Typical Karst Terrain ... 2-12 Figure 2-10 Moisture Variations beneath Roads ... 2-15 Figure 2-11 Cracking Observed in a Residential Development ... 2-15 Figure 2-12 Spring Lines ... 2-21
Abbreviations
Acronym Definition
ADB Asian Development Bank
AGS Association of Geotechnical and Geoenvironmental Specialists ASEP Association of Structural Engineers of the Philippines
BSDS Bridges Seismic Design Specifications (by DPWH) CDF Controlled Density Fill
CNC Certificate of Non-Coverage CPT Cone Penetration Test CRR Cyclic Resistance Ratio CSR Cyclic Stress Ratio
DENR Department of Environment and Natural Resources DGCS Design Guidelines, Criteria and Standards DPWH Department of Public Works and Highways ECC Environmental Clearance Certificate
EGGA Engineering Geology and GeoHazard Assessment FHWA Federal Highway Administration
GSI Geological Strength Index
JICA Japan International Cooperation Agency
LL Liquid Limit
MGB Mines and Geosciences Bureau MSE Mechanically-Stabilized Earth MSF Magnitude Scaling Factor
NAMRIA National Mapping and Resource Information Authority PGA Preliminary GeoHazard Assessment
PHIVOLCS Philippine Institute of Volcanology and Seismology PTCPD Penang Town and Country Planning Department
RMR Rock Mass Rating
Glossary
Acronym Definition
Abstraction Removal of groundwater.
Anisotropy Having different physical properties when measured in different directions. Archipelago A chain, cluster or collection of islands.
Back-sapping Loss of ground, generally on slope, as a result of loss of support in the area below.
Bioengineering The use of mechanical elements in combination with biological elements (e.g.plants) particularly for control of erosion and prevention of slope failures.
Caldera A very large crater associated with a volcano and often formed by the collapse of an underground magma chamber.
Clast Fragment of pre-existing rocks produced by the process of weathering and erosion.
Clay A clastic mineral particle of any composition that has a grain size smaller than 1/256 (0.00391) mm. Counterfort A buttress, usually in a wall.
Creep A slow or gradual movement, applied to soil and superficial accumulations moving under gravity. Downdrag The loading, particularly on piles, caused by settlement of soil in the upper part of the pile. Down-slope At a point on the slope below the reference point.
Escarpment A steep slope or long cliff that occurs from faulting and resulting erosion and separates two relatively level areas of differing elevations.
Far-fault A fault more than 5km distant from the reference point.
Fault A shear fracture in rock along which there has been an observable amount of displacement. Fumarole A hot spring emitting volatiles.
Geohazard Geologic and natural hazards, particularly those that put infrastructure at risk.
Geomembrane Very low permeability synthetic membrane liner of barrier used with any geotechnical engineering related material so as to control fluid (or gas) migration in a human-made project, structure, or system. Geomorphology The study of landforms, their origin and development.
Geoportal A web-based source of data on the earth sciences.
Groundwater Water that exists below the water table in the zone of saturation.
Hydrogeology The study of the interrelationship of geologic materials and processes with water, especially groundwater.
Levee
(alias ‘Dike’) An embankment, generally constructed on or parallel to the banks of a stream, lake or other body of water for the purpose of protecting the land side from inundation by flood water, or to confine the stream flow to its regular channel.
Lineament A large-scale linear feature which expresses itself in terms of topography.
Liquefaction The sudden, large decrease of shear strength of cohesionless soil caused by collapse of the soil structure, produced by small shear strains associated with sudden but temporary increase of pore water pressure.
Mass wasting Down slope movement of soil and/or rock under the influence of gravity. Morphostructural Relating to landforms and the tectonic structure of the rocks.
Near-fault A fault less than 5km distant from the reference point. Near-field The area of the near-fault.
Piping The movement of soil particles as a result of unbalanced seepage forces produced by percolating water.
Pyroclastic Rocks formed by fragmental volcanic materials that have been blown into the atmosphere by volcanic activity.
Seiche Raised water level and wave in inland bodies of water, produced by seismic or storm action. Shear-wave A type of elastic wave, the S-wave, secondary wave, or shear wave is one of the two main types of
elastic body waves.
Slickenside A form of polish with linear grooves and ridges on the two surfaces of a rock which has undergone relative movement as a result of faulting.
Strike-slip A type of fault surface which is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion.
Subduction The process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge.
1
Introduction
1.1
GeoHazards in the Philippines
By reason of its geographic, geologic and tectonic setting the Philippines is prone to geologic and natural hazards that include earthquakes, volcanic eruptions and major mass movements. The more recent geologic events that have caused enormous destruction to lives and property are the earthquake of Luzon on 16 July 1990 and the eruption of Pinatubo Volcano on 13 June 1991. Both incidents killed thousands of people and destroyed millions of pesos of property.
In August 1999, suburban Cherry Hills Subdivision located on a hilly section of Antipolo City experienced yet another disaster in which torrential rains for three consecutive days triggered a landslide that cost the lives of over 50 people and rendered hundreds more homeless. The Philippine government proceeded to issue DENR AO2000-28 as its long-term response to the urgent need of protecting lives and property from destruction brought about by such geologic hazards.
1.2
The Need for a Preliminary GeoHazard Assessment
The guidelines of DENR AO 2000-28, issued as MGB Memorandum Circular No. 2000-33, stipulate that the Engineering Geology and GeoHazard Assessment (EGGA) process requires a land development project proponent to request the appropriate MGB office for a site geological scoping survey. This survey is aimed to determine the scope of geological study to be conducted in and around the site. The project proponent then prepares an Engineering Geological and GeoHazard Assessment Report focusing on potential geologic hazards that may have direct or indirect impact to the project, and their appropriate mitigating measures. The EGGA Report undergoes a technical review by an MGB panel after which a revision may be made before the report is evaluated and finally endorsed to the Environment Management Bureau for consideration in the issuance of the ECC. For private projects, the EGGA is conducted by a privately practicing geologist or qualified engineer while for government projects, the EGGA may be performed by a government geologist or qualified engineer under a Memorandum of Agreement (Aurelio, 2004).
However smaller projects undertaken by DPWH, both as part of their own budget appropriation, and for other agencies, have generally been given a Certificate of Non-Coverage, as not requiring any environmental assessment. Since small projects may not be assessed for GeoHazard, but may nevertheless be at risk from such hazards, it is appropriate to undertake a Preliminary GeoHazard Assessment (PGA) at the time of the project concept development stage for all projects.
This document describes the nature of GeoHazards encountered in the Philippines, the information available to assess their likelihood at any
particular project site in a preliminary assessment, and the procedure by which DPWH will follow from the results of the PGA.
1.3
Mitigation of GeoHazards
Some GeoHazards require to be taken into account as part of the standard design procedures and codes. This is particularly the case for seismic loading, and mitigation measures for this GeoHazard are dealt with in the relevant Volume.
Other hazards: flooding, liquefaction, highly compressible soils, are dealt with as part of routine geotechnical design and are discussed in Volume 3 – Water Projects Design for flooding, Volume 4 – Highway Design in relation to earthworks and earth retaining structures, and in Volume 5 – Bridge Design in relation to bridge structures and approaches.
Mitigation measures for GeoHazards which are less normally dealt with as part of routine design, in particular unstable slopes or landslides and expansive soils, are discussed in the relevant section of this volume or the annex to that section.
2
GeoHazards in the Philippines
2.1
Introduction
The main GeoHazards of significance in infrastructure design and delivery are described in the following sections.
The majority of GeoHazards are naturally occurring; a few are man-made such as un-engineered fills. However the remainder can be a combination of natural and man-made influences. Examples include:
• Flooding which is a natural event but which can be caused or exacerbated by man, as a result of deforestation, building on flood plains and so on.
• Earthquakes which are natural phenomena, but which can be triggered by large dam construction; also it is predicted that sea level rise as a result of climate change (a man-made event) will modify the behavior of earthquakes.
• Contaminated land which is usually man-made but can be from naturally occurring substances such as arsenic, methane gas or radon gas.
Consequently the GeoHazards have been considered as a single set, and man’s influence on their presence is discussed where relevant.
The study of these GeoHazards and their consequences requires the expertise of geologists, geomorphologists, geotechnical engineers and so on. However the Preliminary GeoHazard Assessment described in this guide is intended to be undertaken primarily by engineers without this specialist expertise, which would be called in at design stage, or before, if appropriate. Therefore, the requirement for particular specialists in relation to specific GeoHazards has not been identified as relevant to this stage of a project. The extent to which a specific GeoHazard will affect an infrastructure project is dependent not only on the general type of the project, but its size, strategic importance and other factors; therefore all the GeoHazards identified should be assessed for all projects at the preliminary screening stage which is the PGA.
2.2
Seismicity
2.2.1 The Nature of Seismicity
Earthquakes refer to the ground shaking or ground motion produced by movement along a trench or an active fault or during a volcanic eruption. Earthquakes may therefore be tectonic – either generated by a trench or by an active fault – or volcanic in origin.
Earthquakes may occur at depths that are shallow (0–70 km), intermediate (70–300 km) or deep (300–700 km). Shallow earthquakes may be triggered
by both trenches and faults. Intermediate to deep earthquakes are usually associated with trenches. It is the large shallow earthquakes that cause most damage as shown in Figure 2-1.
In case of such a major earthquake structures, slopes and foundations will be subjected to seismic loading. Earthquakes can trigger other seismic hazards such as landslides, liquefaction, lateral spreading, differential settlement, tsunamis, seiches and even fires.
Figure 2-1 A Collapsed Building during the July 16, 1990 Northern Luzon Earthquake
As shown in Figure 2-2, the Philippine Mobile Belt is sandwiched by trenches on both sides and traversed along its entire length by the Philippine Fault. Palawan and Zamboanga are in the Eurasian margin.
Faults are faults or far-faults; a fault within the 5 km distance is a near-fault while a near-fault beyond that distance is a far-near-fault, located in the far field. The ground acceleration that a site may experience in the far field is a function of distance with the acceleration experienced by a site decreasing as distance from the fault increases. In the case of a near-field fault distance from the fault has little effect.
Figure 2-2 Structural Map of the Philippines PHILIPPINE FAULT M an ila – Ne gr os -C otab at o EUR AS IA N M AR GI N
2.2.2 Faulting
An active fault is one that has moved during the last 10,000 years. Faulting, whether through aseismic fault creep or through a catastrophic ground rupture, refers to actual displacement or dislocation along a fault.
Depending on the orientation of the fault plane and on the direction of displacement, a fault may be classified as a normal fault, a thrust fault or a strike-slip fault. A fault is therefore defined by its geometry – its strike and dip – and displacement.
Sudden movements along faults result in earthquakes which, in turn, can trigger other seismic hazards such as landslides, liquefaction, lateral spreading, differential settlement, tsunamis or seiches.
A relationship is observed to exist between fault length, rupture length, displacement and magnitude. A major fault, such as the Philippine Fault which cuts across the entire length of the archipelago, is capable of producing longer rupture lengths, larger amounts of displacement and larger magnitude earthquakes than a minor fault.
2.2.3 The Preliminary GeoHazard Assessment
For seismic design of vertical buildings, ASEP National Structural Code of the Philippines (2010) requires input of:
Distance from active fault
Soil type
The procedures for selecting the spectrum are then set out. The following requirements need to be considered:
For bridges, requirements of DWPH Bridges Seismic Design
Specifications (DPWH-BSDS), December 2013 JICA Study and the DGCS Volume 5 – Bridge Design.
For earth retaining structures and earthworks, DGCS Volume 4 –
Highway Design recommends designing using the quasi-static method, which will require a peak ground acceleration and then a reduction factor. At this stage the requirements are to identify the distance from active fault and peak ground acceleration at the site.
The distance from active fault can be identified from the PHIVOLCS maps1.
At the country scale is the map shown in Figure 2-2. However for some parts of the country, larger scale maps are available; the most detailed available map for the site should be used, and the scale of the map should be recorded in the Preliminary GeoHazard Assessment.
The peak ground acceleration can also be obtained from the PHIVOLCS web site maps, and an example is shown in Figure 2-3.
1 www.phivolcs.dost.gov.ph
Figure 2-3 Map showing Peak Horizontal Acceleration Values for Rock
These have been arrived at by applying the attenuation model of Fukushima and Tanaka (1990) described in Annex A. If the map scale is found to be inadequate to identify the peak ground acceleration at the site then the values can be calculated directly from the equation set out in Annex A.
2.3
Liquefiable Soils
2.3.1 The Nature of Liquefaction
When saturated soils with little cohesion are loaded rapidly this causes pore pressures to increase and effective stresses to reduce, with a consequent reduction in the strength of the soil. Under some circumstances the strength reduction can be severe or total, the phenomenon referred to as liquefaction, and any structures founded on or in the soils will suffer a major loss of support, often leading to their collapse. Cyclic loading during an earthquake event is the major cause of liquefaction.
Two kinds of liquefaction have been recognized. Flow liquefaction occurs when the initial cyclic loading causes the shear strength to reduce, sufficient for the soil to cause a flow failure. In this case the soil will be initially on a sloping ground.
Figure 2-5 Liquefaction Map
Where the site lies within the liquefaction susceptible zone shown on the map, the PGA Summary Report shall identify this. If the location is not clear, as a result of the small scale of the map or for any other reason, then the Report shall note this along with the reason.
If there is an existing local knowledge about liquefaction potential and zoning, then this should be added to the Report. Additional assessment of liquefaction risk can be undertaken using borehole data; a single SPT value does not identify a liquefaction potential, which is affected by overburden pressure, grading and fines content. The procedure for the assessment is described in Annex B. For the initial PGA, data can be used from previous ground investigations in the general vicinity of the site if the ground conditions are believed to be similar. The assessment can then be repeated during Design Development using actual site data.
District and Regional Offices should aim to build up a database of their ground investigation reports, identifying which sites contain liquefaction susceptible soils, and this information can be fed back to a PHIVOLCS or DPWH national database when resources permit.
2.4
Volcanic Activity
2.4.1 The Nature of the GeoHazard
The Philippines sits on a unique tectonic setting ideal to volcano formation. The archipelago is surrounded by subducting plates as manifested by the trenches that are related to volcano formation.
Volcanoes are classified into three (3) types:
Active volcanoes: erupted within historical times (within the last 600
years), accounts of these eruptions were documented by man; also those that have erupted within the last 10,000 years based on analyses of datable materials. There are twenty three (23) identified active volcanoes;
Potentially active volcanoes: morphologically young looking but with no
historical records of eruption. There are twenty six (26) identified potentially active volcanoes; and
Inactive volcanoes: no record of eruptions; physical form is being
changed by agents of weathering and erosion via formation of deep and long gullies. There are three hundred fifty three (353) identified inactive volcanoes.
Volcanic phenomena directly associated with eruption are:
Lava flow, dome growth
Pyroclastic flow, pyroclastic surge, lateral blast Tephra fall – ash fall, volcanic bomb
Volcanic gas
Volcanic phenomena indirectly associated with eruption are:
Lahar, flooding
Debris avalanche, landslide
Tsunami, seiche
Subsidence, fissuring
Secondary / hydrothermal explosion
Secondary pyroclastic flow
2.4.2 Preliminary GeoHazard Assessment
According to Aurelio (2004) areas are zoned according to the degree of volcanic risk they may be subjected to. Volcanic hazards given attention to in this classification include possible routes of lava flows, lahars, debris and pyroclastic flows, lateral blast and pyroclastic surge materials, as well as the potential extent to be affected by volcanic bombs, ballistic projectiles, ash fall and gas emissions.
Virac, Catanduanes, Philippines
Caramoan Peninsula, Camarines Sur, Philippines
2.6.1 Preliminary GeoHazard Assessment
Locations of karst terrain can be assessed from:
Geological maps to identify presence of limestone rocks directly
underlying superficial soils.
Field investigation to identify any surface expression: caves, sinkholes.
Local knowledge of voids, water losses into the ground or other relevant
features.
2.7
Mining Activities
Mining takes place throughout the Philippines, for metallic and non-metallic deposits (particularly nickel, cobalt, silver, gold, salt, copper) and for limestone.
Mines can be in the form of open pits, and underground workings. Both these types of mine are developed both by companies with authorized mining permits and by illegal small and medium-scale workings.
Shallow pit mining is frequently backfilled with loose spoil, and consequences for infrastructure are similar to those for un-engineered fill as described in Section 2.8.2.
The presence of underground workings can result in uncontrolled long-term settlement, failure of piles founded above the workings, and loss of concrete in bored piles penetrating through the workings, possibly resulting in loss of performance of the pile.
In areas of coal mining, or geological conditions where coal may have formed, there is the additional danger of the generation of naturally occurring methane gas.
2.7.1 Preliminary GeoHazard Assessment
The geological map may indicate that extractable resources are present, though this does not identify that mining has taken place.
No information on the location of deposits or of mining permits is available
from MGB website at present8. If mine workings are suspected then MGB
should be requested to provide available data on permits and extraction for licensed mines, and local knowledge should be used to identify whether the site may have been affected by illegal mining, either on the site or in the vicinity where it could affect the site.
2.8
Problem Soils
2.8.1 Expansive soils 2.8.1.1 Swelling Clay Minerals
The swelling potential of clay varies according to its mineralogy, since different clay minerals have different crystal lattice structure and bonding. The plasticity of the clay, as measured by the Atterberg Limit test, is influenced by these same factors and provides good guidance on the swell potential of clay soils. Since natural clay soils contain a substantial proportion of silt which is non-active, it is convenient to express swell potential in terms of Activity (Plasticity Index / Clay Content)
The main clay mineral groups, in order of increasing expansiveness are shown in Table 2-2.
Table 2-2 Properties of Clay Minerals
Clay Mineral Plasticity Index % Activity
Kaolinite 15-20 0.3-0.5
Illite 30-50 0.9
Smectites (montmorillonite) > 150 1.5 (Ca) to 7.2 (Na)
2.8.1.2 Moisture Content Changes
In order for a clay to swell or shrink there needs to be a change in moisture content. The most common reason for changes in moisture content is seasonal changes in groundwater level due to variation in rainfall.
Other common causes are:
Longer term climate variation, particularly droughts.
Construction, of buildings, roads etc. reducing surface evaporation
locally.
Planting or felling of trees, which have a substantial water demand.
Leakage of water or sewer pipes.
Irrigation practices.
For road projects, the major concern is normally seasonal rainfall effects. These can cause swelling and shrinkage of clay soils in two (2) main ways, as shown in Figure 2-10:
Regional groundwater level changes, which will affect the whole of the
roads if built at grade.
Local surface infiltration and drying of the road formation, more
commonly in the case of roads on embankments. The infiltration and drying effects can be by means of roadside drains, unpaved shoulders or defective pavement.
Figure 2-10 Moisture Variations beneath Roads
2.8.1.3 Indications of Swelling Clay Problems
The effect of swelling clays on roads is initially to cause unevenness of the surface, followed by cracking and rutting. Once the pavement is cracked then the combination of traffic and additional moisture penetration to the formation will quickly result in complete failure of the pavement.
Examination of Figure 2-10 shows that longitudinal cracking should dominate the early behavior, and this has been recorded as shown in Figure 2-11. However the variability of the clay soils and of moisture ingress generally means that the pattern of heave and cracking is by no means uniform.
Figure 2-11 Cracking Observed in a Residential Development
Cavite (2001)
Pavement failures caused by swelling clays can be differentiated from other forms of failures to some extent by the mode of failure, for example:
Longitudinal cracking can occur even on at-grade sections, which
differentiates it from longitudinal cracking caused by embankment instability.
Rutting is not limited to wheel tracks, which is the case where rutting is
caused by overloading.
Unevenness can be quite extreme before the pavement starts to break
up, normally much greater than when the asphalt mix design is poor. However, it is not reliable to attempt to identify swelling clay problems solely from pavement behavior. Worldwide, the identification of swelling clay soil problems has generally developed as a result of specific local experience of road and building failures, coupled with investigation of soil properties and the experience of different types of remedial works for the local conditions.
2.8.1.4 Preliminary GeoHazard Assessment
The procedures for identifying or eliminating swelling clays as a cause of pavement problems should be broadly as follows:
Pavement condition survey
Geological desk study and field survey of soils
Laboratory testing of soils including Atterberg Limits and swell pressure
determinations
Monitoring of groundwater level variations
2.8.2 Fills
Three (3) main types of fill are likely to be encountered during infrastructure development:
Engineered Fills: consisting of selected materials placed and compacted to
provide a stable formation for further development. Such fills should not be a GeoHazard, except for possible liquefaction as discussed in Section 2.3;
Un-engineered Fills: material dumped without selection or compaction,
but excluding waste dumps or landfills. Materials are likely to be compressible and unsuitable for founding of infrastructure but not otherwise be considered a GeoHazard; and
Waste Dumps or Landfills: material containing organic material which will
decay over time. The ground is likely to be highly compressible and also will settle as a result of the organic decay. The generation of methane from such dumps provides a potential hazard to buildings and other structures and to the building users. Such sites should also be assumed to be contaminated and assessed in accordance with Section 2.8.4.
2.8.2.1 Preliminary GeoHazard Assessment
The identification of fill areas should be made by:
Drawing on local knowledge, as described in the desk study section of
Volume 2C – Geological and Geotechnical Investigations.
Examination of topographic maps. In urban areas, examination of old
maps may assist in identifying the stages of development.
Examination of geomorphology maps. If the area has no geomorphology
map then the assessing engineer should commence the development of such a map with the information from the project under consideration.
Field inspection. Trial pitting.
2.8.3 High Compressibility Soils
Soils of high compressibility and significant depth at the site of the infrastructure development require to be identified at an early stage so that adequate allowance is provided for the additional costs of dealing with them in the engineering design.
The two (2) most common types of highly compressible soils are peat and recent soft clay. These are both found mainly in low-lying areas, close to sea level in river basins with a meandering river form. Peat is also found at higher altitudes in depressions in hilly terrain.
Where such soils are underlain by sands and gravels, as is often the case, then it is frequently found that excessive groundwater abstraction occurs from these aquifers. This results in partial drainage of the compressible soils resulting in regional subsidence; the coastal area of Manila is reported to have subsided by up to 10 cm / year until groundwater extraction was controlled, at least in metro Manila. It was also responsible for minor movement along faults (Rodolfo and Siringan, 2006). Ongoing regional subsidence is particularly significant for the design of flood prevention works. Also, subsidence results in down drag on piles, which needs to be taken into account in their design.
2.8.3.1 Preliminary GeoHazard Assessment
General landform and vegetation provide good indicators of the presence of these soils; also damage to existing infrastructure caused by settlement may be apparent or known locally. More guidance on the identification of these soils is provided in Annex E. Regional subsidence is normally identified by sea encroachment, and measured by long-term benchmark data.
Where compressible soils are identified, and regional subsidence is known or believed to exist, the assessment should identify the compressible soils as a hazard, and annotate the report to identify regional subsidence.
2.8.4 Contaminated Soils
Contamination of natural soils by industrial or related activities can result in toxicity of the ground which may be hazardous to users of the land or to the population more widely. Any land which has been used for industrial purposes should be assessed for potential contamination.
Contaminants usually result from dumping of industrial wastes, leakage of product, or demolition of facilities, and fall into the following main categories:
Organic pollutants such as pesticides, organic solvents, petroleum
products
Heavy metals such as lead, arsenic, mercury, cadmium
Acids
Asbestos
Gases
Table 2-3 identifies the main contaminative industries.
Industry profiles which identify the main contaminants found at such sites can be found at the UK Environment Agency website.
Gases are a special concern. Methane gas is generated during the decay process of organic materials in landfill, as well as naturally occurring in organic deposits such as coal. Also radon gas, which is naturally occurring but mentioned here for completeness. Radon is produced by the radioactive decay of radium-226, which is found in uranium ores; phosphate rock; shales; igneous and metamorphic rocks such as granite, gneiss, and schist; and, to a lesser degree, in common rocks such as limestone9.
Table 2-3 Main Contaminative Industries (Environment Agency10)
Industries
Railway land
Engineering works: shipbuilding, repair and shipbreaking (including naval shipyards), airports and railway engineering works
Gas works, coke works and other coal carbonization plants Ceramics, cement and asphalt manufacturing works Sewage works and sewage farms
Road vehicle fuelling, service and repair: garages and filling stations
Metal manufacturing, refining and finishing works: iron and steel works, lead works and non-ferrous metal works
Power stations (excluding nuclear power stations)
Oil refineries and bulk storage of crude oil and petroleum products
Chemical works (cosmetics and toiletries, fertilizer, soap and detergent, organic chemicals and mastics, sealants, adhesives and roofing felt manufacturing works)
Timber treatment works
Engineering works: mechanical engineering and ordinance works and vehicle manufacturing works
Textile works and dye works Food and drink
Waste recycling, treatment and disposal sites: landfills and other waste treatment or waste disposal sites
Animal and animal products processing works Pulp and paper manufacturing works
Engineering works: electrical and electronic equipment manufacturing works (including works manufacturing equipment containing PCBs)
Chemical works: explosives, propellants and pyrotechnics manufacturing works Glass manufacturing works
Printing and book-binding works
Chemical works: linoleum, vinyl and bitumen-based floor covering manufacturing works Chemical works: rubber processing works (including works manufacturing tires or other rubber products)
Chemical works: coatings (paints and printing inks) manufacturing works and mastics, sealants, adhesives and roofing felt manufacturing works
Asbestos manufacturing works Dry cleaners
Waste recycling, treatment and disposal sites: metal recycling sites
2.8.4.1 Preliminary GeoHazard Assessment
The identification of areas of contamination requires a staged approach; with desk study followed, if required, by field investigation.
Drawing on local knowledge, as described in the section on desk study in
Volume 2C – Geological and Geotechnical Investigation.
Examination of topographic maps. In urban areas, examination of old
maps and also historical aerial photographs may assist in identifying the stages of development.
Examination of geomorphology maps. If the area has no geomorphology
map then the assessing engineer should commence the development of such a map with the information from the project under consideration.
Field inspection. Trial pitting.
Particular care should be taken when undertaking field inspection and trial pitting of suspected contaminated sites. Precautions as described in Volume 1 – Introduction and Overview should be adopted and extended as appropriate based on the expected risk.
If an initial site assessment does not identify any prior contaminative uses then it should be identified.
If contamination is suspected then the resulting risk as a result of the planned infrastructure development should be assessed, in accordance with Table 2-4.
Further guidance on the requirements for investigation is given by AGS (2007).
Table 2-4 Contaminated Ground Risk to Infrastructure
Type of
Development Risk during construction Risk to End Users
Road rehabilitation Low Very low
New road construction Medium. Require preliminary investigation at survey stage and / or special measures during construction
Very low
Bridge construction Medium: Piling works may generate contaminated spoil. High: Exposure during excavations.
Medium: Piled foundations may increase linkage between contamination and underlying aquifer.
Buildings: whole site
to be hard covered. High: Exposure during excavations. Very low. Buildings including
open space High: Exposure during excavations. Medium. If child access then High.
2.9
Groundwater
The flow of groundwater out at the surface is known as a spring. It can be permanent or only occur during the wet season of the year. The two (2) main causes of springs are:
The result of uphill groundwater recharge by rainfall and relatively steep
terrain resulting in the phreatic surface meeting the ground surface, as shown in Figure 2-12a.
The result of permeable soils or rocks overlying an impermeable layer,
resulting in a spring line at the boundary of these strata, as shown in Figure 2-12b.
Figure 2-12 Spring Lines
2.9.1.1 Preliminary GeoHazard Assessment
During periods of spring discharge, the spring line should be directly identifiable. At other times, spring lines can be identified by changes in vegetation since the local increase in water provides a different microclimate. Also, there may be surface erosion, and back-sapping of non-cohesive soils at the spring line.
Where springs or spring lines are identified or suspected within the project site or in the immediate vicinity at similar elevations, then this should be identified as a hazard in the PGA.
2.10
Flooding, Scour and Erosion
2.10.1 Preliminary GeoHazard Assessment
Flood hazard maps are available from MGB11. At present the area of coverage
is limited; refer to Annex F for information on the NAMRIA Geoportal and long-term plans for development of this mapping.
Local information on flood-prone areas should be available from local knowledge and should be reported in the PGA. If the proposed project involves significant earthworks then the effect of such earthworks on local flood behavior should be identified.
Scour and erosion are influenced by terrain, soil type and surface water flow velocities. They are best assessed in the initial stage by local inspection of existing scour and erosion, and reporting of any significant locations which could indicate special requirements in design.
DGCS Volume 3 – Water Engineering Projects gives more detailed information on the identification and mitigation required. If flood hazard is identified, then as a minimum a hydrological and hydraulic assessment will
need to be undertaken to determine the extent of the floodplain using the techniques outlined in Volume 3.
2.11
Tsunamis, Seiches, Storm Surges
Tsunamis are large, often destructive, sea waves produced by a submarine
earthquake, subsidence, landslide or volcanic eruption. Being in a seismically active region, the coast of the Philippines is at risk from tsunamis.
Seiches are raised water levels and waves in inland bodies of water,
produced by seismic or storm action. UNESCAP (1999) identified risk of seiches from volcanic calderas in the land using planning of the Tagaytay – Taal area. Giese et al (1999) describe harbor seiches at Palawan Island.
Storm Surges are raised sea levels and accompanying high waves resulting
from high winds and often associated with low barometric pressure, particularly from cyclones.
2.11.1 Preliminary GeoHazard Assessment
A map of tsunami hazard zones in the Philippines was produced in 2007 and is available on the PHIVOLCS website12. This indicates only the coastline at risk. Sites located within 5 km of an at-risk coastline and at an elevation of less than 20 m above sea level should be identified as having a tsunami hazard.
Local knowledge on flood levels and the history of seiches should be investigated in relevant localities and reported on.
Flood hazard maps as described in Section 2.10 should have accounted for storm surges. However unless local knowledge or other data allow an alternative conclusion, any site within 50 m of high tide level should be identified as at risk from storm surge.
2.12
Geothermal Activity
The Philippines obtains some 27% of its power supply from eighteen (18) geothermal plants sited in Luzon, Visayas and Mindanao. However, such plants extract energy from some depth below ground, and are therefore not indicative of locations of surface or near-surface geothermal activity of interest to the GeoHazard assessment.
Geothermal activity is caused by the transfer of heat from depth to the earth's surface. Surface expression of geothermal activity can take various forms13:
12 http://www.phivolcs.dost.gov.ph/index.php?option=com_content&view=article&id=77&Itemid=129 13 After Search: http://www.volcanolive.com/geothermal.html (retrieved 18 September 2013)
Warm Ground: represents a low level of geothermal activity. The ground
temperature is raised at a meter depth but not at the surface. Warm ground is not visible on infrared images but changes to vegetation can be identified.
Hot Steaming Ground: Hot vapors rise near the surface but are not actually
discharged. The vapors condense and drain away without being released to the atmosphere. A thin layer of steam may condense under moist air conditions. If the air is dry then no steam is observed.
Hot Pool: the result of hot water or steam heating a pool of groundwater.
Hot pools may be calm, ebullient (effervescent) or boiling.
Hot Lake: fills hydrothermal depressions in geothermal areas. They are a
subclass of volcanic lakes.
Hot Spring: the most common type of geothermal activity. They are located
where water from a geothermal system reaches the surface.
Fumarole: steam discharge from a hydrothermal or volcanic system. A
solfatara contains sulphur emissions. Steam is the most abundant emission from fumaroles.
Geyser: Vent from which hot water and steam are violently emitted. They
are very rare but well known and extensively studied. Requirements for geyser formation include fractured rocks and boiling water at a shallow depth.
Hydrothermal Eruption: caused by catastrophic discharges of water close
to the boiling point. No ash, incandescence, or clasts are erupted. Hydrothermal eruptions may be caused by a reduction in the overlying pressure.
Geothermal Seepage: A seepage is a general term which describes any
subsurface discharge of warm fluids from a geothermal area. Seepages may occur into rivers or lakes.
The significance of geothermal activity to infrastructure development is dependent on its scale and how close it is to the surface. Risks may be short-term during construction (for example damage to in-situ concrete piling during casting) or long-term to the infrastructure fabric or to site users. Further details of some of the phenomena relating to geothermal activity, the effects on infrastructure, and possible mitigation measures, are given in Annex F.
2.12.1 Preliminary GeoHazard Assessment
Sites within one kilometer of known hot springs, hot pools or one or more of the other manifestations describe above should be classified as hazardous under this heading.
2.13
Effects of Climate Change
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cruz et al, 2007) predicts that climate change will affect the globe over the next one hundred years.
The main effects of the predicted climate change are:
a rise in temperature
a rising sea level
variation in rainfall patterns with increased intensities and greater
drought and rainfall periods in different places
variation in track and increased intensity of cyclones
A further consequence for infrastructure is increased saline intrusion. The Philippines lies third in the world’s countries most vulnerable to climate change and disasters caused by natural hazards (ADB, 2013).
The projected rising temperatures and sea levels, and changes in precipitation, are capable of initiating load changes and elevated pore-pressures sufficient to cause a range of geological and geomorphological processes that have hazard potential. There is already significant evidence, according to McGuire et al (2012), that this will cause a modulation or triggering of seismic, landslide and volcanic activity resulting from small changes in environmental parameters such as solid Earth and ocean tides, atmospheric temperature and pressure, as well as in response to specific geophysical events such as typhoons or torrential precipitation.
Specific events already identified include the violent venting of volcanic gases from Mount St Helens resulting from rainstorms, and collapses of the Soufriere Hills’ lava dome on Montserrat linked to intense tropical rainfall.
Table 2-5 shows the hazards identified as potentially being influenced by climate change. All except glacial outburst floods are relevant to the Philippines.
However the research on the effects of climate change on GeoHazards is at a very early stage and no quantitative predictions are available. They can be considered as a higher order of uncertainty compared with the direct assessment of current GeoHazards. Therefore no attempt is made to incorporate the effects of climate change in GeoHazard assessment in this Guide. For major projects where a full risk assessment is undertaken, including consequence-based risk, the potential effects of such climate-change induced climate-changes to GeoHazard risk may be appropriate using, for example, the approaches described in PIARC (2013).
Specific effects of climate change which will affect engineering structures, including sea level change, storm surge and flooding, are addressed in the Guide Volume 3 – Water Engineering Projects Design.
Table 2-5 Relation of Climate Change to GeoHazard
Potential
hazard Mechanism / potential relationship with climate change Relevant climate drivers Environmental settings
Sub aerial landslides and debris flows
Permafrost thaw; pore-water pressurization; intense rainfall destabilizing regolith
Temperature rise; ice-mass
loss; intense precipitation Mountainous terrain; volcanic landscapes
Glacial outburst
floods (GLOFs) Glacier retreat; accumulation of melt water in pro-glacial lakes Temperature rise; ice-mass loss High latitudes; mountainous terrain; glaciated volcanic landscapes
Earthquakes Ice-sheet and glacier wastage; ocean island and ocean margin loading due to sea-level rise
Temperature rise; ice-mass loss; ocean volume increase
High latitudes; glaciated terrain at mid-to-low latitudes; ocean basins and margins Volcanic activity Unloading due to ice-sheet and glacier
wastage; loading due to sea-level rise; pore-water pressurization; intense rainfall destabilizing regolith
Temperature rise; ice-mass loss; intense precipitation; ocean volume increase
Volcanic landscapes at all latitudes
Tsunamis Submarine and sub-aerial slope failures and volcano lateral collapses; gas-hydrate breakdown; ocean load-related earthquakes; ice-quakes
Ocean temperature rise; ocean volume increase; intense precipitation
Ocean basins and margins
3
Preliminary GeoHazard Assessment
Initial project development requires projects to be identified as requiring an Environmental Impact Assessment, an Initial Environmental Assessment or for projects having no significant environmental impact, a Project Description Report. Projects are then reviewed by DENR and where considered appropriate an Engineering Geological and GeoHazard Assessment is required. This is undertaken by MGB.
According to DENR (2007), unless projects are located in an environmentally critical area or are environmentally critical projects DENR are required to issue a Certificate of Non-Coverage if the project proponent submits only Project Description Report. The Proponent is responsible for identifying whether the project lies in an environmentally critical area and there is no single source for identifying the extent of environmentally critical areas. Consequently the great majority of projects are not considered for an EGGA and therefore there was a potential risk that GeoHazards have not been identified.
The introduction of a PGA at the concept development stage of all projects, including rehabilitation and reconstruction work, is therefore to ensure that smaller projects, which may yet be at risk from GeoHazards, are adequately assessed.
The PGA is carried out at proponent level initially. Its purpose is to identify exceptional conditions that may require special investigation, design measures, additional budget or in the extreme case a relocation of the project.
3.1
Required Expertise
The person undertaking the PGA should be a qualified geologist, or engineer who has undertaken at least geology and geotechnical engineering modules in a university degree level course. Alternatively, the person should have extensive experience and job-training sufficient to undertake the assessment.
3.2
Scope of Preliminary GeoHazard Assessment
3.2.1 Desk Study
The PGA cannot be undertaken without a Project Description. If one has not been prepared then this should be done before undertaking the PGA. Procedures for preparing a Project Description are described elsewhere. The desk study for the PGA is similar in nature to the broader study to be undertaken as part of the site investigation and described in Volume 2C – Geological and Geotechnical Investigations. However, for the PGA, the desk study is limited to the GeoHazards and specific sources of information.
The information to be used in the GeoHazard desk study is listed under the relevant hazard in Section 2 of this Guide.
However the available information is expanding rapidly. Annex F summarizes the available information about likely developments in the next few years, which should be taken into account in undertaking the PGA. In addition to the specific sources, the assessment should make use of topographic maps from the NAMRIA Geoportal, aerial photographs where available, land-use maps if available in the region, and agricultural soils maps.
3.2.2 Reconnaissance
The reconnaissance for GeoHazards is most appropriately undertaken as part of a broader field inspection which may include validation of assumptions contained in the Project Description and, for reconstruction works, identification of the causes of deterioration of the asset.
Before undertaking the field reconnaissance, the desk study should be undertaken and a general sketch and list of potential GeoHazards should be drafted. During the reconnaissance, these potential GeoHazards would be assessed, as well as identifying other possible GeoHazards. Field reconnaissance and procedures for identification of specific GeoHazards are described in Section 2.
Where the project consist of or contains rehabilitation of existing assets, the field reconnaissance should identify specifically those GeoHazards which have contributed to the current deterioration of the asset.
Field inspections of areas where GeoHazards may be present require additional safety measures. The basic requirements for safety during field reconnaissance are described in Volume 2C Geological and Geotechnical Investigations. The person leading the field inspection should undertake a prior safety assessment and adopt appropriate precautions for the inspection team.
3.3
Preliminary GeoHazard Assessment Report
The report shall consist of a one-page summary and attachments. The template for the report is included as Annex H. The person that undertook the field reconnaissance for the assessment is the required signatory on the report.
Where GeoHazards have been identified, or there is remaining uncertainty, attachments should be included showing the information on which the assessment was based.
3.4
Further Action
For the Concept Development Report, the project should be classified from the Preliminary GeoHazard Assessment as one of the following four (4) categories:
No significant GeoHazards identified.
GeoHazards identified and budget for mitigation calculated and included
in project budget.
GeoHazards identified and there is a requirement for further field
investigation and design before the budget can be reasonably assessed. In this case the Concept Development phase may need to be extended with additional budget.
GeoHazards at or adjacent to the site are sufficiently severe that
mitigation measures would not be practical, and it is recommended that the site is unsuitable for the proposed use.
If the responsible person was not able to conclude that no GeoHazards exist, then the assessment should be first completed as far as possible, identifying the outstanding issues. Then there should be consultations as follows:
PHIVOLCS offers a service to provide certification on active faults, lahar,
pyroclastic flow, lava flow, volcano Permanent Danger Zone14. If the identified hazards fall into these categories then PHIVOLCS should be approached for certification, providing them with a copy of the Preliminary GeoHazard Assessment.
MGB have a geology unit based in each of their regional offices. They may
be approached for assistance, once the PGA has been completed. If their input allows the GeoHazards to be identified or discounted then their report should be attached to the PGA, which can be annotated accordingly.
If these approaches do not resolve outstanding issues with the PGA then the District should escalate the matter to the Region, and the Region to BOD Central Office as appropriate.
4
References and Bibliography
ADB, Facts and Figures in http://www.adb.org/themes/climate-change/facts-figures (accessed 8 September 2013)
AGS Quick-Start Guide to Contaminated Land Investigation, Association of
Geotechnical and Geo-environmental Specialists, UK, 2007
http://www.ags.org.uk/publications/agreement.php?docname=AGS%20Q uick%20Start%20Guide%20to%20Contaminated%20Land.pdf
ASEP, National Structural Code of the Philippines, Volume 1: Buildings, Towers and Other Vertical Structures, C101-10, Association of Structural Engineers of the Philippines, 2010.
Aurelio M A, Engineering Geological and GeoHazard Assessment (EGGA) system for sustainable infrastructure development: the Philippine experience.
Engineering Geology for Sustainable Development in Mountainous Areas, Free and Aydin (eds), 2004 Geological Society of Hong Kong. http://info.worldbank.org/etools/docs/library/230308/Session%201/Ses sion%201%20Reading%201.PDF
Barry et al, The Indonesian Geoguides, MSRI Guide No Pt T-08-2002, Ministry of Settlement and Regional Infrastructure, Indonesia, 2002.
E W. Brand and R P Brenner, Soft clay engineering, Elsevier Scientific Pub. Co., 1981
BS 10175:2001 Code of practice for the investigation of potentially contaminated sites, British Standards (2001)
Comité technique AIPCR C.3 GEstion des risques d’exploitation dans l’expoitation routière au plan national et international and Permanent International Association of Road Congresses (PIARC) Technical Committee, Risk Associated with Natural Disasters, Climate Change, Man-made Disasters and Security Threats (2013), PIARC, Paris, France.
http://www.piarc.org/en/order-library/20314-en-Risks%20associated%20with%20natural%20disasters,%20climate%20ch ange,%20man-made%20disasters%20and%20security%20threats.htm Cruz, R.V., H. Harasawa, M. Lal, S. Wu, Y. Anokhin, B. Punsalmaa, Y. Honda, M. Jafari, C. Li and N. Huu Ninh, Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge
University Press, Cambridge, UK, 2007, 469-506.
http://www.ipcc.ch/publications_and_data/ar4/wg2/en/ch10.html (accessed 8 September 2013-11-03
DENR AO 2000-28. Implementing guidelines on Engineering Geological and GeoHazard Assessment (EGGA) as additional requirement for ECC applications covering subdivision, housing and other land development and
infrastructure projects. Administrative Order No. 28, Series of 2000. Department of Environment and Natural Resources, Philippines. 14 March 2000.
DENR AO 2003-30. Implementing Rules and Regulations (IRR) for the Philippine Environmental Impact Statement (EIS) System. Administrative Order No. 30, Series of 2003. Department of Environment and Natural Resources, Philippines. 30 June 2003.
DENR Revised Procedural Manual for DENR Administrative Order No 30 Series of 2003 (DAO 03-30), August 2007.
Environment Agency UK, ‘Progress in 2002 with implementing the Part IIA regime, Dealing with contaminated land in England; (2002), Environment Agency, Bristol, England.
Fukushima, Y. and Tanaka, T., 1990. A new attenuation relation for peak horizontal acceleration of strong earthquake ground motion in Japan, Bulletin of the Seismological Society of America, v.80, no. 4, p. 757-778 German Technical Cooperation (GTZ), UNDP Regional Centre in Bangkok and The Secretariat of the International Strategy for Disaster Reduction. ‘Handbook on Good Building Design and Construction in the Philippines; (2008), International Strategy for Disaster Reduction (ISDR), Philippines http://www.preventionweb.net/files/10329_GoodBuildingHandbookPhili ppines.pdf
Huismann, M. 2000. Lecture Notes, Advanced Soil Mechanics, Mapua Institute of Technology, Manila.
Lobley, Katrina. ‘In Case of Emergency: how Australia deals with disasters and the people who confront the unexpected’, (2007), Australian
Emergency Management Institute (AEMI), Australia.
http://www.preventionweb.net/english/professional/publications/v.php? id=1730.
McGuire B and Maslin M A, Climate Forcing of Geological Hazards [Kindle Edition], 326 pp, Wiley-Blackwell, 2012.
MGB MC 2000-33. Guidelines and outline/checklist for the preparation of an Engineering Geological and GeoHazard Assessment Report as per DENR AO 2000-28. Memorandum Circular No. 33, Series of 2000. Mines and Geosciences Bureau, Philippines, 24 March 2000.
MGB MC 2002-43. Implementation of DENR Memorandum dated 26 November 2001 relative to Executive Order No. 45. Memorandum Circular No. 33, Series of 2000. Mines and Geosciences Bureau, Philippines, 24 March 2000.
Ministry of Public Safety and Solicitor General. ‘Hazard Risk and Vulnerability Analysis Toolkit’, (2004). Provincial Emergency Program Ministry of Public Safety and Solicitor General, Canada.
National Building Code of the Philippines, 2000, Philippine Law Gazette. Vicente B. Foz, Publisher.
Presidential Decree 1586. Establishing an Environmental Impact Statement (EIS) system including other environmental management related measures and for other purposes. Malacañang Palace, Manila, Philippines, 11 June 1978.
Presidential Executive Order 42. Prescribing time periods for issuance of housing-related certifications, clearances and permits, and imposing sanctions for failure to observe the same. Malacañang Palace, Manila, Philippines, 24 October 2001.
Geoff O’Brien, Phil O’Keefe, Joanne Rose and Ben Wisner, Climate change and disaster management, Disasters, 30(1): 64−80. , Overseas Development Institute, Blackwell Publishing, 2006.
PTCPD, 2012 Safety Guideline for Hillsite Development, Penang Town
and Country Planning Department, 2012,
http://www.mppp.gov.my/documents/10124/20fa2155-5a83-4644-8629-64da6405f4e1
Rodolfo K S and Siringan F P, 2006, Global sea-level rise is recognised, but flooding from anthropogenic land subsidence is ignored around northern Manila Bay, Philippines, Overseas Development Institute, Blackwell Publishing 30(1): 118-139. http://www.paase.org/images/Rodolfo-Siringan2006.pdf
Seed, H.B., Idriss, I.M. and Arango, I., 1983. Evaluation of Liquefaction potential using field performance data. American Society of Civil Engineers Journal of Geotechnical Engineering, v.109, no. 3, p. 458-482.
Steinberg M, 1978, Geomembranes and the Control of Expansive Soils in Construction, McGraw-Hill.
Thenhaus, P.C., Hanson, S.L., Algermissen, S.T., Bautista, B.C., Bautista, M.L.P., Punongbayan, B., Rasdas, A., Nillos, T.E. and Punongbayan, R.S., 1994. Proceedings: National Conference on Natural Disaster Mitigation, p. 45-60, 1921, October 1994, Quezon City, Philippines.
Villanueva, M.I.P., Abundo, R.V. and Manipon, C.J.C., in prep. GeoHazards and landslide modelling of Baguio city using thematic maps. Submitted to Journal of the Geological Society of the Philippines. Quezon City, Philippines
Mines and Geosciences Bureau. 2010. Geology of the Philippines, Mines and Geosciences Bureau, Department of Environment and Natural Resources, Quezon City. Philippines, 532 p.
A1
Introduction
To have a better grasp of the seismic hazards in the country, one should understand that the Philippine archipelago is tectonically divided into the Philippine Mobile Belt and the Eurasian Margin as shown in Figure A1-1.
Figure A1- 1 Structural Map of the Philippines
PHILIPPINE FAULT M an ila – Ne gr os -C ota ba to T ren ch EUR AS IA N M AR GI N
The Philippine Mobile Belt refers to that portion of the archipelago sandwiched by the Manila-Negros-Cotabato Trenches on the west and the East Luzon Trough-Philippine Trench on the east and traversed along its entire length by the active Philippine Fault. The Philippine Mobile Belt is therefore tectonically, seismically and volcanically active.
Palawan and Zamboanga, on the other hand, are part of the Eurasian Margin and are therefore tectonically and seismically inactive. There are no earthquake generators within the margin, although it can experience earthquakes generated by bounding structures such as the Sindangan Fault or Cotabato Trench.
A2
Ground Motion
An estimate of the ground motion specific to a site can be calculated. In order to determine the peak ground acceleration that a site can experience in the case of a major earthquake, the attenuation model of Fukushima and Tanaka (1990) is applied. A design earthquake is assumed to occur at a point along the causative fault that is nearest to the site, assessed as described in Section 2.2.3. Correction factors are then applied depending on the type of foundation material.
The attenuation model of Fukushima and Tanaka is written as: log 10 A = 0.41M – log 10 (R+0.032x10 0.4 M) – 0.0034R + 1.30 (6.1)
where:
A = mean peak acceleration (cm/sec2)
R = shortest distance between the site and the fault rupture (km)
M = surface-wave magnitude (also referred to as Ms)
Correction factors are applied to the mean peak acceleration depending on the type of foundation material: rock, 0.6; hard soil, 0.87; medium soil, 1.07; and soft soil, 1.39.
Alternatively the peak ground acceleration obtained from the maps provided by PHIVOLCS can be used, if they are considered accurate enough for the particular site.
PHIVOLCS produce Ground Shaking Hazard Maps at the provincial level within the framework of the READY Project but at present the maps are limited to Aurora, Bohol, Cavite, Dinagat, Leyte, Southern Leyte, Surigao del Norte, and Surigao del Sur. An example of such a map is shown on Figure A2-1.
Figure A2-1 Example of a Ground Shaking Hazard Map (READY Project).
The project site can be located on the map after which the class to which the polygon belongs to is looked up in the legend. The legend is color-coded according to the maximum amount of ground shaking that can be expected. This is expressed in PHIVOLCS Earthquake Intensity Scale. However this scale is not used as input to the infrastructure design process so it is of secondary interest.