Seismic Design of Buried Structures in PH and NZ

Seismic Design of Buried Structures in PH and NZ

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  SEISMIC DESIGN OFBURIED RECTANGULAR STRUCTURES: A LOOK AT CURRENT PHILIPPINES AND NEW ZEALAND DESIGN CODES WITH RECOMMENDED SIMPLIFIED PROCEDURE Lawrence O. Galvez ABSTRACT: Philippines and New Zealand are both situated in the “Ring of Fire” an area within the Pacific wherein 90% of world’s earthquakes and 81% of the world’s largest earthquakes occur. Earthquake- induced ground shaking initiates displacements on our structures which in turn cause internal stresses from structure’s inertial forces. These internal stresses are usually bigger in above-ground structures because of the experienced dynamic amplification effects compared to buried (underground) structures. Buried structures are constrained by surrounding soil or rock and are primarily affected by the deformation of the surrounding ground rather than inertial forces. This paper presents the current usual design practice of buried rectangular structures in the Philippines which was adopted from internationally accepted design methods. Also presented is the proposed seismic design method for buried rectangular structures from Report 611 of U.S. National Cooperative Highway Research Program (NCHRP), this Report 611 generally matches with the proposed design procedures of EQC Project No 01/470 prepared for Earthquake Research Commission Foundation in New Zealand. The proposed simplified design approaches/methods aim to minimize or eliminate hidden conservatism in traditional design of buried structures and extend the present knowledge of the dynamic interaction of box-section structures with the surrounding soil. KEYWORDS: racking deformation; soil-structure interaction; free-field strain; seismic design 1. INTRODUCTION Until now the current standard practice in the Philippines and most of other countries for seismic design of earth-retaining structures is the famous and traditional Mononobe-Okabe (M-O) method. Although M- O method was originally developed for aboveground earth retaining walls its application was widely extended to seismic design of buried structures (e.g. transportation and hydraulic tunnels). This popular theory for determining the increase in lateral earth pressure due to seismic effect is used for earthquake resistant design of submerged tunnels recognized by the Japanese Society of Civil Engineers (JSCE) (1975) and was recommended in several other documents (Converse Consultants 1983; EBMUD 1973). Based on the performance record of this buried structures from previous earthquakes worldwide, it is undoubtedly fair to say that underground structures are less vulnerable to earthquakes than surface structures (Dowding and Rozen 1978; Rowe 1992). National Cooperative Highway Research Program (NCHRP) Report 611 (2008) observed that earth-retaining structures even not designed with earthquake loadings but properly design with gravity loadings and constructed properly still have reserved seismic design capacity to withstand certain levels of earthquake event. Even though there is no available published data showing the actual performance of earth-retaining structures from previous earthquakes here in Philippines, the same general results of acceptable seismic performance is expected. The country does not have yet much underground structures prior to previous major earthquakes that strikes near a developed city, still there are thoughts that portions of old major water infrastructure were likely had been damaged before. Due to on-going rapid urbanization (i.e. improvement of physical infrastructures) a lot of bigger significant projects related to underground
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  structures are inthe horizon, it is the author’s view that engineers take a closer look again on seismic design of this kind of structure taking consideration of some worthy lessons learnt from other earthquake prone countries. Experience from the strong ground shaking of 2010/2011 Canterbury earthquakes in New Zealand confirms the same performance results of earth-retaining structures, Wood (2012) reports that overall performance of 160 earth-retaining structures was satisfactory despite the fact these structures are not specifically designed for earthquake loading. However it was noted that earthquake loads should be considered on higher walls (i.e. greater than 2.4 m), structures retaining moderate to steep backfill slope and when walls are rigidly restrained (e.g. basement walls). The observed reasons are some of the drawbacks of using the M-O method. Similar with the Philippines, there is limited guidance available in New Zealand on earthquake-resistant design of earth-retaining structures. National Structural Code of the Philippines (NSCP C102-97) Volume II – bridge code (adopted from AASHTO Specifications) and New Zealand Transport Authority (NZTA) Bridge Manual (2013) provide seismic design guidance but the focus are mainly on highway bridges and related components such as abutments and wing walls. NSCP C102-97 Section 21.3.1 states that “seismic design is usually not required for buried type (culvert) bridges while Australian Standard (AS) 5100 Bridge Standard which is due for adoption by NZTA Bridge Manual explicitly does not require earthquake loads to be considered for small culverts and subways where maximum cross-sectional dimension < 3 m, but for larger structures varying approaches are specified dependent on the depth of soil cover and form of structure. In lieu of the recent damages and findings of retaining walls in Greater Christchurch, the Ministry of Business, Innovation and Employment (MBIE) of New Zealand released a comprehensive seismic design guideline of retaining structures for residential sites. This guideline still follows the M-O method for flexible walls but with adjustments per the procedure recommended by U.S. NCHRP Report 611. For stiff walls, appropriate equation and chart was provided with reference from works of Wood (1991). It is evident that despite the design conservatism characteristic and generally good performance offered by M-O method, still most design codes are silent or give least guidance specific for seismic design of buried rectangular structures. Table 1 below shows requirements of design codes with regards to earth pressures for Philippines and New Zealand. The succeeding sections will discuss further the limitations of traditional M-O method and will show previous and current literatures which aim on developing comprehensive seismic design approaches and procedures particularly for buried rectangular structures. Table 1. Earth-Retaining Structure Design Code Seismic Requirements in PH and NZ Design Code Item Description Remark NSCP Volume I Retaining walls Section 206.6 “retaining walls shall be designed to resist loads due to lateral earth pressure in accordance with accepted engineering practice”. “..Shall be design using ASD with factor of safety 1.5 for sliding …and 1.5 for overturning…” No consideration for dynamic earth pressure. Current international practice of design is LRFD or limit-state design. Soil lateral loads Section 209 states: - Use at-rest pressure for walls where horizontal movement on top is restricted - Use active pressure for walls free to move and rotate at top No consideration for dynamic earth pressure.
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  - Surcharge loadsshall be added - Basement walls not more than 2.4 m supporting flexible floor may use active pressure NSCP Volume II Earth pressure Section 3.20 only mentions using of Rankine’s formula for earth pressure No consideration for dynamic earth pressure. Load Combination Table 3.22.1A for both ASD & LFD do not give an earthquake load factor for culvert design No consideration for dynamic earth pressure. From notes of Table 3.2.1A, for load factor design: F = 1.0 for rigid culverts E = 1.5 for flexible culverts For culvert loading: E = 1.0 and 5.0 for lateral loads on rigid frames (check both loadings) No consideration for dynamic earth pressure. Unclear if dynamic earth pressure is considered. Earth pressure Section 6.2 only gives value of static earth pressure acting on culverts. No reference for seismic loadings. Soil-reinforced concrete structure interaction system Section 17 only discuss SSI with regards to static earth pressure with consideration on different type of installations No consideration for dynamic earth pressure. Seismic pressure Section 5.5.4 gives guidance on dynamic earth pressure for rigid and semi-gravity walls Dynamic earth pressure is considered using M-O method. AS/NZS 1170.1 Earth pressure Section 4.5, “Earth pressure actions resulting in lateral loads on earth- retaining structures shall be determined suing established methods of soil mechanics”. Section 4.5 (f), For earth pressures: Load factor = 1.0 using ultimate limit state Method Load factor = 1.5 using other methods No consideration for dynamic earth pressure. Unclear if dynamic earth pressure is considered. NZTA Bridge Manual Earthquake- resistant design of retaining walls The bridge manual provides guidance but these are specific for road and highway infrastructure which are subject to higher loadings Dynamic earth pressure is considered for structures in roads and highways. Seismic design of underground structures for culverts and subways Seismic design is considered but applicable for buried structures with moderate depths of cover. Dynamic earth pressure is considered for moderate depths of cover AS 4678 Seismic earth pressure Appendix I consider seismic earth pressure dependent on type of structure and risk of failure. Dynamic earth pressure is considered using M-O method in Clause I14.
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  2. PUBLISHED EARTHQUAKEDAMAGE ON UNDERGROUND STRUCTURES Sharma and Jude (1991) extended the works of Owen and Scholl (1981) by collecting qualitative data for 192 reported observations from 85 worldwide earthquake events of past performance of underground structures. Sharma and Judd correlated the vulnerability of underground facilities with six factors: overburden cover, rock or soil type, peak ground acceleration (PGA), earthquake magnitude, epicentral distance and type of lining. Below are the main findings:  Damage decreases with increasing overburden depth.  More damage occurred in facilities constructed in soil than in competent rock  For PGAs less than 0.15g only 25% of the cases reported damage. For PGAs greater than 0.15g, 69% of the cases reported damage.  More than 50% of the damage reports for earthquakes with magnitude M exceeding 7.  Facilities were most vulnerable when within 25 to 50 km of the epicenter.  The proportion of damaged cases of concrete lines tunnels was greater than for unlined cases. This was attributed to the poor ground conditions that originally required the openings to be lined. 2.1 The 1971 San Fernando Earthquake Owen and Scholl (1981) reported damage five cut-and-cover tunnels and culverts located in soil, with failure of longitudinal construction joints, longitudinal cracks, concrete spalling and formation of plastic hinges at top and bottom of walls. Lew et al (1971) reported severe damage to box culvert sections of Wilson Canyon flood control channel. A large underground reinforced concrete reservoir, part of the Balboa Water Treatment plant, suffered severe damage. The walls, roof slab, floor slab and some of the columns of this 150 m x 150 m x 11.5 m high reservoir were extensively damage. It was thought that the damage was related to settlement and sliding produced by the ground shaking but soil shear strains and earthquake-induced pressures on the walls were significant factor (Priestley et al, 1986). 2.2 The 1995 Hyogoken-Nanbu Earthquake Six underground stations out of the total 21 subway stations in the Kobe area were severely damaged. Sections of tunnels connecting the damaged stations and the tunnel section of the Hanshin Railway sustained damage (Iwatate et al 2000). This caused major collapse of Daikai subway station in Kobe, Japan (Nakamura et al 1996). The damaged structure was constructed by the cut-and-cover method. The station designed in 1962 did not include specific seismic provisions. It represents the first modern underground structure to fail during a seismic event. Figure 1 shows the collapse experienced by the center columns of the station, which was accompanied by the collapse of the ceiling slab and settlement of the soil cover. During the earthquake, transverse wall at the ends of the station and at areas where the station changed width acted as shear walls in resisting collapse of the structure (Iida et al 1996). These walls suffered significant cracking, but the interior columns in these regions did not suffer as much damage under the horizontal shaking. In regions with no transverse walls, collapse of the center columns caused the ceiling slab to kink and cracks 150 – 250 mm wide appeared in the longitudinal direction. There was also significant separation at some construction joints, and corresponding leakage through cracks. Center columns that were designed with very light transverse (shear) reinforcement relative to the main (bending) reinforcement suffered damage ranging from cracking to complete collapse. Iida et al (1996) stated that it is likely that the relative displacement between the base and the ceiling levels due to subsoil movement created the destructive horizontal force. This type of effect may have minor effect in a small structure, but in a large one such as a subway station it can be significant. The non-linear behavior of the subsoil profile may also be significant. It is further hypothesized that the thickness of the overburden soil affected the extent of damage between sections of the station by adding inertial force to the structure. Others attribute the failure to high levels of vertical acceleration. Shear failure of supporting
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  columns caused similardamage to the Shinkansen Tunnel through Rokko Mountain (NCEER 1995). Nishiyama et al (2000) stated that the damage to cut-and-cover tunnels and subways was unexpected as they had been considered to be relatively safe from earthquake effects compared to above-ground structures. Apparently, except for important facilities and those constructed in soft ground, seismic design is not specifically considered for underground structures in Japan. Because of the damage, a number of research programmes have recently been initiated and the seismic design of these structures will undoubtedly receive greater attention in the future (Wood 2004). A number of large diameter (2.0 – 2.4 m) concrete sewer pipes suffered longitudinal cracking during the Kobe Earthquake, indicating racking and/or compressive failures in the cross-sections (Tohda 1996). These cracks were observed in pipelines constructed Figure 1. Section sketch of damage to Daikai subway station (Iida et al 1996) (Source: Y.M.A. Hashash et al) 2.3 The 1999 Chi Chi, Taiwan Earthquake Several highway tunnels were located within the zone heavily affected by the Chi Chi earthquake in central Taiwan. These are large horseshoe shaped tunnels in rock. All the tunnels were observed intact with no visible signs of damage. No damage was reported in the Taipei subway, which is located 100 km from the ruptured fault zone. However, a large partially underground rectangular concrete tank at the Taichung County Water supply treatment plant was extensively damaged with a large section of the roof collapsing (Brunsdon 1999). Causes of the damage are unknown but it is likely that earthquake-induced pressures on the walls were a significant factor. Given the old and recent damaged to rectangular underground structures due to earthquakes, there is a need for more attention in developing better rational approach on seismic design of these structures. 3. BURIED RECTANGULAR STRUCTURE PREVIOUS RESEARCH Wang‘s 1993 monograph still remains the most comprehensive guideline document for seismic design of underground structures. In case of rectangular tunnels, Wang stated three major characteristics of these structures with regards to seismic design standpoint:  Rigid box structures are usually constructed in cut-and-cover method; these are built at shallow depths in soils where seismic ground deformations and shaking intensity are greater. Ceiling slab Base slab
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   Box typetunnels cross sections are usually bigger than circular tunnels; they are usually stiffer relative to the surrounding soil (which is usually soft). These characteristics make soil-structure interaction analysis more important.  The backfilled soil usually may consist of compacted material having different properties than the in-situ soil. This variation should be properly accounted in the design. 3.1 Racking Effect During earthquakes a rectangular box structure in soil or rock will experience transverse rocking deformations (sideways motion) due to the shear distortions of the ground. Ovaling or racking deformations develop in an underground structure when the seismic waves propagate in a direction perpendicular to, or with a significant component perpendicular to, the longitudinal axis, resulting in distortion of cross-section (see Figure 2). Figure 2. Ovaling and racking deformations (Source: Wang 1993) 3.2 Dynamic Earth Pressure Method (Force Method) 3.2.1 Mononobe-Okabe (M-O) Method Originally developed for above-ground earth retaining walls, the M-O method assumes that the wall structure would move and/or tilt sufficiently so that a yielding active earth wedge could form behind the wall. For a buried rectangular structural frame, the ground and the structure would move together, making it unlikely that a yielding active wedge could form. Therefore, its applicability in the seismic design of underground structures has been subject of controversy. Figure 3 shows M-O active wedge form diagram.
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  Figure 3. Mononobe-OkabeActive wedge force diagram (Source: NSCP C102-97) The obvious applicable situation would be a typical “U-section” type of underground construction, where the structure configuration resembles that of a conventional retaining wall. Another situation where M-O method may be applicable is when the structure is located at very shallow depth. There has been an observation that M-O earth pressure when considered as an unbalanced load, may cause a rectangular tunnel structure to rack at an amount that is greater than the deformation of the surrounding ground. The unrealistic result tends to be amplified as the depth of burial increases. This amplification is primarily due to the inertial force of the thick soil cover, which acts as a surcharge and, according to M-O method has to be considered. In spite of this drawback, the method has been shown to serve as a reasonable safety measure against dynamic earth thrust for tunnels buried at shallow depths (e.g. in the Los Angeles Metro Project). 3.2.2 Wood Method Another theoretical method for dynamic earth pressure was derived by Wood (1973). By assuming infinite rigidity of the wall and the foundation, Wood derived a total dynamic thrust that is approximately 1.5 to 2.0 times the thrust calculated by M-O method. Model experiments by Yong (1985) confirmed these theoretical results. A possible application of this method is at the end walls of a subway station, where the end walls act as a rigid shear wall diaphragms and prevent the structure from making sideway movements during earthquakes. However, for regular rectangular cross-sections under plane strain condition, the Wood theory, like the M-O method, would lead to unrealistic results and is not recommended for use in typical tunnel sections with significant soil cover thickness. Rectangular frame structure is exposed on complex earth pressure loadings which will cause the structure to rack; due to its complexity engineers find it more realistic to approach the problem by specifying the loading in terms of deformations. The goal is to ensure that the structure can adequately absorb the imposed racking deformation. 3.3 Free-Field Racking Deformation Method The term “free-field deformations” describes ground strains caused by seismic waves in the absence of structures or excavations. These deformations ignore the interaction between the underground structure
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  and the surroundingground, but can provide a first-order estimate of the anticipated deformation of the structure. Conventionally, it is assumed that the free-field shear distortion is equal to the amount of racking imposed on structure. Free-field deformation method serves as simple and effective design tool when ground shaking intensity is low or the ground is stiff. However, this method will likely result to unnecessary conservatism when the structure is stiff relative to the surrounding soil. The stiff structure may deform less than the surrounding soil. The next section of this paper will show the proposed simplified pseudo-dynamic finite element method procedure prepared by Wood (2004) for the Earthquake Research Commission in New Zealand using this free-field racking deformation method. Wood’s procedure uses graphical solutions adopted from Wang (1993) previous work to estimate the free-field shear deformations without the need for numerical analyses. The analyses are applicable for assessing different parameters (e.g. depth of cover of soil, soil layer depth, varying soil shear modulus with depth, structure geometry and influence of soil Poisson’s ratio). However, analysis of curvature and axial response of long structure tunnels was not considered in this procedure. This simplified procedure can be used by designer in actual practice for small structures and for preliminary design of large structures. Note that NCHRP 2008 also recommends Wang’s (1973) work and recommends this analysis methodology as rational, comprehensive and provides a consistent and unified approach to solving the problem of buried conduits subject to ground shaking whether they are rigid or flexible structures and with some adjustments this approach is also applicable for culverts and pipe structures typically used for highway construction. 4. ANALYSIS METHOD FOR RACKING (BOX CULVERT EXAMPLE) A standard box culvert has internal dimensions of 3 x 3 m and was assumed to be covered by 4 m of soil in 50 m deep soil layer with a shear modulus G varying parabolicaly from zero at the surface to 200 MPa at the rigid base. The average calculated Gs value over the height of the structure was 44 MPa corresponding to shear wave velocity vs of about 150 m/s. This velocity indicates medium density sediments. The design peak ground acceleration ad at the surface was taken as 0.4 g. The walls were assumed to have a uniform thickness of 400 mm although in practice most culverts are constructed with a 50 mm thicker base. 4.1 Analysis Method Steps (a) Calculate the average soil shear modulus over the height of structure. (b) Calculate the structure elastic flexibility, fst ∆ (1) Where; K r E is Young’s modulus for the material equal to 30000 MPa, Iw = and Ir are the moments of inertia per unit length of the wall and roof respectively. H, L and j are defined in Figure 4 below. If the roof and floor have equal flexural stiffness coefficients (j = 1) then Equation (1) becomes: 1 (2)
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  For the caseof infinitely rigid floor, which might be a reasonable approximation for a structure constructed on a rock base, Equation (1) becomes: (3) For multi-barrel or multi-storey structures with complex geometry, the racking flexibility can be readily computed using conventional frame analysis software. Figure 4. Single-barrel box frame Figure 5. Single-barrel box model (Source: Wood 2004) (Source: Wood 2004) (c) Calculate flexibility ratio, Fr and strain ratio, R (d) Calculate design earthquake surface strain and the soil strain at the level of structure using Figure 6 and correct for the soil layer base shear modulus using Equation (3). Note that value of Gave in chart is 100 MPa, for this example it should be corrected to 200 MPa. fc =f1 (4) Where; s = uniform density of soil, Hs = height of soil layers, 1 = first shear mode strain response from Figure 6. (e) Calculate the structure shear deflection from the interaction shear strain using Equation 4 st =st (5) Where; st =fd (6) Where; fd =fc (7)  Rp=st / fd (8) (f) Calculate the earthquake induce moments at top and bottom corners of structure using Equations (8) and (9) respectively. ∆ 1 (9)
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  ∆ (10) Figure 6.First shear mode strain response (Source: Wood 2004) Notations: Ds = soil cover depth = 50 m H = overall height of structure equal to 3.8 m L = overall length of structure equal to 3.8 m tw = wall thickness = 0.40 m tr = roof thickness = 0.40 m tf = floor thickness = 0.40 m Kw = wall stiffness Kf = floor stiffness Kr = roof stiffness fst = structure flexibility fs = displaced block of soil flexibility Fr = flexibility ratio = fst / fs d = assumed ductility factor = 1.0 fsi = inelastic structure flexibility = fst d s = soil density ad = design level peak ground acceleration f1 = 1-g free-field shear strain from Figure 6 st = structure shear strain
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  fc = 1-gfree-field shear strain from Figure 6 corrected for actual value of shear modulus G fd = design level free-field shear strain = fc ad Rp = interaction strain ratio = st / fd st = structure shear deflection Gs = average shear wave velocity of soil Gb = shear wave velocity of soil at base of structure (layers assumed to have parabolic variation) r = ratio of roof/wall thickness = 1.0 q = ratio of wall/roof thickness = 1.0 j = ratio of floor/roof thickness = 1.0 Note: The author recommends referring to work of Wood (2004) for the handy graphs that can be use to easily get Fr and Rp for different parameters (e.g. structure geometry, soil depth of layer, soil cover depth over the structure, varying soil shear modulus). Latest verification of this design procedure is presented in NCHRP Report 611 – Buried structures and is being recommended for adoption in AASHTO specifications. 5. CONCLUSIONS The paper presented a quick review of currently available seismic design requirements in the Philippine for earth-retaining structures. It was compared to New Zealand codes because both countries are prone to strong ground shaking and to utilize the gathered lessons learnt from recent Canterbury. The damaged of previous of earthquakes worldwide shows that buried structures had generally performed well compared to surface structures. However, there were notable damages that had occurred and were observed to be related to some factors that were overlooked in the design due to lack of guidance and/or in the behavior of buried structures during earthquake events. The previous known literature for guidance of seismic design of rectangular buried structures was reviewed to extend the knowledge of engineers for the complex behavior of these structures. It is noted that the traditional dynamic earth pressure method that is still being used today are still applicable for design as long as its limitations are carefully addressed. It was pointed out from old and new literature that buried structures depends on deformation of surrounding ground rather than the inertial forces. A soil-structure interaction analysis should be used to avoid over or under estimation in the design. Recent literatures have provided more simplified design procedure to be use in actual practice without the need of time consuming numerical analyses. The author’s view is to review the recent recommended procedures and come-up with design manual or guidance for buried rectangular structures to minimized disparity in the seismic design and improve efficiency in review of other engineers for these kinds of projects. Due to rapid urbanization happening in the country, projects involving buried structures (e.g. cut-and-cover tunnels for transport and water infrastructure) and rehabilitation of existing ones will be prevalent due to limited space in our cities. REFERENCES Anderson et al (2008) “Seismic analysis and design of retaining walls, buried structures, slopes, and embankments”. NCHRP National Cooperative Highway Research Program Report 611, transportation Research Board, Washington D.C. Kirkaldie, D.K. and Wood J.H. (2008) “Review of Australian Standard AS 5100 Bridge Design with a view to adoption – Volume 1”. New Zealand Transport Agency (NZTA)
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  New Zealand BuildingAct 2004 Section 175 “Seismic design of retaining structures guidance – Version 2”. Ministry of Business, Innovation and Employment NSCP C101-10 National Structural Code of the Philippines, Volume 1 “Buildings, towers and other vertical structures”. Association of Structural Engineers of the Philippines, Inc. (ASEP) NSCP C102-97 National Structural Code of the Philippines, Volume 2 “Bridges - Reprint Edition 2005”. Association of Structural Engineers of the Philippines, Inc. (ASEP) Palermo et al (2011) “Lessons learnt from 2011 Christchurch Earthquakes: Analysis and Assessment of Bridges”. Bulletin of New Zealand Society for Earthquake Engineering, Vol. 44, No.4, December 2011 Wang (1993) “Seismic design of tunnels: A simple state-of-the-art design approach”. Monograph 7, Parsons Brinckerhoff Inc. Wood, J.H. (1973) “Earthquake-induced soil pressures on structures”. EERL 73-05, Earthquake Engineering Research Laboratory, California Institute of Technology. Wood, J.H. (2004) “Earthquake design procedures for rectangular underground structures”. Project Report to Earthquake Commission, EQC Project No. 01/470. Wood, J.H. (2007) “Earthquake design of rectangular underground structures”. Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 40, No. 1. Wood, J.H. (2012) “Performance of retaining walls in the 2010 – 2011 Canterbury earthquakes”. John Wood Consulting, Lower Hutt, New Zealand Hashash, Y.M.A et al (2001) “Seismic design of and analysis of underground structures”. International Tunneling Association (ITA) Working Group No. 2: Research, Tunneling and Underground Space Technology 16 (2001) 247-293 ABOUT THE AUTHOR The author is a registered professional civil engineer and is currently assigned as senior civil/structural engineer at Cardno Philippines. He is an active regular member of ASEP and a life-member of PICE South Metro Manila Chapter. He received his civil engineering bachelor’s degree from Polytechnic University of the Philippines. His 14 years of professional experience involves engineering and design of structures and foundations for various industrial and infrastructure projects using local and international codes/standards and had worked with different nationalities. He is currently involved in physical infrastructure projects in the Philippines. Their office is located at Level 3B, 111 Paseo de Roxas Bldg., Paseo de Roxas cor. Legaspi St., Legaspi Village, Makati 1229. Email: [email protected]. Tel. No: +63 2 728 4027.Mobile No. +63 998 539 4241. ACKNOWLEDGEMENT The author would like to thank the support of the Cardno Philippines in preparing and presenting this paper for the 17th ASEP International Convention.