305DEO1 VITAS HEALTH CENTER (PROPOSED 2-STOREYBUILDING

A.M. Geoconsult & Associates DPWH North Manila Engineering District Geotechnical Investigation Report Vitas Health Center (Proposed 2 Storey Building)

1305DEO1_RGIR_DSR_0 Page 1 of 17

PROJECT INFORMATION

Project Reference #: 1305DEO1

Project Name: VITAS HEALTH CENTER (PROPOSED 2-STOREYBUILDING)

Project Location: VIB COMPOUND, VITAS, TONDO, MANILA

Client: DPWH NORTH MANILA ENGINEERING DISTRICT

Client’s Address: DPWH NAGTAHAN, STA. MESA, MANILA

Consultant: -

Contact Number: -

1.0 INTRODUCTION

The DPWH North Manila Engineering District, henceforth known as the Client, acquires

the services of A.M. Geoconsult& Associates to conduct a subsurface investigation of a

Proposed Two (2) Storey Building (Vitas Health Center) located at VIB Compound,

Vitas, Tondo, Manila, Philippines.

The objectives of this report is to provide geotechnical assessments based on the

results of laboratory tests using soil samples obtained underlying the site.

Recommendations on the following are then provided for the foundation scheme of the

structures:

1. Screening for potential problems such as expansive or liquefiable soils

2. Allowable bearing capacities of possible foundations

3. General guidelines in construction execution



2.0 SCOPE OF WORK SUMMARY

Two boreholes are drilled within the vicinity of the proposed building. Standard

Penetration Testing (SPT) is performed at every 1.50 meter interval and core samples

are taken when hard strata or rock material is encountered. Both boreholes are

advanced to a depth of 15.00 meters for good measure of the underlying material.

The samples are subjected to routine laboratory tests to determine the classification of

the materials using the Unified Soil Classification System (USCS) and their

corresponding engineering properties.

2.1 DETAILS OF FIELD WORKS

Table 1. Summary of field works

Borehole No. Drilling Depth (m) No. of Samples

SPT Coring

1 15.00 10 0

2 15.00 10 0

2.2 DETAILS OF LABORATORY WORKS

Table 2. Summary of laboratory works

Laboratory Test No. of Samples

Particle Size Distribution 20

Moisture Content 20

Atterberg Limits 20

Unified Soil Classification System 20



3.0 GEOLOGY AND SITE CONDITIONS

3.1 GENERAL AREA

The site is located in Tondo, Manila; an area that is near the coast of Manila Bay. The

project location is undoubtedly underlain by alluvial soils. Erosion from high plateau

cities (such as Quezon City) and mountains from the north east are brought to Pasig

River and are eventually deposited to Manila Bay (refer to Figure 1).

Figure 1. General location (Google Earth)

3.2 SITE SPECIFIC

The proposed two storey building is located within a compound with existing

surrounding structures.

Flood is a normal occurrence in the area. This prompts a worst case scenario in

foundation analysis, wherein ground water level is assumed to be at grade elevation.

3.3 SEISMICITY

The nearest seismic source for the project would be the Valley Fault System. The site is

approximately located at a distance of 10 km from an active segment of the West Valley

Fault. A study by Punongbayan et al (1997) predicted that Metro Manila is likely to

experience a magnitude 7.5 earthquake centred along the Valley Fault.

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Although some segments of Valley Fault System are considered active, it has yet to

move. Historically, four (4) seismic sources have been identified as the cause of major

earthquakes in Metro Manila. These are the Philippine Fault Zone, Lubang Fault,

Casiguran Fault, and Manila Trench.

4.0 METHODOLOGY OF THE INVESTIGATION

4.1 FIELD SAMPLING & TESTING

The boreholes are advanced by rotary drilling and wash boring method. Alternately with

these methods, SPT is conducted at every 1.5 meter depth interval on soil layer, while

rotary drilling on hard materials down to the bottom of the hole. Protective casings are

inserted around the hole with a drop hammer to prevent materials from collapsing. The

boring operation entails the following phases:

a) Rotary Drilling

A method employed when hard materials are encountered or where the N-value

exceeds fifty (50). Under rotary action, the 46 mm diameter core bit is advanced into

the rock with core runs between 1.00 to 1.50 meters.

b) Wash Boring

A process in advancing the borehole by applying an up and down twisting motion of

a drill or chopping bit attached to the ends of drill rods while simultaneously allowing

a stream of water pumped through the rods to the soil. The combined action of the

water jet and chopping loosens the soil and is flushed to the surface.

c) Standard Penetration Test (ASTM-D1586)

The main sampling procedure conducted at every 1.50 meter depth interval using a

Donut free fall type of hammer. It involves placing a 50.80 mm (O.D.) diameter split

spoon sampler with the drilling rod into the ground at the bottom of the borehole. The

hammer weighs 63.50 kg and is dropped a distance of 762 mm to produce a

theoretical input driving energy (Ein) of 473.28 Nm. The number of blows to penetrate

every 150 mm interval is recorded successively until the third interval is penetrated.

The first interval blow count is considered as the seating drive and is discarded. The

last two blow counts from the second and third intervals are added to give what is



known as the N-value. Disturbed soil samples obtained by the split spoon were

collected for visual inspection and laboratory testing.

d) Ground Water Level

This measurement is done by lowering a weighted tape down the hole until water

contact is made. Readings are made after water is allowed to stand for a minimum

period of 12 hours following completion of the drilling. The observation made during

this period is assumed as the ground water level.

4.2 DETAILS OF LABORATORY WORKS

The following laboratory tests are performed in accordance with the specified

procedures from the American Society for Testing and Materials (ASTM). Appropriate

test procedures are referenced in ASTM Manuals for the soil tests discussed in the

following sections:

a) Natural Moisture Content (ASTM-D2216)

This test is also known as water content. It is the ratio expressed as a percentage of

the weight of water in a given mass of soil to the weight of the solid particles.

b) Grain Size Analysis of Soils (ASTM-D422)

A process wherein the proportion of each grain size present in a given soil sample

(grain-size distribution) is determined. The grain- size distribution of coarse –grained

soils is determined directly by sieve analysis, while that of fine-grained soils is

determined indirectly by hydrometer analysis. The grain-size distribution of mixed

soils is determined by combined sieve and hydrometer analyses.

c) Atterberg Limits of Soils (ASTM-D4318)

A procedure that consists of several parameters that are primarily water contents

which define the limits of various stages of consistency for fine-grained soils. The

liquid limit (LL) and the plastic limit (PL) define the upper and lower limits,

respectively, of the plastic range of a soil; the numerical difference between these

two limits expresses the plasticity of a soil and is termed the plasticity index (PI).

d) Classification of Soils for Engineering Purposes (ASTM-D2487)



In general, soils are classified based on the Unified Soil Classification System

(USCS). In this system, soil falls within one of the three major categories: coarse-

grained, fine- grained, and highly- organic soils.

5.0 RESULTS OF INVESTIGATION

Below is a summary of the results of each borehole. The profiles of the index properties

and in-situ moisture content of each borehole are also illustrated. The green line

represents the magnitude of the plasticity index, with the left boundary as the plastic

limit and the right boundary as the liquid limit. The blue line corresponds to the in-situ

moisture content. Lastly, the red dashed line shows the measured groundwater level at

the site.

Table 3. Summary of results, BH-1

BOREHOLE 1

DEPTH (m) N-Value USCS DESCRIPTION CONSISTENCY

INDEX PROPERTIES

0.0 – 1.5 8 SC-SM Silty clayey SAND w. gravel Loose

1.5 – 3.0 12 SC Clayey SAND Medium Dense

3.0 – 4.5 31 SC Clayey SAND w/ gravel Dense

4.5 – 6.0 24 SC Clayey SAND Medium Dense

6.0 – 7.5 8 ML SILT w/ sand Medium Stiff

7.5 – 9.0 45 SC-SM Silty clayey SAND Dense

9.0 – 10.5 45 SC Clayey SAND w/ gravel Dense

10.5 – 12.0 53 SM Silty SAND w/ gravel Very Dense



END OF DRILLING



Table 4. Summary of results, BH-2

BOREHOLE 2

DEPTH (m) N-Value USCS DESCRIPTION CONSISTENCY

INDEX PROPERTIES

0.0 – 1.5 7 SC-SM Silty clayey SAND w. gravel Loose

1.5 – 3.0 17 SC-SM Silty clayey SAND Medium Dense

3.0 – 4.5 34 SM Silty SAND Dense

4.5 – 6.0 16 SM Silty SAND Medium Dense

6.0 – 7.5 27 ML Sandy SILT Very Stiff

7.5 – 9.0 43 SM Silty SAND Dense

9.0 – 10.5 45 SP-SM Well-graded SAND Dense

10.5 – 12.0 58 SC Clayey SAND w/ gravel Very Dense

12.0 – 13.5 65 SC-SM Silty clayey SAND w/ gravel Very Dense

13.5 – 15.0 65 GC Clayey GRAVEL w/ sand Very Dense

END OF DRILLING

6.0 ENGINEERING ANALYSIS AND CONSIDERATIONS

6.1 SITE CONDITIONS

The boreholes consistently reveal that the surface layer comprises of alluvial soils

characterized by predominantly sands in varying proportions of fine-grained materials.

There is irregularity with increasing depth; a deeper soil layer may be less dense

compared to shallower layers. This just confirms the predicted geology of a dynamic

alluvial depository area.

With the inconsistencies of the surface soils, it is highly likely that the site will

experience differential settlement.

After the first 9.0 meters, the soils encountered are considered to be competent layers.

The presence of alluvial soils at the surface is also a cause for immediate concern

since these soil types are potentially liquefiable. These layers warrant a closer

inspection prior to recommending foundation schemes.



6.2 LIQUEFACTION POTENTIAL

In evaluating the potential of the soil for liquefaction, the simple criteria provided by the

National Structural Code of the Philippines, (NSCP) 2010, Section 303.4 is used. Soils

meeting all three of the following provisions will be considered liquefiable:

1) Shallow ground water, two meters or less

2) Unconsolidated saturated alluvium (N<15)

3) Seismic Zone 4

The project site is clearly located in a Seismic Zone 4. The upper 9.0 meters of soil is

also considered to be unconsolidated alluvium as derived from the index properties.

Finally, the same upper layers show samples having N-values less than or close to 15.

The hazard map provided by the Philippine Institute of Volcanology & Seismology (refer

to Figure 2) further calls for attention. It shows that the project area is questionably at

the boundary of the said liquefiable soils. This, however, serves only as a guide and

detailed calculations of engineering properties is needed for confirmation.

Figure 2. Liquefaction hazards in Metro Manila (Philvocs)



The loose to medium dense layers classified as predominantly cohesionless soils are

the primary target. Due to lack of testing specific to liquefaction, analysis is done by

correlating to SPT N-values. The Factor of Safety (FS) for liquefaction potential is

calculated as the ratio of the Cyclic Resistance Ratio (CRR) to the Cyclic Tress Ratio

(CSR).

FS=CRR / CSR

Where

Table 5. Summary of potentially liquefiable cohesionless soils

BH No. Depth (m) CRR CSR FS

1

0.0 – 1.5 0.088682 0.508893 0.174264

1.5 – 3.0 0.129916 0.494567 0.262687

3.0 – 4.5 0.341792 0.479559 0.712721

4.5 – 6.0 0.267222 0.471611 0.566615

2

0.0 – 1.5 0.079845 0.511437 0.15612

1.5 – 3.0 0.183471 0.492265 0.372708

3.0 – 4.5 0.509445 0.476764 1.068548

4.5 – 6.0 0.172844 0.470587 0.367294

*amax = 0.4g **the factor of safety is at earthquake magnitude 7.5

These data show that the project area is susceptible to liquefaction. The distribution of

potentially liquefiable soils within the project area is not fully known since the boreholes

show variations in consistencies. What is consistent is the fact that the hazardous

layers are encountered only up to depths of 9.0 meters.



But, as mentioned, this general analysis is based only on SPT correlations. It is

recommended that further testing should be conducted specific to liquefaction.

6.3 FOUNDATION DESIGN RECOMMENDATION

The exact structural details for the proposed school building are not known during the

making of this report. The following are generalized recommendations.

Considering the soil profile from the borehole results and the potential for problems, the

proposed building is recommended to be fitted with the following foundation schemes:

Shallow Foundation:

Mat Foundation

Deep Foundation:

Driven piles

Bored piles

Options are provided for the discretion of the structural designer, however, it is strongly

recommended to incorporate BORED PILES in the design.

It is important to verify, during construction, if the soil profile is consistent throughout the

project area. Discrepancies such as varying soil properties or presence of

discontinuities must be taken into account for the design of the foundation.

6.4 SHALLOW FOUNDATION

The maximum load that the underlying soil may carry from the structure is estimated

using Terzaghi’s (1943) bearing capacity equation below.

Qu = cNcsc+ γ1DfNq + 0.5γ2BNysy

where: Qu = ultimate bearing capacity

c = cohesion

Nc,Ny,Nq = bearing capacity factors

B = width of footing

Df = footing depth (embedment depth)

γ1 = effective unit weight of soil above footing level



γ2 = effective unit weight of soil below footing level

sc = shape factor (strip=1.0, square=1.3)

sy = shape factor (strip=1.0, square=0.8)

Qa = Qu / FS

where: Qa = allowable bearing capacity

FS = factor of safety (standard practice=3.0)

Figure 3. Diagram of a typical footing

It is estimated that settlement will not exceed 25 mm due to the caution provided by the

factor of safety.

a) Mat Foundation

In terms of shallow foundations, mat foundations are the best approach in preventing

damages from differential settlement.

Listed below are the possible bearing capacities for a mat foundation. The building’s

shorter width corresponds to the listed footing widths. The trends of the capacities are

also presented and may be used for estimating values using other dimensions (refer to

Figure 4).

B = width of footing

Df = footing depth



Table 6. Summary of Allowable Bearing Capacities Mat Foundation

Footing Width (B), m Allowable Bearing Capacity (Qa), kPa

Df = 1.0 m Df =1.5 m Df = 2.0 m Df = 3.0m

5.0 175 204 233 291

8.0 246 275 304 362

12.0 341 370 399 456

15.0 412 441 470 527

Figure 4. Trendlines of allowable bearing capacities with varying mat foundation dimensions

b) Other Considerations

The embedment depth requirement of any of the foundation scheme should satisfy the

lateral stability and structural integrity of the proposed structure.

The bearing capacities can be increased by 33% for analysis involving transient loads

in combination with wind and seismic forces.

The pressure due to the excavated material must also be added to the recommended

values. An estimated unit weight of18 kN/m3 may be used.



6.5 DEEP FOUNDATION

The most favourable option for this project is to adopt a deep foundation scheme in a

form of driven or bored piles. With this system, problematic soils are bypassed by

transmitting the loads deeper into competent layers.

It is up to the designer on which pile type to use, but it is recommended to use bored

piles since the project is within an existing campus. Pile driving may cause not only

disturbance to students and civilians, but the vibrations from the force of the hammer

may also cause settlement on the surrounding structures.

Presented below are the recommended pile dimensions and its corresponding

allowable bearing capacities. The NAVFAC Design Manual 7.02 for vertical capacity

analysis is used for deriving the values.

Table 7. Summary of Allowable Bearing Capacities of DRIVEN Piles

Pile Width = 400 mm

Depth (m) *Allowable Bearing Capacity

(kPa)

0.0-1.5 11

1.5-3.0 60

3.0-4.5 189

4.5-6.0 173

6.0-7.5 121

7.5-9.0 453

9.0-10.5 564

10.5-12.0 796

12.0-13.5 944

13.5-15.0 1099

*Allowable bearing capacities are calculated using a Factor of Safety = 3.0



Table 8. Summary of Allowable Bearing Capacities of BORED Piles

Pile Diameter = 600 mm

Depth (m) *Allowable Bearing Capacity

(kPa)

0.0-1.5 11

1.5-3.0 56

3.0-4.5 175

4.5-6.0 168

6.0-7.5 131

7.5-9.0 433

9.0-10.5 545

10.5-12.0 768

12.0-13.5 917

13.5-15.0 1076

*Allowable bearing capacities are calculated using a Factor of Safety = 3.0

It is recommended that the pile foundations should at least penetrate to a depth of 10.0

meters in order to completely bypass any possible liquefiable soils.

For reasons wherein the given recommendations are insufficient, the unit resistances

per layer are listed below and may be used for estimating values using other

dimensions. To compute for the corresponding bearing capacity, the following

equations may be used:

Qu = Qb+∑Qs

where: Qu = ultimate bearing capacity

Qb = ultimate base resistance

Qs = ultimate side resistance

Qu = fbAb+∑fsAs

where: fb = unit base resistance for each layer

fs = unit side resistance for each layer

Ab = area of pile base

As = surface of pile shaft for specified layer

Qa = Qu / FS

where: Qa = allowable bearing capacity



FS = factor of safety (standard practice=3.0)

Table 9. List of pile unit resistances

Recommended Unit Resistances

Depth (m) DRIVEN PILE BORED PILE

fb (kPa) fs (kPa) fb (kPa) fs (kPa)

0.0-1.5 125 8 64 8

1.5-3.0 838 20 411 20

3.0-4.5 2891 37 1430 37

4.5-6.0 2150 45 1057 45

6.0-7.5 739 43 376 43

7.5-9.0 6188 78 3061 78

9.0-10.5 7335 93 3628 93

10.5-12.0 10588 111 5248 111

12.0-13.5 12081 127 5988 127

13.5-15.0 13573 143 6728 143

It must be emphasized that the presented values are derived solely from the borehole

results. Discrepancies are possible, especially around alluvial deposits. It is prudent to

confirm the pile capacities by performing static or dynamic load tests. Results of these

tests may be used to adjust the initial estimations.

6.6 FILL CONSTRUCTION

A layer of crushed gravel should be placed under the footings prior to its construction.

The granular fill shall consist of free-draining granular materials with a minimum

thickness of 200 mm. It will be compacted to a minimum of 95% MDD based on ASTM

D1557. This layer will provide drainage under and around the slab and footings.

Any organic or deleterious material shall be removed and will not be permitted in fills.

No rock or similar irreducible material with a maximum dimension greater than 200mm

shall be buried or placed in fills.

6.7 HYDROLOGICAL FACTORS

The measured ground water levels are consistently encountered at around 2.5 meters.

Groundwater intrusion is definitely a problem during the construction of shallow and



deep foundations, especially since the area is prone to flooding. Proper mitigating

equipment such as water pumps must be prepared. At the least, an efficient drainage

system must be provided to release external sources of water by fitting drains or canal

lines.

6.8 EXCAVATION

The soils at the surface may be problematic during excavation due to the shallow

groundwater. Superficial damage may likely happen during heavy rainfall. It is therefore

prudent to provide temporary support systems during construction.

Excavating adjacent to existing structures will remove resisting lateral forces, resulting

in possible lateral failure. This loss of lateral resisting force may be calculated and be

replaced by corresponding support systems. An estimated unit weight of 18 kN/m3 may

be used.

6.9 PAVEMENT DESIGN

As previously mentioned, the site is susceptible to differential settlement. This may

cause problems for slab-on-grade pavements. Since the floor and the footings might

settle at a different rate, cracks may develop. This is far from a threat to structural

integrity, but the Client may opt to prevent superficial damage. The pavements may be

reinforced or suspended as preventive measures.

6.10 SEISMIC DESIGN CONSIDERATION

The nearest fault that can generate large-scale magnitude earthquake for this site is the

West Valley Fault. This fault is situated at an approximate distance of approximately 10

km east from the project site. To satisfy the NSCP code provisions (2010) for

earthquake design of buildings, the seismic response coefficients and near source

factors was determined. For this site having soil profile type SD, the near source factors

are Na = 1.2 and Nv = 1.6, and seismic response coefficients are Ca = 0.44Na and Cv =

0.64Nv. The site falls in the Seismic Zone 4, having Z=0.4.



7.0 LIMITATIONS

The geotechnical evaluation and recommendation given above were based on the

results from the two (3) boreholes and has been prepared as a guide in the design of

the proposed structure. The analyses and recommendations submitted in this report

are based, in part, on information obtained from field borings and laboratory test in

accordance with the generally accepted engineering principles and practices. Its scope

is limited to the location and type of structure described herein. Variations of subsoil

conditions between the borings may occur, and the nature and extent of these

variations may not become evident until construction is underway. The owner/client

should be aware that unanticipated soil/rock conditions are commonly encountered.

Unforeseen soil/rock conditions, such as perched groundwater, soft deposits, hard

layers, or cavities, may occur in localized areas and may require probing or corrections

in the field to attain a properly constructed project.

In the event that this report is used in other projects for design purposes or

recommendations contained in this report are not followed, the Undersigned disclaim its

responsibility. If there is any difference in location and/or design features as we

understand them and as are defined by the test borings, the Undersigned should be

informed thru this office so that appropriate modification can be made.

Prepared by:

DAVID DENNIS V. STA. ROSA, MS CE (G)

Civil/Geotechnical Engineer

PRC No.: 0118783

June 3, 2013

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305DEO1 VITAS HEALTH CENTER (PROPOSED 2-STOREYBUILDING