2 - DOTr

ANNEX B

GEOLOGICAL AND GEOTECHNICAL INVESTIGATION REPORT FOR STATIONS

TABLE OF CONTENTS Page No. CHAPTER 1 INTRODUCTION................................................................................................... 1 CHAPTER 2 PHYSIOGRAPHY ................................................................................................. 2 Location and Accessibility................................................................................................ 2 PART - I GEOLOGY AND SEISMICITY ..................................................................................... 2 A.

B. C.

Geology ............................................................................................................... 2 1. Quaternary Alluvium ................................................................................. 2 2. Diliman Tuff .............................................................................................. 3 Seismicity ............................................................................................................ 3 Peak Ground Acceleration ................................................................................... 4

Part – II GEOTECHNICAL INVESTIGATION ............................................................................. 5 CHAPTER 3 RESULTS OF GEOTECHNICAL INVESTIGATION............................................... 5 Field Information .............................................................................................................. 5 A. Depth of Water Table ........................................................................................... 5 1. Soil Profiles .............................................................................................. 5 CHAPTER 4 SOIL AND ROCK STRENGTH .............................................................................. 7 CHAPTER 5 FOUNDATION SYSTEM ..................................................................................... 10 A B. C. D.

Pile Foundation .................................................................................................. 10 Modulus of Subgrade Reaction .......................................................................... 11 Susceptibility to Liquefaction .............................................................................. 11 Chemical Analysis of Soil and Groundwater Underlying the Stations ................. 12

CHAPTER 6 CONCLUSION AND RECOMMENDATION ........................................................ 13 LIMITATIONS .............................................................................. Error! Bookmark not defined.

LIST OF TABLES Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8

Maximum Credible Earthquakes.................................................................................... 4 Peak Ground Acceleration............................................................................................. 4 Correlation of N-Value and Clay Strength ...................................................................... 7 Summary of Soil and Rock Properties – Emerald Station .............................................. 7 Summary of Soil and Rock Properties- Masinag Station ............................................... 9 Allowable Pile Capacity ............................................................................................... 10 Modulus of Subgrade Reaction ................................................................................... 11 Result of Chemical Test on Soil Sample from BH-60................................................... 12

Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project

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APPENDICES Appendix-1 Appendix-2 Appendix-3 Appendix-4 Appendix-5 Appendix-6 Appendix-7 Appendix-8

Project Area Location Plan Borehole Location at Emerald Station Borehole Location at Masinag Station Regional Tectonic Setting Seismicity Map Soil Profile at Emerald Station Soil Profile at Masinag Station Summary of Test Results (BH 59 to BH 64)


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CHAPTER 1 INTRODUCTION Apart from the Geotechnical Investigation undertaken on the viaduct alignment, drilling was also made for the proposed Emerald Station (Sta. 24+344.041 to Sta. 24+444.041) and Masinag Station (Sta. 26+796.041 to Sta. 26+896.041) along Marcos Highway. Intended primarily for site geotechnical characterization, three boreholes were drilled at Emerald Station and also three boreholes at Masinag Station. All the boreholes were advanced adequately to reach the highly dense soil (N>50 blows) and/or bedrock level. The borehole locations at Emerald Station are indicated at Appendix-2, and for the Masinag Station, at Appendix-3. Earlier, 58 boreholes were drilled along the viaduct alignment. Not all the boreholes reached bedrock level but the information obtained generally indicated appreciable alluvium thickness at Santolan Station (more than 40 meters thick) and that it progressively decreases towards the end of the project at Masinag. The drilling investigation is done to determine the soil and rock types, their vertical and lateral persistency and engineering properties. The boreholes are correlated to obtain indications on the general soil distribution and variability. As mentioned in the earlier report on the viaduct alignment, the LRT Line-2 East (Masinag) Extension Project is entirely located along Marcos Highway. It is sandwiched between two active major faults, the West and East Valley fault systems. As the traces of these active faults are less than 2 km from the site, ‘a near field’ tectonic movement could be expected in case any of the two fault systems rupture. Assessment of the regional seismicity had been covered in the previous report. However, a brief discussion of the surrounding fault generators cannot be ignored in this report because the liquefaction susceptibility of the underlying structural foundations has to be analyzed.


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CHAPTER 2 PHYSIOGRAPHY Location and Accessibility LRT Line-2 East (Masinag) Extension Project spans the entire Marcos Highway starting from the existing Santolan Station until Masinag, Antipolo, Project Area Location Plan (Appendix-1). For the 4.1 km long extension two stations shall be added: (1) Emerald Station at Sta. 24+344.041 to Sta. 24+444.041 and (2) Masinag Station at Sta. 26+796.041 to Sta. 26+896.041. Emerald Station is situated between the two malls, Robinsons and Sta. Lucia while Masinag Station is near SM Masinag. Marcos Highway is connected to Cubao, Quezon City via Aurora Boulevard. The entire project area is located within Marikina Valley. The topography is essentially flat to broadly rolling near the end of the alignment at Masinag. It is bounded by hilly to mountainous terrain on the east of Masinag and by slightly elevated flat to rolling terrain on the west (Quezon City side). Rock crops out at Quezon City and at Masinag but the entire viaduct alignment is blanketed with alluvial soils of variable thickness.

PART - I GEOLOGY AND SEISMICITY The geological setting and seismicity have been covered on the Engineering Geological and Geotechnical Report (EGGAR). However because of its importance on the assessment of liquefaction of the soil foundation it will be discussed briefly in this report. The existence of active faults, the valley fault system near the project site, is a compelling reason to include discussion of these items in this report. A.

Geology As the project area is covered with thick alluvium, no rock crops out at the two stations and along the entire viaduct alignment. Consequently, the site geological environment is based on the rock exposures outside of the project area and on the results of drilling. 1. Quaternary Alluvium Drilling information indicated very thick deposits of sediments reaching more than 40 meters near the Santolan Station. Within the first few hundred meters from Santolan Station to Masinag the sediments consist mainly of layered clays largely varying in composition from clay and clayey silt invariably with high degree of plasticity. Occasionally, it includes thin beds of silty sand, sandy silt and sandy clay. Deep boreholes indicated the presence of bedrock at variable depths but not shallower than 43 meters beneath the ground surface. However sediment thickness gradually diminishes as the distance increases from Santolan Station. At the end of the alignment at Masinag the thickness is reduced to less than 10 meters. Sand and gravel beds tend to increase in proportion to clay towards Masinag. At the Emerald Station, about 1.20 km from Santolan, the sediments are still relatively thick, ranging from 25 to 35 meters thick. The upper section, up to about 15 to 18 meters below the surface, is predominantly clay but changes largely into gravel and sand beds at the lower section. The sediments overlie Diliman tuff at variable depth, varying from 25 to 35 meters below the surface. At Masinag Station the sediment thickness is relatively limited and it consists mainly of gravel and sand with limited clay beds. The underlying Diliman tuff bedrock lies about 7 to 9 meters below the ground surface.


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2. Diliman Tuff Diliman tuff, the upper member of the Pliocene to Pleistocene Guadalupe Formation, is the bedrock at the project area. It is not known to crop out anywhere within the project area. The only known exposures are near Masinag Market and at nearby slopes in Quezon City. Commonly, it is comprised of pyroclastic rocks mainly tuff, commonly with inter-layered tuffaceous sandstone and agglomerate. Based on borehole information however Diliman tuff consists predominantly of tuffaceous sandstone with associated tuff beds at the project area. At Emerald Station the underlying bedrock consists of thinly bedded tuffaceous sandstone in close association with agglomerate and limited tuff. Thinly layered, the bedrock trends N10 W and dips slightly towards the SW. The rock occurs at the bottom of the boreholes at depths of 25 to 33 meters below the surface. Geologically, Diliman tuff is classified as soft rock as its unconfined compressive strength usually ranges from 1 to 5 MPa. Rock strength is commonly affected by degree of weathering and the associated fractures. At the site, the Diliman tuff is commonly slightly weathered to fresh. Its unconfined compressive strength averages 33 Kg/ cm2. B.

Seismicity The regional tectonic setting is indicated in Appendix-4. The Philippine Archipelago is surrounded by opposite trending subduction zones such as the Manila Trench, the Negros Trench and Sulu Trench on the western side and the East Luzon Trough and Philippine Trench on the eastern side. Most of the major earthquakes, volcanic activity and orogenic processes are associated with plate tectonics. Apart the subduction zones, major active faults are known to occur within a radius of 200 km of the site. The most prominent of these is the Philippine Fault Zone whose mapped fault trace extends at least 1200 km long from northern Luzon to eastern Mindanao. As far as the project area seismicity is concerned, however, the presence of the Marikina Valley Fault System whose mapped fault trace is less than 2 km away from the site is the most disturbing. Other active faults that are expected to contribute to the area seismicity include the East Luzon Trough, Manila Trench, Casiguran fault, Lubang fault, and Macolod Corridor fault. The seismicity associated with the various active fault zones, subduction zones and trenches has been discussed in the main report. Recent earthquakes associated with the various active faults as well as their distances with respect to the project area were covered in the report. The seismicity related with the Marikina Valley Fault System however requires special consideration because of its nearness to the project area. The Marikina Valley Fault System (MVFS) consists of two parallel northeast trending dextral faults, Appendix-5 shows the Seismicity Map located on the eastern and western borders of the valley. The fault on the western side, whose mapped length is longer, is referred to as the West Valley Fault (WVF) while the other fault system on the eastern side the East Valley Fault. Obscured by thick alluvial over, the continuity of the faults near the project site is hardly discernible. Because of very close juxtaposition to the site, a ‘near field’ seismic activity could be expected. No historical record which suggests that the MVFS is active. It is known to have displaced Pleistocene Diliman tuff but it has not been established. The northern half of


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the WVF had been mapped recently by PHIVOLCS but its continuity to the south was established mainly on the basis of photo geologic interpretation and satellite imagery. Detailed investigation consisting of trenching, geologic mapping and soil sampling by PHIVOLCS in cooperation with USGS (US Geological Survey) indicated that 3 to 4 earthquake events have occurred during the past 1200 to 1400 years. With a mapped length of at least 150 km, the MVFS is believed capable of generating as much as Ms 7.1 magnitude. Table 1 below indicates the maximum credible earthquakes that the various fault zones are capable of generating as well as the distance of the nearest fault traces to the site. Table 1 Maximum Credible Earthquakes Source of Earth Earthquake Philippine Fault Zone Manila Trench East Luzon Trough Lubang Fault West Valley Fault Casiguran Fault

C.

Distance, km 75 100 120 80 2 200

Magnitude, Ms 8.0 8.0 7.6 7.5 7.1 7.5

Peak Ground Acceleration The ground motion parameter relevant to structural design as well as to analysis of susceptibility to liquefaction is peak ground acceleration (PGA). Owing to utter lack of instrumental record determination of the PGA is extremely difficult. Usual practice is to assume the validity of attenuation relation developed in other countries provided the tectonic environment is highly similar to that of the Philippines. The Fukushima- Tanaka equation, shown below, finds wide acceptance in this country. Log10 A= 0.41 M- Log10 (R + 0.032 x 10 0.41M) – 0.0034 R + 1.30 Where: A = peak ground acceleration in cm/ sec 2 R = shortest distance between the site and fault rupture in km M = surface wave magnitude According to Fukushima and Tanaka, the PGA level at very short distances from the earthquake source is 0.632 g, irrespective of the earthquake magnitude. Considering medium ground condition site soil condition, the PGA expected anywhere within the project site is 0.55 g. Applying the Fukushima-Tanaka equation and assuming medium ground soil condition, the PGA’s attributable to the other earthquake sources are indicated in Table 2. Table 2 Peak Ground Acceleration Earthquake Sources Philippine Fault Zone Manila Trench East Luzon Trough Lubang Fault West Valley Fault System Casiguran Fault

Distance, km 75 100 120 80 2 200


Maximum Credible Earthquake, Ms 8.0 8.0 7.4 7.4 7.1 7.4

Peak Ground Acceleration in g’s 0.16 0.13 0.10 0.10 0.55 0.02

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Part – II GEOTECHNICAL INVESTIGATION CHAPTER 3 RESULTS OF GEOTECHNICAL INVESTIGATION Field Information The results of the field investigation are presented in the form of borehole logs and soil profiles. The borehole logs contain all the drilling information including penetration resistance values, and results of laboratory tests, and description and classification of the soil and rock types. Depth of water table below the sites is also indicated. Plates 59 to 61 are borehole logs of drill holes at Emerald Station while Plates 62 to 64 are for Masinag Station. The boreholes were drilled adequately to reach obtain bedrock level and obtain specimen for unconfined compression test. The lateral persistency and variability of the sedimentation are indicated by correlation of the boreholes. These are indicated in the form of soil profiles. A.

Depth of Water Table Depths of water table below the ground surface are measured after completion of the boreholes. Depth of water table measured in August varies from 3.0 to 3.50 meters. Despite measurements made during the rainy season the depths measured are similar to the information gathered in late May. Piezometers have been installed at BH- 60 at Emerald Station and at BH-63 at Masinag Station. The piezometers are intended to obtain long term data base on water table depth fluctuation. This information is crucial in analysis of susceptibility to liquefaction of the soil foundations. Hopefully, the LRTA management would continue gathering the required information. 1. Soil Profiles The soil profiles represent the soil and rock types, N-Values, depth of water table and unconfined compressive strength of the core samples. The soil types encountered by the various drill holes are correlated so as to obtain indications on the soil variability laterally and vertically. A line connecting the dense soils intercepted by the boreholes are indicated. Dense soil in this report is defined as the soil type whose minimum N-Value is 50 blows. In the same manner a line is also drawn in the soil profile indicating the top of bedrock. Soil Profile -Emerald Station The soil profile at Emerald Station is shown in Appendix- 6. The figure indicates that the initial 14 to 18.50 meters depth consist wholly of cohesive soils. Under the Unified Soil Classification System (USCS) the cohesive soils are classified as clay and clayey silt. The clay and clayey silt are inter-layered and because of variability the soil beds tend to shrink and swell along the line of section. Small lenses of silty clay are occasionally included. The clay and clayey silt are brown to gray and characteristically with elevated plasticity. The liquid limit is generally more than 70 % and the plasticity index almost reaching 40 %. The N-Value distribution with depth is erratic but it slightly indicates a tendency to increase with increasing depth. Average N-Value varies from hole to hole but appears relatively higher below BH-60 and BH-61.


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About 14 to 18.50 meters below the ground surface, the cohesive soil changes to granular soils comprising mainly of gravel and sand. The sand at the lower section is generally medium dense to very dense but quite unexpectedly a thin very loose sand bed (N= 2 to 3 blows) is indicated at 27 to 28 meters below BH- 60 (Emerald Station). The very loose sand is sandwiched between very dense silty sand and very hard clay beds. At such depth range all the sediments encountered by all the boreholes including those drilled along the viaduct alignment are consistently with dense relative density. The reason for the presence of the loose sand at such depth range cannot be explained. As has been consistently observed in practically all the boreholes drilled in the project area, the sediments usually bottomed in very dense gravel and/ or gravelly sand before reaching bedrock level. The hard clays commonly encountered at the near bottom of the boreholes are presumed part of the bedrock except that it is highly weathered. BH-59 and BH-60 intercepted bedrock at the bottom of the holes. BH-61 bottomed on about 9 meters thick of very dense silty sand and gravel beds. Thick succession of tuffaceous sandstone and agglomerate lie beneath the Emerald Station. The rock strength varies from a low of 20.70 kg /cm 2 to a high of 51.95 kg/ cm2. The low strength rocks are moderately weathered while the fresh rocks are much stronger. Soil Profile – Masinag Station The soil profile at Masinag Station is shown in Appendix- 7. It is highly apparent that the soil foundations underlying Masinag Station are widely different from that of Emerald Station in terms of soil type and thickness. Instead of cohesive soils, non-plastic granular soils comprised the overlying soil overburden. Thin beds of silty gravel, clayey sand, clayey gravel and silty sand occur in profusion. In comparison, very limited amount of sandy silt and clayey silt are occasionally associated. N-Value distribution with depth is highly erratic but the upper soil layers are generally relatively loose. The dense soils occur at the bottom, just before reaching bedrock level. The highly dense soil (N> 50 blows) and/or bedrock level lies at much shallower depth as compared to Emerald Station. As expected, the underlying bedrock is similar to those below the Emerald Station. Tuffaceous sandstone inter-layered with tuff, agglomerate and lapilli tuff lies beneath the sediments. Unconfined compressive strength varies from 25.90 to 94.12 kg/cm2. Considering a relatively high average compressive strength of 56.43 kg/cm2, the underlying bedrock appears sound, strong, well cemented and generally fresh.


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CHAPTER 4 SOIL AND ROCK STRENGTH The soil properties are determined on the basis of the SPT information. Rock strength is measured based on unconfined compression tests done on core samples. Difficulty is in measurement of cohesive strength because of the generally stiff consistency of the clayey soils. The unit weight of the soil is measured in the field. Soil samples contained in the split tube sampler are weighed and the volume is measured to obtain the wet unit weight. Sample is obtained to determine the moisture content. Strength of cohesive soils is based on SPT correlation as indicated in Table 3. Table 3 Correlation of N-Value and Clay Strength Clay Consistency

Range of N-Value

Very Soft Soft Firm (medium) Stiff Very Stiff Hard

Below 2 2-4 4-8 8-15 15-30 > 30

Estimated Unconfined Compressive Strength, kPa < 12 12-25 25-50 50-100 100-200 > 200

In the case of granular soils (sand), the angle of internal friction is determined based on the SPT- effective friction angle correlation made by Peck, Hanson and Thornburn (1974) and mathematically approximated by Wolff (1989). Such equation is indicated below: Effective friction angle phi = 27.1 + 0.30 N (adj) – 0.00054 N2 (adj) Where: N (adj) – N-Value adjusted for field condition (overburden pressure, Borehole depth, diameter, etc The N-Values indicated for gravel/ gravelly soils are generally inaccurate especially if the size of the gravel components is large. The N-Value in this case has to be adjusted to a much lower value. The soil properties are summarized and presented in Table 4 for Emerald Station and Table 5 for Masinag Station. Table 4 Summary of Soil and Rock Properties – Emerald Station BH No

Depth m

Soil Type

Field N

N-adj

1.50 3.0 4.50 6.0 7.50 9.0 10.50 12.0 13.50 15.0 16.50 18.0 19.50

SP-SM SM CH CH CH CH CH CH CH MH CH SM SM

10 13 5 6 8 13 21 25 17 19 25 27 13

32 20 7 7 10 14 22 23 14 14 17 17 8

Unit Wt KN/m3

Ave, N

Friction Angle

Cohesion kPa

UCT Kg/cm2

BH-59


16.97

20 ↑

17.60

Ave N=14

17.60

↓

33

Ave 60

17.13

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BH No

Depth m 21.0 22.50 24.0 25.50 27.0 28.50 30.0 31.50 33.0

Soil Type SM SM GM GM TS TS TS TS TS

1.50 3.0 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 16.50 18.00 19.50 21.00 22.50 24.00 25.50 27.00 28.50 30.00 31.50 33.00 34.50 36.00 37.50 39.00 40.50 42.00 42.50 1.50 3.00 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 16.50 18.00 19.50 21.00 22.50 24.00 25.50

Field N

N-adj

16 27 52/18 50/2 Coring Coring Coring Coring Coring

9 14 266 359

MH MH CH CH MH MH CL CH CH CH MH MH GP-GM SP-SM SM SM SC SP-SM SP-SM CH GM GM GM Agglo Agglo Agglo Agglo Agglo Agglo

14 16 17 16 14 14 27 35 35 36 28 42 56 72 91 97 14 3 3 33 38 67 50/2 Coring Coring Coring Coring Coring Coring

43 25 24 19 16 14 26 30 27 26 19 26 33 39 46 45 6 1 1 12 13 22 247

SM MH MH CH CH MH MH MH CH SM SM GM GM SM SM GP GP

16 19 30 40 52 50 53 21 30 42 76 118 119/19 60/6 60/10 118/16 107/25

49 29 42 48 60 50 50 18 23 30 51 72 108 160 90 105 58

Unit Wt KN/m3

Ave, N

Friction Angle

Cohesion kPa

UCT Kg/cm2

> 40 > 40 10.80

20.70 40.40

BH-60

17.76

↑

↑

Ave N=19

Ave C=75

↓ 17.92

↑

↓ ↑

17.92

Ave N=25 ↓

Ave C=125

↑

↓

Ave N=31 ↓ Ave N=2 ↑ Ave N=15 ↓

34 deg

27 deg 32 deg

>40 deg 50.8 51.9 29.3 35.7 32.5 41.9

BH-61


↑

↑

Ave N=39

150

17.92

18.23

17.76

↓

↓

Ave. N=20 ↑ Ave N=40 ↓

C=100 36 deg

18.23 40 deg

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Table 5 Summary of Soil and Rock Properties- Masinag Station BH No

Depth m

Soil Type

Field N

N-adj

Unit Wt KN/m3

1.50 3.00 4.50 6.00 9.00 10.50 12.00 13.50 14.00

GM GM SC ML Tuff Tuff Tuff Tuff

4 7 9 21 Coring Coring Coring Coring

13 11 13 27

1.50 3.00 4.50 6.00

GC GC SM GC

18 20 7 22

56 32 10 27

17.7 17.60

7.50

MH

77

82

18.07

9.00

TS

Coring

51.0

10.50

TS

Coring

58.2

12.00

TS

Coring

42.9

13.50

TS

Coring

48.8

15.00

TS

Coring

64.4

1.50 3.00 4.50

SM GC GC

14 32 13

44 50 19

6.00 7.50 9.00 10.50 12.00 13.50 15.00 16.50

MH MH GP-GM Agglo TS TS TS TS

22 28 106/25 Coring Coring Coring Coring Coring

27 29 91

Ave, N

Friction Angle

Cohesion kPa

UCT Kg/cm2

BH-62 16.97 17.13 83.3 48.7 25.9 94.1

BH-63 ↑ Ave N=23 ↓

↑ 33 deg ↓

BH-64 ↑ Ave N=14 ↓

16.97 16.97

↑ 33 deg ↓

N=28 17.92

↑ C=100 ↓ 63.9 57.7 55.5 45.1 44.4

Notes: CH MH CL GM SC

-

Clay Clayey silt Silty clay Silty gravel Clayey sand

TS Agglo SM GC


-

Tuffaceous Sandstone Agglomerate Silty Clayey gravel

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CHAPTER 5 FOUNDATION SYSTEM A

Pile Foundation

Evidently deep foundation is required. The ultimate static pile capacity is calculated for various pile dimensions and a factor of safety of 2.50 is applied to arrive at the proposed pile capacity summarized in Table 6. The soil properties listed under Tables 4 and 5 were used in the calculation. The soil profile at Emerald Station generally indicates high variability in terms of soil types and penetration resistance, both vertically and along the section lines. The various sediment beds generally occur in lenses which tend to pinch and swell even at a short distance laterally. This means the pile lengths could be expected to vary within a short distance. The depths to the highly dense soil (N= 50 blows) and rock line below the surface are shown in the soil profile but these could also be expected to vary. The pile lengths are designed in such a way that the pile tips are embedded well within very dense sand and/ or gravel layer or the underlying bedrock. The rock line indicated in the soil profile could be used to determine the length of the piles particularly in locations without borehole information. At Masinag Station the soil distribution with depth is fairly homogenous. The soil overburden thickness is comparatively limited in all the three boreholes. The N-Values are generally low but the presence of bedrock at shallow depth shall provide the required pile capacity. All the boreholes which intercepted at least 6.50 meters thick of fresh, highly strength rock showed no fossil soil. Table 6 indicates the pile capacities at various pile lengths and dimensions. Table 6 Allowable Pile Capacity Location Emerald Station BH-59 BH-60 BH-61 Masinag Station BH-62 BH-63 BH-64

Pile Length, m

Static Pile Capacity, tons Pile Diameters, m 1.0

1.50

2.0

2.50

20 26 20 33 15 20

290 690 275 795 490 670

550 1390 445 1455 935 1300

880 2335 630 2290 1510 2125

1285 3500 840 3295 2215 3145

10.50 10.50 10.50

350 370 380

770 800 810

1345 1400 1420

2080 2170 2180

It will be noted that at BH-60 the presence of very loose sand is ignored for proposed 20 meter long pile. At 20 meters embedment depth the tip of the pile is some 4 meters above the loose sand. With such adequate buffer depth the presence of the loose sand could be ignored. Needless to say, pile load tests are necessary to obtain more accurate information on the allowable pile capacity and pile deflection.


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B.

Modulus of Subgrade Reaction

Lateral pile deflection is commonly determined during pile load tests. However this can be approximated with the use of the following relationships: ks = 80 (SF) qa + C q Nq kN /m3 Where: ks = modulus of subgrade reaction qa= allowable bearing capacity SF = safety factor C = constant = 40 q= effective overburden pressure Nq = bearing capacity factor The moduli of subgrade reaction for the boreholes drilled below the stations are summarized in Table 7. Table 7 Modulus of Subgrade Reaction Pile Length, m

Modulus of Subgrade Reaction, MN/m3

Emerald Station BH-59 BH-60 BH-61

20 20 15

180 270 310

Masinag Station BH-62 BH-63 BH-64

10.50 10.50 10.50

600 565 660

Location

C.

Susceptibility to Liquefaction

As discussed under Section 2.3 Seismicity the project area lies very close to active faults, (WVF and EVF), and that if any of these fault system ruptures a ‘near field’ tectonic movement shall be experienced. For this reason the possibility of soil liquefaction is a cause for concern. The soil materials most vulnerable to liquefaction failure are fully saturated impervious fine sands especially if it’s relative density is loose to very loose. However, being very close to active faults even medium dense sands are presumably unstable. The soil profiles indicate a thick succession of silty sands at Emerald Station. The sands occur at lower depths of the soil profile, ranging from 18 to 23 meters (mid-section of sand bed) below the ground surface. Generally fine grained, the silty sand is relatively impervious and thus appears liquefiable. However penetration test data indicates that the sand is generally dense (N> 30 blows) and because the mid-section lies comparatively deep beneath the ground surface it is highly possible that the silty sand bed is highly resistant against liquefaction. Based on the case history the liquefiable soils occur at depths less than 30 feet or 9 meters below the surface.


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Granular soils mainly clayey gravel underlies the Masinag Station. This soil type with clayey sediments is not liquefiable. Consequently, the soil foundations underlying Masinag Station can be assumed stable against liquefaction. D.

Chemical Analysis of Soil and Groundwater Underlying the Stations

The results of chemical analysis as shown on Table 8 on soil sample taken from BH-60 done by the Bureau of Soils and Water Management indicated very low concentration of chloride and sulfate. Sulfate concentration of 37.72 to cause attack on concrete is described as negligible. Table 8 Result of Chemical Test on Soil Sample from BH-60 Source Location BH-60


Sulfate, ppm

Chloride, ppm

37.72

8.98

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CHAPTER 6 CONCLUSION AND RECOMMENDATION On the basis of the foregoing discussions the following can be concluded: (a)

The LRT Line-2 East (Masinag) Extension Project includes construction of two stations: Emerald Station at Sta 24 + 394.041 and Masinag Station at Sta. 26 + 846.041. Three boreholes were drilled in each of the stations.

(b)

Located within Marikina Valley, no rock crops out anywhere within the project area. The boreholes information indicated the rock types as well as the exposures obtaining on the rolling to mountainous terrain east of Masinag and on the slopes separating Marikina Valley and Quezon City.

(c)

The project area is underlain by thick alluvium reaching more than 40 meters at the vicinity of the start of the project at Santolan to less than 10 meters at the end of the project at Masinag. The soil thickness is variable but generally indicated a decreasing thickness towards Masinag.

(d)

At the two stations the soil cover is relatively thick at Emerald Station, reaching as much as 34.50 meters thick. At Masinag Station the soil thickness is limited to 7.50 to 9 meters thick.

(e)

Both stations are underlain by pyroclastic rocks belonging to the Pliocene to Pleistocene Diliman tuff. It consists mainly of bedded tuffaceous sandstone inter-layered with agglomerate and tuff.

(f)

At Emerald Station the soil thickness is highly variable, ranging from 25.50 to as much as 34.50 meters. It consists of cohesive soils, highly plastic clay and clayey silt on the upper 14 to 18.50 meters and sand and gravel beds at the lower section. At Masinag Station the sedimentation is different, consisting largely of clayey gravel and sand with only minor clayey silt and sandy silt beds.

(g)

Soil strength is deduced mainly on the penetration resistance of the clays while the rock strength is determined on the basis of unconfined compression test on the core samples. The soil and rock properties are presented in the text. In general, the clay consistency is variable. At Emerald Station, it is generally stiff for the initial 9 meters depth but generally becomes very stiff to hard as the depth increases.

(h)

Penetration resistance of the granular soils is likewise variable. A relatively thick zone of highly dense sand and gravel beds is identified at BH-60 and BH-61 but no such layer exists beneath BH-59. Quite unexpectedly, very loose sand beds, N= 2 to 3 blows, was intercepted below BH-60 but such soil condition was not encountered by the other boreholes. Before bedrock level all the three boreholes indicated very dense gravel at the base. The pyroclastic rocks are geologically classified as soft rock. Based on strength tests done the unconfined compressive strength ranges from 10.80 to 94.1 kg/ cm2. Average rock strength is about 40.37 kg/cm2.

(i)

At Masinag the upper lying sediments are generally medium dense gravel and sand beds. The N-Value increases with depth. All the boreholes bottomed in rock.

(j)

The presence of active faults very near the project area is a cause of concern. A ‘near field’ tectonic event is actually expected should any of the two active faults near the site ruptures. The peak ground accelerations (PGA) expected from the earthquake


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generators within 2000 km radius of the project area is evaluated on the basis of the Fukushima- Tanaka equation. The PGA varies from 0.02g to as much as 0.16g. The lower value applies to the Casiguran fault, 200 km away, and the larger number to the Philippine Fault System. In the case of the Valley fault system, the PGA expected is 0.55g, based on medium soil site condition. (k)

Pile foundation is recommended. The static pile capacity is computed for various pile diameters and various pile lengths, based on factor of safety of 2.5. Actual pile capacity must, however, be based on several pile load tests which will be done in the future. The moduli of subgrade reaction are also determined and included in the text.

(l)

The thick sand beds underlying Emerald Station are fine grained. The sand layer is presumably not susceptible to liquefaction because it is generally dense and it occurs too deep below the ground surface. Liquefiable soils are located within about 30 feet below the surface.


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APPENDIX-1 PROJECT AREA LOCATION PLAN

FORESIGHT DEVELOPMENT & SURVEYING COMPANY

SOOSUNG ENGINEERING COMPANY, LTD.

KOREA RAIL NETWORK AUTHORITY

LIGHT RAIL TRANSIT AUTHORITY

DEPARTMENT OF TRANSPORTATION AND COMMUNICATIONS

2 - DOTr

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