A. Investigation and Research on Engineering Geology and Subsurface Geology of Metropolis Kaohsiun
|(1) Geologic boring and sampling
Geologic boring and sampling in the Kaohsiung Metropolitan area was divided into two bore-hole
categories: geologic bore-holes and engiineering bore-holes, boring operations were undertaken by
separate contractors. Geologic boring used HQ core barrels, and continuous sampling was performed,
the purpose was to obtain continuous cores for use in geologic environment analysis and subsurface
geologic study. Engineering bore-holes were bored using NX core barrels, and cores as well as samples
of soils from different depths were collected to conduct laboratory tests. In-situ tests were also
performed during drilling of bore-holes. These tests were designed in accordance with engineering
geological investigation and research requirements. These tests would yield rock and soil mechanical
parameters. These parameters would be correlated with results from laboratory tests, this would
establish the relationship between the two. .In fiscal year 2002 ninteen geologic bore holes and
niinteen engineering bore holes were drilled.
|(2) Investigation and research on subsurface geology
This project makes use of cores from the geologic bore holes to establish cross sectional profiles for
study on the subsurface geology of the areas drilled. The geologic structural framework, and
stratigraphic configuration , the depths of basement rock masses would be unraveled. Through
understanding on the characteristics of the Quaternary sediments, the depositional environments, the
paleontology and age dating data, with reference to field outcrop observation, the subsurface geology
of metropolitan Kaohsiung, the Quaternary sedimentary environments as well as the history of geological
development of the area would be clarified.
Investigation and research results indicated that the Kaohsiung area is mainly covered with
unconsolidated lagoonal facies argillaceous sand beds. These loose sand beds were deposited as late as
several thousand of years before present. The structural geological framework is simple, straight
forward. Lithologies of the drill cores revealed that there were sedimentary structures, intense
bioturbation, fossil mollusks, ilmenite, plant rootlets, concretions and signs of podolization. Twenty
two facies had been recognized. Through facies association, three sedimentary environments were
identified, these are: near-shore-shore face environment, estuary bay environment, and braided
stream-meander stream environment.
|(3) Investigation and research on engineering geology
Investigation and research on engineering for the Kaohsiung metropolitan area included boring and
sampling of engineering bore holes, in0situ tests. Current information on engineering geology in the
area were also collected and compiled. The characteristics of soil formations and a geotechnical
division of the area was later performed after evaluation and analysis. Through this investigation and
research project, the complete characteristics of geotechnical engineering environ for the Kaohsiung
area will be established.
Basing on available results, the geotechnical characteristics of metropolitan Kaohsiung are:
- The average ratio of Qc of silty clay for entire area of Kaohsiung to N values is about 2.8, the Qc for silty sand to N values is about 4.
- The sensitivity value for clay for the entirer Kaohsiung area falls between 2~7, thus it is a non-sensitive to moderate sensitive soil. Subsurface excavation will not encounter hazard from loosening of soil resulting from stress relieve.
- The relationship between CPT-qc and depth is qc= (3.7 ~ 5.0) depth.
- Soil liquefaction hazard index analysis results indicated that the alluvial plain of the Kaopinghsi holds the highest potential and most serious, whereas both the Fengshan Hills and the Panpingshan-Shoushan mountains are the areas with lowest liquefaction potential.
|(4) Investigation and research on ground movement characteristics
1. Geophysical Survey
In the plain zone west of metropolitan Kaohsiung there are suspect faults Shoushan, Yuchang and
Chihkang Faults. Reflective seismic survey results indicated that the location for Shoushan Fault is
not too far from the location depicted in CGS' publication 1:50,000 scale geological map sheet 61.
In the Yuchang survey area, the occurrence of the Yuchang Fault is very much enhanced. Further more,
when the attitude of the Yuchang Fault is compared with the attitude of the Panpingshan Anticline,
the two showed little difference, thus Yuchang Fault could very well be a fault on the northwest of
the Panpingshan Anticline.
2. Investigation and research on ground movement characteristics
||Results from down-hole velocity surveying
The shear-wave velocity besides being an important geotechnical parameter, is also a primary
requirement in ground movement researches. The results from down-hole p-wave s-wave velocity
survey results coincided well with results obtained through geological boring investigation.
||Simulation on ground movement characteristics
The subsurface geological structure reconstructed through down-hole p- and s-wave velocity
survey can be used in simulating the ground movement characteristics. Comparing the ratio
between the theoretical and actual transformation functions preliminarily showed that
simulation through 1-D Herz transformation is quite good, thus indirectly showed the efficiency
of down-hole velocity survey.
||Site seismic effects
For understanding the site seismic effect in the Kaohsiung area, TSMIP strong quake station
records from 1992-1998 were collected. The frequency spectrum ratio from a single seismologic
station was calculated from these strong quake records. In principle, during calculation, 1.5
seconds before arrival of the s-wave, 10 – 20-second windows were obtained, then the calculation
for frequency spectrum ratio from a single seismologic station began. This was then followed by
contouring of the isograms of the regional H/V ratios. From these isograms, it was deduced that
the sediment cover on Kaohsiung is very thick., but decreases fromo the edge of the haarbor
towards Shoushan, Panpingshan, Nantzu, Tashe and the Fengshan Anticline to the east.