Chairman, Committee on Housing
Sangguniang Panlungsod ng Davao City
Dear Councilor Cabling,
We would like to furnish your office a copy of the Geotechnical Investigation with Slope Stability Analysis conducted by QSTS on the DMC-UPDI property in Ma-a (please see attached Annex A). According to the Mines and Geoscience Bureau in their letter dated Oct. 5, 2007 (refer to Annex B), there is a supplemental study that was required from DMC-UPDI and the same has been reviewed and favorable endorsed by MGB to the Environmental.Management Bureau. We have already requested for a copy of the supplemental study and the technical review from MGB, but in the meantime, we would like to bring to give emphasis on the following observations in the Geotechnical Report conducted by QSTS:
The gentle slopes and the adjacent flat terrain are predominantly covered by colluvium (loose rock & soil at the base of a cliff or steep slope), and thin layers of conglomerates (rock comprising pieces of other rocks) and are undifferentiated with calcareous or chalky limestone formation.
Comment: This explains the sandy sediments which is carried by the rain and accumulates in the road canal which causes it to overflow and flood Ma-a road and neighboring subdivisions.
Also observable are the coalescing gullies which are the drainage paths for surface run-off during heavy rains. Drainage paths where the spine road traversed are significantly overlain with debris flows of colluvium and highly weathered limestone and shale. These drainage paths showed some sign of slope instability as shown by the propagation of fissures that are characteristic of minute scarps or tension cracks.
Comment: The spine road they constructed serve as “canals” for surface run-off which contributed to flooding along Ma-a road. The cracks and fissures along the road and drainage path shows that the composition of the rock/soil is prone to erosion.
The calcareous limestone is highly permeable and to some degree fragmented.
The material composition as well as the physical and mechanical properties of the soil/rock formation on site is described as follows: the site is predominantly underlain with clastic and calcareous limestone overlain with thin differentiated topsoil composed of conglomerates and argillaceous sediments.
Comment on 3 & 4: If this is the case, heavy and continuous rain may cause the clastic and calcareous limestone to become soft and prone to erosion.
It is worth to note that the factors of safety derived from the slope stability analysis may all change through time due to several factors: a) removal of support by erosion, cuts and excavations, removal of retaining wall system, removal of support at toe; b) overloading by heavy and persistent rainfall, construction of fill at upper slopes, water leakages in culverts and pipes and sewers; c) slope modification during construction activities; d) earthquake induced cracks and fissures which may allow unnecessary seepage or secondary drainage.
Comment: Except for earthquake, all the factors that could decrease the slope stability is a natural consequence of a major subdivision project. Hence, the factor of safety is expected to change drastically once the subdivision project is in full swing. Note also that the median factor of safety is only 1.383. Considering that a value of 1.0 implies that the slope is stable, a median factor of 1.383 indicates that there is a minimum variance between stable and marginally stable slope stability.
In view of the above observations, it is easy to surmise that the development of the area into a residential subdivision has questionable safety issues not only for the residents in the immediate vicinity but also for the prospective buyers of this housing project.
More importantly, please take into serious consideration the Zone Critical to Landslide and Erosion included in the Geotechnical Report where it clearly shows that Trinidad Greenhills Subdivision is in the direct path of landslide/erosion should this happen in the property owned by DMC-UPDI. We implore you to secure the lives, homes and properties of us residents and our future generation.
CONSEQUENTLY, WE REQUEST YOUR GOOD OFFICE TO CAREFULLY EVALUATE THE FINDING OF THE GEOTECHNICAL REPORT CONDUCTED BY QSTS AND ORDER THE DMC-UPDI TO STOP THEIR PROPOSED SUBDIVION PROJECT IN MA-A.
Thank you and we appreciate your preferential attention to our concerns.
The gentle slopes and the adjacent flat terrain are predominantly covered by colluvium (loose rock & soil at the base of a cliff or steep slope), and thin layers of conglomerates (rock comprising pieces of other rocks) and are undifferentiated with calcareous or chalky limestone formation.
Comment: This explains the sandy sediments which is carried by the rain and accumulates in the road canal which causes it to overflow and flood Ma-a road and neighboring subdivisions.
Also observable are the coalescing gullies which are the drainage paths for surface run-off during heavy rains. Drainage paths where the spine road traversed are significantly overlain with debris flows of colluvium and highly weathered limestone and shale. These drainage paths showed some sign of slope instability as shown by the propagation of fissures that are characteristic of minute scarps or tension cracks.
Comment: The spine road they constructed serve as “canals” for surface run-off which contributed to flooding along Ma-a road. The cracks and fissures along the road and drainage path shows that the composition of the rock/soil is prone to erosion.
The calcareous limestone is highly permeable and to some degree fragmented.
The material composition as well as the physical and mechanical properties of the soil/rock formation on site is described as follows: the site is predominantly underlain with clastic and calcareous limestone overlain with thin differentiated topsoil composed of conglomerates and argillaceous sediments.
Comment on 3 & 4: If this is the case, heavy and continuous rain may cause the clastic and calcareous limestone to become soft and prone to erosion.
It is worth to note that the factors of safety derived from the slope stability analysis may all change through time due to several factors: a) removal of support by erosion, cuts and excavations, removal of retaining wall system, removal of support at toe; b) overloading by heavy and persistent rainfall, construction of fill at upper slopes, water leakages in culverts and pipes and sewers; c) slope modification during construction activities; d) earthquake induced cracks and fissures which may allow unnecessary seepage or secondary drainage.
Comment: Except for earthquake, all the factors that could decrease the slope stability is a natural consequence of a major subdivision project. Hence, the factor of safety is expected to change drastically once the subdivision project is in full swing. Note also that the median factor of safety is only 1.383. Considering that a value of 1.0 implies that the slope is stable, a median factor of 1.383 indicates that there is a minimum variance between stable and marginally stable slope stability.
In view of the above observations, it is easy to surmise that the development of the area into a residential subdivision has questionable safety issues not only for the residents in the immediate vicinity but also for the prospective buyers of this housing project.
More importantly, please take into serious consideration the Zone Critical to Landslide and Erosion included in the Geotechnical Report where it clearly shows that Trinidad Greenhills Subdivision is in the direct path of landslide/erosion should this happen in the property owned by DMC-UPDI. We implore you to secure the lives, homes and properties of us residents and our future generation.
CONSEQUENTLY, WE REQUEST YOUR GOOD OFFICE TO CAREFULLY EVALUATE THE FINDING OF THE GEOTECHNICAL REPORT CONDUCTED BY QSTS AND ORDER THE DMC-UPDI TO STOP THEIR PROPOSED SUBDIVION PROJECT IN MA-A.
Thank you and we appreciate your preferential attention to our concerns.
Respectfully yours,
TRINIDAD GREENHILLS HOMEOWNERS ASSOC. INC.
(SGD) Ma. Miranda C. Cordova
Secretary
(SGD) Norma Javellana
President
CC:
Director Metodio Turbella, Environment Management Bureau
Director Edilberto L. Arreza, Mines and Geosciences Bureau
Engr. Joaquin B. Cui Jr., City Engineer’s Office
Engr. Mario Luis Jacinto, City Planning & Development Office
Engr. Lorna Ricardo, Asst District Engineer, DPWH
Federation of Homeowners Association in Bgy. Maa
Bgy Chairman Jun Laud, Bgy. Ma-a
No comments:
Post a Comment