1. MAIN DAM FOUNDATION EXCAVATION
1.1OBJECTIVE
The main objective of this method statement is to describe in detail the quence of works and establish priorities of work to allow embankment filling to start by scheduled in the baline programme on 17-Jan-2003. An immediate objective will be to expedite works and expo the plinth at the dam foundation for geotechnical investigation.
This method statement and includes the following:
•Haul roads and disposal areas,
•Preparation of condary river crossings,
•Dewatering,
•Preparation of loading platform, and
•Earth/rock excavation for integrated cofferdam foundation.
1.2ZONING OF WORK AREAS:
From the drawing, ‘by drawing a line connecting the highest point of the ridges of both left and right banks, the main dam work area is divided into the following
work zones:
•Area 1: From downstream face of auxiliary cofferdam to the dam axis of integrated cofferdam;
•Area 2: From the dam axis of integrated cofferdam to the main dam axis, below elevation 130m for the right bank, below elevation 140 for the left bank, and
including the riverbed.
•Area: From the main dam axis to the down stream limit of Main Dam, below elevation 130m for the right bank, below elevation 140 for the left bank, and
including the riverbed downstream of MD Axis.
五谷是指哪五谷•
•Area 4: From the dam axis of integrated cofferdam to downstream limit of the Main Dam, above elevation 130m for the right bank, above elevation 140 for
the left bank.
Each work zone is is further divided into sub-areas, each subdivision is basically
defined into left abutment, riverbed and right abutment ctions.
Plea refer to drawing no. MDEX-MS-001 (Attachment 1)
1.3METHODOLOGY
1.3.1P REPARATION OF H AUL R OADS &D ISPOSAL A REAS
1.3.1.1Haul Roads
The following haul roads shall be prepared for haulage of excavated
material:
•Road R1: Main haul road
•Road R1-1: Connects right abutment at EL 210 to R1.
•Road R1-2: From loading platform at Right Abutment @EL 130, to the upstream face of auxiliary cofferdam, and connected to R2 at Down Stream.
•Road R2: From loading platform at Right Abutment @EL 70, to the disposal areas near W4, and Northern side of W6.
•Road L2: From riverbed EL 50 to disposal areas near W4, and Northern side of W6.
Plea refer to “Access Road Arrangement for Main Dam/Power Hou
Excavation--- First Stage” (Attachment 2)
1.3.1.2Disposal Areas
The designated disposal areas will be as follows:日本品牌
•Upstream face of auxiliary cofferdam: Designated as disposal area and at the same time a 20m-width access road across the river is to be constructed
adjacent to the auxiliary cofferdam.
•Near W4: Disposal area at low line areas adjacent to W4.
•Northern side of W6: Disposal area at low line areas at Northern side of W6.
•W 14, and
•W 15.
Plea refer to Attachment 3”Disposal Area & Temporary Stockpil e for
Main Dam and Powerhou Excavation” for the layout plan of the
aforesaid disposal areas.
1.3.2M ETHOD OF O VERBURDEN E XCAVATION
The following loading platforms shall be prepared to collect the material
(earth/rock) pushed from the higher elevation:
微波炉鸡蛋羹
•Top platform – for the interfacing with the main dam excavation:
o Right Abutment: EL 130
o Left Abutment: EL 140
The above platforms shall be at least 15m width. It shall be prepared by
桀骜不驯的拼音forming temporary slope from higher elevation and shall be benched deeper into the design formation of slightly weathered/sound rock layer.
As for the Main Dam excavation above elevation EL 130 (Right) and EL
140 (Left), the aforesaid platforms will rve as loading platforms to collect excavated material pushed downslopes from higher elevation working
areas.
•Intermediate platform – This will rve as an intermediate collecting point for excavated material to control the overall dozing distance within 30m ~ 40m.
三年级好句
o Right Abutment: EL 100 and EL 70
三包服务Following the topography and terrain at the right abutment where there are
well-defined mountain ridges and gullies, intermediate platforms will be
constructed in between ridges. The area will be cleared from logs or
undergrowth, slopes trimmed to provided wider area, and filling to form the platform.
o Left Abutment: Nil
There are no apparent ridges at left abutment. In addition, the thickness of overburden at the left bank is comparatively thinner and the original slope is comparatively steeper than the right bank. Hence, intermediate platforms becomes unfeasible at this area.
•Final platform – Located at the riverbed at approximately EL 50. Formed by the excavated material pushed towards the riverbed during the process of
foundation excavation, will rved as the final loading platform before the
riverbed is to be excavated up to the required rock strata. This platform will mainly rve to load and haul overburden pushed downslopes from the leftbank excavations.
Pleas refer to drawing MDEX-MS-001 (Attachment 1).
1.3.3F ILLING OF S ECONDARY C ROSSINGS/B UNDS.
Secondary crossings will be constructed across, by filling the riverbed with suitable material taken from excavation works forming a crossing to both banks, and, also, ctionali the riverbed work areas. This is to minimize interference of works when excavation works of riverbed and upper elevation are carried out simultaneously at alternate zones.
The crossings will also rve containment bunds to prevent excavated material from contaminating the integrated cofferdam work areas.
空调有味By forming the crossings, the river is “transformed into ponds”, and the allows dewatering of the river to be gmentalized.
1.3.4D EWATERING
A combination of 10’’ and 14” water pumps will be stationed at parate gments
of riverbed. Two -720,000 gallons per day pumps will be installed at the downstream side of the river. Smaller pumps may be installed at the river ctions formed by the riverbund, to keep and maintain the area dry during riverbed excavation and plinth construction.
1.4IMPLEMENTATION PROGRAM
1.4.1T IME F RAME
The time frames for respective zones are summarized as follows:
o Zone 1 25-Aug-03 to 07-Oct-03
o Zone 2 20-Aug-03 to 19-Dec-03
o Zone 3 01-Oct-03 to 15-Jan-04
o Zone 4 01-Dec-03 to 20-Dec-04.
Plea refer to Work Program on Main Dam Excavation (Attachment 4) for威海好玩吗
details.
1.4.2R ESOURCES
Refer to Attachment 5: Table of Work Areas and Process” and
Attachment 6: “Main Dam Excavation –Equipment”
1.5SAFETY
As a safety barrier, gabion wall in 2-1 arrangement shall be built (if necessary) as protective armor at the upper platforms (mentioned in Section 1.3.2) to prevent materials pushed downslopes from causing injuries to works at the lower ctions of the dam. The gabions will also rve to contain excavated materials, sludges, debris and other objects from contaminating embankment work and
permanent excavation slopes. The gabion walls will be “wrapped” with geotextiles to allow clean water pass through to the cut off drains.
Also, cut off trenches, of sufficient shall also be provided at the upper platforms which will also prevent runoff carrying silt from contamination the dam foundation at lower elevation.
Kindly refer to Attachment 7: Section View of Typical Work Sequence.
