Measuring and testing – Internal combustion engine or related engine system or... – Compression
Reexamination Certificate
2002-07-02
2004-10-19
Williams, Hezron (Department: 2856)
Measuring and testing
Internal combustion engine or related engine system or...
Compression
Reexamination Certificate
active
06804994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dynamic loading system for piles which serve as a foundation of a structure, a dynamic loading method for estimating the bearing capacity of a pile, and a dynamic loading test method.
2. Description of the Background Art
Soil under strain can be treated as an elastic body when the strain is equal to or smaller than 10
−4
, or in a region of 10
−5
if the soil is relatively soft. When the soil is subjected to a strain exceeding these values, its plastic nature gains greater importance.
When a load exerted on a pile driven into the ground is small and strain occurring in the pile is remarkably small, strain occurring in the ground which is in contact with the pile is also remarkably small, so that the ground can be treated as an elastic body. In this case, the strain in both the pile and the ground is eliminated and they resume their original form when the load is removed. The load applied in this case falls within a range not exceeding their ultimate bearing capacity.
When the applied load is increased, the strain occurring in the pile increases, also causing a large amount of strain in the ground. When the plastic nature of the ground becomes of greater importance as a consequence, plastic deformation occurs in the ground which is in contact with the pile. The plastic deformation of the ground does not disappear and the pile does not return to its original position even when the load is removed. The load applied in this case falls within a range exceeding the ultimate bearing capacity.
Conventionally, stationary loading tests, dynamic loading tests and rapid loading tests are performed as methods for evaluating the ultimate bearing capacity (hereinafter referred to as the bearing capacity) of a pile.
The stationary loading test is a method of determining the stationary bearing capacity of a pile from the relationship between a load and the amount of sinking of the pile when the load is exerted on the pile to be tested.
FIG. 15
is a diagram showing the structure of a conventional stationary loading system
1000
for measuring the bearing capacity of a pile. In this Figure, designated by the numeral
1001
is a test pile whose bearing capacity is to be measured, designated by the numeral
1002
is one of reacting piles, designated by the numeral
1003
is a loading beam, designated by the numeral
1004
is a hydraulic jack, designated by the numeral
1005
is a control unit for controlling the hydraulic jack
1004
, and designated by the numeral
1006
is a gauge. Further, the marking GL indicates the ground level.
The stationary loading test method carried out by the stationary loading system
1000
thus constructed is described in the following. As shown in the Figure, the reacting piles
1002
are provided around the test pile
1001
to be tested. While supporting a loaded weight with the reacting piles
1002
, a load is applied to the test pile
1001
. This load is applied by the hydraulic jack
1004
which is provided between the loading beam
1003
supported by the reacting piles
1002
and the test pile
1001
. The hydraulic jack
1004
applies the load to the test pile
1001
in a vertical direction according to a control quantity fed from the control unit
1005
. After loading, the amount of sinking of the test pile
1001
is measured by the gage
1006
and the bearing capacity is assessed from the relationship between the amount of the loaded weight and the amount of sinking.
Although the bearing capacity of a test pile can be measured with high reliability by this kind of conventional stationary loading test method, it necessitates considerably large-scale work, such as driving the reacting piles and installing the loading beam for producing a sufficient load to be applied to the test pile, involving the provision of a sizable testing facility. In addition, movement of the facility requires considerable expenses and time, resulting in extremely poor efficiency. It has therefore been difficult in practice to measure the bearing capacities of a large number of piles.
In a conventional dynamic loading test method, on the other hand, a load is dynamically exerted on a test pile by hammering its head and the bearing capacity of the test pile is estimated by analyzing a response obtained by a vibration sensor mounted on the pile head.
Although this kind of dynamic loading test method does not require a large-scale facility like that of the stationary loading test method, loading time is as short as a few milliseconds and the wavelength of elastic vibrations produced is sufficiently short compared to the length of the test pile. Therefore, it is necessary to carry out a complicated analytical treatment based on a wave theory by regarding the pile body as a one-dimensional elastic body in a stage of estimating the bearing capacity from waveforms detected by the vibration sensor. In addition, estimated values of the bearing capacity fluctuate to a large extent because information obtained from the pile head is limited.
In a conventional rapid loading test method, a load is exerted on a test pile by exploding a propellant like an explosive and applying a resultant impact force to the pile head. In this method, it is possible to obtain about ten times as longer a loading time as in the conventional dynamic loading test method and apply the load in a more stationary state. This method has problems in practical applications, however, because it involves a lot of limitations including the need for careful handling of the explosive.
Another conventional dynamic loading test method disclosed in Japanese Laid-open Patent Publication No. 10-153504 is described in the following with reference to
FIG. 16
as an example of a method intended to overcome the problems of the aforementioned dynamic loading test method.
In hammering a pile head by dynamic loading of this test method, a load is exerted at a desired frequency by successively dropping a plurality of split hammer blocks at regular intervals.
In a stationary loading system shown in
FIG. 16
, a guide shaft
2002
is installed upright on an anvil
2001
and a hook
2003
is provided at the top of the guide shaft
2002
. The anvil
2001
has at its lower portion a pile cap
2004
which is fitted over the head of a pile P. Measuring equipment, such as a load meter
2005
, is provided between the anvil
2001
and the pile head for measuring the load and a displacement meter
2006
is provided on a side surface of the pile cap
2004
for measuring the displacement of the pile head. A hammer includes a plurality of hammer blocks M
1
-Mn, each hammer block M having a through hole
2007
at a central position for passing the guide shaft
2002
.
Next, operation of this stationary loading system is described below.
The hammer blocks M mounted on the guide shaft
2002
are hung by wire ropes
2008
which are hooked on the hook
2003
. Each wire rope
2008
is equipped with an unillustrated latch and the hammer blocks M are retained at regular intervals d. The hammer blocks M are simultaneously released by disengaging the hook
2003
. As a result, the individual hammer blocks M fall successively onto the pile head striking against it and exerting a series of loads thereupon. The loads are measured by the load meter
2005
and the displacement of the pile head is determined by the displacement meter
2006
.
In the aforementioned loading method, the regular spacing d between the successive hammer blocks M defines uniform time intervals between them, so that dropping time intervals can be varied by altering the spacing d. Thus, this method makes it possible to control the frequency of the entire loads and apply the loads in a state much closer to stationary conditions.
Even by the aforementioned improved dynamic loading test method the prior art, however, it is difficult to continually apply loads for an extended period of time. In addition, it is necessary to adjust the spacing between hammer blocks for controlling the frequency of the loads a
Miller Rose M.
Williams Hezron
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