Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Rock Press-fitting Excavation Record by Pipe Drilling MethodTerumichi HATA
Mechanical Engineering Center, Kajima Corporation, Tokyo, Japan
Email: hata@kajima.com

Masaaki KASAKAWA
Hokuriku Branch, Kajima Corporation, Niigata, Japan
Email: kasakawa@kajima.com

Keisuke OHTSU
Hokuriku Branch, Kajima Corporation, Niigata, Japan
Email: ohtsu@kajima.com

ABSTRACTIn the earlier method of excavating a rock with rotary all casing boring machine, it was common to disintegrate the rockmass by freely dropping heavy weight (chisel etc.) inside the casing. However, in that method (dropping chisel), thefoundation rock was getting damaged and whenever it was necessary to provide a water proof wall to the rock bed layer,
this was a disadvantage. At the same time when crushing with chisel, there was a problem that the drilling efficiency
used to drop significantly in the case of a large depth and under water excavation. In order to solve these problems, anexcavation was carried out by a pipe drilling method (our developed technology) that reliably transmitted rotational
torque from a rotary all casing boring machine and excavated without cracking the rock, this has yielded good results
and hence we are reporting the summary and results.
Key words: Rotary press fitting, Rock drilling

1. Pipe drilling method

For this reason, the hydraulic control device suffers large

1.1. Outline of construction method

scaling and the workability drops due to the handling of

The pipe drilling method is a construction method in

the hydraulic hose.

which the torque of the rotary all casing boring machine is

The remarkable point of this method is thetransmitted to the pipe drill by a link mechanism which
does not require hydraulic pressure to cut the hard ground.
Compared to the conventional method of crushing, thismethod can control the drilling efficiency in water anddeep excavation. This method allows the rock excavation
with low noise and low vibration without damaging thefoundation rock. The excavation diameter corresponds to
φ 1,000 mm to φ 3,000 mm.
1.2. Points for developing construction method
In the conventional digging device, a hydraulicmechanism such as a hydraulic cylinder was applied totransmit the rotational torque of the casing to the bucket.

- 627 -

Photo 1.

Overview of Pipe drillProceedings of the First International Conference on Press-in Engineering 2018, Kochi

restore-protrude mechanism of the pins; the pins that are

hanging pins to the “reaction windows”, the torque of theattached on the drill synchronously are restored when theboring machine can be transmitted to the pipe drill. It is a

drill is hung and protrude when the drill reach the bottom

simpleand set on the ground, corresponding to the movement ofdetachment of the first casing and the pipe drill by thethe stabilizer (Fig 1). After the drill reaching the bottom,pin.

mechanismthatrealizes

attachment

andthe pins are hung to the corner of the “reaction windows”

Since this transmission mechanism does not depend(Fig 2), a dent placed inside the casing, corresponding toon the frictional resistance by grip, which may cause

the rotational movement of the boring machine. Byslippage of the casing, it is possible to transmit therotational torque of the casing to the pipe drill in better
reliability.
1.3. Pipe drilling mechanism
The mechanism of Pipe drill is as follows. When themain body is inserted into the casing and reach the bottom,
the hanging wire become loosened, the stabilizer descends
and the pin protrudes (Photo 2).
After reaching the bottom, by rotating the casing, thepins are hung in the corner part (as shown in Photo 3) of
the “reaction window”. Thus, the torque force of therotary all casing boring machine is transmitted to the pipe
drill and dig the rock.

Fig. 1

Overview of pipe drill mechanism

Fig. 2

Inner view image of First Casing- 628 -

Photo 2.

Pipe drill

Photo 3.

First CasingProceedings of the First International Conference on Press-in Engineering 2018, Kochi

After completion of excavation, by rotating thelayer consists of alluvial sand layer (As layer), alluvial

casing reversely and lifting the main body, the pins are

gravel layer (Ag layer), diluvial layer (Dg layer) and therestored, the main body is detached from the first casing,layer of granite (Class D, Class CL or higher). As aand it can be lifted up.

special feature, the riprap layer of the caisson issandwiched between the landfill layer and the alluvium

1.4. Excavation mechanism
A conical bit is applied as a bit of the cutting edge ofdeposit at the steel pipe sheet pile area, and at the area ofthe pipe drill. The conical bit is capable of cutting the rocksurface uniformly by rotating the bit itself under the highpressure on the surface, which contributes to mitigating
the abrasion of the bit. Basically, one conical bit is set on
one trajectory, but it is also possible to set two bits on one
trajectory according to rock strength (Photo 4). In
addition, to facilitate bit exchange, three spokes areformed as a box structure, and the bit is attached and fixed
by a snap ring (Photo 5). The casing bits are also attachedto the outer surface of the casing. The image of settled
pipe drill is shown in Photo 6.
Photo 4.

Drilling bit shape

2. Outline of construction
2.1. Structure form
The workability of such pipe drilling method wasevaluated, and it was applied to actual construction.
This construction is to build a steel pipe sheet pileand a columnar wall as a water retaining wall as well as asoil retaining wall around the excavation area forfoundation construction in the landfilled coastal areas inJapan.
The steel pipe sheet piles are designed to be adopted
to the deep excavation area. The columnar wall made of
mud mortar and H-steel are designed to be adopted to theshallow area.

Photo 5.

Bit shape in large figure

Photo 6.

Pipe drill setting status

The steel pipe sheet piles are constructed bypress-fitting and inner excavation in combination,
preceded with replacing the soil by mud mortar. The
columnar walls are constructed by replacing the soil by
mud mortar and inserting H-steel. The all casing boringmachine is applied for replacing excavation, and the pipe
drill method is adopted for drilling the rock layer, which ispossible to cut the rock without loosening the hard layer.
2.2. Geological conditions
The surface ground in this site consists of a landfill
made of crushed rock with maximum diameter of
300mm. The stratigraphic composition under the landfill- 629 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

columnar wall, rock layer lays just right under thelandfilllayer.

Thegroundwaterlevel

fluctuatessynchronously with the tide level.

Table 1 and Fig. 4 show an example of excavation
results. The excavation diameter is φ1,500 mm, the depthof excavation is GL - 14.5 m, and the rock classification
mainly consists of middle hard rocks of Class CL or

2.3. Construction period
The construction started from 2010 and lasted until

higher.

2011.

qu = 60 to 100 N / sq mm grade. The time for pipe drilling

In this site, the pipe drill was applied for hard rock of
was about 30% of the total time for rock excavation on

3. Construction results

average, although it varied depending on the rock3.1. Construction procedure
The excavation was basically done by hammer grab,

classification. The excavation time per 1 meter is 83.5 min

and the pipe drill was applied when reaching the hard

efficiency of the conventional method of chisel drillingrock layer, removing the crushed rock by hammer grab

(reference: cumulative basis 92.8 min / m). The image of(Fig. 3). The construction procedure of the pipe drilling

drilled wall and the bottom are shown in Photos 7 and 8.

on average, which is about 10% faster than the drillingis shown below. The drilling length of one stroke is set toabout 0.4 m.

3.3. Troubles during replacement excavation① Pre-drilling by casing

Several troubles happened during replacement② Pipe drill insertion, cutting, lifting

excavation such as shown below.

③ Earth removal by hammer grab

(1) Collapse of the surrounding ground
During the replacement excavation, the groundbeneath the rotary all casing boring machine frequently
collapsed into a mortar shape. It was assumed to becaused by the evacuation of landfilled soil into theclearance between the revetment caisson and ground. Asa countermeasure, void filling and protection of cavity
wall by mud mortar were carried out.
(2) Resumption of excavation
The excavation was stopped for several times due tothe reasons such as abrasion of casing bit, blockage ofTable 1.

Fig. 3

Excavation procedure

3.2. Record of the pipe drill excavation
Rotary press-fitting and cutting by the pipe drill
made stable results regardless of hardness of the ground.
Since hard ground appears in the deeper portion ofexcavation, the construction cycle time is influenced by
the abrasion extent of the casing bit for pre-drilling. For
this reason, it is important to notice the timing for casing
bit exchange.
- 630 -

Excavation record

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 4

Drilling depth and drilling timecasing by big boulder and acute increase of torque force

countermeasure, supplemental drilling by a rotary(Photo 9).

percussion drill with diameter of 165mm, number of 18

As a countermeasure, the casing was pulled out andwas carried out around the casing in order to reduce there-drilling was carried out after filling back with original

friction. Afterward, locked casing was resumed using thesoil or mud mortar.

rotary all casing boring machine.

(3) Lock of casing(4) Pipe drill blockage

Casing was locked by jamming several times; byThere was a case that pulling up the pipe drill has

the impossibility of drilling due to excessive frictional

been impossible. The reason was assumed to beresistance between the casing and the ground. As aexcessive pushing of the pipe drill as much as 40cm

- 631 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Photo 7.

Drilled wall after excavation

Photo 10.

Adhering of crushed rock3.4. Quality control
In order to ensure the function of water barrier, it isnecessary to ensure the lap of the mud mortar in theembedment part. For this reason, the vertical accuracy ofexcavation is required to satisfy the regulation shown inTable 2.
As mentioned above, the geological condition inthis construction was not a homogeneous stratum andriprap layer or presence of boulder were also expected.
Photo 8.

Drilling bottom

Therefore, taking the data obtained from the excavator
such as rotation torque, current value etc., and thegeological conditions into account, the thrust load andthe rotation speed was controlled. In addition, theverticality of the casing was examined by transit fromtwo directions. As a result, the vertical accuracy ofdrilling in this construction resulted in becoming lessthan 1/400 measured by ultrasonic measurement, which
satisfied the requirement.
In this type of pile construction, grasping thePhoto 9.

Table 2.

Inner blockage of casing by boulder

deeper than the bottom of casing or blockage of the gap
between casing and the pipe drill (about 7 cm) bycrushed rock (Photo 10).
As a countermeasure, the top of the pipe drill in thecasing was hit with a reverse rod to cut the friction
between the pipe drill and the casing.

- 632 -

Drilling vertical accuracy

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

position of the pile applying GNSS, etc. has already beenaddressed. However, it will be necessary for contractors
in near future to collect all the data concerned withdrilling such as excavation depth, ground type,embedment depth, drilling time and photos of excavatedsoil and to develop the integration system of those data
including torque, current, pressing force, inclination andmachine position, so called ICT construction so that theconstruction of qualified structure that satisfy the clients’demand will be possible without relying on the skilledworkers.
4. Conclusion
According to this work, the pipe drilling method
confirmed that excavation is possible even for hard rocksof qu = 60 to 100 N / sq mm. Moreover, the adequate
performance was confirmed also in underwater rock
drilling at the maximum depth of GL - 42 m.
Since this method is focused on not damaging thebearing rock, it is widely applicable to waterproof wallconstruction and water barrier wall construction withrock drilling.
Regarding the safety aspect, there was almost no
shaking of the crane while using the pipe drill, so there
was a sense of security compared to crushing by chisel.
From now on, this method can be widely deployed as
one of the tools for rock drilling work with rotary all
casing boring machine. The development of this method iscontinuing so that this method shall be developed overvarieties of engineering field.

- 633 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi- 634 -