JPH02491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving soft and viscous soil by injecting a cement milk-based liquid into the ground, and an apparatus used in the method.

It has already been experimentally confirmed that the soft and viscous soil is destroyed and cracks are formed by injecting the ground using an injection liquid mainly composed of cement milk, and the Mohr-Coulomb failure theory Although it can be theoretically proven by
This is a method for improving soft and viscous soil, and (b) an injection device for a cement milk-based liquid for a method of improving soft and viscous soil, which also serves as a determination device for improvement standards.

The methods that have been generally used to improve soft and cohesive soil are broadly divided into replacement methods and dehydration consolidation methods, and each method has several types and characteristics. Regarding the latter, for example, there are pre-loading methods, sand drain methods, paper drain methods, etc., each of which has its advantages and disadvantages, but what they all have in common is that they generally take a fairly long construction period; It is necessary to carry cargo. In civil engineering work that targets soft and cohesive soil, it is useful even when constructing a new road or embankment, or when such earth structures have been damaged by sliding or earthquakes and must be quickly restored. , In the current social structure, a long construction period is a major obstacle. In some cases, there are conditions that make it impossible to use loaded cargo, and there are also cases where it is economically disadvantageous to have to go back.

The present invention aims to provide an improved construction method and equipment for soft and viscous soil that can be constructed safely in a short period of time and is more economical by eliminating the drawbacks of the conventional construction methods as described above. purpose.

Next, the configuration of this invention will be explained.

First, the principle of ground improvement of the present application will be explained as the overall structure of the present application with reference to FIGS. 4 and 5.

FIG. 4 is a schematic diagram of measuring the penetration resistance value of soft ground using a tip cone according to the prior art.
In other words, 1 shows the state in which the penetration device is set at a certain depth in the construction ground, but if you want to measure the penetration resistance value only at the tip, it is necessary to remove the frictional resistance acting on the circumferential surface of the connecting rod. Therefore, it is necessary to have a double pipe structure as shown in the diagram. At this time, if pressure p is applied to the rod head by mechanical or artificial force as shown in step 2, the tip cone penetrates into the ground. In this case, the condition for penetrating the tip cone into the ground is that the pressure p must be greater than the strength q of the ground, and unless the relationship p>q holds, the target ground cannot be destroyed.

In this application, by applying the principles described above, the pressure p
Instead, if p′ is the pressure (injection pressure) obtained by adjusting (a) the liquid pressure determined by the density of the injected liquid and the height of the injection pipe, and (b) the pumping pressure to a certain relationship, then p If the condition for ' is p'> q, the target ground can be destroyed by ground injection as shown in Figure 5.

In the case of Fig. 4, if you want to measure the ground strength continuously, you have to repeat the operation of pressing in the outer tube and inserting the tip cone, but in the case of Fig. 5, the failure condition of p' does not change. In this case, since the destruction continues to proceed as it is, the injection liquid in this process is flowing, and the injection liquid forms a fluid and the destruction by the injection liquid continues until p′ = q. The area will expand. When attempting to improve and strengthen the poured ground so as to obtain a strength q' that is greater than the ground strength q at the time of construction, a new failure condition p'' is set and controlled injection is performed so that p''>q'. I do.

Regarding Figure 5, all the experimental results confirmed that the injection body formed in this way creates a layered fluid in the vertical or oblique vertical direction from the time of injection until solidification. It was done.

In this case, mainly based on the ground improvement plan,
There are two main types: cases in which the improvement area is set vertically upward from the injection point and cases in which the improvement area is set downward. In general, the improvement area expands downward from the injection point of the injection liquid, but when trying to improve and strengthen the area above a certain depth of the improvement plan, using a lightweight injection material,
The injection device is set as shown in Fig. 1B, and high-pressure injection is performed. In either case, a nearly vertical layered fluid is formed.

According to the principle and injection mechanism described above, the ground injection progresses, the fracture area expands, and fluids are formed one after another, growing quantitatively and qualitatively. When the injection material is injected into the completely saturated soft and viscous ground, the gap that makes up the ground is replaced with the injection material. Therefore, in this process, the balance between the two is constantly maintained during injection, so as long as injection continues under the same conditions, the initial injection pressure will not be lost. In other words, within a certain improvement range, the injection pressure gradually increases from a state where the initial pressure continues as it is, and the degree of improvement increases accordingly. On the other hand, if the intended improvement is completed within a certain range and the final control pressure is exceeded, the fluid will expand outside the target range, so in this case, the injection pressure will naturally be less than the final control pressure.

Incidentally, as shown in FIG. 6, the injection pressure is expressed as the sum of the liquid pressure determined by the density of the injection liquid and the injection height L of the injection point, and the pumping pressure from the grout pump to the injection point. In Fig. 6, 21 is a high-pressure rubber hose for pumping the cement milk main liquid, 22 is a swivel (swivel joint),
23 is an adjustment device for setting the position of the tip cone.

In this way, in order to prevent the injection liquid from escaping outside the intended target area, in practice,
As shown in Figure B and Figure 3, (1) the barrier structure is constructed in advance using temporary materials such as sheet piles, or (2) the barrier structure is first constructed at the outside of the multiple injection points in the construction area. A method is adopted in which the structure of the peripheral wall is created by first injecting the injection points, and then the inner part is injected.

Regarding the above, to summarize the effects achieved by the present construction method, the characteristics of the present construction method are (1) in-situ rapid loading effect, (2) in-situ rapid dewatering effect, and (5) in-situ drain effect. , (4) in-situ consolidation effect, and (5) in-situ substitution effect can all be obtained almost simultaneously in the same process. In this case, it is the injection liquid (cement milk-based liquid) that is responsible for all of these effects. Among these, if we talk about the mechanisms of effects (1) to (3), the injection solution is
(2) functions as a pressurized dewatering material, and (3) functions as a drain material, and the process up to this point continues to be injected into the ground with a predetermined injection liquid under a preset improvement plan. This is a condition of the present construction method, and is an epoch-making invention not found in the prior art. Hence the general term infusion,
Since grout (pouring material) and the like cannot express the above-mentioned characteristics, "fluid" was used as the invention term. Also being injected into the ground (1)
After the effect of (3) is obtained, the injection liquid (cement milk-based liquid) solidifies at the same position where it was injected within about 24 hours, so the effect after about 24 hours is ( (4) in-situ consolidation effect and (5) in-situ displacement effect. In other words, the effects (1) to (3) take effect within about 24 hours, so the consolidation dewatering and drainage are completed during this time.

There are various methods to improve soft and cohesive soil using conventional technology, but the typical example that uses consolidation and dewatering as the improvement principle is the "dewatering consolidation" method that uses loading such as embankment, and the method to promote consolidation. This is a ``sand drain'' construction method that uses sand pillars as drain material.

Even though the principles are the same, a comparison between the "dehydration consolidation" mechanism of the prior art and the "dehydration consolidation" mechanism of the present application is as follows.

Figure 7 shows a mechanism that performs dewatering and consolidation using only the loading load of the embankment, and Figure 8 shows a mechanism that promotes dewatering and consolidation using a drain material such as a sand drain, and the vertical lines indicate the drain material. be. In this way, with the conventional technology, when the soft cohesive soil layer is thick,
Since the load can only be applied to the ground surface, it is difficult for the stress to be transmitted to the lower layers, so consolidation time takes a long time, and in reality, it is difficult to achieve how much consolidation density can be achieved in what time, in what area, and in what area. It was extremely difficult to check each time, and there was no other way than to check at regular intervals (periods). In addition, advance predictions can be made to some extent based on consolidation theory, but even with current technology there is a considerable difference between theory and actual construction.

As stated above, the drawbacks of the prior art are due to the fact that the following three points required for the consolidation theory to hold true are not satisfied. That is, (1) The speed of consolidation is most effective and progresses in a short time, the shorter the distance of drainage that affects the target improvement area (depth and spread).

(2) At the same time, in relation to (1), the greater the magnitude of the applied load acting on the range of (1), the faster the consolidation speed.

(3) If (1) and (2) do not act at the same time and at the same location at the same time, the consolidation effect will be reduced.

One of the most basic features of the proposed method is that it attempted to solve the above three points at the same time.
(in-situ) technical philosophy was introduced.

As shown in FIG. 11, the mechanism of dewatering consolidation of the present application is that the layered fluid in the vertical or oblique vertical direction formed during the ground injection is the loading surface, and the embankment of the prior art is Equivalent to. Therefore,
The proposed construction method does not require embankment, which is a necessary condition of the conventional technology (the dotted line in Figure 9 corresponds to this).
In addition, the injection pressure becomes a loading load during ground injection with multiple loading surfaces, and this loading load is not limited like the embankment load of conventional technology, but can be freely adjusted according to the purpose of improvement. I'm starting to be able to do it.

Further, as shown by the vertical lines in FIG. 9, the distance between the fluid bodies formed by the injection liquid in the substantially vertical direction corresponds to the drainage distance D in the method of the present application. Therefore, compared to the drainage distance D of the prior art shown in FIGS. 7 and 8, it can be greatly shortened.

In addition, the symbol B in FIGS. 7 to 9 indicates embankment,
The symbol H indicates the thickness of the consolidated layer, and the symbol S below it indicates the unconsolidated layer (sandy soil layer).

Here, the meaning of "limited" means that, on the one hand, the height of the embankment is technically or artificially limited, and on the other hand, it means that the height of the embankment is technically or artificially limited, and on the other hand, it is necessary to prevent sliding damage caused by the embankment, and to prevent the ground from collapsing around the embankment. Deformation (swelling,
This means that the proposed construction method can be sufficiently controlled to prevent ground destruction or deformation, and that the optimum load that satisfies the improvement design must be determined in advance and the construction method must be avoided. You can also manage the inside. Therefore, the injection liquid has the function of an adjustable pressurizing material during ground injection, and acts in substantially the same physical amount over the entire area of the fluid being injected. In other words, it is completely different from the consolidation mechanism of the prior art in that it works at the same position (in-situ) as it is injected, and the greatest advantage of the consolidation mechanism of the present application is that it works in the same position (in situ) as it is injected. Adjustable in-situ loading.

Next, we will discuss the dehydration mechanism. In the case of a completely saturated soft and viscous soil, it is composed of pores occupied by pore water and gas components and soil particles, and consolidation (compression) is a process in which these pores decrease. It is. Therefore, in the case of ordinary ground, the gas component can be ignored, so pore water is dehydrated from the ground and discharged outside the ground to be improved; conversely, if it is not dehydrated and discharged, it will not be consolidated. (compression) phenomenon does not occur. The reason why the consolidation shown in FIG. 10 takes a long time in the prior art is that pore water is not easily dehydrated and drained.

In the case of consolidation phenomena, the methods to make it possible to dehydrate and drain this pore water in a very short period of time are (1) applying a load to the natural ground at its original location (in-situ loading); , (2) Same position (original position)
There is no other way than to build a drainage channel and drain the pore water dewatered by the applied load out of the ground. Moreover, (1) and (2)
The necessary condition is that they act simultaneously on the same space at the same time.

The injection liquid is not just an injection liquid, but has a function that satisfies the above-mentioned requirements, and in this application, the term "fluid" is used in this sense in addition to the above-mentioned meaning. Therefore, dehydration does not involve dehydrating only the area sandwiched between the fluids, but instead replaces the fluid itself formed by injection in situ.

Next, we will discuss the drainage mechanism.

During injection, the fluid is always controlled at the injection pressure required by design. In addition, the injection liquid is made with a specific composition of multiple injection materials, mainly cement, and is designed to solidify within about 24 hours after injection. By rationally adjusting these two factors, an appropriate ground improvement plan that meets the purpose is designed.

In order for the injection liquid to be injected into the target ground to form a fluid, it is necessary that the pore water in the target ground be dehydrated and discharged to the outside of the ground.

The specific drainage mechanism is as follows.

When considering the process by which pore water in the ground is dehydrated, there are several factors to consider: (1) whether the ground has good permeability, (2) whether water permeation occurs statically or dynamically, and (3) the load. and (4) drainage distance are factors related to dehydration.

In connection with (1) to (2), if it is performed statically, it is necessary to compress and generate excess pore water pressure.
In the dynamic case, the condition is to provide a hydraulic gradient, that is, flow. In the conventional technology, for example, dewatering by applying the load of only the embankment is a problem of water permeability (1), and drain materials such as sand drains are used to speed up dewatering as much as possible. Also (1)
In order to make (2) work more effectively, (3) the size of the applied load and (4) the drainage distance become issues. However, since most of the actual load is the load of the embankment, there are realistic restrictions on its size. In other words, (a) if the embankment is carried out rapidly all at once, the embankment base will be destroyed, and the area around the embankment base will sink or swell, so the embankment must be done in stages; and (b) the soft layer is thick. In some cases, it is difficult for the load to be transmitted to the entire soft layer. This also applies when drains are installed.

Conventional methods for creating a hydraulic gradient include pumping dewatered pore water through sand drains using lift pumps, but these methods cause ground subsidence over a wide area, so they are rarely used today.

On the other hand, in the case of the present construction method, regarding (1), the permeability of the soft and weakly viscous soil, which is a ground condition common to the conventional technology and the present construction method, is 10 ^-7 if expressed in terms of permeability coefficient. It is on the order of cm/sec or more.
Regarding (2), even in a static case, the proposed construction method is a technology that mainly uses in-situ loading and in-situ dewatering, so there is a significant difference when compared to the loading of conventional technology. . In addition, with regard to dynamic means, the possibility of practical application is limited as described above in the conventional technology, but in the present construction method, in-situ drainage is the most efficient method because the injected liquid is a fluid. Therefore, if the sand drain of the prior art is a drainage channel with an extremely small hydraulic gradient, the drainage mechanism of the present method corresponds to a drainage channel with an extremely large hydraulic gradient.

Based on the above, the mechanism of "drainage" is detailed as follows.

Regarding the construction method of the present application, (1) If the pore water dehydrated by injection is captured in an instantaneous state immediately after injection, it will be incorporated into the fluid and the injection liquid will be diluted.
This is experimentally clear from the fact that when fluid leaks to the ground surface, it flows out in the following order: water (pore water) → thin (diluted) cement milk-based liquid → undiluted cement milk-based liquid. .
In other words, in the area covered by the cement milk-based liquid that is continuously injected one after another, that is, at the end of the destruction area, the degree of dilution of the injected liquid is highest, so the failure range (destruction condition) becomes the limit, and no further failure will occur. cannot occur (fluid growth stops)
Therefore, the injected liquid flows backwards and leaks to the ground. Also,
If a drainage layer such as a sandy soil layer exists in the target ground, the water will be discharged into this drainage layer. (2) If the injection actually continues, it is due to the following mechanism, which has been confirmed through experiments. In other words, if we consider the cross section of the fluid being injected as shown in Figure 11, the center of the fluid is occupied by the undiluted cement milk solution, but the part in contact with the injected ground, that is, the outside of the fluid, Cement milk-based liquid diluted from the original solution as the part moves away from the center →
Since it is water (pore water), the part where the fluid comes into contact with the injection ground plays the role of a drainage channel, which is the most basic consolidation-dewatering-drainage mechanism of the present method.

In addition to this, there is also dehydration due to vacuum action, but this can be done by temporarily stopping the injection during ground injection.
It has been confirmed that when the injection hole is blocked, the blockage is drawn into the hole, and this is thought to be part of the secondary dehydration mechanism.

By repeating the above steps, the strength of the clayey soil at each stage increases step by step, and as a result, the soft clayey soil can be purposefully improved.

The second invention of this invention, that is, the soft and viscous soil improvement device, is achieved by attaching a cone made of a double tube device to the tip of an injection pipe that is vertically inserted into the soft and viscous soil, and press-fitting the inner tube. This device can determine the ground strength of the target improvement area in advance and immediately determine the criteria for the soil improvement plan (mixture of injection liquid - type, concentration, injection pressure, injection depth, injection direction, etc.). It also serves as an injection device that adjusts the injection pressure and injection method in accordance with the criteria determined for the ground improvement plan.

Embodiments of the present invention will be described below with reference to illustrative drawings.

FIG. 1 shows a sectional view of the main parts of the soil improvement determination device and injection device of the present invention. first,
In order to improve soft and viscous soil, the position of injection depth, injection direction, cement milk-based liquid (e.g. water/cement ratio of cement milk, mixing of cement milk with powder or fine solids such as fly ash or plastic), etc. It is necessary to decide on adjustments such as the mixing ratio of liquids, etc.
It is necessary to understand the characteristics of the target ground (mainly ground strength). Therefore, FIG. 1A shows the apparatus, and numeral 1 is an inner tube used for determining the strength of the ground, and a cone (pointed metal fitting) is attached to the tip. Reference numeral 2 denotes an injection pipe which also serves as a protection pipe for the inner tube 1 with a tip cone. This is because when determining the ground strength, without the protective pipe, circumferential frictional resistance is added, which does not indicate accurate strength at the depth of injection, so only the tip resistance is measured separately. Next, as shown in Figure 1B,
Set the device at a certain depth in the ground to be measured, fix the injection pipe 2, and gently press in only the inner tube 1 with the tip cone for 10 to 20 cm, then measure the press-fit strength P (Kg). /cm ² ) is read on the ground. Therefore, the cement milk-based liquid was adjusted by taking the average value of the injection strength at the penetration length of the cone and used as the ground improvement judgment reference value, and the injection length (depth from the ground surface + ground level) was adjusted according to this adjusted liquid. Determine the pipe length), flow direction 3 of the injection liquid (upward or downward direction), and injection pressure (pump pressure).
In this case, as shown in the example in Figure 2, there are three injection methods that can be selected depending on the positional relationship between the adjustment liquid, injection pressure, and tip cone. It will look like Figures C and D. That is, Fig. 1C shows a case in which injection is to be performed in a range below the set depth, and Fig. 1 shows a device in which injection is to be performed in a similar manner in a range above the set depth. . In addition,
Since the ground composition is not necessarily homogeneous, and rather, heterogeneous ground is common, the injection method common to each device is to use an injection pipe 2 to improve the soil strength starting from weak areas. Inject while rotating slowly.

FIG. 2 shows an example of construction using diagrams C and D in FIG. 1. A in Figure 2 is a common construction method, and is an example of pouring downward from the top (using the equipment and construction method shown in Figure 1 C).
In cases such as excavation and embankment construction, it is relatively easy to improve the required area. In this example, the injection method is to limit the flow range to the range from the upper limit 6 to the lower limit 7 of the improved ground. (Using the equipment and construction method shown in Figure 1 C or D) In this case, if the improvement range is limited to only one side in the horizontal direction, it may be separated by temporarily installing a temporary structure 8 such as a sheet pile on one side. Or, as shown in Figures 3 and 4, in the first injection, the outer periphery of the necessary range (improved range) is covered by the underground wall 9, and the injection holes 10 of the injection pipes 1, which are not included in the enclosure, are placed within the range of the underground wall 9. The barrier 11 is formed by injecting the cement milk main liquid. In the two-stage construction example shown in FIG. 3, the second injection is performed from the injection pipe 1 inside the barrier 11 to the inside of the improved area 12. In this case, in the primary application within the barrier 11, the amount of the cement milk main liquid injected from each injection hole 10 is adjusted by injection pressure, etc., and is mainly injected within a certain distance on a concentric circle. In this example, as in the case of Figure A, the improved ground is adjusted in order from the lowest limit 7 to the highest limit 6. Furthermore, depending on the ground conditions, the length of the soft layer may be significantly thicker than the intended improvement range, or the middle part of the thick layer of the soft layer may be attempted to be improved. In such cases, even if a regulating liquid with a low specific gravity is used, the length of injection from the ground surface is too long, and if the injection method described above is adopted, the flow range will extend beyond the range that requires improvement. This will expand and become extremely uneconomical. Therefore, in such an example, as shown in FIG. Make less. The injection method in this case is to perform high-pressure injection using the apparatus shown in Fig. 1D and inject in the opposite (upward) direction.

As described above, this invention is superior to the conventional dewatering consolidation method using loads such as embankments, or the construction method using a combination with a drain method such as sand drain or paper drain as an auxiliary method to promote dewatering consolidation. Therefore, although the method of the present application is a stand-alone construction method, it does not require embankment and can improve soft ground systematically and safely in an extremely short period of time. Although there was a huge gap between theory and actual construction, the proposed construction method can be constructed rationally and economically based on an accurate improved design, and since the proposed construction method does not require large-scale equipment, it is suitable for terrain. Grounds to which conventional construction methods cannot be applied due to environmentally restricted conditions can be improved and strengthened very easily.

In addition, the effect of the present method is that by injecting the cement milk-based liquid into the ground, the design is managed according to the degree of softness of the soft and viscous ground, and the entire soft ground is homogenized into the desired improved ground. . In this case, the cement milk-based liquid to be injected forms a nearly vertical layered fluid during injection, and the layered fluid increases qualitatively and quantitatively as the injection progresses, and in the process, especially Since the soft layer sandwiched by the fluid layer is rapidly compressed, the cement milk-based liquid acts as an in-situ load acting laterally on the soft ground, resulting in immediate dewatering and consolidation. Through this process, the target ground is rapidly consolidated and densified due to the chain effect of dewatering and drainage, which not only increases the strength of the ground, but also forms a solidified bone core of the soft ground after consolidation. be. In other words, by injecting the cement milk-based liquid into the ground using a specific injection liquid and an injection device selected or adjusted depending on the purpose of construction, the fluid that spreads into the target ground one after another is injected. In order to force rapid loading action in situ on the ground in contact with each fracture surface during each flow path and its growth process, the pore water in the target ground is dehydrated and at the same time this pore water is immediately injected with the injection liquid. It functions to drain water into the fluid itself. After injection, the fluid injected solidifies quickly, creating a bone core structure in the target ground as an in-situ solidified body, and softens the part that has been compressed and strengthened by dehydration consolidation. It is possible to integrate the entire ground into a composite ground and improve and strengthen it into a stable ground structure. Therefore, the injection material according to the present invention functions to perform the functions of consolidation, dewatering, drainage, solidification, and replacement in one step, and can obtain all the effects immediately, and is effective in constructing soft and cohesive soil. It is intended to be improved and strengthened according to the purpose.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIGS. 1A, B, C, and D show a cement milk-based liquid injection device for improving soft and weak viscous soil soil and an improvement standard determining device used in the method of this invention. A cross-sectional view showing the main part, Figures 2A, B, and C, a cross-sectional view showing the construction method for soil improvement of soft and viscous soil using the injection device shown in Figure 1, and Figure 3 is a plan view of the same. It is. Figure 4 is a schematic diagram of measuring the penetration resistance value of soft ground using a tip cone using the conventional technology.
The figure is a schematic diagram showing the state of destruction of the target ground by injecting liquid into the ground using the construction method of the present invention, Figure 6 is an explanatory diagram of the injection pressure, and Figure 7 is an explanatory diagram of the mechanism that performs dewatering and consolidation using only the loading load of the embankment. , FIG. 8 is an explanatory diagram of a mechanism for promoting consolidation using various drain materials, FIG. 9 is an explanatory diagram of a mechanism for dehydration consolidation of the present invention, and FIG. 10 is an embodiment of dehydration consolidation and drainage in the prior art. The explanatory diagram, FIG. 11, is an explanatory diagram of aspects of dewatering consolidation and drainage according to the present invention. 1... Inner tube with tip cone (pointed metal fitting), 2
... Injection pipe, 3 ... Flow direction of injection liquid, 4
...Temporary tank for adjusting liquid to be injected, 5...Ground that requires improvement, 6...Maximum limit of improved ground, 7...Lowest limit of improved ground, 8...Temporary construction such as sheet piles, 9...
Basement wall, 10...Primary injection hole, 10'...Secondary injection hole, 11...Barrier, 12...Improvement range, 13...
...Cone (pointed metal fitting).

Claims (1)

[Claims] 1. By injecting the cement milk-based liquid into the soft and viscous soil, forced dehydration and rapid consolidation are performed at the same position where it is injected, that is, at the original position, and the cement milk-based liquid being poured is Immediate drainage via fluid compresses the soft and viscous soil in an extremely short time, increasing the strength of the ground and solidifying the injected liquid in situ.
Replace the bone core structure of the soft and viscous soil,
A method for improving soft and viscous soil, which is characterized by integrating the entire soft and viscous soil to improve and strengthen it into a stable foundation. 2. An inner tube with a cone at the tip is inserted into an injection pipe that is vertically inserted into soft and viscous soil, and is used as a soil strength determination device and a soil improvement standard determination device, as well as being able to be used as is as a soil injection device. A device for improving soft and viscous soil.