What Is Dimension Stone?

Curb stone is a mark stone placed between the road surface and other structures. Curb stones are generally required between the divider and the pavement of urban roads, and between the sidewalk and the pavement. Curb stones are often required at the edges of the central divider of the highway, the right edge of the carriageway, or the outer edges of the road shoulders. ^[1]

Overview

Existing curbstones usually come in two forms, one is prefabricated for ordinary concrete, and the other is stone processing. They are both impermeable materials. The foundation under the curb is generally fine concrete, and it is also impervious. The bottom layer of the pavement is a thick, compacted foundation layer, which is an impermeable layer. In addition, the curbstone and the underlying foundation are impermeable, resulting in the water in the pavement layer cannot seep down or be discharged through the curbstone and its foundation. Water on the pavement structure layer and the interface between the surface layer and the base layer cannot be smoothly discharged from the pavement structure, which is one of the causes of early damage to the pavement. Based on a patented technology, a new type of concrete curb stone was designed. The new type of curbstone can discharge the water inside the pavement layer, and the cost is not much different from the commonly used curbstone.

1Concept of new curb stone

The new curb stone adopts a double-layered upper and lower composite structure. The upper layer is ordinary concrete and the lower layer is porous concrete, so that the lower layer of the curb stone has a water seepage function. At the outer side of the curb stone, at least the inside of the porous concrete layer has a recessed notch hole that extends longitudinally with the curb stone. Han, so that it has the function of diversion.

The upper layer of curbstone is made of ordinary concrete, and its impermeability can prevent the pavement rainwater from being poured into the pavement structure, and at the same time, the surface layer has a strong structural strength; the lower layer is made of porous concrete to form a water-permeable layer, which allows the water in the pavement structure to pass through. The permeable layer is smoothly discharged (usually the same cross section of the road, the road is higher than both sides, and the water inside the pavement structure flows to both sides under the action of gravity, and the porous concrete layer that enters the edge stone is discharged when it reaches the edge of the road). Inside the porous concrete layer on the outside of the curb stone, there are recessed notch holes and culverts that extend longitudinally with the curb stone, and guide the seepage and drainage into the rainwater wells on the side of the curb, thereby completely draining the water inside the pavement structure.

2New curbstone for asphalt pavement

As a new type of curbstone for asphalt pavement, its dimensions are similar to the existing curbstone. It has a rectangular structure with length, width and thickness of 75 cm × 35 cm × 12.5 cm, the upper layer is 6.5 cm thick ordinary concrete, and the lower layer is 6 cm Porous concrete is cast in composite, and the outside of the back has 5cm × 3 cm through the recessed holes and culverts along the length direction. The edge stone is suitable for roads whose asphalt surface thickness is not greater than 10.5 cm. . The internal surface of the asphalt surface structure leaks underwater to the top surface of the base layer, and the interface water between the same surface layer and the base layer (the main source of interface water: internal water of the asphalt surface structure, the ground water entering the interface from the edge of the road or the gap between the road surface, Groundwater, etc.), together, it flows to the roadside under the effect of gravity, flows through the porous concrete of the curbstone to the culvert, and then flows from the culvert to the rainwater well to realize the drainage of water inside the pavement layer.

For asphalt concrete pavements with large voids, such as semi-graded or open-graded asphalt concrete pavements, the number of holes and culverts should be increased both vertically and horizontally at the bottom of the curb stone to facilitate the drainage of rainwater during rainfall.

3New curbstone for cement pavement

New type of curbstone for cement pavement, similar in dimensions to existing curbstones. It has a rectangular structure with a length, width and thickness of 75 cm × 35 cm × 25 cm. The upper layer is 19 cm thick ordinary concrete and the lower layer is 6 cm thick. Porous concrete is compositely cast, and the outer side of the back has 5cm × 3cm penetrating recessed holes and culverts along the length direction. The edge stone is suitable for roads with a cement surface thickness of 22 cm (roads with a cement surface thickness greater than or less than 22 cm). cm). The internal surface of the cement surface structure leaks underwater to the top surface of the base layer, and the interface water between the same surface layer and the base layer (the main source of interface water: the internal water of the cement surface layer structure, the ground water entering the interface from the edge of the road or the pavement gap, and the water passing through the base layer) Groundwater, etc.), together, it flows to the roadside under the effect of gravity, flows through the porous concrete to the culvert, and then flows from the culvert to the rainwater well to realize the drainage of water inside the pavement layer. For cement concrete pavement with shallow groundwater level or permeable base course, the number of holes and culverts should be increased both vertically and horizontally at the bottom of the curb stone to facilitate the drainage of the interface water between the surface course and the base course.

4New curb stone prefabrication

According to the thickness of the road surface layer and the type of the base layer, determine the thickness of the ordinary concrete on the road edge and the porous concrete on the lower layer, and consider the number and size of the culverts according to the local heavy rain intensity and the dredging conditions during use. The vertical mold is mixed with ordinary concrete and porous concrete for use. The ordinary concrete layer of curb stone is first poured into the mold according to the required thickness, and then the porous concrete layer is poured into the mold according to the required thickness. The porous concrete layer is provided with holes and culverts as required. . Curb stone maintenance and other requirements are the same as existing curb stone prefabrication. The mechanical properties of curb stones should meet the relevant requirements in the specifications of concrete curb stones.

5New Curb Stone Construction

The new curbstone construction process is as follows:

1) Open holes in the corresponding part of the well of the rainwater well. The number and size of the holes are the same as those of the new curbstones. The holes of the well of the rainwater well shall be inclined downward from the outside to the inside. Should not be less than 15 °.

2) Pouring fine stone concrete foundation, placing road edge stone, which is prefabricated with common concrete. For roads with only flat-edged stones, the foundation's elevation should be leveled when the fine stone concrete foundation is poured.

3) Level the foundation and ensure the flatness of the gap of the new curb stone. The foundation of the hole and culvert should be treated with mortar.

4) A new type of curbstone is placed, with the ordinary concrete layer on the top and the porous concrete layer on the bottom.

5) Check the holes and culverts between every two rainwater wells to ensure that the holes and culverts between the two rainwater wells are connected.

6) Before the surface layer is applied, apply a layer of oil to the side of the ordinary concrete on the upper layer of the edge stone, and the side of the lower layer of porous concrete on the edge stone should be blocked when the layer of oil is applied.

7) The remaining construction requirements are the same as the existing curb construction technology.

6 conclusion

Through the improvement of the existing curbstone, a new type of curbstone is formed, and the water inside the pavement is discharged without increasing the cost. However, the effect of the new curbstone on excluding the internal water of the pavement needs to be tested in practice And keep improving. ^[2]

Overview

In highway design, comfort and safety are very important issues that should be considered first. However, in the construction of expressways, the requirements for comfort and safety often require wider lanes and gentle longitudinal slopes, which is inconsistent with economics. Therefore, designers should try to make full use of existing theories to make reasonable designs. Under the same project cost, a more smooth, comfortable and safe design scheme is proposed. In contacting and discussing with Western experts for technical assistance from the Asian Bank, and when referring to the Highway Capacity Manual issued by the U.S. Highway Department, it was found that the layout of some existing highway curbs and guardrails is worthy of further discussion and needs further demonstration. .

First of all, according to the research results of the Highway Capacity Manual of the United States, the ideal pavement width condition of a highway is: the minimum lane width is 12m (3.66 feet); the minimum distance between the inside and outside lane edges and obstacles It is 6m (1.83 feet); the width of the expressway in our province is 3.75m, which meets the previous condition. However, the distance between the curbstones, guardrails and lane edges of existing highways on the inside and outside of existing cross sections are all less than 1.25m, which do not meet the requirements of the latter condition. Because the inside and outside conditions are similar, the inside situation is mainly discussed here, and the outside situation can be explained by the same principle. From a comfort point of view, in order to avoid hitting curbs and guardrails at close distances when drivers overtake, they need to take "avoidance" measures, that is, the vehicle should drive as far as possible away from the central partition and close to the second lane, (this (The phenomenon is discussed in the Highway Capacity Manual, and there are photos to illustrate that the author also noticed this phenomenon on the highway, and confirmed this phenomenon by interviewing three experienced drivers.) Paying great attention to the obstacles on both sides (including curbs and vehicles on the right), which reduces the degree of freedom of vehicles in the passing lane and reduces its capacity. From a safety perspective, it is also unscientific for curbs to rise above the pavement and be located outside the guardrail. If the driver avoids the vehicle due to fatigue or emergency, especially when there are obvious reflective signs on the guardrail at night, but not on the curb stone, if the driver cannot see the position of the curb stone, it is easy to cause the curb stone to hit the vehicle and cause the vehicle to jump After it hits the crash barrier, it can easily cause the vehicle to overturn or even roll over, which is extremely detrimental to the driver's life and the vehicle, causing a great threat. Without the role of curbstones, a car hitting a guardrail would not pose such a serious threat and would generally not cause a rollover. So it is necessary to improve and research here. Before proposing improvement plans, the role of curb stones should be discussed first. Curb stone is an auxiliary facility of urban roads.Its main role is twofold:

1) Restrict vehicles to only drive in the lane, in order to separate the crowd from the vehicle and induce sight;

2) Centralized drainage. However, in the expressway, the first role has been replaced by the guardrail, and the second role is very limited. As the linear parameters of the current expressway have been greatly improved, most sections have not been set with superelevation.Even if superelevation is set, most of them are two-way slopes.Therefore, there is no pavement water flow in the central dividing zone of most sections. There is no problem of centralized drainage. For the section where the local superelevation is relatively large and a unidirectional cross slope has been formed, if there is no curbstone in the center, the drainage problem of the central partition needs to be further demonstrated. (Two reference solutions are proposed later). The concentrated drainage of the curbs on the outside of the road is not negligible, but for safety reasons, the western approach is to eliminate curbs and replace them with grass protection on the slope. It is also more economically reasonable.

Based on the above considerations of comfort and safety, as well as the role played by curbs, I refer to photos of various foreign highways and consulted technical assistance experts to propose the following improvements.

1The straight line section of the main line or the curved section that is still a two-way slope

The curbstones are cancelled, and the distance between the central guardrails can be shortened. (Some highways in the United States even merge the two rows of the pillars of the central guardrail into one row, and properly encrypt the pillars. ), This will help the guardrail away from the edge of the carriageway, and increase the capacity of the passing lanes on both sides of the central divider. Dirt shoulders and slopes on both sides of the road are planted with grass in spring to prevent scouring.

2 main line curve segments

In this case, if the curb stone is eliminated, there are two options for reference.

1) The pavements on both sides are connected as a whole, and a thin asphalt treatment or asphalt penetrating surface layer is laid on the central separation zone for waterproof treatment. The shoulders and slopes on both sides are protected with grass. This method has good waterproof effect and simple construction, but it is not conducive to maintaining the continuity of greening of the central partition.

2) Set a triangular mortar gravel greening groove in the central divider to prevent rainwater from seeping into the roadbed. The central divider is still planted with grass and trees, and the shoulders and slopes on both sides are protected by grass planting. This method is also ideal for waterproofing and maintains the green continuity of the central partition, but the construction is more complicated. The above improvement schemes improve the capacity and safety of the middle lane of the expressway, and the effect is obvious.

In addition, most of the bridges on the main highway of our province are protected by crash walls, and there is no corresponding connection between the crash walls and the subgrade guardrails, which weakens the cooperative protective effect between the two, forming weak points, Dangerous point. If the car hits the guardrail at these locations, it will continue to deviate to the outside, and then hit the facade of the crash wall bridge, causing a serious accident. If the collision wall and the guardrail are connected to each other, a car hitting the guardrail will be blocked by the guardrail to the lane, which will not cause the front of the collision wall bridge head to be hit forward, reducing accident losses. Therefore, the proper connection between the crash wall and the guardrail is very important here, and it is worthy of attention. In summary, the role of curbs and guardrails on the highway is indeed worthy of further study and discussion. Since highways serve high-speed vehicles, their smoothness and safety are particularly important. The author here only put forward several suggestions for improvement in this area, in order to communicate and discuss with the relevant designers. ^[3]